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3750-24-TS loosing Multicast packets on buffer

Hi Forum,

I am testing WS-C3750G-24TS-S with 12.2.35.SE2 in the lab and I can see the switch is dropping small percentage of packets.

I have done a sniffer capture and the input interface is rececing the packets but the output interfaces is dropping a small number of packets in transit (multicast traffic). Both interfaces are running 1000Full copper.

1. I see no drops/discards on the physical interface.

2. I can see buffer drops/missed - see output bellow.

3. CPU and DRAM utilisation is normal

4. The physical interfaces is under utilised.

5. All routing conditions are stable and no issues.

6. I am hacing the same issue on another switch same model/IOS.

Is this a software bug?

Is there a way of increasing the RXQ buffers? I am unable to find the command. I can change the small/mid/large buffers but not the pools.

Cisco TAC has been unable to help either.

Thanks

SW-3750-LAB#show buffers

Buffer elements:

1360 in free list (500 max allowed)

427862216 hits, 0 misses, 1024 created

Public buffer pools:

Small buffers, 104 bytes (total 50, permanent 50, peak 116 @ 7w0d):

49 in free list (20 min, 150 max allowed)

274760380 hits, 23 misses, 69 trims, 69 created

0 failures (0 no memory)

Middle buffers, 600 bytes (total 25, permanent 25, peak 79 @ 7w0d):

23 in free list (10 min, 150 max allowed)

436736 hits, 3333 misses, 9999 trims, 9999 created

0 failures (0 no memory)

Big buffers, 1536 bytes (total 50, permanent 50, peak 113 @ 1w5d):

36 in free list (5 min, 150 max allowed)

137413060 hits, 626 misses, 1878 trims, 1878 created

0 failures (0 no memory)

VeryBig buffers, 4520 bytes (total 16, permanent 10, peak 16 @ 7w0d):

1 in free list (0 min, 100 max allowed)

238 hits, 3 misses, 4432 trims, 4438 created

0 failures (0 no memory)

Large buffers, 5024 bytes (total 0, permanent 0):

0 in free list (0 min, 10 max allowed)

0 hits, 0 misses, 0 trims, 0 created

0 failures (0 no memory)

Huge buffers, 18024 bytes (total 0, permanent 0):

0 in free list (0 min, 4 max allowed)

0 hits, 0 misses, 0 trims, 0 created

0 failures (0 no memory)

Interface buffer pools:

-------------- part ommited ------------

RxQ6 buffers, 2040 bytes (total 128, permanent 128):

0 in free list (0 min, 128 max allowed)

24957 hits, 25217 misses

RxQ7 buffers, 2040 bytes (total 192, permanent 192):

63 in free list (0 min, 192 max allowed)

15860100 hits, 590624 misses

RxQ8 buffers, 2040 bytes (total 64, permanent 64):

0 in free list (0 min, 64 max allowed)

45046271 hits, 105186406 misses

RxQ9 buffers, 2040 bytes (total 5, permanent 5):

2 in free list (0 min, 5 max allowed)

3860495340 hits, 3167898801 misses

RxQ10 buffers, 2040 bytes (total 64, permanent 64):

1 in free list (0 min, 64 max allowed)

240731188 hits, 54069950 fallbacks

RxQ11 buffers, 2040 bytes (total 16, permanent 16):

0 in free list (0 min, 16 max allowed)

977 hits, 1318 misses

RxQ12 buffers, 2040 bytes (total 96, permanent 96):

0 in free list (0 min, 96 max allowed)

96 hits, 0 misses

RxQ13 buffers, 2040 bytes (total 16, permanent 16):

0 in free list (0 min, 16 max allowed)

1315594 hits, 1389090 misses

RxQ15 buffers, 2040 bytes (total 4, permanent 4):

0 in free list (0 min, 4 max allowed)

845635197 hits, 845635193 misses

1 REPLY
Silver

Re: 3750-24-TS loosing Multicast packets on buffer

Here is the action plan to solve this issue.

1. Show platform port-asic stats drop port asic will give the drops, if any on the egress for a specific port. For newer codes, you can try 'show platform port-asic stats drop , instead of giving port and asic numbers. Check in this output if you see the egress drop counters incrementing.

If you see drops on egress, it indicates oversubscription. Tuning of buffers is only possible when QoS is enabled

2. To check CPU drops, the command is:

Show controller cpu-interface.

This will give you the number of packets hitting each of the 16 queues in the CPU and if any packets were dropped from any of the queues and if the drops are increasing.

3. And Also check you are hitting bug CSCsd84624 3750 drop Fragment multicast packet drop when (S,G) entry is expired.

4. To reduce fragment multicast packets from server and try.

5. To change threshold values on qos configuration in 3750

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