Monday, July 27, 2020

Building eBGP Peering




When two BGP routers that belong to different Autonomous System establish session, they effectively form an eBGP session. Here is an example of configuring eBGP session between R2 (AS 65100) and R8 (AS 65089).



R8 Configuration:

router bgp 65089
 bgp router-id 10.8.8.8
 bgp log-neighbor-changes
 neighbor 172.16.28.2 remote-as 65100

Now R2 Configuration:

router bgp 65100
 bgp router-id 10.2.2.2
 bgp log-neighbor-changes
 neighbor 172.16.28.8 remote-as 65089

Verification of the session.

R2#show ip bgp summary
BGP router identifier 10.2.2.2, local AS number 65100
BGP table version is 1, main routing table version 1

Neighbor        V           AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd
172.16.28.8     4        65089       5       5        1    0    0 00:01:29        0
R2#

All is good here.

More elaborate output:

R2#show ip bgp neighbor 172.16.28.8
BGP neighbor is 172.16.28.8,  remote AS 65089, external link
  BGP version 4, remote router ID 10.8.8.8
  BGP state = Established, up for 00:05:02
  [snip]
  Local host: 172.16.28.2, Local port: 179
  Foreign host: 172.16.28.8, Foreign port: 12099

In preparation to next lab I want to advertise a few prefixes on R8, so that R2 can learn them.

First, I am going to create a few loopback interfaces with IP addresses.

interface Loopback0
 ip address 10.8.8.8 255.255.255.255
!
interface Loopback10
 ip address 10.8.0.1 255.255.255.240
!
interface Loopback11
 ip address 10.8.0.17 255.255.255.240
!
interface Loopback12
 ip address 10.8.0.33 255.255.255.240
!
interface Loopback13
 ip address 10.8.0.49 255.255.255.240
!
interface Loopback14
 ip address 10.8.80.1 255.255.255.0
!
interface Loopback15
 ip address 10.8.81.1 255.255.255.0
!
interface Loopback16
 ip address 10.8.82.1 255.255.255.0
!
interface Loopback17
 ip address 10.8.83.1 255.255.255.0
!

As for advertising networks in BGP, this protocol is unlike IGP protocols such as IS-IS, OSPF, EIGRP.

Those observations deserve a separate post.

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