Relationship between BGP routes and core route tables

Technorati labels: BGP, CCIE, default-information, originate, route

BGP default-information originate function testing report

1, Requirement description

This Testing need check MAIPU and cisco bgp default-information orginate compatible with each other or not.

2, Testing topology

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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:

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

MP3840 # show ip bgp

BGP table version is 3, local router ID is 6.6.6.6

Status codes: s suppressed, d damped, h history, * valid, & gt; best, I-internal,

S Stale

Origin codes: I-IGP, e-EGP ,? -Incomplete

Network Next Hop Metric LocPrf Weight Path

[S] * & gt; 0.0.0.0/0 0.0.0.0 0 32768?

On CISCO router, MAIPU bgp neighbor use "default-information originate", the default routing was announced to peer CISCO 7200.

CISCO7200 # show ip bgp

BGP table version is 5, local router ID is 2.1.1.1

Status codes: s suppressed, d damped, h history, * valid, & gt; 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, I forgot one thing. Today I will review the relationship between the core route table and the bgp route table. Why does show ip bgp have route entries, but show ip route does not?

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

Generally, these two commands are used to define a router as an ASBR and an internet egress gateway.

If you want to reach a goal on cisco7200, but the route table on cisco7200 does not, at this time, 3840 will advertise its default route to cisco7200through bgp, so that all unknown routes will be sent to the egress gateway of 3840.

Therefore, if a device needs to be configured as 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

However, this does not mean that everything is fine.

Use this instance to describe the problem. Note that the above configuration has been modified, and 6.6.6.7 does not exist.

Let's take a look at the route table of this vro2.1.2.1.1.1:

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Here we can see. In the bgp routing table, 6.6.6.7 is declared as the default gateway. Advertised from 2.1.1.2.

However, show ip route only has two direct connection routes.

This is because if you want to write the route entries in the bgp Route table into the IGP table, you need to use the optimal route.

That is, [B] * & gt;

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

To make the route entries in the bgp Route table optimal, there are two conditions: whether to enable synchronization or achieve the goal.

Obviously, none of them match.

The solution is to configure a route on v2.1.1.1 to reach 6.6.6.7.

In addition, 6.6.6.7 needs to actually exist in the network. As long as the two conditions are met, the information shown on the cisco7200 router should be:

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