Announce a single IP of a network via BGP

[Netzmarkt]

Hey,

we are migrating to Google HA VPNs using their community tutorial:

https://cloud.google.com/community/tutorials/using-ha-vpn-with-cisco-asa

While the VPN and BGP parts are working fine we ran into following issue:

Previously we had static routes for only a few IPs of a subnet (directly on the ASA). Now that we are using BGP i have not found a way to advertise a singe IP of a subnet via BGP, since there is only the route for the subnet.

Did we miss something? Thanks!

[Richard Burts]

Am I correct in understanding that in your previous environment that you had some static routes for specific IP addresses and that in the process of changing to migrate to Google HA VPN that you have removed those static routes?

I do not know much about your particular environment and so can not give good advice about your particular environment but I can say that in general if you want BGP to advertise something then that entity must appear (with correct IP address and subnet mask) in your routing table. So if you want BGP to advertise a specific IP address then there must be an entry in your routing table for that IP address with a /32 mask. The easiest way to get a host address into your routing table is to configure a static route for it.

[Netzmarkt]

Hey, do you know if its possible to add a route (e.g. "192.168.1.7") if there is an interface configured like this:

interface Port-channel1.2000
  vlan 2000
  ip address 192.168.1.1 255.255.255.0

It seems like static routes can only have next-hop targets and no interfaces.

Thanks for your help!

[Richard Burts]

I would think it would be possible to configure this: ip route 192.168.1.7 255.255.255.255 port-channel1.2000. It is an unusual config but I think it should work.

Certainly the more common configuration of static routes does specify a next hop. But it is possible for the static route to just point to an outbound interface. There is advice about static routes that says that a static route specifying only an outbound interface and not a next hop should not be used for Ethernet interfaces. But in your situation I believe it is called for and should work.

[Netzmarkt]

Hey Rick,

the command you mentioned doesn't work for me.

Hardware: ASA5525

ASA Version 9.14(3)9

fw/pri/act(config)# ip route
                       ^
ERROR: % Invalid input detected at '^' marker.


fw/pri/act(config)# route INTERNAL 192.168.1.7 255.255.255.255 port-channel1.2000
                                                               ^
ERROR: % Invalid Hostname

Do i need to be in a specific sub menu?

Thanks a lot for your help!

[Richard Burts]

My mistake. In writing my response I did not remember that this is on an ASA. The syntax that I suggested is for router or switch. Syntax would be different for ASA. And realizing that this is an ASA I am not as confident that a static route specifying only the outbound interface would be accepted. Give it a try and let us know the outcome.

[Netzmarkt]

I was unable to find a syntax that would do this. Can anyone confirm that the ASA does not support routes directly to an interface?