Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Announcements
Webcast-Catalyst9k
New Member

BGP route advertisement

I have (2) 2800 routers that each have connections to the same ISP. These routers then both connect in to an ASA cluster. The ISP has given us a /28, and the internal ip addresses of the routers and the external of the ASA is in this subnet. My problem is that I wish to advretise a /29 out on pipe and a /29 out the other so that we can load balance. I have each 2800 with an Ebgp session to the ISP, and an Ibgp to each other. The problem is that the ISP just sees the /28 being announced.

2 ACCEPTED SOLUTIONS

Accepted Solutions
Hall of Fame Super Gold

Re: BGP route advertisement

Scott

I believe that the immediate problem is shown in this statement:

Since the specific /29 routes are not in the routing table, I added them to null0 with an admin distance of 255.

The admin distance of 255 prevents them being put into the routing table. And if they are not in the routing table then BGP can not advertise them. I suggest changing the admin distance to something high but less than 255 (even 254 would do).

Try changing the admin distance and let us know how it works.

HTH

Rick

Re: BGP route advertisement

Hi scott,

Just advertising both subnets to your ISP via both links wont help. Your Outgoing policy will affect the incoming traffic. If you want to advertise subnet 172.16.100.0/29 to your ISP via router1 then you should also make sure that the ISP send the return traffic via the same link and fall backs to the other only during failure.

You will have to Manipulate your metrics while advertising (either by MED or AS prepend)

As prepend may not work if ur AS is private as ISP may filter it. MED wil also only work when the ISP is ready to accept the MEDs from you.

HTH

Narayan

8 REPLIES
New Member

Re: BGP route advertisement

Also, yes you are right in that we wish to load balance. My concern is that if I route some traffic out one link, the return path will be different and it will cause problems.

Re: BGP route advertisement

could you show us the output of:

show ip bgp 172.16.100.0

and

show ip bgp 172.16.100.8

and

show ip route 172.16.100.0 255.255.255.248

show ip route 172.16.100.8 255.255.255.248

Vlad

Hall of Fame Super Gold

Re: BGP route advertisement

Scott

I believe that the immediate problem is shown in this statement:

Since the specific /29 routes are not in the routing table, I added them to null0 with an admin distance of 255.

The admin distance of 255 prevents them being put into the routing table. And if they are not in the routing table then BGP can not advertise them. I suggest changing the admin distance to something high but less than 255 (even 254 would do).

Try changing the admin distance and let us know how it works.

HTH

Rick

Re: BGP route advertisement

Hi scott,

Just advertising both subnets to your ISP via both links wont help. Your Outgoing policy will affect the incoming traffic. If you want to advertise subnet 172.16.100.0/29 to your ISP via router1 then you should also make sure that the ISP send the return traffic via the same link and fall backs to the other only during failure.

You will have to Manipulate your metrics while advertising (either by MED or AS prepend)

As prepend may not work if ur AS is private as ISP may filter it. MED wil also only work when the ISP is ready to accept the MEDs from you.

HTH

Narayan

Re: BGP route advertisement

This is quite simple to accomplish, if you are using 2 IPs on the ISP to establish your peers:

router bgp AS

aggregate 172.16.0.0 255.255.255.248 summary-only

aggregate 172.16.0.8 255.255.255.248 summary-only

Then using prefix-list to filter out which prefix you want to send to each ISP.

neighbor 1.1.1.1 prefix-list pl_1 out

neighbor 2.2.2.2 prefix-list pl_2 out

ip prefix-list pl_1 permit 172.16.0.0/29

ip prefix-list pl_2 permit 172.16.0.8/29

you'll need some network statements as well to make this work:

router bgp AS

network 172.16.0.0 mask 255.255.255.248 (this need to match your IGP routing table)

network 172.16.0.8 mask 255.255.255.248 (this need to match your IGP routing table)

if you dont have these specific routes on your routing table , you could try:

ip route 172.16.0.0 255.255.255.248 NULL0 255

ip route 172.16.0.8 255.255.255.248 NULL0 255

But, I dont believe you need to do this in order to load balance. You're probably talking about load sharing (ie. part of your network will flow through 1 link and the other will go to the other.

anyway, give us more details on your configs, it will be easier to help.

Vlad

New Member

Re: BGP route advertisement

Thank you for helping..

Here is a sample config:

2800-1

fa0/0 ip add 10.10.10.1/30 (goes to ISP)

fa0/1 ip add 172.16.100.2/28 (goes to ASA)

router bgp 65123

network 172.16.100.0 mask 255.255.255.248

network 172.16.100.8 mask 255.255.255.248

neigh 10.10.10.2 remote 200

neigh 172.16.100.3 remote 65123

------------------------------------------

2800-2

fa0/0 ip add 20.20.20.1/30 (goes to ISP)

fa0/1 ip add 172.16.100.3/28 (goes to ASA)

router bgp 65123

network 172.16.100.0 mask 255.255.255.248

network 172.16.100.8 mask 255.255.255.248

neigh 20.20.20.2 remote 200

neigh 172.16.100.2 remote 65123

Since the specific /29 routes are not in the routing table, I added them to null0 with an admin distance of 255. However, the routes are not being sent..

Re: BGP route advertisement

what is the IOS version?

did you disable auto-summary and synchronization?

router bgp 65123

no auto-summary

no synchronization

by the way, you will not be able to load-balancing between a IBGP peer and EBGP peer.

vlad

New Member

Re: BGP route advertisement

12.4T

yes, I disabled auto-summ and synch

163
Views
0
Helpful
8
Replies
CreatePlease to create content