BGP Advertisment

[dschuckman]

Good Evening.

I am having a serious issue right now. I currently have two DS3's that provide bandwidth to my network and am awaiting the installation of an OC3 to replace one of the DS3's. I currently am struggling with some bandwidth issues for the following reasons. My two DS3's come from two seperate carriers. However one DS3 seems to be prefered over the other. I am maxing one DS3 out while the other is only running at aproximately 50-60%. I believe the issue to be caused by the path for each DS3. Both DS3's eventually terminate in CHicago however one is a direct connect(Maxed DS3) and the other show a longer path or it has an extra hop before making it to chicago. I run BGP between the two routers supporting the DS3's and then BGP between my networks and my SP's so what I am working with is a multi-homed bgp network. Is there anyway to manipulate the advertisement so that both paths look equal and hopefully bandwidth will equal out? so lets say add a weight to the maxed DS3 and make it look as though it is the same disatance as the not so maxed DS3. I know that this message is a little bit all over the place that is waht happens when you are half asleep and trying to figure out a solution to by sometime until the new link is completed.

Thanks for any help.

David

[pkhatri]

Hi David,

Can you advise whether the traffic problem is inbound or outbound or both ? In which direction(s) is the DS3 maxed out ?

Paresh

[dschuckman]

Sorry about that. The DS3 is maxed on the inbound. I am running 97% on the return from the internet or on downloads for uploads or outgoing it is only around 30%.

[pkhatri]

Hi again,

Here's a strategy I would use:

1. Configure AS-PATH prepending on the routes you advertised out via the stressed DS3. Start of with pre-pending one instance of your AS#

2. Soft-clear your connection and let the routes dissipate over the Interet

3. Observe traffic for a few hours and compare with the corresponding period before the change

4. If there is not much difference, go back to step 1 and add another instance of your AS#

You should find that you reach a point where you start getting a nice balance between the two links.

Hope that helps - pls rate the post if it does.

Paresh

[dschuckman]

Can you verify for me is the following the configuration that I would want to attempt.

eg.

router(config)#route-map setfromtag permit 10

router(config-route-map)#match tag 5

router(config-route-map)#set as-path prepend 120 120

router(config-route-map)#end

router(config)#router bgp 120

router(Config-router)#redistribute ospf 101 route-map setfromtag

Does that look like what I should attempt?

I am also going to open a tac case on this to verify. Thanks for the assitance thus far.

Thanks

David

[pkhatri · Accepted solution]

Hi,

Actually, I'm not sure that would work - you would have to pre-pend by applying a route-map to the BGP neighbor, as such:

neighbor route-map PREPEND out

!

route-map PREPEND permit 10

match ip address

set as-path prepend 120

Hope that helps - pls rate the post if it does.

Paresh