WG: Problems configuring multihop BGP setup

22 Jul 2021

      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