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Webcast-Catalyst9k
New Member

Basic BGP config below is wrong, isn't it ?

Hi, I just would like to confirm that the IP addresses outlined below for RouterA 'neighbor' command is wrong. Please confirm I am not missing anything.

RouterA RouterB

AS 65111 AS65222

loopback 0 192.168.255.1/30 loopback0 192.168.255.5/30

loopback 1 192.168.254.1/30 loopback1 192.168.253.1/30

e0 172.16.1.1/24 e0 172.17.1.1/24

s0 172.31.255.1/30 s0 172.31.255.2/30

s1 172.31.255.5/30 s1 172.31.255.6/30

hostname RouterA

int loopback0

ip add 192.168.255.1 255.255.255.252

int loopback1

ip add 192.168.254.1 255.255.255.252

int e0

ip add 172.16.1.1 255.255.255.0

int s0

ip add 172.31.255.1 255.255.255.252

int s1

ip add 172.31.255.5 255.255.255.252

router bgp 65111

network 172.16.1.0 255.255.255.0

no auto-summary

neig 192.168.250.1 remote-as 65222 !<--- This is wrong, isn't it ? It should 'neig 192.168.255.5 ?

neig 192.168.250.1 ebgp-multihop !<--- This is wrong, isn't it ? It should 'neig 192.168.255.5 ?

neig 192.168.250.1 update-source

hostname RouterB

int loopback0

ip add 192.168.250.1 255.255.255.252

int loopback1

ip add192.168.254.2 255.255.255.252

int e0

ip add 172.17.1.1 255.255.255.0

int s0

ip add 172.31.255.1 255.255.255.252

int s1

ip add 172.31.255.6 255.255.255.252

router bgp 65222

network 172.17.0.0 255.255.255.0

no auto-summary

neig 192.168.255.1 remote-as 65111

neig 192.168.255.1 ebgp-multihop

neig 192.168.255.1 update-source

1 ACCEPTED SOLUTION

Accepted Solutions
Cisco Employee

Re: Basic BGP config below is wrong, isn't it ?

Router A is definitely using the wrong address to peer to Router B. Router B is ok.

Hope this helps,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
3 REPLIES
New Member

Re: Basic BGP config below is wrong, isn't it ?

I have attached a .txt file in case the format above isn't good.

Cisco Employee

Re: Basic BGP config below is wrong, isn't it ?

Router A is definitely using the wrong address to peer to Router B. Router B is ok.

Hope this helps,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
Cisco Employee

Re: Basic BGP config below is wrong, isn't it ?

Hi,

The config is wrong, but in a different way as you have pointed out.

"neig update-source" command allows the BGP process to use the IP address of a

specified interface as the source IP address of all BGP updates to that

neighbor. We use a loopback interface, because it will be available as long as the router is operational OR in cases where we have multiple paths b/w 2 ibgp neighbors.

Thus, you should use local loopback address as update source, i.e 192.168.255.1 for router A and so forth.

You have specified two different ips for loopbacks, the one mentioned on top is different than in configs. Pls tell which one is valid for loopback 0 on router B:

loopback0 192.168.255.5/30

OR

int loopback0

ip add 192.168.250.1

Considering 2nd is valid,the ip in 1st neighbor statement is fine, else 255.5 should be there.

Please post as applicable.

Thanks.

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