Ask the Expert: Border Gateway Protocol (BGP) Fundamentals and Troubleshooting

[Monica Lluis]

Welcome to this Cisco Support Community Ask the Expert conversation. This is an opportunity to learn and any ask questions about how to configure and troubleshoot and design netowrk using  Border Gateway Protocol with Cisco expert Vinit Jain.

Ask questions from Tuesday Janury 12 to Friday January 22, 2016

Border Gateway Protocol (BGP) is one of the most widely deployed protocols in networks today and is the definitive routing protocol in the Internet. BGP is a flexible protocol, in that a variety of options are available to network engineers. Furthermore, extensions and implementation enhancements make BGP a powerful and yet complex tool. Because of BGP's pervasive deployment across multiple networks and the large number of use-cases that BGP can be applied to, it is becoming increasingly important to understand how to troubleshoot BGP issues quickly and easily. Viinit will be helping you answer your queries on how to troubleshoot BGP

Vinit will be helping you with all your queries on all of the above.

Vinit Jain presented at  Cisco Live in June 2015 on Troubleshooting BGP 
Click here for More Information

Vinit Jain, 3X CCIE #22854 is a Technical Lead in HTTS (High Touch Technical Support) team supporting customers in areas of routing, MPLS, TE, IPv6, multicast and a wide variety of platform issues like High CPU, Memory leak, etc IOS, IOS XE, IOS XR and NxOS code base. Has been delivering trainings within Cisco on various technology as well as platform troubleshooting topics. He has also written workbook on IOS XR fundamentals on Cisco Support Community. Vinit has CCIE in R&S, SP and Sec and holds multiple certifications on programming and databases.

Vinit  might not be able to answer each question due to the volume expected during this event. Remember that you can continue the conversation on the WAN, Routing and Swiching sub-community

Find other  https://supportforums.cisco.com/expert-corner/events.

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[Vinit Jain]

Hello Vinay, 

yes the session is recorded. You can find the link below and on the section above as well:

https://supportforums.cisco.com/video/12747706/webcast-video-recording-border-gateway-protocol-bgp-fundamentals-and-troubleshooting

[vinay_pit]

Cheers Vinit.

[Monica Lluis]

Vinit, 

Another question from the webcast event:

Can you advertise a /16 from one site, but also advertise a /24 in the /16 from a different location?

[arvindsingh1989]

Yes, it is possible.

Commonly used for load sharing on Internet. 

[Vinit Jain]

It can be done, but it should be kept in mind that more specific prefix will be chosen as best and installed in the routing table and the traffic will be redirected accordingly.

[Monica Lluis]

Another question from the live event:

Is there any difference of commands for BGP in Nexus?

[Vinit Jain]

Yes, there is a slight difference between how BGP is configured on IOS and NX-OS. NX-OS is more hierarchical like IOS XR. Another differentiator is you have to enable "feature bgp", before you can configure BGP.

[Monica Lluis]

Another question from the audience:

Do I  have to run BGP in MPLS-L3?

[arvindsingh1989]

Yes, you have too for exchanging the MPLS Labels  RD. 

[Vinit Jain]

Yes, Multi-Protocol BGP (MP-BGP) is required for MPLS L3 VPNs.

[Monica Lluis]

Another question from the live audience:

How can we control redistribution of static routes into BGP ? what is the best practice?

[Vinit Jain]

Redistribution of static routes should ideally be performed along with route-maps with match statements.

Also, ensure the seq of the route-map is deny statement, so that any other unwanted static route doesnt get added and distributed into BGP network.

Regards

Vinit

[Monica Lluis]

Another question form the audience:

Looks like most tier-1 ISP's don't take prefixes smaller than /24, is it a
gentleman's rule?

[Vinit Jain]

It depends on how the prefixes are being advertised and the policies of an ISP.

If there is a MPLS Layer-3 VPN services being provided by ISP, then it should not matter which subnet prefix you are advertising to ISP.

If you are advertising the BGP prefix directly to ISP into the Internet, then it might not be a good practice. This is because, if there is a bigger subnet-block advertised by another organization, and if a more specific prefix is advertised of that same subnet (knowingly or unknowningly), then this will cause the more specific prefix to be selected as best in the Internet and the traffic will be redirected towards the more specific subnet.

This is one reason, why ISPs might refrain from accepting more specific subnets.

But otherwise, there is no such rule.

[Monica Lluis]

Another question from the live audience:

What use case would suit confederations vs. route reflectors?