R1 _____2______ R2
Routing Protocol: ISIS
Tracking Protocol: BFD
In a network a Eth-trunk is configured to increase its link capacity. ISIS is runinng on Eth-trunk and dynamic bfd is enable in ISIS bfd for fast convergense. For this above topology we found that wheneven a link down happend ISIS goes down and come up in few second. This issue is causing services outages for few seconds.
timer lsp-generation 1 50 50 level-2
bfd all-interfaces enable-------------------------------> Check
timer spf 1 50 50
We found ISIS state down alarms and eth-trunk doen alarms in the router after 1 link down.We also found the bfd down alarms After few second again logs will come that ISIS state came to up state.
To handle this issue we need to we have to ways, which are:
1) Block ISIS bfd form Eth-trunk and configure Interface based staic BFD for fast convergence.
2) Use packet based Load-balancing
For point 2, if their is Tx link we cant trunk Tx link as in 2 different Tx paths their may be different delay and in packet based load balancing if sequenced packets delivered with different delay can also cause issue.
So ponit 1 is sutable to deploy and will work file
Use below command to Block isis in Eth-trunk view:
[Router A-Eht-Trunk1]isis bfd block.
At the time for analysis and checking the logs we found below things:
1) whenever a member link of eth-trunk goes down ISIS bfd is also goes down for a momenet
2) It is causing ISIS state to down state.
3) Eth-trunk is runing in session based loadsharing.
4) ISIS BFD session is established on the same link which goes down.