Dual ISP BGP dual router auto failover

[Mwinula]

Hello,

I would appreciate your suggestion, I have BR1 connected to ISP1 also PE1(Distribution router) connected to BR1 and BR 2 connected to ISP2, and PE2(Distribution router2) connected to BR2. How will I configure auto-failover between these two ISPs?

[Richard Burts]

There are things that we do not know about your environment that could impact our advice. For example we do not know if the ISPs are advertising only a default route or are advertising some other routes in addition to a default route. My suggestion is based on these assumptions: both ISP are advertising only a default route and your edge routers are running EBGP with ISP and IBGP with each other, and you want to have a primary ISP and  backup ISP (not doing load sharing). My suggestion is to configure local preference in BGP to make one ISP preferred and the other ISP as backup.

[Mwinula]

Hello Rick,

You are right, all ISPs are advertising only the default route to me, and in addition, I have my own Public AS with /22 public IPs, where Primary ISP1 provides 600Mbps and other ISP2 provides 300Mbps internet bandwidth and they both advertise my whole block to the internet. ISP2 should be on standby. All routers in my enterprise are running IBGP as per your assumption

[Richard Burts · Accepted solution]

Thank you for confirming that my assumptions were correct. In this case configuring local preference should establish ISP1 as primary and ISP2 as backup. If there is a problem (ISP1 goes down or withdraws its advertised route, etc) then failover to ISP2 would be automatic.

The fact that you have your own Public /22 is something that we need to consider separately. Local preference is effective in controlling how your network sends traffic to the Internet. But it does not do anything about how the Internet sends traffic to you. For this your best option is to use AS prepending on what you advertise to ISP2.

[Mwinula]

Let me review my configs and test then will update.

Thanks

[Mwinula]

Hello,

I did it over the weekend with the results as follows.
1. Outgoing traffic worked well failing over between the two ISPs
2. Incoming traffic is going via ISP2 only even if I set AS-PATH prepend but still prefer it.
What could be the reason for this?

[paul driver]

Hello
Can you share the configuration of your two wan rtrs and also a topology diagram.

[Richard Burts]

I agree with Paul that we do not have enough information to be able to give good advice about your new issue. Router configs would be a good start. It would also be useful if you post the output of show ip bgp neighbor <ip> advertised.