Problems configuring multihop BGP setup

[Alexander Zubkov]

Hello,

Why do you want your BGP sessions to be multihop? If you have direct
links, it is better if they are direct. From the first sight, you have
"protocol direct" disabled. This may cause your routes to be
"unreachabe" and that is why they are not propagated correctly.

On Thu, Jul 22, 2021 at 4:13 PM Rainer Kulow <rainer.kulow at online.de> wrote:
>
> I'am sorry, the ascii graphic was somehow wrapped a bit strangely.
>
> Here is a better version of it (now using the correct AS-Numbers):
>
> +-----------------+
> |  AS 60007    |
> |10.70.0.1/16|
> |                       |
> +-------+--------+
>             |  172.16.18.1/30
>             |
>             |  172.16.18.2/30
> +-------+--------+
> |  AS 60002    |
> |10.20.0.1/16|
> |                       |
> +-------+--------+
>            |  172.16.96.1/30
>            |
>            |  172.16.96.2/30
> +-------+--------+
> |  AS 60005    |
> |10.50.0.1/16|
> |                       |
> +-----------------+
>
>
> On 22-07-2021 15:43, Rainer Kulow wrote:
> >Hello bird community,
> >
> >I am trying to establish complete connectivity using BGP in the following
> >setup containing three AS with direct links:
> >
> >    172.16.18.1/30         172.16.18.2/30     172.16.96.1/30
> >172.16.96.2/30
> >+--------------+                                    +--------------+
> >+--------------+
> >| AS 60007 +---------------------------+ AS 60002
> >+---------------------------+ AS 60005 |
> >+--------------+                                    +--------------+
> >+--------------+
> >10.70.0.1/16                                   10.20.0.1/16
> >10.50.0.1/16
> >
> >The goal is that every address from one of the /16 networks can reach all
> >addresses in the other /16 networks.
> >
> >My current setup (here for the middle AS, the others are configured
> >analogously):
> >AS 60002 has three network cards, one with 172.16.18.2, one with
> 172.16.96.1
> >and one 10.20.0.1.
> >
> >log syslog all;
> >router id 10.20.0.1;
> >
> ># interface scan every 10s
> >protocol device {
> >       scan time 10;
> >}
> >
> ># no automaic generated direct routes to all network interfaces
> >protocol direct {
> >       disabled;
> >}
> >
> ># synchronize BIRD routing tables with the OS kernel
> >protocol kernel {
> >        ipv4 {
> >              import all;
> >              export all;
> >        };
> >        merge paths on;
> >}
> >
> ># static IPv4 routes
> >protocol static static1{
> >      ipv4;
> >      route 10.20.0.0/16 via 10.20.0.1;
> >}
> >
> ># BGP peers
> >template bgp bgp_peer{
> >      local as 60002;
> >      multihop;
> >
> >      ipv4 {
> >              import filter {
> >                  if proto = "static1" then reject;
> >                  accept;
> >              };
> >              export all;
> >              next hop self;
> >      };
> >
> >}
> >
> >protocol bgp a_b from bgp_peer {
> >      description "BGP a-b";
> >      neighbor 172.16.18.1 as 60007;
> >}
> >
> >protocol bgp b_c from bgp_peer {
> >      description "BGP b-c";
> >      neighbor 172.16.96.2 as 60005;
> >}
> >
> >
> >If I delete "multihop" and "next hop self" from the template, I get all
> >routes, but can only ever ping the closest AS.
> >With "multihop" I also get all routes, but the routes to other AS are
> marked
> >as unreachable.
> >I would be glad if someone could tell me how to realize this multihop
> >scenario. It would also be interesting that the solution scales, so that I
> >can hang, for example, more AS in the chain above.
> >
> >Thanks in advance,
> >Best regards,
> >Rainer