Troubleshoot #1 (BGP)
Last updated
Last updated
Load vpnv4.intra-as.tshoot1.init.cfg
Currently R1 and XR2 have no reachability between each other in VRF A. Explain the problem and fix it without making changes to the CEs and without configuring any neighbor-specific commands on the PEs.
The CEs are in the same ASN. This requires either for the as-path loop dection to be disabled on the CEs, or for the PEs to use “as-override.” The lab forbids using neighbor-specific commands on the PEs, so “as-override” is not allowed.
The CEs already have allowas-in configured, so why is traffic not working?
Checking on R1, we can see that it properly learns and accepts XR2’s routes:
However, on XR2 we do not see R1’s routes:
The reason for this is due to how IOS-XE and IOS-XR differ in their support for transmit side loop detection. This feature allows a router to not advertise paths containing the neighbor’s own AS, with the idea that they would just drop these routes for as-path loop prevention anyways.
IOS-XE does not enable this feature by default. To enable it you would have to manually apply an outbound route-map or filter-list to the neighbor.
IOS-XR does enable this feature by default. This is why XR1 does not advertise R1’s routes to XR2. To turn this feature off, we must turn it off for the VRF’s address families.
Now XR2 can see R1’s routes, which it accepts due to the allowas-in command:
