4-1 default-information originate

Syntax Description:

This command has no arguments.

Purpose: To allow BGP to advertise the default route 0.0.0.0. A default route can also be advertised on a per-neighbor basis. See sections 8-3 and 8-4.

Cisco IOS Software Release: 10.0

Configuration Example: BGP Default Route Advertisement

Router B in Figure 4-1 needs to be configured to advertise a default route to Router A via BGP. The configuration requires a combination of commands that we will step through to illustrate the process.

Figure 4-1. Using BGP to Advertise a Default Route

 Router A  router bgp 1   neighbor 172.17.1.1 remote-as 2   Router B   router bgp 2    default-information originate    neighbor 172.17.1.2 remote-as 1  

Check the BGP tables on Routers A and B to determine if the default route is being advertised:

 rtrA#  show ip bgp  There are no routes in the BGP routing table. rtrB#  show ip bgp  There are no routes in the BGP routing table. 

A default route is not being advertised by Router B. Let's try modifying the configuration on Router B so that a static default route points to the serial interface:

 Router B  router bgp 2   default-information originate   neighbor 172.17.1.2 remote-as 1   !   ip route 0.0.0.0 0.0.0.0 serial 2/0  

Verify the static route on Router B, and then check to see if this route is being propagated by BGP:

 rtrB#  show ip route static  S*   0.0.0.0/0 is directly connected, Serial2/0 rtrA#  show ip bgp  rtrB#  show ip bgp  

We still do not have the default route being propagated via BGP. We need to redistribute the static route into BGP on Router B. Before redistributing the route into BGP, remove the default-information originate command from the BGP configuration on Router B:

 Router B  router bgp 2   redistribute static   neighbor 172.17.1.2 remote-as 1   !   ip route 0.0.0.0 0.0.0.0 serial2/0  

Is the default route being advertised? Check the BGP tables on Routers A and B:

 rtrA#  show ip bgp  There are no routes in the BGP routing table. rtrB#  show ip bgp  There are no routes in the BGP routing table. 

Finally, add all the commands we have used so far to the BGP configuration on Router B:

 Router B  router bgp 2   redistribute static   neighbor 172.17.1.2 remote-as 1   default-information originate   !   ip route 0.0.0.0 0.0.0.0 serial2/0  

Verification

Examine the BGP tables on Routers A and B to see if we were able to advertise the default route:

 rtrA#  show ip bgp  BGP table version is 5, local router ID is 144.223.1.1 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal Origin codes: i - IGP, e - EGP, ? - incomplete    Network          Next Hop            Metric LocPrf Weight Path *> 0.0.0.0          172.17.1.1               0             0 2 ?  ___________________________________________________________________________  rtrB#  show ip bgp  BGP table version is 3, local router ID is 172.16.2.1 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal Origin codes: i - IGP, e - EGP, ? - incomplete    Network          Next Hop            Metric LocPrf Weight Path *> 0.0.0.0          0.0.0.0                  0         32768 ? 

We have demonstrated that advertising a default route via BGP requires three steps:

Step 1. Create a static default route.

Step 2. Redistribute static into BGP.

Step 3. Use the BGP command default-information originate.

Troubleshooting

Step 1. Verify that the BGP neighbors are in the Established state using the show ip bgp neighbors command.

If the neighbor relationship is not in the Established state, see section 8-23. For IBGP and loopbacks, see section 8-33.

Step 2. Verify that a static default route has been configured.

Step 3. Verify that static routes are being redistributed into BGP.

Step 4. Verify that default-information originate has been configured on the advertising BGP router.