Network Engineer Interview Questions

Network Engineer Interview Questions http://study-ccna.com/ospf-configuration/

http://career.guru99.com/top-100-networking-interview-questions-answers/ 8. What kind of salary do you need? A loaded question. A nasty little game that you will probably lose if you answer first. So, do not answer it. Instead, say something like, That’s a tough question. Can you tell me the range for this position? In most cases, the interviewer, taken off guard, will tell you. If not, say that it can depend on the details of the job. Then give a wide range. Top materials: ebook: 75 interview questions with answers, top 7 cover letter samples, top 8 resume samples. Free pdf download 9. Do you have any questions to ask us? Never ask Salary, perks, leave, place of posting, etc. regarded questions. Try to ask more about the company to show how early you can make a contribution to your organization like “Sir, with your kind permission I would like to know more about induction and developmental programs?” OR Sir, I would like to have my feedback, so that I can analyze and improve my strengths and rectify my shortcomings.

I thought some of you might find this list interesting. I work in a NOC that supports an international network and these are the interview questions that our manager picks from when he does interviews. Enjoy General -Describe whether you are a network admin or server admin? -Are you currently or have you worked as a member of a team? If yes, name some of the challenges and how you handled them. Are you currently or have you worked as a member of a team? If yes, name some of the challenges and how you handled them. -Do you prefer routing or switching? -What are your strengths and weaknesses? -How do you troubleshoot network slowness issues? Switching -On a Cisco switch, when would you use a "ip default-gateway" command, and when a default route ip route 0.0.0.0 0.0.0.0 x.x.x.x -You create an SVI on 3560 switch, and its IP does not respond to ping. What could be the problem? -On 3560 switch -What command would you use to view the mac table? -On 6500 switch(IOS) - What command would you use to view the mac table? -On 6500 switch(CATOS) - What command would you use to view the mac table? -On Foundry(FOS) - What command would you use to view the mac table? -What is the Native Vlan? -3750 Switch-stack: which switch's flash holds the image that will run in

RAM when the stack is powered-up? -What commands would you use to set up a trunk between 2 cisco switches -What commands would you use to set up a trunk between 1 cisco switch and 1 cisco router -Difference between BPDUGUARD/BPDUFILTER -Explain how STP works -What is spanning tree protocol and how does it work? -Difference between a trunk and an access layer switch port? -Two PCs attached to 2 different switches. The switches are connected to each other but the PCs can't ping each other. Possible reasons? Steps to troubleshoot? -Link status is up, but line protocol is down - what's wrong? -You have a switch that won't power on. How do you get it replaced? -Describe how multiple VLANs can exist on a single switch link -Name a trunking protocol you have used and how it works ( Routing -OsPF- configuration statement -HSRP - what is "interface tracking" used for ? -Which has a higher admin distance- EBGP(20) or EIGRP(90) -Which has a better admin distance- EBGP or EIGRP -BGP- When would you apply a Weight to a BGP neighbor? -BGP- When would you prepend an AS path? -BGP- If you prepend a prefix's AS Path, does the prefix look better or worse to the world? -BGP- What command would you use to see your BGP neighbors? -BGP- Who controls routing with an AS? -EIGRP-Do Juniper routers run EIGRP? -EIGRP- What is the difference between the EIGRP topology table, and the routing table -EIGRP- In a network with dual redundant paths, how could you use an offset list -What is the (TCP) 3-way handshake? -How do you set up an OSPF network? -You want to add an attached network into your OSPF configuration. What are the command(s)? -What is redistribution in terms of routing protocols? What is mutual redistribution? -What would be some problems with mutual redistribution? -The LEC can't loop the CSU or NIU on a T1 circuit. Should you get the Cisco WIC replaced? OSI Model -In OSI terms, briefly describe what happens when you enter "www.google.com" in your browser address bar, and hit enter -Name the 7 layers -What layer is TCP? -What layer does a proxy server operate at? -Describe the process by which one layer communicates with the next Subnetting -Usable hosts in a /23? -How many bits for hosts are there in a /27? -What's the dotted decimal equivalent of a /28?

DNS -How do you look up a MX record? -What is a CNAME? -What is an A record? Other -How can you view routing information in a Unix server? -How can you configure a static route in a Unix server? -What is the command to list your current directory in Unix? -Give an example of a regular expression used with the "|" character, in Cisco, or Unix -Trick question--If you change the "bandwidth" on a router interface, and the interface utilization drops, what could be an explanation? -Have you used Wireshark? -If I give you a Ethernet cable and pair of scissors can you make me a DS-1 loop back plug ....? -Stateful firewall vs. access-lists vs. proxy server - how are they different? -How do you show the arp table on a linux box? On a windows box? On a Cisco router? -Briefly explain the difference between static and dynamic NAT -Briefly explain the use of a virtual IP address in HSRP or VRRP Interviewing Sr. Network Engineers

I am interviewing some Sr. Network engineers for the next 2 weeks. I've composed a list of questions and am posting them here for feedback purposes. Let me know what you think. Questions to determine level of network/Internet experience and knowledge. 1. Describe some network projects you have done. What did you do? Why? How? 2. From a high level view explain how the Internet works. (should explain transit providers, peering (public and private), tier1, tier2, root routers, DNS and root DNS servers) 3. What is the purpose of an Internet Routing Registry? Is it important? Name some of the top Internet Routing Registries. 4. Are you familiar with ARIN, RIPE, APNIC, LACNIC and AfriNIC? What role do they play in networks? 5. Where do you usually go to find AS, peering and IP info for particular networks? 6. Do you use looking glasses? Which ones? 7. How does a router work? How does a switch work? Can some switches be routers too? 8. What troubleshooting steps and procedures do you typically take when trying to isolate network issues? Give some examples. 9. What information resources do you use when designing networks? When managing networks? When troubleshooting problems? 10. How do you obtain your own IP space from ARIN? Is this important? Explain your answer.

11. What is the purpose of dynamic routing protocols? If dynamic routing protocols exist are static routes required? Explain your answer. 12. Explain design process from high level. (i.e. what is involved in designing a network?) 13. Are you familiar with Change Management. When do you use it? 14. How do you like to securely remote into network devices? 15. Explain how MPLS works from high level view. Advantages, limitations. 16. Where would you go to find official Internet Protocol standards? Why is this important? 17. What dynamic routing protocols are best suited for large diameter networks? Which ones have you worked with? What did you do? (should be BGP, OSPF, IS-IS) 18. What dynamic routing protocols are best suited for small diameter networks? Which ones have you worked with? What did you do? (should be E/IGRP, RIP) 19. Why was the OSI model developed? Is it useful? Where did it originate from? 20. Why would you upgrade the operating system of a network device? How would you execute the upgrade? 21. How do you keep up to date on trends and technologies? 22. Explain differences between IPv4 and IPv6. Explain structure of each and significance of structure. Why important? Advantages and disadvantages. 23. Explain BGP from a high level view. (should mention eBGP, iBGP, AS’s, peers, maybe even filters) 24. Explain different OSPF area types and how they function in relationship to each other. (i.e. how are routes advertised and route tables populated). Why would this be important in a network design? 25. What type of circuits have you worked with? (answer should be Point-to-point and point-tomulti-point ATM, serial, frame-relay, Ethernet, wireless) 26. Explain the role of DNS servers, syslog servers, TFTP servers, terminal servers, monitoring servers in the network. Why are they important? 27. How do different VLAN’s on a layer 2 switch communicate with each other? Is there a method that can be used if no router exists? 28. In your opinion what does network security involve? (should mention physical access, procedures, filters, monitoring, etc..) 29. Explain the differences between Layer2, 3 and 4 capable devices. 30. In your opinion, how important are network protocol timers and metrics? Explain 31. What are some typical procedures you follow prior to working on production network equipment? (backup configs and constant pings should be among top 5.) 32. What is a broadcast storm? An ARP storm? 33. How does a workstation or server connect to the network? What procedures does it go through? Trivial technical questions: (not too important and ability to answer them will not impact my decision) 34. Explain differences between Native and Hybrid mode on Cisco 6500’s. What are advantages, disadvantages of each? http://www.cisco.com/en/US/products/...800c8441.shtml 35. Does a Cisco 6500 Sup1a support SFM or SFM2 modules? What do SFM modules do?

36. You are running BGP on a Cisco 6500 Sup1a-MSFC. What does Cisco recommend with this config? 37. What does the BGP Scanner process do in Cisco IOS? How often does it run? 38. How many flash systems does a Foundry FastIron switch have? 39. What is the maximum combined throughput of a 10Mbps full duplex line? 40. How many metrics/attributes does BGP support? 41. What is the RFC number for HSRP? 42. Name the 7 steps OSPF goes through to become fully adjacent to a neighbor. 43. How does traceroute work? 44. Is Ping unicast, multicast or broadcast? 45. What is CAIDA? Is it useful? 46. Name 5 of the top 10 providers according to number of peering sessions. 47. What network equipment vendors support STP? 48. You have 5 carriers connecting to a single edge router and receiving the full BGP table from each. Is this scenario possible? Would you run into any problems? What is recommended best practice? 49. Name a protocol(s) used for failover that support virtual router interfaces. 50. What is the size of the current Internet routing table? 51. Explain how a single server with two NIC’s can connect to two separate upstream switches so that in the event one upstream switch fails then the server will not go down.

1. senior systems administrator interview questions In this file, you can ref interview materials for senior systems administrator such as types of interview questions, senior systems administrator situational interview, senior systems administrator behavioral interview… For top job interview materials for senior systems administrator as following, please visit: topinterviewquestions.info • Free ebook: 75 interview questions and answers • Top 12 secrets to win every job interviews • Top 8 interview thank you letter samples • Top 7 cover letter samples • Top 8 resume samples • Top 15 ways to search new jobs Top materials: ebook: 75 interview questions with answers, top 7 cover letter samples, top 8 resume samples. Free pdf download 2. What challenges are you looking for in this senior systems administrator position? A typical interview question to determine what you are looking for your in next job, and whether you would be a good fit for the position being hired for, is "What challenges are you looking for in a position?" The best way to answer questions about the challenges you are seeking is to discuss how you would like to be able to effectively utilize your skills and experience if you were hired for the job. You can also mention that you are motivated by challenges, have the ability to effectively meet challenges, and have the flexibility and skills necessary to handle a challenging job. You can continue by describing specific examples of challenges you have met and goals you have achieved in the past. Top materials: ebook: 75 interview questions with answers, top 7 cover letter samples, top 8 resume samples. Free pdf download 3. Describe a typical work week for senior systems administrator position? Interviewers expect a candidate for employment to discuss what they do while they are working in detail. Before you answer, consider the position you are applying for and how your current or past positions relate to it. The more you can connect your past experience with the job opening, the more successful you will be at answering the questions. It should be obvious that it's not a good idea talk about

non-work related activities that you do on company time, but, I've had applicants tell me how they are often late because they have to drive a child to school or like to take a long lunch break to work at the gym. Keep your answers focused on work and show the interviewer that you're organized ("The first thing I do on Monday morning is check my voicemail and email, then I prioritize my activities for the week.") and efficient. Top materials: ebook: 75 interview questions with answers, top 7 cover letter samples, top 8 resume samples. Free pdf download 4. What is your biggest weakness? No one likes to answer this question because it requires a very delicate balance. You simply can’t lie and say you don’t have one; you can’t trick the interviewer by offering up a personal weakness that is really a strength (“Sometimes, I work too much and don’t maintain a work-life balance.”); and you shouldn’t be so honest that you throw yourself under the bus (“I’m not a morning person so I’m working on getting to the office on time.”) Think of a small flaw like “I sometimes get sidetracked by small details”, “I am occasionally not as patient as I should be with subordinates or co-workers who do not understand my ideas”, or “I am still somewhat nervous and uncomfortable with my public-speaking skills and would like to give more presentations and talk in front of others or in meetings.” Add that you are aware of the problem and you are doing your best to correct it by taking a course of action. Top materials: ebook: 75 interview questions with answers, top 7 cover letter samples, top 8 resume samples. Free pdf download 5. Why should the we hire you as senior systems administrator position? This is the part where you link your skills, experience, education and your personality to the job itself. This is why you need to be utterly familiar with the job description as well as the company culture. Remember though, it’s best to back them up with actual examples of say, how you are a good team player. It is possible that you may not have as much skills, experience or qualifications as the other candidates. What then, will set you apart from the rest? Energy and passion might. People are attracted to someone who is charismatic, who show immense amount of energy when they talk, and who love what it is that they do. As you explain your compatibility with the job and company, be sure to portray yourself as that motivated, confident and energetic person, everready to commit to the cause of the company. Top materials: ebook: 75 interview questions with answers, top 7 cover letter samples, top 8 resume samples. Free pdf download 6. What do you know about our company? Follow these three easy research tips before your next job interview: 1) Visit the company website; look in the “about us” section and “careers” sections 2) Visit the company’s LinkedIn page (note, you must have a LinkedIn account — its free to sign up) to view information about the company 3) Google a keyword search phrase like “press releases” followed by the company name; you’ll find the most recent news stories shared by the company Remember, just because you have done your “homework”, it does not mean you need to share ALL of it during the interview! Reciting every fact you’ve learned is almost as much of a turn off as not knowing anything at all! At a minimum, you should include the following in your answer: 1. What type of product or service the company sells 2. How long the company has been in business 3. What the company culture is like OR what the company mission statement is, and how the culture and/or mission relate to your values or personality Top materials: ebook: 75 interview questions with answers, top 7 cover letter samples, top 8 resume samples. Free pdf download 7. Why do you want to work with us? More likely than not, the interviewer wishes to see how much you know about the company culture, and whether you can identify with the organization’s values and vision. Every organization has its strong points, and these are the ones that you should highlight in your answer. For example, if the company emphasizes on integrity with customers,

then you mention that you would like to be in such a team because you yourself believe in integrity. It doesn’t have to be a lie. In the case that your values are not in line with the ones by the company, ask yourself if you would be happy working there. If you have no issue with that, go ahead. But if you are aware of the company culture and realize that there is some dilemma you might be facing, you ought to think twice. The best policy is to be honest with yourself, and be honest with the interviewer with what is it in the company culture that motivates you. Top materials: ebook: 75 interview questions with answers, top 7 cover letter samples, top 8 resume samples. Free pdf download 8. What kind of salary do you need? A loaded question. A nasty little game that you will probably lose if you answer first. So, do not answer it. Instead, say something like, That’s a tough question. Can you tell me the range for this position? In most cases, the interviewer, taken off guard, will tell you. If not, say that it can depend on the details of the job. Then give a wide range. Top materials: ebook: 75 interview questions with answers, top 7 cover letter samples, top 8 resume samples. Free pdf download 9. Do you have any questions to ask us? Never ask Salary, perks, leave, place of posting, etc. regarded questions. Try to ask more about the company to show how early you can make a contribution to your organization like “Sir, with your kind permission I would like to know more about induction and developmental programs?” OR Sir, I would like to have my feedback, so that I can analyze and improve my strengths and rectify my shortcomings. Top materials: ebook: 75 interview questions with answers, top 7 cover letter samples, top 8 resume samples. Free pdf download 10. Top useful job materials for senior systems administrator interview: The below materials are availabe at: topinterviewquestions.info • Free ebook: 75 interview questions and answers • Top 12 secrets to win every job interviews • Top 36 situational interview questions • 440 behavioral interview questions • 95 management interview questions and answers • 30 phone interview questions • Top 8 interview thank you letter samples • 290 competency based interview questions • 45 internship interview questions • Top 7 cover letter samples • Top 8 resume samples • Top 15 ways to search new jobs Top materials: ebook: 75 interview questions with answers, top 7 cover letter samples, top 8 resume samples. Free pdf download 11. Other interview tips for senior systems administrator interview 1. Practice types of job interview such as screening interview, phone interview, second interview, situational interview, behavioral interview (competency based), technical interview, group interview… 2. Send interview thank you letter to employers after finishing the job interview: first interview, followup interview, final interview. 3. If you want more interview questions for entry-level, internship, freshers, experienced candidates, you can ref free ebook: 75 interview questions and answers. 4. Prepare list of questions in order to ask the employer during job interview. 5. Note: This file is available for free download. Top materials: ebook: 75 interview questions with answers, top 7 cover letter samples, top 8 resume samples.

Are you looking for job as a network engineer/network administrator? Or are you thinking to leave your current position for a new job as a network engineer/administrator with a new company in a routed LAN/WAN environment? If you answered yes to either of those questions, then this article is for you and any of described technologies and questions may be asked of you during the interview! ?Click here to download additional interview questions in .doc and PDF Network Engineer is a higher-level position, often with a “junior” or “senior” prefix. The major responsibility of a network engineer is to determine “how to implement technologies” in a routed LAN/WAN environment. They design and implement both the hardware and software technologies needed for a computer network. They have high-level technical skills in local area networks (LANs) or wide area networks (WANs). Network Administrator is responsible for the smooth, efficient, and secure operation of computer networks. In general, they configure and administer existing networks rather than designing networks from the beginning. They play a very challenging role in a routed LAN/WAN environment, including customization of the network as per the organization’s needs, such as adding software and hardware, performance monitoring, troubleshooting, logging errors, backing up and restoring data, assigning permissions to users, and helping users with network issues. Before facing any Interview for network engineer/administrator position, make sure that you have enough knowledge on below technologies. General network concepts: •Data communication and transmission techniques •Fundamentals of OSI and TCP/IP model •Router’s basic operations (startup, NVRAM, flash/IOS backup and recovery) IP addressing and summarization: •IP address classes •Classful and classless IP addresses •IP subnetting •Understating wild card masks •CIDR,FLSM,VLSM •IPv6 fundamentals Routing: RIP •Difference between RIPv1,RIPv2 and RIPng •Passive Interface •RIP Timers •RIP AD and Multicast Address •Split Horizon and Route Poisoning

EIGRP •Auto and Manual Summarization •Neighborship Conditions •Passive Interface •Split Horizon •Authentication •EIGRP Stub Routing and Stuck in Active •Equal and Unequal Load Balancing •EIGRP ADs and Multicast Address OSPF •OSPF Area Types •OSPF Neighborship Conditions •Concepts of ABR and ASBR Router •DR/BDR Fundamentals and Election •OSPF Times and Authentications •OSPF Summarizations (Inter-Area, External, and Default Info Originate) •OSPF AD and Multicast Addresses •OSPF Network and LSA Types BGP •BGP Fundamentals – Why and When to Use BGP? •BGP States and Message Types •BGP Neighborship Conditions •iBGP and eBGP •BGP Summarization •Use of Update Source, eBGP-Multi-Hop, Next-Hop-Self Commands •BGP Path Attributes •BGP Synchronization and Split-Horizon Rule •BGP Address Families •BGP Communities MPLS •MPLS Fundamentals – IP CEF, LIB, LFIB •LDP and TDP •P, PE and CE Routers •PUSH,POP,SWAP Functions •PHP – Penultimate Hop Popping •BGP – VPN •MPLS over ATM /Frame Relay QoS •QoS Models and Tools •Difference between L2 and L3 Queues •Characteristics of CoS, ToS, IPP, DSCP AF and EF

•Class Maps and Policy Maps Route Filtering •Access-List Fundamentals •Route-Maps •Prefix-Lists •Distribute-Lists •Filter-Lists IP Services and Network Securities •First-Hop Redundancy Protocols (HSRP,VRRP,GLBP) •Network Address Translation (Static, Dynamic, PAT) •Network Time Protocols, Syslog Server, SNMP •Basics of VPNs (IPsec, Site to Site , DMVPN, Remote VPN) •IP Multicast Routing (IGMP,PIM SM/DM, MSDP) •Policy-Based Routing •IP SLA My Best Questions for an Interview of Network Engineer/Network Administrator: All of the questions below are very common and must be prepared for before facing any interview for the data-WAN environment. 1. What is a router? Or define the basic requirements of a router? Answer: A router is a layer 3 network device used to establish communication between different networks. Basic roles performed by a router are: •Inter-network communication •Best path selection •Packet forwarding •Packet filtering 2. What is the use of routing? or Why we use routing? Answer: By default, a router provides inter-network communication only for directly connected networks. To establish communication between indirectly connected networks, we require ROUTING. We can use static or dynamic (IGP or EGP) routing, according to topology requirement. 3. Define the criteria for best path selection of a router? Answer: A router’s routing table contains only best route. To select a route as best, a router considers the following parameters; •Longest prefix match •Minimum AD (administrative distance) •Lowest metric value

If all listed parameters are the same, then it would perform equal cost load balancing. 4. Define “stuck in active.” Answer: If a successor route (best route) fails, then the router sends a query message to its neighbor demanding a feasible successor (back-up route) and a query received by the router may be forwarded to other neighbors that could lead to a loop, as well. The wait for the response of query message is called “stuck in active” (SIA). 5. Can we use OSPF without backbone area? Answer: Yes, but it will be limited to intra-area (same area) communication. By default, Interarea communication is not possible without backbone area. 6. What do you mean by OSPF transit area ? Answer: A transit area is the area that has a virtual link connecting two or more ABRs attached to this area. 7. What is the difference between an OPPF neighbor and an adjacent neighbor? Answer: Neighbors are the routers that are in the same area and exchange hello packets, but not LSA information. Adjacent routers are routers that have fully exchanged their LSA information and are stable. If OSPF state is in 2WAY/DROTHER, it means a neighbor relationship and, if the state is FULL/DR or FULL/BDR, it means that the adjacency is formed. 8. BGP neighborship is not coming up. Please define the various steps to troubleshoot it. Answer: To troubleshoot BGP, first we need to check neighbor state using “show ip bgp summary.” If the state is Idle, it means that the peer address or AS is not defined properly; if the state is Active, it means that TCP port 179 is not open, the peer is not reachable, network congestion, or BGP misconfiguration. Common neighbor stability problems of BGP •Misconfigured neighbor’s IP address and AS number •Reachability issues when interfaces other than directly connected interfaces are used while peering (update-source issue). •Authentication must be properly implemented (if configured) •Router-ID must be unique You can get more information from my BGP Tshoot article. 9. What is route reflector and why it is required?

Answer: Route reflector is a solution for BGP split horizon. The rule says “prefix learned from an iBGP neighbor will not be advertised to another iBGP neighbor.” To overcome this situation, we have multiple options: 1.Make your network a full mesh 2.Route confederation 3.Confederation Route reflector is something like a central point acting as a route reflector server: Rather than peering with every iBGP router in a full mesh, it makes IBGP neighbors as route reflector clients to overcome the split horizon issue. 10. What is the difference between standard and extended ACL? Answer: Standard ACLs are source-based, whereas extended ACLs are source- and destinationbased. Standard ACLs can only filter layer 3 network traffic, while extended ACLs can be used to filter layer 3 and layer 4, as well. 11. What is the use of distribute-list? Answer: To filter a routing database, we use distribute-list, which can be applied over most routing protocols. This means that, If you don’t want any specific network in your routing table, then you can use distribute-list. 12. MPLS works on which layer? Answer: MPLS operates between layer 2 and layer 3, so it is sometimes called layer 2.5. 13. What is penultimate hop popping (PHP) and what is its use? Answer: PHP is the technique for removing the (POP) MPLS label before the egress router. The MPLS label on a switched packet is popped by either the egress router or the penultimate router, depending on your configuration. If you decide to use penultimate hop popping, you essentially terminate the LSP one hop earlier. The MPLS labels are popped by the routers that connect to the egress router, rather than all of them being popped by the same egress router. 14. What is the difference between layer 2 and layer 3 QoS? Answer: L2-QoS is at the MAC layer and can be applied by using CoS (class of service) filed in the VLAN header. This will be used to prioritize traffic. Later, a QOS scheduler can use the COS filed to qualify the traffic into different QOS queues. L3 QOS is required for IP level classification; it can be achieved through ToS (type of service) priority values—IPP (3-bit), DSCP (6-bit), which can be set in the TOS field of the IP header. This TOS will later be used by scheduling process to achieve QOS.

L2 queues are hardware-based, while L3 queues are software-based. That’s why we can modify L3 queues to meet our requirements. The questions above are very tricky and important from the standpoint of clearing any interview for a network engineer/administrator position. It is not possible for anyone to explain all kinds of questions, but you can get more frequently asked interview questions for network engineer/network administrator positions from the download link posted here. If you find any difficulty in answering any questions, then you can write me @ Comment section. Tips for Preparing for an Interview •Study: Before an interview, take a quick recap of relevant technologies. •Updated Resume: Read your resume through; don’t copy and paste your resume. You must be aware of your strengths and weaknesses. •Professional Certifications: One of the best ways to prove the technical skills mentioned in your resume is through certifications. This gives a new employer an easy way to understand your knowledge level. •Updated LinkedIn Profile: Update your LinkedIn profile regularly; make sure that your work experience, qualifications, and project details match with your resume. This article is the output of lots of my research and extensive work experience. With this article I have tried to help/guide candidates about interview preparation for getting a network engineer/network administrator position in a routed LAN/WAN environment. Don’t forget to post your queries and feedback in the comment section. You can join our Facebook group, http://www.facebook.com/intenseschool, to get updates on new posts and technologies.

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Are you looking for job as a BGP/MPLS network professional? Or are you thinking about leaving your current position for a new job in a “BGP/MPLS Network Domain” with a new company? If you answered yes to either of those questions, then this article is a must-read for you and any of described technologies and questions may be asked of you during the interview! ?CLICK HERE TO DOWNLOAD ADDITIONAL INTERVIEW QUESTIONS IN PDF FORMAT An Introduction to BGP/MPLS Network Professional’s Roles and Responsibilities: Nowadays, almost every service provider around the world is using BGP and MPLS deployments throughout their cloud for providing and managing millions of clients’ network

infrastructure with better service availability and performance. >MPLS is particularly well suited in carrier networks and commercial wide area networks. BGP/MPLS deployments ensure flawless connectivity and routine activities in a multi-protocol network infrastructure and maintain the excellent communication service approach without any barrier as both are open standard technologies. A BGP/MPLS network professional must have moderate to excellent understanding of enterprise or carrier’s network infrastructure. Their job roles often involve 24×7 support for network services with both planned and unplanned work shifts. A BGP/MPLS network professional is responsible for performing the following functions: •Configuration and maintenance of exterior gateway routing (BGP)/MPLS Cloud •Evaluation and recommendations of BGP path selection for ingress/egress traffic •Configuration and maintenance of MPLS L2VPN/L3VPN, MPLS traffic engineering •Stability and availability of access and core network services in carrier networks •Network scalability, incident response, and review of network issues •Researching and learning new technologies adopted by the clients •Technical interaction with higher management, vendors, and clients •Installation of network hardware and software Required Key Skills for a BGP/MPLS professional: Good knowledge of following BGP functionalities: •BGP fundamentals and inter-AS communication techniques •BGP neighbor (iBGP and eBGP) peering and security •BGP path Selection (path attributes) •BGP synchronization rule •BGP split-horizon: 1.Route reflector (role of cluster-id and originator-id) 2.Confederation •BGP communities (standard and extended)

•BGP AS-path filtering with regular expressions •MP-BGP (multiprotocol BGP) with appropriate address families Good knowledge of following MPLS functionalities: •VRF introduction and Implementation (with RD and RT functionalities) •VRF-based routing and redistribution •Functional approach of P, PE and CE routers •Understanding of PHP, LDP, TDP, LIB, LFIB, LSR, Push, Pop, Swap functions •MPLS L3VPN Implementation, sham link •Any Transport over MPLS (AToM), VPLS •MPLS TE and QoS techniques •Ethernet VPN (EVPN) and provider backbone bridging EVPN (PBB-EVPN) •Multicast label distribution protocol (mLDP) •Unified MPLS (seamless MPLS) Apart from above BGP/MPLS skill set, candidate must have strong analytical and subjective knowledge of following key skills: •In depth understanding of carrier network architecture •Sound knowledge of network layered approach •Good understanding of multi-vendor network devices, such as Cisco, HP, Juniper, Nortel, etc. •Good understanding of networking IOS (IOS, IOS-XE, IOS-XR, NX-OS) •Knowledge about network management/ analysis/ monitoring tools •General understanding of rollback, and failovers handling •Ability to handle multiple assignments with deadlines •Able to communicate network issues effectively and in a comprehensible manner with clients and team members My Best Questions for an Interview about BGP/MPLS Network Architecture All of the questions below are very common and must be well prepared for before facing any interview in BGP/MPLS network environment so you can be honest and confident while answering. Most of interviews in BGP/MPLS network environment start with following set of common questions: “Tell me something about yourself.” Questions related to current/previous job roles. “What is your understanding about enterprises or carrier’s (service provider’s) network?” “Do you have any experience in a carrier network?” “What are your major strengths and weaknesses?”

“Share some of your achievements as a network professional?” “What is your salary expectation for this position?” While answering questions about your current and previous jobs, don’t forget to mention your responsibilities with recent activities and achievements. Apart from the above HR/Personal questions, let’s discuss some important technical questions as well. Q. What do you mean by MPLS? What are the benefits of using MPLS? A. This is one of the most common questions asked during the MPLS interviews, so this question must be prepared for before facing the interview. Here you should start answering by introducing MPLS. Multiprotocol label switching (MPLS) offer a mechanism to process packets on the basis of labels. It is a data forwarding service that provides high-end network communications from one network node to the next on the basis of labels rather than routing table lookups. Routing table lookup for each packet makes communication sluggish but MPLS uses LFIB/forwarding table to process label from one node to another. The main benefits of using MPLS are: •QoS integration: supports multiple levels of QoS, to manage latency, jitter and packet loss for various types of traffic (voice, video, email, bulk file transfers, etc.) •Fast convergence: label-based switching, no need to look up routing tables •Scalability to IP VPNs •Low network congestion using MPLS TE •Reliable and secure For further understanding, use the following link: http://www.cisco.com/c/en/us/products/ios-nx-os-software/multiprotocol-label-switchingmpls/index.html Q. Describe PUSH, SWAP, POP functions in MPLS and also explain penultimate hop popping (PHP).

A. Label switching is a discrete mechanism from IP forwarding; here LSR regulates what label function needs to be performed, such as Push, Pop, or Swap, to process a packet throughout the MPLS backbone using label switching. Push: Add a label Pop: Remove a label Swap: Exchange/ replace a label To know more about these functions, click the following link: http://www.ciscopress.com/articles/article.asp?p=680824 Penultimate hop popping is a technique to remove the label one hop before its destination so that untagged packet will be received by the destination PE router and only IP lookup will be performed by destination PE router to forward it to the directly connected CE interface. Q. What is Any Transport over MPLS (AToM)? Do we require VRF or BGP-VPN to form AToM connectivity? A. Any Transport over MPLS (AToM) enables service providers to deliver Layer 2 connectivity over a MPLS backbone to connect different clients’ sites with existing data link layer (Layer 2) networks. BGP-VPN or VRF is not required to configure AToM; to form AToM connectivity we do use xconnect (cross connect) peering with unique VC-ID to distinguish multiple clients. For more information on AToM, visit the following web page: http://www.cisco.com/c/en/us/td/docs/ios/12_0s/feature/guide/fsatom28.html Q. Describe the roles of RD and RT in MPLS L3VPN? Is it possible to assign a same RD to multiple customers? A. Route distinguisher (RD) is used to distinguish identical routes in different VRFs, whereas route target (RT) is used to share routes between them. Route target also specifies which prefixes get imported or exported on the PE router. No, we can’t assign same RD to multiple customers on a PE router because the main purpose of defining RD is limited to provide uniqueness in different VRFs. To know the structural detail of RD, refer to the following link: https://en.wikipedia.org/wiki/Route_distinguisher Q. How can you differentiate VPNv4 and IPv4 address-family?

A. Address-family VPNv4 is used to transport VRF traffic, which is quite heavier (96 bits) than normal IPv4 packets, and address-family IPv4 is used to transport traditional 32-bit IPv4 packets. When we deploy L3VPN, we need VPNv4 peering between the PEs to take the VRF routes (labeled with RD, RT) to the corresponding destination PE router. Q. What are LIB and LFIB? If we disable CEF (on a Cisco device) will MPLS work? A. The difference between two is almost like RIB and FIB, as RIB uses FIB to forward traffic. Label Information Base (LIB) is a table where prefix to label bindings are built and stored in the control plane and can be seen with “show mpls ldp bindings.” Label Forwarding Information Base (LFIB) is another MPLS table used to forward label packets throughout the MPLS network and build in the data plane. To check LFIB, run “show mpls forwarding-table.” The lookups are in fact done in the LFIB, not the LIB. If CEF is disabled, MPLS will not work, as it uses LFIB to forward labeled packets and LFIB built from the FIB table. Q. Name BGP path attributes to control incoming and outgoing traffic. A. BGP has multiple path attributes to influencing traffic flow. In the most common practice we do manipulate incoming traffic using AS-Path prepending and MED (multi-exit discriminator). And, to influence outgoing traffic, weight and local preference are the best choices. Q. My BGP is showing 0.0.0.0 as router-id; what could be the possible reason? A. This happens when we configure BGP on a router that has non-IP interfaces, meaning that if a router’s interfaces are not configured with any IP address, then BGP cannot get the router-id. In that case, BGP assumes 0.0.0.0 as router-id. Q. If my BGP neighbor is stuck in idle or active state, what should I do? A. If BGP peer is in idle state, then it could be due to physical connectivity failure or the neighbor is not defined properly with respective AS. In connect state, BGP tries to establish a TCP session over port number 179; if it fails to establish the connection, then it goes to active state, where it tries again to establish a TCP connection. By using “debug ip bgp” and “debug ip tcp transactions” commands, we can learn the exact cause of TCP connection failure. Lack of the “update-source” or “ebgp-multihop” command can also be a reason of neighbor active state; to know more, visit the following link: http://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/13752-24.html Q. Explain BGP recursive lookup and site of origin (SoO). A. BGP recursive lookup involves the router looking up the BGP route and BGP next hop to reach a destination in the remote AS. Then the router will look up the route into IGP to reach the BGP next hop. This mechanism is known as BGP recursive lookup.

BGP site of origin (SoO) is a loop prevention technique in the MPLS backbone environment. BGP SoO is associated with a CE-neighbor; that’s why whenever the PE router advertise a prefix to a CE neighbor, it check the SoO of the prefix with the SoO of the BGP neighbor to avoid loops. Q. What do you understand by BGP split-horizon rule? A. This rule states, “Network prefixes learned from an iBGP peer will not be shared with another iBGP peer” to prevent routing loops. BGP uses the AS_PATH attribute to avoid routing loops, which means a route will not be accepted if the AS_PATH contains the same AS number of the router where it is receiving. Route-reflector and confederation techniques are used to share iBGP learned networks with another iBGP neighbor. Q. Describe BGP communities. Name well-known communities. A. BGP communities are commonly used to control route policies in the BGP environment and used as flags in order to mark it over the set of network prefixes. BGP communities’ information can be shared with a neighbor by using the command “neighbor x.x.x.x send-community standard | extended | both” and can be applied using route-maps to a defined neighbor. Some well-known BGP communities are: Local-AS: Share the prefixes with iBGP-confederation peers only. No-Advertise: Do not share the prefixes with anyone. No-Export: Do not share the prefixes with another Global AS, share within the Public-AS only. Internet: Share the prefixes with all. The questions above are very collective and important from the standpoint of clearing an interview in BGP/MPLS network environment. In this article, I have tried to explain many of the frequently asked questions, and you can get more frequently asked interview questions for BGP/MPLS’s Jobs from the download link posted here. If you find any difficulty in answering any question, please write me @ Comment section. Before facing any Interview, a candidate should take care of the following points: •A quick recap of relevant technologies •Read your resume throughout; and detail your strengths/weaknesses, achievements and prior job roles and responsibilities

•Professional certifications allow the interviewer to understand your knowledge level, so point to your certifications (if you have any) •An updated LinkedIn profile helps you a lot in getting job recommendation and referrals for your desired job roles This article is the output of my extensive research and work experience, and my team, corporate clients, and colleagues helped me a lot in developing this article. With this article, I am trying to help/guide candidates in interview preparation for getting an engineering or administrative position in BGP/MPLS network environment. I hope this article will be appreciated so that I will be able to offer more in this segment. You can write me @comment section below for providing any query/feedback; I will try my best to resolve your queries at the earliest. And don’t forget to spread the link of this article on your Facebook, Twitter, and LinkedIn accounts so the maximum of people can get this exclusive piece of information. Keep reading @ Instanseschool.com and consider joining our Facebook group, http://www.facebook.com/intenseschool, to get updates on new posts and technologies.

Top Interview Questions for Network Operations Manager / Network Engineer Candidates Posted in Business Skills on December 21, 2015 ?Share

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PMP Boot Camp 93%+ Pass Rate, come see why! Get Certified! Skillset What's this? Network Management Network Security Networking Fundamentals

Are you looking for job as a network operations engineer? Or are you thinking of leaving your current position for a new job as a “manager: network operations” with a new company? If you answered “Yes” to either of those questions, then this article is a must read for you and any of described technologies and questions may be asked of you during the interview! ?CLICK HERE TO DOWNLOAD ADDITIONAL INTERVIEW QUESTIONS in PDF FORM An Introduction to Network Operations Manager/Engineer Roles and Responsibilities: Nowadays, every business is running on the shoulder of a computer network or third-party cloud deployments and managing today’s complex hybrid IT infrastructure is a tough job; both private and public cloud infrastructure creates complexity for IT services to run and operate. The network operations engineer ensures flawless installation activities and routine troubleshooting of network infrastructure to maintain the maximum possible service availability and performance. A network operations engineer/manager must have moderate to excellent understanding of networks and systems. Network operations engineers often escalate issues in a hierarchic manner; in case an issue is not resolved by a given deadline, the next level will be used for problem remediation. Their job roles often involve 24×7 support for network services with both planned and unplanned work shifts.

Network operation centers sometimes have multiple levels of engineers, which shows the experience and skillset of a NOC engineer. For example, a newly hired NOC engineer might be considered a “level 1,” whereas an engineer who has several years of experience may be considered “level 2” or “Level 3”. A network operations manager/engineer is responsible for performing the following functions: •Ensuring stable and reliable network services of access and core networks •Effective analysis of network visibility and availability •Network performance monitoring and reporting •Incident response and review of network’s issues •Installation and maintenance of network monitoring, analysis and reporting tools •Evaluating recommendations to resolve network issues •Researching and learning new technologies adopted by the clients •Technical interaction with higher management, vendors, and clients •Installation of network hardware and software Required Key Skills for a Network Operations Manager/Engineer: Strong analytical and subjective skills, along with the following knowledge set: •Understanding of network architect designing and managing LAN, WAN, and VoIP networks •Sound knowledge of network-layered approach •Good understanding of multi-vendor network devices such as Cisco, HP, Juniper, Nortel, etc. •General understanding of hardware network devices installation •General understanding of networking IOS (IOS, IOS-XE, IOS-XR, NX-OS) •Knowledge about network management/ analysis/ monitoring tools •General understanding of rollback and failovers handling •Ability to handle multiple assignments with deadlines •Able to communicate network issues effectively and in a comprehensible manner with clients and team members

My Best Questions for an Interview of Network Operations Manager/ Engineer All of the questions below are very common and must be well prepared for before facing any interview for the management/engineering position in network operations and be honest and confident while answering. Most interviews for NOC positions start with common questions such as: “Tell me something about yourself” “Questions related to current/previous job roles” “How can you handle a team of engineers?” “What are your major strengths and weaknesses?” “How do you find your qualification and experience as a NOC manager?” “Share some of your achievements as a network professional?” “What is your salary expectation for this position?” While answering about current/previous job role, don’t forget to mention your responsibilities with recent activities and achievements. Apart from above HR/ Personal questions, let’s discuss some important technical questions as well. Q. Describe some of network tools you are familiar with. A. This is one of the most common questions asked during the management/engineering position in network operations, so this question must be prepared for before facing the interview. Here you can share the list of tools you have worked with and you can even provide the name of your known network tools. You should consider our recently published articles on network tools: http://resources.intenseschool.com/top-10-network-management-tools/ http://resources.intenseschool.com/top-10-network-analysis-tools/ http://resources.intenseschool.com/top-10-network-security-tools/ http://resources.intenseschool.com/top-10-network-scanning-tools/ http://resources.intenseschool.com/top-7-network-troubleshooting-tools/ Q. How to troubleshoot a high CPU utilization problem in a router?

A. This symptom is the sign of abnormal functionality in a router. First we should know the exact reason for increased CPU utilization, and we can use “show processes cpu ,” “show interface stat” commands to check the process utilizations. It could be due to high traffic flow (congestion), complex ACL or VPN deployments, ARP/TCP issues etc. To know more, visit the following links: http://www.cisco.com/c/en/us/support/docs/routers/10000-series-routers/15095-highcpu.html http://www.cisco.com/c/en/us/support/docs/routers/7500-series-routers/41180-highcpuprocesses.html Q. If a router’s WAN link goes down, what you will do in that situation? A. First we need to verify the exact reason for failover; it could be due to physical or protocol issues. If it is a “protocol down” problem, then valid reasons could be link authentication failure, encapsulation mismatch, clock rate not configured, improper access control, MTU or Duplex mismatch, etc. For more information visit the following web page: http://www.cisco.com/en/US/docs/internetworking/troubleshooting/guide/tr1915.html Q. Is it normal to get CRC errors on MPLS WAN links? A. It could be normal if it is less than 1% of total traffic on that interface with no packet drop And it is recommended to resolve link issues in case cyclic redundancy check (CRC) errors are more than 1% of the total interface traffic. The most common reason for receiving CRC errors is the duplex setting, as most of providers set their interface to “auto” mode.\ Q. if a router’s WAN link goes down, we are not getting any alert or notification. What could be the issue? A. Proper syslog or SNMP configuration is required to get the alerts of a link failure. For advanced alert or notification management, network management tools can be configured to track such kind of alerts. Q. What will happen if one of the ports goes down of an 8 port EtherChannel? A. The overall bandwidth of an EtherChannel interface depends on its active member links. An EtherChannel with 8 active 100 Mbps links should indicate a bandwidth of 800 Mbps and, if one of its physical ports fails, the available bandwidth of port-channel interface will be evaluated as 700Mbps without flapping the port-channel. Q. How to perform password recovery in a switch?

A. Every switch series has its own set of recovery methods. Here you can describe the procedure of password recovery for the switches on which you have shown your work experience. You can also refer following links to get an idea of password recovery on well-known Cisco switches. http://www.cisco.com/c/en/us/support/switches/catalyst-2960-series-switches/productspassword-recoveries-list.html http://www.cisco.com/c/en/us/support/switches/catalyst-3750-series-switches/productspassword-recoveries-list.html http://www.cisco.com/c/en/us/support/switches/catalyst-4500-series-switches/productspassword-recoveries-list.html http://www.cisco.com/c/en/us/support/docs/switches/catalyst-6000-series-switches/14981pswdrec-6000IOS.html Q. How to access a layer 2 switch from a remote location? A. To access a layer 2 switch remotely, a management SVI (switch virtual interface) is required with proper Telnet/SSH access and IP address of SVI must be reachable. Q. What is the significance of the variable IP-OSPF-Transmit-Delay? A. If OSPF is configured on low bandwidth links, IP-OSPF-Transmit-Delay is used to increase the time of the age field of a LSA update. By default it is set to 1 second and, to make it effective, it must be added before transmission over a link. Q. What does “%OSPF-5-NBRSTATE: ospf-1 [5330] Process 1, Nbr 10.3.3.14 on Vlan44 from FULL to EXSTART, BADSEQNUM OSPF” log message mean? A. This log message pops up when an OSPF DBD exchange process uses a bad sequence number (due to packet loss or packet exploitation) for the synchronization of the database with its neighbors. Q. If my BGP neighbor is stuck in idle, or active state, what should I do?\ A. If BGP peer is in idle state then it could be due to physical connectivity failure or neighbor is not defined with properly with respective AS. In connect state, BGP tries to establish TCP session over port number 179 if it fails to establish TCP connection then it goes to Active state where it retries to establish TCP connection. By using debug ip bgp and debug ip tcp transactions commands, we can find out the exact cause of TCP connection failure. Lack of “update-source” or “ebgp-multihop” command can also be a reason for neighbor active state; to learn more visit the following link: http://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/13752-24.html

Q. How to resolve a BGP neighbor issue while receiving “hold time expired” notification message? A. This log message is common when a BGP peer flaps. If reachability breaks or fluctuates to a defined BGP neighbor, then it goes down, but after the hold time expires. To resolve this problem, you will need to fix BGP peering; possible issues could be due to MTU, unicast drop, SP circuit down, or misconfiguration under BGP process. The questions above are very collective and important from the standpoint of clearing an interview for a NOC engineer/manager position. It is not possible for anyone to explain all kinds of questions, but you can get more frequently asked interview questions for network operation’s jobs from the download link posted here. If you find any difficulty in answering any question, then you can write me @ comment section. Before facing any Interview, a candidate should take care of following points; •A quick recap of relevant technologies •Read your resume throughout and detail your strength/weaknesses, achievements, and prior job roles and responsibilities •Professional certifications allow the interviewer to understand your knowledge level, so point out your certifications (if you have any) •Updated LinkedIn profile helps you a lot to get job recommendation and referrals for your desired job roles This article is the output of my extensive research and work experience, and my team, corporate clients, and colleagues helped me a lot to develop this article. With this article, I am trying to help/guide candidates about interview preparation for getting an engineering or management position in the field of network operations. I hope this article will be appreciated so that I will be able to offer more in this segment. You can write me @comment section below for providing any query/feedback; I will try my best to resolve your queries at the earliest. And don’t forget to spread the link of this article on your Facebook, Twitter, and LinkedIn accounts so the maximum of people can get this exclusive piece of information. Keep reading @ Intenseschool.com and consider joining our Facebook group, http://www.facebook.com/intenseschool, to get updates on new posts and technologies.

Introduction Routing Protocol Selection Guide - IGRP, EIGRP, OSPF, IS-IS, BGP

Overview The purpose of routing protocols is to learn of available routes that exist on the enterprise network, build routing tables and make routing decisions. Some of the most common routing protocols include IGRP, EIGRP, OSPF, IS-IS and BGP. There are two primary routing protocol types although many different routing protocols defined with those two types. Link state and distance vector protocols comprise the primary types. Distance vector protocols advertise their routing table to all directly connected neighbors at regular frequent intervals using a lot of bandwidth and are slow to converge. When a route becomes unavailable, all router tables must be updated with that new information. The problem is with each router having to advertise that new information to its neighbors, it takes a long time for all routers to have a current accurate view of the network. Distance vector protocols use fixed length subnet masks which aren't scalable. Link state protocols advertise routing updates only when they occur which uses bandwidth more effectively. Routers don't advertise the routing table which makes convergence faster. The routing protocol will flood the network with link state advertisements to all neighbor routers per area in an attempt to converge the network with new route information. The incremental change is all that is advertised to all routers as a multicast LSA update. They use variable length subnet masks, which are scalable and use addressing more efficiently.

Interior Gateway Routing Protocol (IGRP) Interior Gateway Routing Protocol is a distance vector routing protocol developed by Cisco systems for routing multiple protocols across small and medium sized Cisco networks. It is proprietary which requires that you use Cisco routers. This contrasts with IP RIP and IPX RIP, which are designed for multi-vendor networks. IGRP will route IP, IPX, Decnet and AppleTalk which makes it very versatile for clients running many different protocols. It is somewhat more scalable than RIP since it supports a hop count of 100, only advertises every 90 seconds and uses a composite of five different metrics to select a best path destination. Note that since IGRP advertises less frequently, it uses less bandwidth than RIP but converges much slower since it is 90 seconds before IGRP routers are aware of network topology changes. IGRP does recognize assignment of different autonomous systems and automatically summarizes at network class boundaries. As well there is the option to load balance traffic across equal or unequal metric cost paths.

Characteristics 

Distance Vector



Routes IP, IPX, Decnet, Appletalk



Routing Table Advertisements Every 90 Seconds



Metric: Bandwidth, Delay, Reliability, Load, MTU Size



Hop Count: 100



Fixed Length Subnet Masks



Summarization on Network Class Address



Load Balancing Across 6 Equal or Unequal Cost Paths ( IOS 11.0 )



Update Timer: 90 seconds



Invalid Timer: 270 seconds



Holddown Timer: 280 seconds



Metric Calculation = destination path minimum BW * delay (usec)



Split Horizon

Enhanced Interior Gateway Routing Protocol (EIGRP) Enhanced Interior Gateway Routing Protocol is a hybrid routing protocol developed by Cisco systems for routing many protocols across an enterprise Cisco network. It has characteristics of both distance vector routing protocols and link state routing protocols. It is proprietary which requires that you use Cisco routers. EIGRP will route the same protocols that IGRP routes (IP, IPX, Decnet and Appletalk) and use the same composite metrics as IGRP to select a best path destination. As well there is the option to load balance traffic across equal or unequal metric cost paths. Summarization is automatic at a network class address however it can be configured to summarize at subnet boundaries as well. Redistribution between IGRP and EIGRP is automatic as well. There is support for a hop count of 255 and variable length subnet masks.

Convergence Convergence with EIGRP is faster since it uses an algorithm called dual update algorithm or DUAL, which is run when a router detects that a particular route is unavailable. The router queries its neighbors looking for a feasible successor. That is defined as a neighbor with a least cost route to a particular destination that doesn't cause any routing loops. EIGRP will update its routing table with the new route and the associated metric. Route changes are advertised only to affected routers when changes occur. That utilizes bandwidth more efficiently than distance vector routing protocols.

Autonomous Systems

EIGRP does recognize assignment of different autonomous systems which are processes running under the same administrative routing domain. Assigning different autonomous system numbers isn't for defining a backbone such as with OSPF. With IGRP and EIGRP it is used to change route redistribution, filtering and summarization points.

Characteristics 

Advanced Distance Vector



Routes IP, IPX, Decnet, Appletalk



Routing Advertisements: Partial When Route Changes Occur



Metrics: Bandwidth, Delay, Reliability, Load, MTU Size



Hop Count: 255



Variable Length Subnet Masks



Summarization on Network Class Address or Subnet Boundary



Load Balancing Across 6 Equal or Unequal Cost Paths (IOS 11.0)



Hello Timer: 1 second on Ethernet / 60 seconds on Non-Broadcast



Holddown Timer: 3 seconds on Ethernet / 180 seconds on Non-Broadcast



Metric Calculation = destination path minimum BW * delay (msec) * 25



Bidirectional Forwarding Detection (BFD) Support



Split Horizon



LSA Multicast Address: 224.0.0.10

Open Shortest Path First (OSPF) Open Shortest Path First is a true link state protocol developed as an open standard for routing IP across large multi-vendor networks. A link state protocol will send link state advertisements to all connected neighbors of the same area to communicate route information. Each OSPF enabled router, when started, will send hello packets to all directly connected OSPF routers. The hello packets contain information such as router timers, router ID and subnet mask. If the routers agree on the information they become OSPF neighbors. Once routers become neighbors they establish adjacencies by exchanging link state databases. Routers on point-to-point and point-to-multipoint links (as specified with the OSPF interface type setting) automatically establish adjacencies.

Routers with OSPF interfaces configured as broadcast (Ethernet) and NBMA (Frame Relay) will use a designated router that establishes those adjacencies.

Areas OSPF uses a hierarchy with assigned areas that connect to a core backbone of routers. Each area is defined by one or more routers that have established adjacencies. OSPF has defined backbone area 0, stub areas, not-so-stubby areas and totally stubby areas. Area 0 is built with a group of routers connected at a designated office or by WAN links across several offices. It is preferable to have all area 0 routers connected with a full mesh using an Ethernet segment at a core office. This provides for high performance and prevents partitioning of the area should a router connection fail. Area 0 is a transit area for all traffic from attached areas. Any inter-area traffic must route through area 0 first. Stub areas use a default route injected from the ABR to forward traffic destined for any external routes (LSA 5,7) to the area border router. Inter-area (LSA 3,4) and intra-area (LSA 1,2) routing is as usual. Totally Stubby areas are a Cisco specification that uses a default route injected from the ABR for all Inter-area and external routes. The Totally Stubby area doesn't advertise or receive external or Inter-area LSA's. The Not-So-Stubby area ABR is a transit area that will import external routes with type 7 LSA and flood them to other areas as type 5 LSA. External routes aren't received at that area type. Inter-area and intra-area routing is as usual. OSPF defines internal routers, backbone routers, area border routers (ABR) and autonomous system boundary routers (ASBR). Internal routers are specific to one area. Area border routers have interfaces that are assigned to more than one area such as area 0 and area 10. An autonomous system boundary router has interfaces assigned to OSPF and a different routing protocol such as EIGRP or BGP. A virtual link is utilized when an area doesn't have a direct connection to area 0. A virtual link is established between an area border router for an area that isn't connected to area 0, and an area border router for an area that is connected to area 0. Area design involves considering geographical location of offices and traffic flows across the enterprise. It is important to be able to summarize addresses for many offices per area and minimize broadcast traffic.

Convergence Fast convergence is accomplished with the SPF (Dijkstra) algorithm which determines a shortest path from source to destination. The routing table is built from running SPF which determines all routes from neighbor routers. Since each OSPF router has a copy of the topology database and routing table for its particular area, any route changes are detected faster than with distance vector protocols and alternate routes are determined.

Designated Router Broadcast networks such as Ethernet and Non-Broadcast Multi Access networks such as Frame Relay have a designated router (DR) and a backup designated router (BDR) that are elected. Designated routers establish adjacencies with all routers on that network segment. This is to reduce broadcasts from all routers sending regular hello packets to its neighbors. The DR sends multicast packets to all routers that it has established adjacencies with. If the DR fails, it is the BDR that sends multicasts to specific routers. Each router is assigned a router ID, which is the

highest assigned IP address on a working interface. OSPF uses the router ID (RID) for all routing processes.

Characteristics 

Link State



Routes IP



Routing Advertisements: Partial When Route Changes Occur



Metric: Composite Cost of each router to Destination (100,000,000/interface speed)



Hop Count: None (Limited by Network)



Variable Length Subnet Masks



Summarization on Network Class Address or Subnet Boundary



Load Balancing Across 4 Equal Cost Paths



Router Types: Internal, Backbone, ABR, ASBR

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Area Types: Backbone, Stubby, Not-So-Stubby, Totally Stubby

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LSA Types: Intra-Area (1,2) Inter-Area (3,4), External (5,7)

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Fast Hello Timer Interval: 250 msec. for Ethernet, 30 seconds for Non-Broadcast

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Dead Timer Interval: 1 second for Ethernet, 120 seconds for Non-Broadcast

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Bidirectional Forwarding Detection (BFD) Support

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LSA Multicast Address: 224.0.0.5 and 224.0.0.6 (DR/BDR) Don't Filter!

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Interface Types: Point to Point, Broadcast, Non-Broadcast, Point to Multipoint, Loopback

Integrated IS-IS Integrated Intermediate System - Intermediate System routing protocol is a link state protocol similar to OSPF that is used with large enterprise and ISP customers. An intermediate system is a router and IS-IS is the routing protocol that routes packets between intermediate systems. IS-IS utilizes a link state database and runs the SPF Dijkstra algorithm to select shortest paths routes. Neighbor routers on point to point and point to multipoint links establish adjacencies by sending hello packets and exchanging link state databases. IS-IS routers on broadcast and NBMA

networks select a designated router that establishes adjacencies with all neighbor routers on that network. The designated router and each neighbor router will establish an adjacency with all neighbor routers by multicasting link state advertisements to the network itself. That is different from OSPF, which establishes adjacencies between the DR and each neighbor router only. IS-IS uses a hierarchical area structure with level 1 and level 2 router types. Level 1 routers are similar to OSPF intra-area routers, which have no direct connections outside of its area. Level 2 routers comprise the backbone area which connects different areas similar to OSPF area 0. With IS-IS a router can be an L1/L2 router which is like an OSPF area border router (ABR) which has connections with its area and the backbone area. The difference with IS-IS is that the links between routers comprise the area borders and not the router. Each IS-IS router must have an assigned address that is unique for that routing domain. An address format is used which is comprised of an area ID and a system ID. The area ID is the assigned area number and the system ID is a MAC address from one of the router interfaces. There is support for variable length subnet masks, which is standard with all link state protocols. Note that IS-IS assigns the routing process to an interface instead of a network.

Characteristics 

Link State

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Routes IP, CLNS

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Routing Advertisements: Partial When Routing Changes Occur

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Metric: Variable Cost (default cost 10 assigned to each interface)

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Hop Count: None (limited by network)

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Variable Length Subnet Masks

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Summarization on Network Class Address or Subnet Boundary

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Load Balancing Across 6 Equal Cost Paths

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Hello Timer Interval: 10 seconds

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Dead Timer Interval: 30 seconds

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Area Types: Hierarchical Topology similar to OSPF

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Router Types: Level 1 and Level 2

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LSP Types: Internal L1 and L2, External L2

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Designated Router Election, No BDR

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Bidirectional Forwarding Detection (BFD) Support

Border Gateway Protocol (BGP) Border Gateway Protocol is an exterior gateway protocol, which is different from the interior gateway protocols discussed so far. The distinction is important since the term autonomous system is used somewhat differently with protocols such as EIGRP than it is with BGP. Exterior gateway protocols such as BGP route between autonomous systems, which are assigned a particular AS number. AS numbers can be assigned to an office with one or several BGP routers. The BGP routing table is comprised of destination IP addresses, an associated AS-Path to reach that destination and a next hop router address. The AS-Path is a collection of AS numbers that represent each office involved with routing packets. Contrast that with EIGRP, which uses autonomous systems as well. The difference is their autonomous systems refer to a logical grouping of routers within the same administrative system. An EIGRP network can configure many autonomous systems. They are all managed by the company for defining route summarization, redistribution and filtering. BGP is utilized a lot by Internet Service Providers (ISP) and large enterprise companies that have dual homed internet connections with single or dual routers homed to the same or different Internet Service Providers. BGP will route packets across an ISP network, which is a separate routing domain that is managed by them. The ISP has its own assigned AS number, which is assigned by InterNIC. New customers can either request an AS assignment for their office from the ISP or InterNIC. A unique AS number assignment is required for customers when they connect using BGP. There are 10 defined attributes that have a particular order or sequence, which BGP utilizes as metrics to determine the best path to a destination. Companies with only one circuit connection to an ISP will implement a default route at their router, which forwards any packets that are destined for an external network. BGP routers will redistribute routing information (peering) with all IGP routers on the network (EIGRP, RIP, OSPF etc) which involve exchange of full routing tables. Once that is finished, incremental updates are sent with topology changes. The BGP default keepalive timer is 60 seconds while the holddown timer is 180 seconds. Each BGP router can be configured to filter routing broadcasts with route maps instead of sending/receiving the entire internet routing table.

Characteristics 

Path Vector

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Routes IP

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Routing Advertisements: Partial When Route Changes Occur

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Metrics: Weight, Local Preference, Local Originated, As Path, Origin Type, MED

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Hop Count: 255

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Variable Length Subnet Masks

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Summarization on Network Class Address or Subnet Boundary

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Load Balancing Across 6 Equal Cost Paths

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Keepalive Timer: 60 seconds

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Holddown Timer: 180 seconds

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Bidirectional Forwarding Detection (BFD) Support

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Designated Router: Route Reflector

BGP Routing Table Components 

Destination IP Address / Subnet Mask

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AS-Path

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Next Hop IP Address