Multihoming BGP and static route

[gasparmenendez]

Hi friends,

I'm using 2 ISPs (ISP-A and ISP-B), have my own block of public IP addresses (170.X.X.0/22) and my ASN (26XX25). I'm using a Cisco ASR1001-X Router. Besides, I have a BGP session established with ISP-B and ISP-A is using default route (in a few days I should have BGP with this ISP too). I need to make ISP-B my primary provider and pass all my traffic through it, but right now all my traffic is through ISP-A, even when I have in my ASR a static route to ISP-B: ip route 0.0.0.0 0.0.0.0 187.X.X.112, where 187.X.X.112 is the gateway for ISP-B. A couple days ago ISP-A went down and I losted internet access, even when my ISP-B were up. Is it possible what I want to do?? Can anybody help me please?? Thanks in advance.

[Richard Burts]

Gaspar

I am glad that my explanations have been helpful. I am not sure what you are meaning when you say that you will ask the ISP just for transit. But I believe that you do want both ISP to act in the same way, so if just for transit is what you asked ISP B then that is probably what you want to ask ISP A.

Load balancing with two ISP can be a bit complicated. For one thing you want to be sure that some route that you learn from ISP A is not then advertised to ISP B. Otherwise you may become a transit link between ISP A and ISP B. You would typically resolve this using a filter list which permits only locally originated routes.

I suggest to you that when doing load balance with two ISP that it helps to think about incoming traffic and outgoing traffic separately. The kind of things that you do to balance incoming traffic will have no impact on outgoing traffic.

HTH

Rick

[gasparmenendez]

sorry for my English Rick...by transit I mean that I'm going to advertise my subnet myself, so ISP becomes a transit system I believe. And precisely mi idea is to ask both providers for the same things. Right now I'm waiting for ISP-A to establish BGP session. Once it is done, I need to start tu run some tests.

Thanks.

[Richard Burts]

Gaspar

Thank you for the clarification. Yes with that understanding of transit only I agree that this is what you need to establish with both ISP. And when running BGP for transit only and properly configured with two ISP then failover if one ISP stops processing (and failback when they recover) works automatically.

HTH

Rick

[gasparmenendez]

that's what I hope Rick, besides, I going to split my network block in 2 halves (/23) to use load-sharing...

thanks.

[Richard Burts]

Gaspar

Splitting your address space into two parts is frequently an effective way to achieve load sharing of traffic from the Internet coming into your network.

HTH

Rick

[gasparmenendez]

Rick,

maybe you can help me with something: right now I have configured my ASR for BGP like this:

router bgp 26XX25
 bgp router-id 187.X.X.113
 bgp log-neighbor-changes
 network 170.X.X.0 mask 255.255.252.0
 neighbor 187.X.X.112 remote-as 13XX9
 neighbor 187.X.X.112 password 7 000271
 neighbor 187.X.X.112 soft-reconfiguration inbound

.

.

ip route 0.0.0.0 0.0.0.0 187.X.X.112
ip route 0.0.0.0 0.0.0.0 208.X.X.181 10
ip route 170.X.X.0 255.255.252.0 Null0

my question is : what do I need to add (or modify) to that configuration when ISP-A finally uses BGP and I can start using both providers ASAP, I mean before load-sharing or anything else...(let's say that ASN for ISP-A would be i.g. 14587) ???

thanks.

thanks.

[Richard Burts]

Gaspar

When you are ready to start using BGP with ISP A there is one thing that I believe that you need to have BGP active with both ISP.  It is a filter list to prevent learning some route from one ISP and then advertising that route to the other ISP. It would look something like this

neighbor 187.x.x.112 filter-list 10 out

!

ip as-path access-list 10 permit ^$

And then your config for ISP A would be similar (of course with different neighbor addresses and AS number).  This should be sufficient to get both ISP running BGP with you. There are other things that you might want to use to fine tune the BGP and to set up the load sharing. But this should be sufficient to get BGP running with both ISP. You would also want to remove the static default routes.

HTH

Rick

[gasparmenendez]

thanks Rick!

[castro]

Please who can help me configure static route on cisco ASR1001-X 

[Richard Burts]

If you are running BGP which learns a default route from the provider and also have a static default route then the static default route should take precedence and be used rather than the default route learned from BGP. With a static default route it becomes more of a challenge to failover if the primary ISP experiences a problem. So when running BGP multi homed to two providers it is most common to not have a static default route. But your question asks about the situation where you do have the static route and so we need to answer in terms of that environment.

Your post says that your static default route goes through ISP B but that all traffic is going through ISP A. Can you provide some clarification of that? Perhaps the output of show ip route would be a good place to start.

HTH

Rick

[bohra_ajay]

I'm also using the same scenario where in I've ISP A with default route and ISP B with BGP.

for this I'm using two routers. One for ISP A (10.1.1.2) and other for ISP B. Now I've made the DG for my users to be one interface of ISP B router. and I've configured Static routes for ISP A with AD defined. In case ISP goes down using IP SLA my users start going to ISP A. And also, I've redistributed connected in the BGP config for ISP B.

This setup solves my purpose. HTH.

I'm also in talks with ISP A to provide BGP, once that'll be done I'll go with the Wieght LP & MED settings.

[gasparmenendez]

hi my friend,

my case is different since I'm using only one Router....but I suppose it can be done, just need to figure out how!!

[gasparmenendez]

hello Richard,

output of #sh ip route is already posted.

and about what I describe in my post is exactly that way, all my traffic is passing through ISP-A, even when I've configured a static route to ISP-B. My ASR config is already posted as well.

Thanks!