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Jumbo Frames over 10/100 link

Unanswered Question
Apr 3rd, 2012
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Hi everyone,

I read that Jumbo frames, when enabled on Gig ingress interfaces on a switch, will be dropped if the egress interface is 10/100. Does this hold true if the actual egress interface on the switch is a gig interface however the port on the other end of that interface is 10/100 only such in a case of a PC. Would the frames still get dropped?

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rizwanr74 Tue, 04/03/2012 - 12:23
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"Would the frames still get dropped?"

No. But it will fragment frames and which will cause high CPU utilization and delay.

Hope that answers your question.


cpembleton Tue, 04/03/2012 - 18:07
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Kinda depends on your switch/pc.  There are some switches that have support for jumbo frames at 10/100.  Like some of the line cards of a 6500.  So if your switch supports jumbo on 10/100 and your host supports jumbo frame on 10/100 then no, nothing is dropped.  Assuming the Jumbo value set is not larger than either side can support. 

But if either the switch and/or pc doesn't then it will be dropped.  Fragmentation only occurs over a layer3 boundry as long as the DF flag isn't set.   




Ricky S Wed, 04/04/2012 - 06:49
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Hi gents, thanks for your responses. I am going to play around with this setting however since a switch reload is required after turning it on, I will have to wait for a window. I'll update this thread with the results.


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