Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Announcements

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. If you'd prefer to explore, try our test area to get started. And see here for current known issues.

New Member

BGP and EIGRP

We are implementing a new datacentre and consilidating our networks. We plan to introduce EIGRP for routing within this facility and any other we add. We peer with the internet at various locations and obviously I dont want to push all the internet routing table into EIGRP. I can inject a static default route into the internal routers from the borders using a command like:

router eigrp 20

redistribute static route-map default-only

network 1.11.111.0 0.0.3.255

network 1.12.111.0 0.0.0.127

distribute-list 10 out Vlan201

auto-summary

ip prefix-list default seq 5 permit 0.0.0.0/0

ip prefix-list default seq 10 deny 0.0.0.0/0 le 32

route-map default-only permit 10

match ip address prefix-list default

set tag 20

If I implement this on both border routers then I get the default routes through on eigrp. The only thing is that I then have a null route on the borders which will bin any unknown traffic. Is this a bad thing? Should I look to inject all the /8 networks from bgp into eigrp so that the interior routers correctly forward traffic? Any pointers anyone has on using BGP on the borders with EIGRP on the inside would be greatly appreciated.

Cheers,

Richard

1 ACCEPTED SOLUTION

Accepted Solutions

Re: BGP and EIGRP

Hi,

in fact the Null0 route saves you some traffic looping around. Well, in brief, if BGP does not know the network you would drop it anyhow. Also remeber that IP routing uses longest match. So the Null0 route is not bad at all.

It is installed automatically to avoid the following scenario:

R1 - R2

R1 has a route 10.0.0.0/8 to R2 and R1 has a route 0.0.0.0/0 to R1.

If 10.1.1.0/24 is not used, traffic for 10.1.1.1 would loop between the two routers. Thus the route to Null0, which will drop traffic to networks not in use.

Using the default route is for sure a common practice and redistributing the /8 will not bring you further, because you still need the Null0 routes (and then lots of them!) to avoid looping of traffic.

Hope this helps! Please rate all posts.

Regards, Martin

4 REPLIES
Cisco Employee

Re: BGP and EIGRP

You could ask your SP to send you a default route, if he doesn't already send it to you, and redistribute it directly from BGP to EIGRP. This way, if you loose the local link to the ISP, the default route will stop being injected into EIGRP from this specific router.

Hope this helps,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México 
Paseo de la Reforma 222 Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
New Member

Re: BGP and EIGRP

Hi,

We get full routes and filtered from multiple isp's and private peers. That was why I was considering using /8's from bgp into eigrp if that is possible.

Thanks,

Richard

Re: BGP and EIGRP

Hi,

in fact the Null0 route saves you some traffic looping around. Well, in brief, if BGP does not know the network you would drop it anyhow. Also remeber that IP routing uses longest match. So the Null0 route is not bad at all.

It is installed automatically to avoid the following scenario:

R1 - R2

R1 has a route 10.0.0.0/8 to R2 and R1 has a route 0.0.0.0/0 to R1.

If 10.1.1.0/24 is not used, traffic for 10.1.1.1 would loop between the two routers. Thus the route to Null0, which will drop traffic to networks not in use.

Using the default route is for sure a common practice and redistributing the /8 will not bring you further, because you still need the Null0 routes (and then lots of them!) to avoid looping of traffic.

Hope this helps! Please rate all posts.

Regards, Martin

New Member

Re: BGP and EIGRP

Hi Martin,

Exactly what I needed thankyou.

Richard

313
Views
2
Helpful
4
Replies