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Community Member

Routing Design

Hi, I have a design where I am trying to decide if it would be better to run EIGRP vs iBGP on a crosslink connection for failover purposes. Attached is a diagram

- R3 and R4 are internal distribution Switches that connect via EIGRP and are dual homed to the internal Core Switches (The core is depicted as internal network. There are 2 core boxes Core 1 and Core 2 not shown on the diagram)

- R3 and R4 are also connected to each other via Cross-Over cable and are running iBGP between them.

1. I am considering running EIGRP between them because per my understanding if R3 which is the Primary Switch loses its connection to both the Core's than it won't have any routes to get back to the Core's via R4 because I am not redistributing EIGRP into BGP since its not required. I could put a network statement in BGP but I am thinking this might not scale well if there are a lot of routes that are not summarizable. I could use static routes but would rather avoid them. Can anyone provide any thoughts on this setup?

2. In addition I am also considering if I should remove iBGP as well between R3 and R4 if I go with running EIGRP between them. I can't see the benefit of running iBGP between R3 and R4 if I have another IGP running between these devices. All iBGP will be doing is advertising the routes, that R3 receives via eBGP from R1, to R4 and the same for R2 and R4.

Thx for your help.

2 ACCEPTED SOLUTIONS

Accepted Solutions
Hall of Fame Super Bronze

Re: Routing Design

I can't see the benefit of running iBGP between R3 and R4 if I have another IGP running between these devices. All iBGP will be doing is advertising the routes, that R3 receives via eBGP from R1, to R4 and the same for R2 and R4.

And if you do so, are you planning to redistribute BGP into EIGRP?

The beauty of having iBGP between R3 and R4 is that you can perform traffic engineering by using BGP attributes for traffic entering and leaving the network.

For instance, if you decide to have R4 be the primary gateway for traffic towards AS 1234, you can simply use the local-pref and you are done. This is kind of hard when each router is eBGP towards AS 1234 but there isn't any iBGP within AS 4567.

Without knowing all the requirements, it's kind of hard to make a formal recommendation but you need to take into account the benefits of having iBGP which is traffic engineering for BGP routes.

Regards

Edison.

Hall of Fame Super Bronze

Re: Routing Design

In this case per my understanding Traffic Engineering is not going to be that critical since all routes that I receive via eBGP from R1 to R3 and R2 to R4 will be preferred due to them being eBGP routes on the R3 and R4. When redistributing routes into EIGRP the default metric is higher on R4 so I am preferring all traffic coming to R3.

I'm referring to traffic engineering in/out of your network between the two edge devices, not internal devices.

I still stand by recommendation to leave the iBGP running between the two edge devices and redistribute from BGP to EIGRP and EIGRP to BGP where needed. It provides a more scalable solution and deterministic traffic flow.

Regards

Edison.

9 REPLIES
Community Member

Re: Routing Design

Diagram Attached. Thx

Hall of Fame Super Bronze

Re: Routing Design

I can't see the benefit of running iBGP between R3 and R4 if I have another IGP running between these devices. All iBGP will be doing is advertising the routes, that R3 receives via eBGP from R1, to R4 and the same for R2 and R4.

And if you do so, are you planning to redistribute BGP into EIGRP?

The beauty of having iBGP between R3 and R4 is that you can perform traffic engineering by using BGP attributes for traffic entering and leaving the network.

For instance, if you decide to have R4 be the primary gateway for traffic towards AS 1234, you can simply use the local-pref and you are done. This is kind of hard when each router is eBGP towards AS 1234 but there isn't any iBGP within AS 4567.

Without knowing all the requirements, it's kind of hard to make a formal recommendation but you need to take into account the benefits of having iBGP which is traffic engineering for BGP routes.

Regards

Edison.

Community Member

Re: Routing Design

Hi Edison,

Thanks for responding. eBGP will be getting redistributed into EIGRP on R3 and R4. Just as a FYI this is not the entire internet DMZ so I am not redistributing the entire internet routing table. R3 is the Primary Switch because it connects to the Primary Firewall. The firewalls are in active/standby state hence traffic flow will always go to the active firewall FW1 since it owns the active VRRP.

In this case per my understanding Traffic Engineering is not going to be that critical since all routes that I receive via eBGP from R1 to R3 and R2 to R4 will be preferred due to them being eBGP routes on the R3 and R4. When redistributing routes into EIGRP the default metric is higher on R4 so I am preferring all traffic coming to R3.

Also what would be your recommendation on running EIGRP between R3 and R4 per my original question. Thx

Community Member

Re: Routing Design

Anyone have any suggestions. thx

Community Member

Re: Routing Design

Really appreciate a bit of help over here. Thx

Hall of Fame Super Bronze

Re: Routing Design

In this case per my understanding Traffic Engineering is not going to be that critical since all routes that I receive via eBGP from R1 to R3 and R2 to R4 will be preferred due to them being eBGP routes on the R3 and R4. When redistributing routes into EIGRP the default metric is higher on R4 so I am preferring all traffic coming to R3.

I'm referring to traffic engineering in/out of your network between the two edge devices, not internal devices.

I still stand by recommendation to leave the iBGP running between the two edge devices and redistribute from BGP to EIGRP and EIGRP to BGP where needed. It provides a more scalable solution and deterministic traffic flow.

Regards

Edison.

Community Member

Re: Routing Design

Hi Edison,

Thx for replying.

I'm referring to traffic engineering in/out of your network between the two edge devices, not internal devices.

Could you possibly elaborate a little more on the above.

I still stand by recommendation to leave the iBGP running between the two edge devices and redistribute from BGP to EIGRP and EIGRP to BGP where needed. It provides a more scalable solution and deterministic traffic flow. .

On the above just need to be absolutely certain that you are recommending instead of running EIGRP on the crosslink to redistribute the EIGRP routes into BGP and than have iBGP propogate to R3. Thx

Hall of Fame Super Bronze

Re: Routing Design

Could you possibly elaborate a little more on the above.

I touched on that subject in my original post. There is a whole chapter on the subject on any routing book - here is a sample:

http://oreilly.com/catalog/bgp/chapter/ch06.html

What's the benefit from removing the iBGP peering? You will still need BGP on the routers anyway..

On the above just need to be absolutely certain that you are recommending instead of running EIGRP on the crosslink to redistribute the EIGRP routes into BGP and than have iBGP propogate to R3.

Any recommendations made on these forums will never be certain. We offer suggestions based on the poster information. Remember, this is a volunteer forum. If you want assurance, I recommend hiring someone to provide an in-depth analysis of your network.

Regards

Edison.

Community Member

Re: Routing Design

Hi Edison,

Thx for your response.

I realize this is a volunteer forum and I was just trying to reconfirm my understanding of your suggestion. Apologize if it sounded otherwise. I am/was asking myself the same questions with regards to iBGP and removing it since it was there anyway hence I posed the query to get a independant perspective. Appreciate the help. thx

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