NE40 router, with the version VRP5.30-0238.07. NE40's Cpos interface connected with Cisco's 76XX device's E1 interfaces through a convertor. Both devices configured MPgroup (on C76XX device it is Multilink).
After Cisco's Multilink interface went down, NE40's Mpgroup interface went down; But, when C76XX's multilink interface UP again, NE40's Mpgroup interface cannot UP normally. When we tested using only one membership interface for Mpgroup, it worked fine, without problem.
No alarm. When NE40's Mpgroup cannot be up, the physical status shown up, the protocol status shown down.
1. When we found the Mpgroup cannot be Up, we test every single serial interface, and found every serial link is OK.
2. We delete MPgroup configuration and re-configure it (before we have aproblem about MPgroup disordered, it can be solved by deleting MPgroup and re-configure it, please refer to the case:SE0000337810), but it is still the problem. That means it is not the known problem.
3. We test using only one membership interface for Mpgroup, it worked.
4. All the above tests shown that the link and interface have no problem. We doubt it is VRP problem. With HQ's assistance, we determined to upgrade the VRP.
5. It can be solved to upgrade version to V300R002C01B599.
The root cause is that our VRP cannot recognize the non-standard protocol number sent by Cisco's device.
When the problem happening, we captured the packets on NE40, found that when MPgroup cannot be up, the packet received on NE40 is as follow:
ffff ffff ffff 0000 0000 0000 d200 0400 f80a 43a7 c004 0943 8401 0943 0000 001c
0000 1f00 ff03 8004 0001 c002 ff03 003d 8021 0200 000a 0306 6300 0001 0000 0000
0000 0000 0000 0000
According to a standard PPP packet structure, the protocol number is following with ff03, so the protocol number here is 003d, but NE40 cannot recognize this protocol number and discard this kind of packets.
When there is only one membership interface inside MPgroup, the packet received on NE40 is as follow:
ffff ffff ffff 0000 0000 0000 d200 0400 f80a 4327 c004 0943 8401 0943 0000 001a
0000 1f00 ff03 8004 0001 c009 ff03 8021 01fe 000a 0306 6300 0002 0000 0000 0000
0000 0000 0000 0000
NE40 can recognize it is IPCP, so the negotiation process is successful.
If you face a similar MPgroup issue during integration with Cisco's device, suggest to upgrade to V300R002C01B599 or later versions.