Problems configuring multihop BGP setup

[Rainer Kulow]

I'am sorry, the ascii graphic was somehow wrapped a bit strangely.

Here is a better version of it:

+-----------------+
|  AS 64517    |
|10.70.0.1/16|
|                       |
+-------+--------+
            |  172.16.18.1/30
            |
            |  172.16.18.2/30
+-------+--------+
|  AS 64512    |
|10.20.0.1/16|
|                       |
+-------+--------+
           |  172.16.96.1/30
           | 
           |  172.16.96.2/30
+-------+--------+
|  AS 64515    |
|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
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