This article describes a scenario when FPC may suddenly crash if tunnel bandwidth configuration is changed when there were active pseudowire subscribers on this FPC, and provides more information regarding ways how this such crash could be prevented.

The issue could be seen if the following conditions are met:

• pseudowire subscribers are present on FPC:

  user@device> show subscribers summary port
  Interface Count
  ps1: lt-3/0/0 2
  
  Total Subscribers: 2

• configuration of tunnel services bandwidth is changed without logging out all subscribers:

  {master}[edit]
  user@device# show | compare
  [edit chassis fpc 3 pic 0 tunnel-services]
  - bandwidth 40g;
  + bandwidth 10g;
  
  {master}[edit]
  user@device# commit
  re0:
  error: Active BBE subscribers in lt-3/0/0 interface, changing tunnel-service bandwidth can cause issues
  configuration check succeeds
  re1:
  error: Active BBE subscribers in lt-3/0/0 interface, changing tunnel-service bandwidth can cause issues
  configuration check succeeds
  error: Active BBE subscribers in lt-3/0/0 interface, changing tunnel-service bandwidth can cause issues
  error: Active BBE subscribers in lt-3/0/0 interface, changing tunnel-service bandwidth can cause issues
  commit complete
  re0:
  commit complete

If the issue is hit, FPC will crash few minutes after such commit. FPC core dump will be present in the output of "show system core-dumps" command:

user@device> show system core-dumps
-rw-r--r-- 1 root wheel 77648402 Nov 14 13:41 /var/crash/core-RMPC3.gz.core.0

On MX platforms, when there are active pseudowire subscribers on FPC, tunnel service bandwidth should not be changed for this FPC. It's a catastrophic change which will terminate all subscriber sessions and might trigger crash of this FPC. If such change is needed, all pseudowire subscribers need to be logged out first.

The fix for PR1628628 added the following warning "Active BBE subscribers in lt-<> interface, changing tunnel-service bandwidth can cause issues" but it wasn't possible for user to react to this warning or stop this commit:

user@device# commit
error: Active BBE subscribers in lt-0/0/0 interface, changing tunnel-service bandwidth can cause issues
error: Active BBE subscribers in lt-0/0/0 interface, changing tunnel-service bandwidth can cause issues
commit complete

The fix for PR1849552 will reject such commit attempts:

user@device# commit
error: Active BBE subscribers in lt-0/0/0 interface, changing tunnel-service bandwidth can cause issues
error: foreign file propagation (ffp) failed