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Newbie BGP Questions

Cox Communications provides us high speed Internet access via an Ethernet interface in our router. Although this interface always stays up, we lose Internet access several times a year for several hours at a time. In order to avoid this, we ordered a T1 frame relay circuit from UUNet, which will be installed next week. A T1 can only carry a fraction of our traffic so we expect response time will be poor when the Cox network isn't working. Therefore, we only want to use the UUNet T1 when it's the only path available. Obviously, I also want return packets to usually take the Cox path unless my router is not reachable that way, in which case they should take the UUNet path.

1) Will the following code achieve these goals?

router bgp 11244 no synchronization network xx.248.12.0 mask 255.255.254.0 neighbor xx.248.12.1 remote-as 22520 (Cox) neighbor xx.248.12.1 weight 100 neighbor 157.130.138.245 remote-as 701 (UUNet) neighbor 157.130.138.245 route-map mypath out route-map mypath set as-path prepend 11244

2) I would like to only store the routes to my two upstream neighbors in the BGP route table and have BGP install a default route (or functional equivalent) that will change as needed into the IP routing table. Is this possible?

3) Cox assigned us our /23 address space, which is just a tiny piece of their block. Will they stop advertising our network if something in their network gets broken beyond my neighbor router? How does this work and how will my router know to start sending packets out the UUNet path? How long does convergence typically take?

-- Bob Simon remove both "x"s from domain for private replies

Reply to
Bob Simon
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Hi Bob,

To confirm what you said, you want COX as your primary and want UUNET as your backup. The easiest way to do this would to run communities with UUNET - on your outbound announcement, you create a route-map that matches a community that lowers the pref within UU's network. This will ensure they don't propagate the route upwards at all and will ensure that any traffic originating from UUNET won't come across the T1 you have with them, rather it will traverse the Internet. Then, for inbound traffic, just lower the local-pref with a route-map from anything learned from UUNET. This will ensure symetrical routing.

For example:

route-map UUnet-out permit 10 set community 701:xxx

Then, you can also create a route-map inbound for UUnet to lower pref for anything you receive from them inbound:

route-map UUnet-in permit 10 set local-preference 90

Once you have both route-maps defined, you can apply that to your neighbor peer-group:

conf t ip prefix-list DEFAULT-ROUTE seq 5 permit 0.0.0.0/0 ip prefix-list AS11244-net seq 5 permit xx.248.12.0/23 ! router bgp 11244 no synchronization bgp log-neighbor-changes no auto-summary neighbor UUNET peer-group neighbor UUNET remote-as 701 neighbor UUNET send-community neighbor UUNET desc ** UUnet Peer (Backup) ** neighbor UUNET prefix-list DEFAULT-ROUTE in neighbor UUNET prefix-list AS11244-net out neighbor UUNET route-map UUnet-in in neighbor UUNET route-map UUnet-out out ! neighbor 157.130.138.245 peer-group UUNET

That should pretty much cover it... this will do the following:

1) Only permit a default-route from UUNET (and you'll filter everything else)

2) Only announce your netblock upwards to them (you'll filter everything else)

3) You tag your outbound so UU receives it with a lower pref (anything less than 100)

4) You take your inbound from UU so that it's less preferred

All UUNET will need to do is (1), permit your prefix, (2) send you only a default route, (3) run communities with you.

Using AS numbers will work, but it may not give you the desired results as sometimes you have to add/remove AS#'s to your announcements. One last thing to consider is that you may want to just get internal routes from one peer and a default from the other so that you can use both lines actively. This is more involved but it's another option.

Good luck!

-Vikas

Reply to
vikas.khanna

Vikas, Thanks for your generous reply but I am having some trouble with several points you made. I would very much appreciate your giving me a bit more help with this.

1) You said that I should "run communities with UUNET." Does this mean that I coordinate with UUNet and ask them to create community 701:xxx, then I reference it in my outbound route-map? Or is it my job to define this community?

2) After your example config you identified what it accomplishes. You said, "3) You tag your outbound so UU receives it with a lower pref (anything less than 100)". Which statement lowers the preference of the UUNet outbound path?

3) Your config included no statements for the Cox neighbor router. I presume I need the following additional commands. Is this correct? neighbor xx.248.12.1 remote-as 22520 neighbor xx.248.12.1 weight 100

Thanks again!

Bob

-- Bob Simon remove both "x"s from domain for private replies

Reply to
Bob Simon

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