The generation principle of BGP routing black hole and its solution and configuration

The problems that arise:

A) R1 has a 7.7.7.0/24 route on it, but Ping 7.7.7.7 is not reached. (R7 same)

Now view the R1 routing table

R7#sh IP route

B 1.1.1.0 [20/0] via 5.5.5.5, 00:02:54/To save space incomplete display

It can be seen that R7 learned the route of the R1, from the surface to see the experiment is perfect, for the purpose, but then the problem arises, make a test, on the R7 ping R1

R7#ping 1.1.1.1

Type escape sequence to abort.

Sending 5, 0-byte ICMP Echos to 7.7.7.7, timeout:

.....

What the hell is going on here? Originally, we turned off synchronization on the R5, when it would send a route that was not optimized to R7, when R7 to send to the R1, it sees R5 is its next hop, then sends the packet to R5, then R5 and then looks at its routing table, finds R1 's next hop is R2, and continues to find, Found in the through R3 can reach R2, so it sent the data to R3, when the problem arises, because R3 does not run BGP, it does not know how to go R1, so it dropped packets, resulting in the route of the black hole. Thus, the importance of BGP and IGP synchronization, what is synchronization? In the last article I have mentioned, no more elaboration. (similarly R1 cannot access R7, but has R7 routing entries)

Solution

i) Full MESH

Establish the r2,r3,r5 of the whole interconnected BGP relationship. Full interconnection requires the establishment of n (n-1)/2 neighbor relationships, which is obviously inappropriate when routers are numerous.

Although the theory is so, but in a small number of routers, still very effective, the use of technology is not much.

To establish the logical "full interconnect" fully Mesh for the physical "string link"

The configuration is as follows:

R2:

Neighbor 3.3.3.3 Remote 200

Neighbor 3.3.3.3 Update-source Loopback 0

Neighbor 3.3.3.3 Next-hop-self

Neighbor 5.5.5.5 Remote 200

Neighbor 5.5.5.5 update-souce Loopback 0

Neighbor 5.5.5.5 Next-hop-self

R3:

Neighbor 2.2.2.2 Remote-as 200

Neihgbor 2.2.2.2 update-source Loopback 0

Neighbor 5.5.5.5 Remote-as 200

Neighbor 5.5.5.5 Updata-source Loopback 0

R5:

Neighbor 2.2.2.2 Remote-as 200

Neighbor 2.2.2.2 Update-source Loopback 0

Neighbor 3.3.3.3 Remote-as 200

Neighbor 3.3.3.3 Update-source Loopback 0