In this tutorial, we are going to set up a simple eBGP routed network.
The scenario will illustrate how you would connect one customer site to an ISP.
In effect you are routing between two different BGP autonomous systems. Since the site is using the ISP connection for corporate internet access, we will have the ISP router inject a default route into the customer’s router.
The following is a diagram illustrating how we are going to connect the two autonomous systems.
The customer router, router A, has one network locally connected off fast ethernet 0/0, 172.16.3.0/24. Once the circuit is up, & all interfaces have been addressed, we can proceed to enable BGP routing. The following shows each routers BGP configuration:
When you configure the autonomous system, make sure you use different AS number for each router, since we are configuring eBGP between two different AS.
Soft-reconfiguration: If you don’t configure this & BGP config changes are made, you will have to intrusively clear the session between the BGP peers, which will break connectivity momentarily. However, using this BGP configuration can adversely effect router performance, due to additional memory use, especially if set for multiple BGP peers. Also, when first issuing the “soft-reconfiguration inbound” command to enable it in the configuration, it will cause the session
to reset.
SYNTAX |
DESCRIPTION |
| router A | |
conf t |
Enter global configuration mode |
| router bgp 326 | Turns on the BGP process & configures the local AS |
| redistribute connected | Advertises directly connected network 172.16.3.0/24 to BGP neighbor (network statement can be used also) |
| neighbor 10.1.1.1 remote-as 1112 | Defines neighbor IP address & neighbor AS |
| neighbor 10.1.1.1 soft-reconfiguration inbound | Allows for BGP policy changes & route refreshing without intrusively bouncing the BGP neighbors |
| no auto-summary | Disables the default behavior of automatic summarization |
| neighbor 10.1.1.1 password <PASSWORD> | Optional command that allows for a extra layer of security in requiring passwords to be exchanged prior to becoming “established” neighbors |
| router B | |
| Conf t | Enter global configuration mode |
| router bgp 1112 | Turns on the BGP process & configures the local AS |
| redistribute connected | Advertises directly connected network 172.16.3.0/24 to BGP neighbor (network statement can be used also) |
| neighbor 10.1.1.2 remote-as 1112 | Defines neighbor IP address & neighbor AS |
| neighbor 10.1.1.2 soft-reconfiguration inbound | Allows for BGP policy changes & route refreshing without intrusively bouncing the BGP neighbors |
| no auto-summary | Disables the default behavior of automatic summarization |
| neighbor 10.1.1.2 password <PASSWORD> | Optional command that allows for a extra layer of security in requiring passwords to be exchanged prior to becoming “established” neighbors |
| neighbor 10.1.1.2 default-originate | Configures router to advertise via BGP a default route (0.0.0.0) to neighbor 10.1.1.2 |
