Ask the Expert: How to configure and troubleshoot EIGRP, OSPF and BGP.

[Cisco Moderador]

This topic is a chance to discuss more about about the most widely deployed Routing Protocols in today’s Enterprise Networks, such as EIGRP, OSPF and BGP. The use of dynamic Routing Protocols is necessary in order to keep the network operational, provide scalability and reduce complexity. Routing Protocols are easy to set up, however, inner workings and predicting the network reconverge might be a challenge specially in failover scenarios.

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Ask questions from Monday, August 8 to August 19th, 2016

Featured Expert

Hector Gustavo Serrano is a Customer Support Engineer in the Global Cisco Technical Assistance Center. He is part of the Routing Protocols team, specialized in troubleshooting Routing issues, additionally he educates about best practices of Routing Protocols deployed on customer’s networks. For the last 6 six years he has worked with Cisco platforms for Enterprise Networks, specially focused on US customers. Hector Gustavo also holds a CCIE in Routing & Switching (49102) and a Bachelor’s degree in Telecommunication engineering.

Hector Gustavo 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  Contact Center Community 

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[Basavaraj Ningappa]

Hi,

What is the difference between ibgp sessions and ibgp neighbors ? if i run ibgp everywhere in my network

don 't i need any IGP protocol ?

Thanks

Basava

[Hector Gustavo Serrano Gutierrez]

Hello Basavaraj karikal,

We can say that the Router will establish an iBGP session with an iBGP neighbor.

iBGP (internal BGP) is known as the BGP session between 2 Routers configured in the same Autonomous System (AS).

Since BGP uses IP/TCP to establish adjacency, it is possible to make the Router to establish an iBGP session between another Router not Directly Connected. For that purpose, the network needs to be running an IGP protocol to accomplish reachability between the Routers and avoid 'blackholes'.

Routing on an Enterprise Networks, usually run EIGRP or OSPF to share internal reachability and almost never exclusively iBGP. It all comes to network design.

An scenario to run iBGP on an Enterprise Network would be on Dual Home Routers connecting to the Internet (iBGP between the 2 WAN Routers).

I hope this information has been useful for you.

Best Regards.

[mishaal-thabet]

Hello Hector,

 i think i came in the last moment, and the event is about to end.

i am running a full internet BGP route where i run a huge traffic of VoIP the fiber optical cable between me and the international peers, due to cable cut or other circumstance “which happen a lot at my place “we encounter some errors that effect the BGP session to drop and at this moment the VoIP traffic got interrupted.

so is there any best practices and recommendation to tune up BGP for VoIP also what tuneup should be made to STMx interfaces to handle out any cut smoothly.

Best Regards,

Mishaal

[Hector Gustavo Serrano Gutierrez · Accepted solution]

Hello mishaal-thabet, thanks for your participation on this event.

Basically, BGP as a Control Plane protocol, ultimately helps the Router to know where to send the traffic next based on the Destination IP address of the IP Header included in the traffic received. This regardless of the type of IP traffic.

We know VoIP is actually just IP traffic.

A cable or fiber cut with the ISP will eventually bring the BGP adjacency down after 180 seconds as it is the Hold Time BGP uses by default. In some scenarios, BGP will immediately detect a network failure when the link used to reach the neighbor goes down (unfortunately, this doesn't always happen). This will start the process of network convergence so your VoIP traffic can reach its destination again via a Backup path.

Regardless of the type of interface that is used to connect to your ISP, the first step that kicks in network convergence is to detect the network failure.

Bidirectional Forwarding Detection (BFD) can be used by BGP to detect network failures quickly so the network re-convergence process can start faster reducing the total outage time.

- Bidirectional Forwarding Detection

BFD needs to be running on both BGP peers.

Of course, I am assuming your network has redundancy.

I hope this helps.

Best Regards.

[mishaal-thabet]

Thank you Hector Gustavo

BFD is a great practice but i am not sure why I have some preservation in my mind about enabling BFD in POS interface !

Regards

[Hector Gustavo Serrano Gutierrez]

Hello mishaal-thabet,

With circuits that are not reliable enough to run BFD, we can also reduce the BGP timers to obtain faster convergence times as an alternative.

I am assuming your network has redundancy.

I hope this helps.

Best Regards.

[mishaal-thabet]

Thank you Hector Gustavo

yeah My network has redundany.

just one more things is any thing else i could use besdie the Timers and BFD.

appreciate it and i will be glad if there are any documents about that.

[Hector Gustavo Serrano Gutierrez]

No problem mishaal-thabet, I am glad the information has been useful for you.

BGP already incorporates a KEEPALIVE mechanism that senses link failures and brings the adjacency down, allowing the network to convergence and find a new path towards the destinations.

IP SLA Object Tracking is another 'keepalive' mechanism that can be used to trigger network convergence after a failure. It can be used in scenarios where you need to 'tweak' the failover manually modifying static routes. It might be redundant in scenarios where the Routing Protocol is already doing that for you.

However, you can test the solution that works better for you.

Documents:

- Cisco IOS IP Routing: BGP Command Reference

- Configuring IP SLAs ICMP Echo Operations 

- Configuring Enhanced Object Tracking

I hope this helps.

Best Regards.