Information Technology Reference
In-Depth Information
Figure 10-9
AS_PATH Loop Scenario
172.16.0.0/16
AS_PATH:
65000
172.16.0.0/16
AS_PATH:
100 65000
AS 100
X
AS 65000
AS 65000
CE1
PE1
PE2
CE2
VPNa
VPNa
To provide connectivity between CE1 and CE2, a new procedure called
AS Override
must
be implemented. When you configure AS Override on a PE, the PE replaces every occur-
rence of the connecting CE device's AS number in the entire AS_PATH with its own AS
number before sending the updates to the CE.
With AS Override, AS_PATH length is preserved.
NOTE
Figure 10-10 shows the scenario in Figure 10-9 after AS Override is configured on PE2.
When AS 65000 is replaced by AS 100, CE2 accepts the update. Note that a similar config-
uration must be made on PE1 if full connectivity is needed.
Figure 10-10
AS Override Allows CE-CE Communication
172.16.0.0/16
AS_PATH:
65000
172.16.0.0/16
AS_PATH:
100 100
AS 100
AS 65000
AS 65000
CE1
PE1
PE2
CE2
VPNa
VPNa
address-family ipv4 vrf VPNa
neighbor CE2 as-override
