Splitting traffic via BGP

[DavidGIP]

Hello.

We have two 10gig circuits connected to our ASR9000. Two different ISPs going in two different directions. Our traffic is going through one of the 10G circuits, while the other was being used as a backup. We now want to use the second circuit for traffic as well.

We added Maximum-path egrp 2, as well as bgp best-path as-path multipath-relax. Unable to get traffic flowing through the second link. I am trying to see if this is a fool's errand, or is there a way to accomplish this.

I am including the config to see if there is anything I may be missing. Thank you.

router bgp OUR ASN
bgp bestpath as-path multipath-relax
address-family ipv4 unicast
maximum-paths ebgp 2
network xxx.xxx.xxx.xxx/20
network yyy.yyy.yy.yyy/22
!
neighbor 111.111.111.111
remote-as OUR ASN
description iBGP
address-family ipv4 unicast
maximum-prefix 1600000 80 warning-only
next-hop-self
soft-reconfiguration inbound always
!
!
neighbor 222.222.222.222
remote-as ASN1
description Current IP Transit
address-family ipv4 unicast
route-policy RPL_WAN_IN1 in
maximum-prefix 1600000 80 warning-only
route-policy RPL_WAN_OUT2 out
next-hop-self
soft-reconfiguration inbound always
!
!
neighbor 333.333.333.333
remote-as ASN2
password encrypted 10425A0D08444305
description Backup IP Transit
address-family ipv4 unicast
route-policy RPL_WAN_IN1 in
maximum-prefix 1600000 80 warning-only
route-policy RPL_WAN_OUT2 out
next-hop-self
soft-reconfiguration inbound always

[M02@rt37]

Hello @DavidGIP 

BGP best path selection is based on various attributes. Make sure that the attributes are consistent for both paths, allowing BGP to load balance. These include AS-path, MED, and others. If there are discrepancies, BGP might prefer one path over the other.

Could you please share for one prefixes the attributes attached with each neighbor 222 and 333.

[Harold Ritter]

Hi @DavidGIP ,

I presume you are not only receiving the default route from your ISPs, right? In this case one ISP might be better connected to the Internet and provide shorter AS Paths to most destinations, which defeats the purpose of load balancing.

The option would be to only take a default route from both ISPs, which will allow outbound load balancing.

Inbound load balancing is another story. Depending on your public IP addresses, you might be able to advertise half of it on one side and the other half on the other side.

Regards,

[DavidGIP]

Thank you for the response. We are looking to do load balancing with our inbound traffic. How would I be able to advertise just half of my public IP addresses?

I apologize for the question. I am pretty green when it comes with BGP, hence the questions. 

[Harold Ritter]

Hi @DavidGIP ,

As I mentioned in my previous post, it depends of the block you own. If you own just a /24, there is not much you can do. You can't break it down into longer prefixes, as a /24 is the longest prefix you are allowed to propagate on the Internet. You will have to advertise it as a /24 to both ISP and hopefully get some load balancing.

On the other hand, if you have something like a /23, the technique is normally to advertise first /24 out of that /23 to one ISP and the second /24 to the other ISP. You would also advertise the /23 to both ISPs for redundancy purposes, so if you loose the link to one ISP all traffic would reconverge to the other ISP.

Regards,

[MHM Cisco World]

Your config is correct 

Do you see prefix in routing table with two next-hop?