L-chip HDRF errors may be reported on FPCs due to MTU errors (L-chip is used in T/M320 FPCs). These errors do not have any operational impact on production routers and be ignored. Or users can adjust the MTU settings on the related interfaces to eliminate the MTU errors.

For transit packets whose packet size is bigger than the MTU of the outgoing interface, and if the DF (Do-Not-Fragment) bit is set in the packet header, these packets will be dropped at the outgoing interface and output MTU errors will be counted. If the MTU error is increasing rapidly, L-chip Lout HDRF errors on the outgoing FPC may occur.

Steps to check L-chip HDRF errors and MTU errors.

1. Check the L-chip Lout HDRF errors

   root@m320> show pfe statistics error
   Slot 6
    
   LCHIP Error statistics:
    
   LCHIP                  0        1        2        3
   -------------------------------------------------------
   Lin PIF:               0        0        0        0
   Lin SRCTL:             0        0        0        0
   Lout NLIF:             0        0        0        0
   Lout DESRD:            0        0        0        0
   Lout HDRF:             0        0       37        6
   <...>

   From the above output, the L-chip HDRF error is happening on L-chip 2 and L-chip 3

2. Go to PFE shell to check HDRF error type on L-chip 2

   user@m320> start shell pfe network fpc6
    
   FFPC6(m320 vty)# show lchip 2 error
   <...>
   Lout Error Statistics:
   <...>
   HDRF:
     -------------------------------------------
     Timeout Error cnt   :          0
     Parity  Error cnt   :          0
     MRQ Full drop cnt   :          0
     MRQ limit drop cnt  :         37
     MRQ clash drop cnt  :          0
    
     Total ucode err cnt :          0
     Total MTU err cnt   :        193
     Total redirect cnt  :          0
     Total split_horizon cnt :          0
   <...>

Here, the HDRF error is introduced by the MRQ Limit Drop cnt .  There are also many MTU errors logged on the same L-chip.  MRQ limit drop cnt  means MTU/redirect rate limit drop counters. It is a global counter that counts the number of MTU or ICMP redirect messages dropped due to the queue being full. When there is a MTU error happening or ICMP redirect message, the PFE will send a notification to the RE via a rate-limit queue. The  MRQ limit drop cnt  will increase if the queue is full.

In the above case, since the  total redirect cnt  is 0 and  MTU error cnt  is 193 .  This shows that it is the MTU error causing the L-chip HDRF errors

Eliminating the MTU errors on the outgoing interfaces will also make the L-chip HDRF error disappear. This L-chip HDRF error does not mean there is any hardware failure or have any operational impact on production routers. Since it is quite normal that there are some big packets existing in the network,  this error can be ignored. Or you can adjust the MTU settings on the related interfaces to eliminate the MTU errors.

2017-06-06: Added that L-chip is used by T/M320 FPCs and fixed formatting.