Issue Description
AR531 running V200R005C00SPC100 can't run a BFD session with Cisco 3700 router. The session can't be established when they're connected directly by ethernet cable. Since BFD session never establish, high reliabilty wasn't possible to be implemented.
Alarm Information
The AR will only show that the BFD session is offline, no any other alarm is shown in the equipment.
Handling Process
To rectify the fault in the BFD session between the equipment it was needed that the AR equipment change the TTL value of the IP header to 255, the same as the Cisco device. The following configuration was done in the AR to modify the TTL to 255.
bfd
peer-ip x.x.x.x ttl multi-hop 255
Changing the TTL to 255 the session was finally established between the devices.
Root Cause
Port mirroring was used in AR router to monitor the packets exchanged between the routers, the packet showed that BFD hello packets were sent bidirectionally and in the time configured in the both equipments.
Checking the inside content of the packet it was noticed that Cisco packet device has a different TTL value on the IP header of the packet from Huawei device, Cisco device show 255 int TTL as a multihop BFD session while AR show a TTL of 1 as single hop.
Suggestions
When connecting a BGP BFD session with a Cisco device is always neccesary to modify the tll values to 255
