Troubleshooting guide

Basic BGP Configuration Using the CLI

There are several commands that must be issued for BGP to operate at the basic level. The following steps

outline the minimum configuration required to enable BGP on an AOS device.

Step 1: Enable BGP and Specify the Local AS

When enabling BGP, the local AS number must be specified from the Global Configuration mode:

(config)#router bgp <AS number>

<AS number> Specifies the AS number of the local system of which this BGP router is a member.

Range is 1 to 4294967295.

Step 2: Advertise Local Networks

Specify the local networks that remote sites should be able to access. Only networks that originate within

the local AS should be advertised. The following command is used from the BGP Configuration mode to

allow BGP to advertise a network:

(config-bgp)#network <ipv4 address> mask <subnet mask>

<ipv4 address> Specifies the IPv4 network address for the neighbor that AOS will advertise over

BGP. IPv4 addresses should be expressed in dotted decimal notation (for example, 10.10.10.0).

<subnet mask> Specifies the subnet mask that corresponds to a range of IPv4 addresses (network) or a

specific host. Subnet masks can be expressed in dotted decimal notation (for example, 255.255.255.0).

For example, to advertise the private network 10.1.10.0 255.255.255.0, enter:

(config-bgp)#network 10.1.10.0 mask 255.255.255.0

BGP is a classless protocol. Therefore, networks with variable length subnet masks can be specified. BGP

can send out a route summary for the entire range of local subnets. For example, a customer’s site includes

16 /24 networks from 10.1.0.0 /24 to 10.1.15.0 /24, which together make up network 10.1.0.0 /20. You can

specify the entire range of subnets by entering:

(config-bgp)#network 10.1.0.0 mask 255.255.240.0

Since the BGP router is advertising a route, it searches its routing table for a route to the specified

networks. It then sends this route to all authorized neighbors.

Upon entering this command, the AOS device is now in BGP Configuration mode. All

subsequent commands in this section are entered from the BGP Configuration mode unless

otherwise noted. If you are using AOS firmware 18.3 or later, please note that the command

syntax and organization of BGP has changed. Refer to the configuration guide Multi-VRF

in AOS, available online at http://kb.adtran.com (article number 3524) for more

information.

The subnet mask is an integral part of the IPv4 network address. If the BGP interface is

specified to advertise routes to network 10.1.0.0 /20, it will not advertise routes to network

10.1.0.0 /16 or 10.1.0.0 /24. Therefore, when advertising a network or range of networks, it

must be verified that the routing table includes the exact route that has been specified

(including the same subnet mask or corresponding prefix length).