Information Technology Reference
In-Depth Information
Figure 7-37
Persistent Convergence Oscillation with Improper IGP Metrics in Confederation
Confederation ID 100
5
AS 65000
R1
R8
15
6
AS 65001
20
10
R2
R4
R3
MED: 10
10
10
10
MED: 6
MED: 5
AS 200
AS 300
R5
R6
172.16.0.0/16
172.16.0.0/16
AS 400
R7
The following steps briefly describe the process that leads to persistent convergence
oscillation:
All three border routers in Confederation 100 announce 172.16.0.0/16
with next-hop-self. The neighbor and path information is shown in
Table 7-27. The IGP metric is the cumulative link metric from the router
to the BGP next hop.
Step 1
Table 7-27
Neighbor and Path Information from Three Border Routers
Router
BGP Next Hop
AS_PATH
MED
IGP Metric
R2
R5
200 400
10
10
R3
R6
300 400
5
10
R4
R6
300 400
6
10
Initially, R1 has two paths in its BGP RIB, as shown in Table 7-28.
Step 2
Table 7-28
Initial Paths on R1
BGP Next Hop
AS_PATH
MED
IGP Metric
R2
200 400
10
15
R3
300 400
5
20
