The Simplest BGP Configuration

What is BGP?

Autonomous system refers to the entire network of all IP networks and routers under the jurisdiction of one (sometimes multiple) entity. They implement common routing policies for the Internet.

BGP is different from Interior Gateway Protocol (IGP) such as RIP and OSPF. It belongs to the Exterior Gateway Protocol (EGP). BGP can transfer routing information between different autonomous systems. If you use BGP within the same autonomous system, it is called IBGP (internal BGP). If BGP is used between different autonomous systems, it is called EBGP (external BGP).

Since the simulator does not support IBGP, we will only configure EBGP below.

The simplest configuration steps

Enter the BGP setting menu of the specified AS number -> Announce directly connected network segment, mask -> Specify the AS number and IP of the neighboring router -> Complete

The most obvious difference between the BGP configuration process and other interior gateway protocols is that you must manually specify the AS number and IP of the neighboring router.

Network Topology Description

As shown in the figure, the entire network is divided into four ASs, each of which is an AS. The following only describes the BGP configuration method of EBR1. If the other three words are modified, only the directly connected network segments and neighbors advertised under this rule can be used. The configuration of the interface and IP will not be discussed.

Configuration steps

1. Enter BGP configuration mode with AS number 2

R1>enable 

R1#configure terminal

R1(config)#router bgp 2

2. Announcement directly connected to the network segment

R1(config-router)#network 10.0.0.0 mask 255.255.255.0

R1(config-router)#network 10.0.1.0 mask 255.255.255.0

R1(config-router)#network 192.168.1.0 mask 255.255.255.0

3. Specify the AS number and IP of the neighboring router

R1(config-router)#neighbor 10.0.0.2 remote-as 1

R1(config-router)#neighbor 10.0.1.2 remote-as 4

R1(config-router)#exit

The setup is complete.

The method for setting up the other three routers is exactly the same. You can change the directly connected network segment and neighbors.

Validation results

Check the configuration file

R1#show running-config

The following only intercept BGP configuration.

router bgp 2

 bgp log-neighbor-changes

 no synchronization

 neighbor 10.0.0.2 remote-as 1

 neighbor 10.0.1.2 remote-as 4

 network 192.168.1.0

 network 10.0.0.0 mask 255.255.255.0

 network 10.0.1.0 mask 255.255.255.0

!

Check the BGP routing table

R1#show ip route bgp

B    10.0.2.0 [20/0] via 10.0.1.2, 00:04:52

B    10.0.3.0 [20/0] via 10.0.0.2, 00:04:52

B    192.168.2.0/24 [20/0] via 10.0.0.2, 00:04:52

B    192.168.3.0/24 [20/0] via 10.0.0.2, 00:04:52

B    192.168.4.0/24 [20/0] via 10.0.1.2, 00:04:52

As you can see, the entire network has successfully learned the routing table.

Learn More:

6 Types of OSPF LSA

Five OSPF Area Types