Question about BGP Routing Configuration

[rene.schmid]

Hi Everyone,

I have a question regarding BGP configuration. I work for a small ISP and I have to configure a BGP connection to a new customer with 2 locations.

The szenario is following.

We have our RouterA wich is the prefered Internet Router for our customers. RouterB is the backup Router but he is still active and works also for the Internet Traffic.

A new customer want's to connect 2 locations.

Location1 will be connected to RouterA and receives the network X.X.248.160/28 from us.

Location2 will be connected to RouterB and receives the network X.X.248.176/28 from us.

Now I need to configure the BGP config for the two locations and I need to configure RouterA as a backup for Location2 and RouterB as a backup for Location1.

I wrote a sample configuration for our two Routers but I'm not 100% sure how to configure the route priority or preference. I don't want to do some wrong configurations on our BGP Routers.

Here are the config lines.

RouterA connected to customer network X.X.248.160/28 and should be backup for network X.X.248.176/28

address-family ipv4

  neighbor X.X.255.81 activate

  neighbor X.X.255.81 default-originate

  neighbor X.X.255.81 soft-reconfiguration inbound

  neighbor X.X.255.81 password XXXX

  neighbor X.X.255.81 prefix-list Neo_IT_out out

  neighbor X.X.255.81 route-map neopref in

ip prefix-list Neo_IT seq 5 permit X.X.248.160/28

ip prefix-list Neo_IT_out seq 10 permit 0.0.0.0/0

route-map neopref permit 10

match ip address prefix-list Neo_IT

RouterB connected to customer network X.X.248.176/28 and should be backup for network X.X.248.160/28

address-family ipv4

  neighbor X.X.255.83 activate

  neighbor X.X.255.83 default-originate

  neighbor X.X.255.83 soft-reconfiguration inbound

  neighbor X.X.255.83 prefix-list Neo_IT_out out

  neighbor X.X.255.83 route-map neopref in

ip prefix-list Neo_IT seq 5 permit X.X.248.160/27

ip prefix-list Neo_IT_out seq 10 permit 0.0.0.0/0

route-map neopref permit 10

match ip address prefix-list Neo_IT

Thanks for any help.

Rene

[Vivek Ganapathi]

Hi Rene,

This needs to be achieved from the customer's side. Preferring a link/path is solely customer's choice

As per my understanding, you don't have a physical link running from your RouterB to Location_A or RouterA to LocationB of the customer. So, influencing failover is not in your control. You can only send in the default routes to the customer, rest they have to take care.

Customer can use local preference on Location_A router to influence / prefer the outgoing traffic via your Router_A. Same needs to be done on Location_B via Router_B.

Hope this helps

Regards

Vivek

[rene.schmid]

Hi Vivek,

yes correct there is no connection between RouterA and Location2 and RouterB and Location1.

There is an failure in my posted config.

It should be

RouterA

ip prefix-list Neo_IT seq 5 permit X.X.248.160/28

RouterB

ip prefix-list Neo_IT seq 5 permit X.X.248.176/28

Or should I route on our side network X.X.248.160/27  to both sides?

Rene

[varununiyal · Accepted solution]

Think in terms on as-path prepend.

Your scenario:

RouterA primary for X.X.248.160/28 and should be backup for network X.X.248.176/28

route-map

match ip address prefix-list

set as-path prepend --> make the a-path longer than whats advertised throguh router B making sure that router-A is backup

Do vice-versa for Router-B.

[rene.schmid]

Hi,

shoul I use the subnet X.X.248.160/27  or should I work with the subnets?

Best Regards

Rene