The relationship between BGP Routing and core routing table

BGP Default-information originate function testing

1, requirement description

This testing need check Maipu and CISCO BGP default-information orginate compatible with each or.

2, testing topology

3, testing configuration

MP3840:

Interface Loopback0

IP address 6.6.6.6 255.255.255.255

Exit

Interface Fastethernet0

IP address 2.1.1.2 255.255.255.0

Exit

Router BGP 100

No auto-summary

No synchronization

Redistribute static

Neighbor 2.1.1.1 Remote-as 100

Default-information originate

Exit

IP Route 0.0.0.0 0.0.0.0 loopback0

CISCO7200:

Interface fastethernet1/0

IP address 2.1.1.1 255.255.255.0

Duplex full

Speed auto

Router BGP 100

No synchronization

BGP log-neighbor-changes

Neighbor 2.1.1.2 Remote-as 100

No auto-summary

4, Test Result:

More Wonderful content: http://www.bianceng.cnhttp://www.bianceng.cn/Network/lyjs/

On Maipu 3840, due to this static routing already into BGP redistribute table, so:

Mp3840#show IP BGP

BGP table version is 3, the local router ID is 6.6.6.6

Status Codes:s suppressed, D damped, H history, * valid, > Best, I-internal,

S Stale

Origin codes:i-IGP, E-EGP,? -Incomplete

Network Next Hop Metric locprf Weight Path

[s]*> 0.0.0.0/0 0.0.0.0 0 32768?

On Cisco router, Maipu BGP neighbor use "default-information originate", the default routing is announced to peer CISCO 7200.

Cisco7200#show IP BGP

BGP table version is 5, the local router ID is 2.1.1.1

Status Codes:s suppressed, D damped, H history, * valid, > Best, I-internal,

R Rib-failure, S stale

Origin codes:i-IGP, E-EGP,? -Incomplete

Network Next Hop Metric locprf Weight Path

* I 0.0.0.0 2.1.1.2 0 100 0?

cisco7200#

Here, a little I have forgotten, today to do this test report just review, the core routing table and the relationship between the BGP routing table, why show ip BGP have routing entries, but show ip route not?

On the router MP3840, the default-information originate is configured below the BGP 100 process, and the static default route must be fully sent in.

The purpose of these two commands is to say that the router acts as a asbr and an Internet outlet gateway.

If you want to reach a goal on cisco7200, but the routing table on cisco7200 is not, then 3840 will send its default route via BGP to cisco7200. This way, all the unknown routes are sent to the 3840 exit gateway.

So, the condition is that if a device needs to be configured to be the Internet default gateway, the following two commands are required:

Router BGP 100

No auto-summary

No synchronization

Redistribute static

Neighbor 2.1.1.1 Remote-as 100

Default-information originate

Exit

IP Route 0.0.0.0 0.0.0.0 6.6.6.7

But that doesn't mean it's all right.

Take this example to illustrate the problem. Note that the above configuration I have made changes, 6.6.6.7 this gateway does not exist.

Let's look at the 2.1.1.1 router's routing table:

Here you can see. In the BGP routing table, the 6.6.6.7 is actually declared as the default gateway. Announced from the 2.1.1.2.

But show IP route has only two direct-link routes.

This is because if you want to write the routing entries for the BGP routing table in the IGP table, you need to be the optimal route.

Which is expressed as:[b]*>

There is no greater than symbol, which indicates that it is not the optimal route.

To get the routing entries of the BGP routing table to be optimal, there are two conditions, either to turn on synchronization or to achieve the goal.

Obviously, none of this is consistent.

The workaround is to configure a route on the 2.1.1.1 router to reach the 6.6.6.7 route.

There is 6.6.6.7 need to be in the network real existence, as long as these two conditions are reached, and finally in the router cisco7200 above show the information should be:

This article is from the "hank--me, only focus on the principle" blog, please be sure to keep this source http://361531.blog.51cto.com/351531/898650