iBGP problem with full meshed routers

[Michael McConnell]

Hello Martin,

I think you need a static route along the multihop path for this to work or use OSPF in parallel. 

Cheers,
Mike

--
Michael McConnell
WINK Streaming;
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> On Aug 18, 2019, at 10:11 AM, Martin Bosner <m.bosner at x-ion.de> wrote:
> 
> Hello,
> 
> i'm a little desperate and helpless because i can't get any further with my current problem: 
> 
> My current setup (all same AS only physical):
> 
> router A   ----   router B --- router C ------- router E  --- router G
> (has full                   \            |                    |                 |
>  table uplink)             \          |                    |                 |
>                                    \         |                    |                 |
>                                         router D  ------- router F --- router H
> 
> Router ABCD and router EFGH are each at the same location in a L2 network. There are no additional static routing information but the one from the interfaces and they are all connected via BGP using the same AS. All routers can ping each other and no router has a default gw. All BGP sessions are using the same table and are up and alive. All direct connected routers have a "direct" connection and all non direct connected routers use multihop.
> 
> The problem is that router G and router H only have invalid global routes learned from router A while E and F are fine:
> (using 223.230.128.0/22 <http://223.230.128.0/22> is just a random pick for demonstration)
> 
> 
> router G and H (PROBLEM):
> 
> BIRD SHOW ROUTE
> birdc show route 223.230.128.0/22 <http://223.230.128.0/22> all
> BIRD 2.0.5 ready.
> Table master4:
> 223.230.128.0/22 <http://223.230.128.0/22>     unreachable [routerG_to_routerA 03:15:02.410 from 153.92.124.4] * (100/-) [AS45609?]
> Type: BGP univ
> BGP.origin: Incomplete
> BGP.as_path: 15943 9498 45609
> BGP.next_hop: 153.92.124.4
> BGP.local_pref: 100
> 
> KERNEL
> route -n | grep 223.230.128.0
> 223.230.128.0   -               255.255.252.0   !     32     -        0 -
> 
> CONFIG
> protocol bgp routerG_to_routerA{
>   local as 60664;
>   neighbor 153.92.124.4 as 60664;
>   source address 185.27.180.133;
>   enable route refresh yes;
>   multihop;
>   allow local as 60664;
>   ipv4 {
>           import all;
>           export all;
>           next hop self;
>             };
> }
> 
> 
> router E and F (VALID):
> 
> BIRD SHOW ROUTE
> birdc show route 223.230.128.0/22 <http://223.230.128.0/22> all
> BIRD 2.0.5 ready.
> Table master4:
> 223.230.128.0/22 <http://223.230.128.0/22>     unicast [routerE_to_routerA 02:42:58.878 from 153.92.124.4] * (100/?) [AS45609?]
> via 192.168.0.1 on external
> Type: BGP univ
> BGP.origin: Incomplete
> BGP.as_path: 15943 9498 45609
> BGP.next_hop: 153.92.124.4
> BGP.local_pref: 100
> 
> KERNEL
> route -n | grep 204.34.123.0
> 204.34.123.0    192.168.0.1     255.255.255.0   UG    32     0        0 external
> 
> CONFIG
> protocol bgp routerE_to_routerA{
>   local as 60664;
>   neighbor 153.92.124.4 as 60664;
>   source address 192.168.0.2;
>   multihop;
>   allow local as 60664;
>   ipv4 {
>           import all;
>           export all;
>           next hop self;
>             };
> }
> 
> 
> router A
> 
> BIRD SHOW ROUTE
> birdc show route 223.230.128.0/22 <http://223.230.128.0/22> all
> BIRD 2.0.5 ready.
> Table master4:
> 223.230.128.0/22 <http://223.230.128.0/22>     unicast [routerA_to_external 23:01:24.661] * (100) [AS45609?]
> via 84.44.0.210 on xge1
> Type: BGP univ
> BGP.origin: Incomplete
> BGP.as_path: 15943 9498 45609
> BGP.next_hop: 84.44.0.210
> BGP.local_pref: 100
> 
> KERNEL
> route -n | grep 204.34.123.0
> 204.34.123.0    84.44.0.210    255.255.255.0   UG    32     0        0 xge1
> 
> CONFIG E (valid)
> protocol bgp routerA_to_routerE{
>   local as 60664;
>   neighbor 153.92.124.2 as 60664;
>   source address 153.92.124.4;
>   direct;
>   allow local as 60664;
>   ipv4 {
>           import all;
>           export all;
>           next hop self;
>             };
> }
> 
> CONFIG G (problem)
> protocol bgp routerA_to_routerG{
>   local as 60664;
>   neighbor 185.27.180.133 as 60664;
>   source address 153.92.124.4;
>   multihop;
>   allow local as 60664;
>   ipv4 {
>           import all;
>           export all;
>           gateway recursive;
>           next hop self;
>             };
> }
> 
> 
> I am using bird 2.0.5 and ubuntu 18.04 with 4.15.0-54-generic and already played around with and without "next hop self"  etc. but without luck.
> 
> There seems to be a problem with my configuration or with the next hop calculation, right? Or did i miss something else?
> 
> Thank you in advance
> Martin Bosner
> 

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