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

[ciscomoderator]

With Sandeep Sharma

Welcome to the Cisco Support Community Ask the Expert conversation.  This  is an opportunity to learn and ask questions about issues encountered while configuring and troubleshooting Border Gateway Protocol (BGP) across various Cisco platforms with expert Sandeep Sharma.

BGP is the most widely deployed routing protocol across service provider and enterprise networks.

For more information, visit the introduction to Border Gateway Protocol at:

www.cisco.com/en/US/tech/tk365/tk80/tsd_technology_support_sub-protocol_home.html.

Sandeep Sharma is a customer support engineer in the High-Touch Technical Services Routing Protocols team based in Bangalore. He provides support to major service providers and enterprise customers for routing and MPLS technologies. He has more than seven years of experience working with large enterprise and service provider networks. He also holds a CCIE certification (#39002) in routing and switching.

Remember to use the rating system to let Sandeep know if you have received an adequate response. 

Because of the volume expected during this event, Sandeep might not be able to answer every question. Remember that you can continue the conversation in the Network Infrastructure community, subcommunity WAN, Routing, and Switching shortly after the event. This event lasts through October 4, 2013. Visit this forum often to view responses to your questions and the questions of other Cisco Support Community members.

[snarayan62]

Hi Sandeep,

Can you please explain what is BGP peer groups and what is the benift of using this.

Regards

SN Gautam

[Sandeep Sharma]

Hi Satnarain

BGP peer group is a good concept which is very helpful in reducing the CPU processing for the BGP running device.You can group BGP neighbors who share the same outbound policies together in what is called a BGP peer group. Instead of configuring each neighbor with the same policy individually, a peer group allows you to group the policies which can be applied to individual peers thus making efficient update calculation along with simplified configuration.

Benifits of configuring BGP peer group:

============================

The major benefit you achieve when you specify a BGP peer group is that a BGP peer group reduces the amount of system resources (CPU and memory) necessary in an update generation. In addition, a BGP peer group also simplifies the BGP configuration. A BGP peer group reduces the load on system resources by allowing the routing table to be checked only once, and updates to be replicated to all peer group members instead of being done individually for each peer in the peer group. Based on the number of peer group members, the number of prefixes in the table, and the number of prefixes advertised, this can significantly reduce the load. It is recommended that you group together peers with identical outbound announcement policies.

Hope this answers your queries. Please feel free to contact in case you need any further clarification.

Thanks & Regards

Sandeep

[santoshautade]

When Ebgp & Ospf is configured on router and we have to ospf route should prefer rather than ebgp route???

[snarayan62]

Hi Sandeep,

Can you please explain what is BGP peer groups and what is the benift of using this.

Regards

[Sandeep Sharma]

Hi Satnarain

I think by mistake you have posted the query twice. I have responded to your query please refer the above section/reply.

Thanks & Regards

Sandeep

[snarayan62]

Hi Sandeep

Your posted reply is very helpful to my team

Thanks

SNG

[hanuman121]

Hi Sandeep

Need to know what is the best possible way that RTA should reach network 160.10.0.0 directly via RTB rather taking the path to RTC because here in this router RTA will have the this route preferred via EBGP (Ad=20) as compared to EIGRP. Do we have any other option that changing the AD value to achieve this? Refer the below link for diagram

Thanks

Hanuman

[Sandeep Sharma]

Hi Hanuman

Considering your query and diagram, RTA and RTC are running EBGP, and RTB and RTC are running EBGP. RTA and RTB are running Eigrp.By definition, EBGP updates have a distance of 20 which is lower than the Eigrp (90) distances.

RTA will receive updates about 160.10.0.0 via two routing protocols: EBGP with a distance of 20 and EIGRP with a distance higher than 20 (=90).

On way to fulfil your requirement s to change EBGP's external distance or IGP's distance, but which is not recommended. So the solution to your problemis to Use BGP backdoor.

BGP backdoor makes the IGP route the preferred route.

Command to configure Backdoor

========================

The configured network is the network that we would like to reach via IGP. For BGP this network will be treated as a locally assigned network except it will not be advertised in BGP updates.

    RTA#

    router eigrp 10

    network 160.10.0.0

    router bgp 100

    neighbor 2.2.2.1 remote−as 300

    network 160.10.0.0 backdoor

Network 160.10.0.0 is treated as a local entry, but is not advertised as a normal network entry.

RTA learns 160.10.0.0 from RTB via EIGRP with distance 90, and also learns it from RTC via EBGP with distance 20. Normally EBGP is preferred, but because of the backdoor command EIGRP is preferred.

Hope it answers your query. Please feel free to contact in case you have any query or need any further clarification.

Thanks & Regards

Sandeep

[hanuman121]

Hi Sandeep

Thanks for your given solution I implemented this solution and working fine

Thanks and Regards

Hanuman