BGP Advertisements

[Simon Young]

I have an issue where I am migrating from one location to another.

I want to advertise the same prefix from two seperate sites but I want to advertise individual unicast addresses from separate sites

This is where I am at, any help would be much appreciated as I can't seem to get this to work. All the traffic is just routed to one site. I do have the other site as backup but not as the primary for individual routes

ip access-list standard Denied-SiteA
permit host 192.168.1.1
permit host 192.168.1.2

ip access-list standard Allowed-SiteA
permit 192.168.1.0 0.0.0.255

ip access-list standard Allowed-SiteB
permit any

route-map SiteA permit 10
match ip address Denied-SiteA
set as-path prepend 11111 11111

route-map SiteA permit 20
match ip address Allowed-SiteA
set as-path prepend 11111

route-map SiteA permit 30
match ip address SiteB
set as-path prepend 11111 11111

router bgp xxxxx
neighbor xxxx route-map SiteA out
end

************************************************************

ip access-list standard Denied-SiteA
permit host 192.168.1.1
permit host 192.168.1.2

ip access-list standard Allowed-SiteA
permit 192.168.1.0 0.0.0.255

ip access-list standard Allowed-SiteB
permit any

route-map SiteB permit 10
match ip address Denied-SiteA
set as-path prepend 22222

route-map SiteB permit 20
match ip address Allowed-SiteA
set as-path prepend 22222 22222

route-map SiteB permit 30
match ip address SiteB
set as-path prepend 22222

router bgp xxxxx
neighbor xxxx route-map SiteB out
end

[Harold Ritter]

Hi Simon,

Can you please more information. Are these site connected to the Internet or a private network. If they are connected to the Internet, the /32 prefixes will likely not make it beyond your ISP because of prefix filtering on the Internet. In this case only the /24 would be seen on the Internet.

Regards

[Simon Young]

Hi

Its a private MPLS cloud. I am advertising the routes to other sites within the same cloud.

Thanks

[Harold Ritter]

Thanks for the info. I see in the route-map that you advertise 192.168.1.1/32 and 192.168.1.2/32 but I do not see 192.168.100/32 and 192.168.1.105/32 being advertised on the other side. Can you please provide the complete bgp config from both side.

[Simon Young]

I don't have a complete BGP configuration to post as its a production environment, that I have replicated in my lab and I have modified the IP address to post here

I was hoping that 192.168.1.100 and 105 would be caught under permit 192.168.1.0 0.0.0.255 (i put them in purely to illustrate different IPs and can see that might be a bit confusing)

I was hoping to have site A as the primary path for the 192.168.1.x subnet (except for 192.168.1.1 and .2). Everything else including 192.168.1.1 and .2 via Site B

	Location	Primary	Secondary
192.168.1.1	Site B	prepended 22222	prepended 11111 11111
192.168.1.2	Site B	prepended 22222	prepended 11111 11111
192.168.3-254	Site A	prepended 11111	prepended 22222 22222
All other Routes	Site B	prepended 22222	prepended 11111 11111

I have a backup path as the two data centres are linked. Each has dual MPLS but as an absolute fail over there is also a link between them.

I can't seem to fine tune my configuration so that individual addresses are removed from the main /24. Currently I go to one site only

Thanks for your replies.

[Harold Ritter]

Hi Simon,

I would recommend to just announce 192.168.1.0/24 from site A and just the more specific (192.168.1.1/32 and 192.168.1.2/32) from site B. This way site A would attract all traffic to 192.168.1.0/24 except for .1 and .2 and you would not need to play with the prepend at all.

Hope this help

[Simon Young]

I had thought about doing that with aggregate addressing but I was hoping for a way of not having to change the network statements

I want to scale this up to many prefixes, not just a single one.

Also I need a backup route to the second site, in case the primary fails, thats why I want the pre-pend

Either way thanks for responding, I appreciate the feedback

[Harold Ritter · Accepted solution]

Hi Simon,

You should still be able to do the following:

advertise from site A:

192.168.1.0/24

192.168.1.100/32

192.168.1.105/32

Advertise from site B:

192.168.1.0/24

192.168.1.1/32

192.168.1.2/32

And prepend only on 192.168.1.0/24 depending on which site you want to prefer.

Hope this helps

[milan.kulik]

Hi,

as Harold said, it should be possible to configure what you want.

But it's difficult to say what's wrongin your config without having it available.

So just guessing:

Are there the host routes (static I suppose) configured on your routers?

If not present in RIB, BGP can't advertise them.