I'm not sure if this is what you are seeing or not, but, ISL trunking encapsulates the entire Ethernet frame. This adds to the size of the frame. If the frame is at or near the maximum size it will become a giant. Is this what you are seeing?
Assumption: MFD stands for MultiMode Fiber Duplex, as a search of Cisco did not result with anything resembling MFD. Even if it's not fiber and it's copper, these steps should still work.
Try these steps to solve the problem. I always try to clear my equipment first. On MFD I/F's you can do a short duration loopback with your cables and look at your counters on each box. This will clear your cable and interfaces.
Now the guessing part. 1. I would hazard to guess that when you loopback the 1900 via the fiber patch cables, you not see errors. (make sure you check both cables). If you don't see errors, you've cleared the 1900 and the fiber patch cables ( a good starting point) 2. If you don't see errors, take the cables do a L/B on the 3524. If you don't see errors, then you have to figure out what 'software' setting/configuration is not right, because if you don't see errors, then you've cleared all your hardware and it's configuration problem. Now, if you do see errors with the L/B on the 3524, I would suggest that you try a longer patch cable. Stranger things have happened due to reflections etc. If that doesn't work. Then I would guess you have a hardware interface problem, and would open a job with TAC, as I believe all the 3500 series have a lifetime warranty on them.
I hope that you follow the logic in these steps. The reasoning is to clear each part in series so that in the end, you can point at one piece and say with confidence that it is the culprit. Another hint, use the same cables in each part of the test, else you've introduced other anomalies into the equation.
Turn the channel mode on the 1900 to non-negotiate trunking instead of dynamic or auto trunking.
CSCdm31600 2900XL/3500XL gets CRC when trunking to a cat5k/1900
Release-notes: When trunking between a 2924xl and a ws-x5225r or a ws-x5213a and DTP is running on cat5000, CRC errors are reported on 2924 due to the reception of non-ISL (DTP) packets. The workaround is to use "nonegotiate" trunk mode on cat5000 so that DTP will not be running.
Hi everyone, I would like to thank you in advance for any help you can provide a newcomer like myself!
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