This article provides troubleshooting steps for addressing "Info cell drops" and "Resource errors" on Juniper MX routers, indicating network congestion and potential performance issues.

>show pfe statistics traffic | grep "Info cell drops"
Info cell drops : 522400

>show pfe statistics traffic | grep "Info cell drops"
Info cell drops : 522455

>show pfe statistics traffic | grep "Info cell drops"
Info cell drops : 522458

>show pfe statistics traffic | grep "Info cell drops"
Info cell drops : 522495

>show pfe statistics traffic | grep "Info cell drops"
Info cell drops : 522587

Physical interface: et-4/1/0, Enabled, Physical link is Up
  Input errors:
    Errors: 242423, Drops: 0, Framing errors: 0, Runts: 0, Policed discards: 0, L3 incompletes: 242423, L2 channel errors: 0, L2 mismatch timeouts: 0, FIFO errors: 0, Resource errors: 522587 <<< 
  Output errors:
    Carrier transitions: 7, Errors: 0, Drops: 4113499, Collisions: 0, Aged packets: 0, FIFO errors: 0, HS link CRC errors: 0, MTU errors: 1, Resource errors: 0
 Egress queues: 8 supported, 6 in use
 Queue counters:    Queued packets Transmitted packets   Dropped packets
  0          16125742465661    16125738352162       4113499 <<<<<<
  1            2043637915      2043637915          0
  2                0          0          0
  3            9726965895      9726965895          0
  6            1207555716      1207555716          0
  7             10105385       10105385          0
 Filter statistics:
  Input packet count     13759288849301
  Input packet rejects        522587 <<<<<<<<<<<<<<<
 Preclassifier statistics:
  Traffic Class    Received Packets  Transmitted Packets   Dropped Packets
  real-time              0           0          0
  network-control      53931474727      53931474727          0
  best-effort      13705357374564     13705356851977        522587 <<<<<<<<<<<<<<<<

Solution:
Info cell drops always occur within the pre-classifier, as indicated by `precl_get_global_stats`. These drops typically happen when MQ/XM performs flow control on the input interfaces, often because the Lookup Unit (LU) cannot sustain the lookup throughput. This issue is reflected not only as a global PFE counter but also as resource errors at the interface level, often accompanied by MAC pause frames being sent. Overall, this indicates congestion.

When "Info cell drops" are noticed, we see "resource errors" under the input error category on the affected interface.

Resource errors typically occur when the router is experiencing high traffic volume, leading to congestion and causing the input buffers to overflow. If MQ/XM performs flow control on the input interfaces, it can result in drops. This flow control may be necessary if the LU cannot sustain the required throughput. When the interface sends or receives MAC pause frames, it also indicates that the network segment is experiencing congestion.

Next Actions:

1. Clear the PFE statistics and check if "Info cell drops" are still incrementing under "show pfe statistics traffic".
2. Check if "Fabric drops" are also increasing under "show pfe statistics traffic".
Run the following commands:
show log messages | match error
show log messages | match drop
show chassis fabric summary
show chassis fabric plane
show chassis fabric fpcs
show chassis fabric destinations
show chassis fabric degradation
show chassis fabric reachability
show chassis fabric map
show pfe statistics traffic
show class-of-service fabric statistics

3. Collect the outputs for the following commands from the FPC shell:
> start shell pfe network fpc<slot number>
# show syslog messages
# show pfe statistics traffic detail (Collect 2-4 times)
# show precl-eng 1 statistics (Collect 2-4 times)
# show pfe statistics error

4. Toggle the affected interface and check if the resource errors are still noticed:
> show interfaces <et-*> extensive | match drops (Collect 2-4 times to check if the resource error are incrementing)

5. If still the issue is persisting try to to offline and online the affected FPC X in the MW.

Following the above steps will help identify and mitigate the causes of info cell drops and resource errors.