Scalable iBGP Design and Implementation Guidelines - BGP Design and Implementation - page 283

Figure 7-25 Prefix Propagation in Steps 9 and 10

R8 R1 R8

R1

RR

RR RR

NEXT_HOP:
R4

Withdraw

NEXT_HOP:
R4

R2 R3 R4 R2 R3 R4

Client Client Client Client Client Client

Step 9 Step 10

Step 10 Table 7-20 shows the updated BGP RIB on R8. Path 1 is the best because
it has a lower IGP metric. Next, R8 sends updates to its neighbors, as
shown in Figure 7-25.

Table 7-20 BGP Paths on R8

Path BGP Next Hop AS_PATH MED IGP Metric

1 *

R4 300 400 6 6

2 R2 200 400 10 20

Step 11 With the update from R8, R1 now has three paths, as shown in Table 7-21.
Notice that this is exactly the same BGP RIB as described in Step 3. From
here, the same convergence cycle starts over again and continues
indefinitely.

Table 7-21 BGP Paths on R1

Path BGP Next Hop AS_PATH MED IGP Metric

1 R4 300 400 6 11

2 R2 200 400 10 15

3 * R3 300 400 5 20