08-25-2008 01:48 AM - edited 03-03-2019 11:15 PM
Hi,
is it possible for R1-AS100 and R2-AS300 to exchange BGP routing while there is a Router3 in the middle of them with Static routing ?
BGP without direct link
http://home.netpower.no/paal/bgp-possible.jpg
regards,
Paal
08-25-2008 03:15 AM
Hello!
Yes it is possible with ebgp-multihop "x"
where x in your case should be 2 (number of the hops to the other peer side)
You have a small template above how I would do it:
--------------
R1-AS100
int lo0
ip address 1.1.1.1 255.255.255.255
router bgp 100
bgp log-neighbor-changes
neighbor 2.2.2.2 remote-as 300
neighbor 2.2.2.2 description R2
neighbor 2.2.2.2 ebgp-multihop 2
neighbor 2.2.2.2 update-source Loopback0
ip route 2.2.2.2 255.255.255.255 "next-hop-IP"
----------
R2-AS300
int lo0
ip address 2.2.2.2 255.255.255.255
router bgp 300
bgp log-neighbor-changes
neighbor 1.1.1.1 remote-as 100
neighbor 1.1.1.1 description R1
neighbor 1.1.1.1 ebgp-multihop 2
neighbor 1.1.1.1 update-source Loopback0
ip route 1.1.1.1 255.255.255.255 "next-hop-IP"
Hope it's ok for you. If you have any concern reply here.
Good luck!
Cheers,
Calin
08-25-2008 12:10 PM
Hello Calin,
in this case there is another router in the middle so it needs:
neigh x.x.x.x ebgp-multihop 3 if using loopbacks
Hope to help
Giuseppe
08-25-2008 12:24 PM
Hi Giuseppe,
I'm sure that is ebgp-multihop 2, I just tried :)
The idea, as I understand ebgp-multihop, is that this is counting the hops until destination. 1st hop is the router in the middle, the 2nd hope is bgp router's interface connected to the middle router and the 3 hop is actual the destination, and this is not count as hop.
If you want to talk more about this write to me: calin@ezeea.com . I don't want to transform this question into a flame here :)
Cheers,
Calin
08-25-2008 01:15 PM
Calin,
You are completely right that a TTL of 2 is sufficient to establish the session in this scenario. In principle, you should also be able to establish a session with a directly connected router using a TTL of 1, even if the session is establish using the loopback interface address. But in reality, establishing a session to the loopback interface address of a directly connected router requires to set the TTL to 2 on the ebgp-multihop command, unless you use the "neighbor disable-connected-check" command.
Regards
08-25-2008 01:17 PM
you have to remember that if the router in the middle is not running BGP, unless you're doing some kind of mpls switching, most likely your packets will drop. Unless you have all the static routes possible that you need for that router in the middle. And running BGP i doubt it but i could be wrong. You can always create a GRE tunnel and do it that way.
08-25-2008 01:29 PM
Hello Calin,
what works is correct.
I couldn't try but I had always used multihop 2 to establish an eBGP connection on loopbacks so I thought a value of 3 was needed.
I should have written it as a possible suggestion !
Thank you for your feedback and I've remarked your useful answer.
Best Regards
Giuseppe
08-26-2008 02:46 AM
thanks for your engagement!
This is the whole case, I have tried with the ebgp-multihop command, but still no luck.
new drawing :
http://home.netpower.no/paal/bgp-possible2.jpg
BGP sessions seems to be established:
Description: R1
BGP version 4, remote router ID 192.168.116.90
BGP state = Established, up for 00:17:39
I can not ping 193.214.20.211 from 192.168.234.163
There is no routing on R3 since the interfaces are DirectConnected
When I :
R2-AS300#ping 193.214.20.211 source fa0
there is no response
the following is my config:
R1-AS100
---------
!
interface FastEthernet0
ip address 192.168.116.90 255.255.255.0
!
interface FastEthernet1
ip address 172.28.10.9 255.255.255.252
!
router bgp 100
no synchronization
bgp log-neighbor-changes
redistribute static
neighbor 172.28.10.2 remote-as 300
neighbor 172.28.10.2 description R2
neighbor 172.28.10.2 ebgp-multihop 2
neighbor 172.28.10.2 update-source Fa1
no auto-summary
!
ip route 172.28.10.2 255.255.255.255 172.28.10.10
ip route 193.214.20.211 255.255.255.255 192.168.116.1
R2-AS300
---------
!
interface FastEthernet0
ip address 192.168.234.1 255.255.255.0
!
interface Vlan2
ip address 172.28.10.2 255.255.255.252
!
router bgp 300
no synchronization
!bgp router-id 172.28.10.2
bgp log-neighbor-changes
network 192.168.234.0
neighbor 172.28.10.9 remote-as 100
neighbor 172.28.10.9 description R1
neighbor 172.28.10.9 ebgp-multihop 2
neighbor 172.28.10.9 update-source vlan2
no auto-summary
!
ip route 172.28.10.9 255.255.255.255 172.28.10.1
08-26-2008 02:53 AM
Hi there!
OK, so step by step:
1.
give us the output on both routers of
show ip bgp sum
2.
from R1-AS100 can you ping 172.28.10.2 ?
the same
from R2-AS300 can you ping 172.28.10.9
3. try this on both router bgp config
neighbor 172.28.10.2 ebgp-multihop 1
neighbor 172.28.10.9 ebgp-multihop 1
Actual you have only one hop to the destination of peer bgp.
Good luck!
Cheers,
Calin
08-26-2008 03:37 AM
I am able to ping
172.28.10.2 from R1
and
172.28.10.9 from R2
When I set
neighbor 172.28.10.9 ebgp-multihop 1
the BGP State = Idle
reset connection with :
R1-AS100#clear ip bgp 300
when I set
neighbor 172.28.10.9 ebgp-multihop 2
BGP state = Established, up for 00:00:07
I thinks that's because it is 2 hops ?
Output of 'show ip bgp sum' is in the new drawing with 'show ip route'
http://home.netpower.no/paal/bgp-possible2.jpg
additional info:
R2-AS300#traceroute 193.214.20.211 source vlan2
Type escape sequence to abort.
Tracing the route to 193.214.20.211
1 172.28.10.1 0 msec 0 msec 0 msec
2 172.28.10.1 !H * !H
R2-AS300#
R2-AS300#traceroute 193.214.20.211 source fa0
Type escape sequence to abort.
Tracing the route to 193.214.20.211
1 * * *
2 * * *
3 * * *
Many thanks,
Paal
08-26-2008 06:16 AM
Paal,
It will definitely not work with "ebgp-multihop 1". You need "ebgp-multihop 2".
As someone already mentioned, you need to make sure that the router in between will be able to route the traffic via static routes (might be cumbersome), MPLS, etc.
Regards,
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