[c-nsp] MTU size, fragmentation and drops

CiscoNSP List CiscoNSP_list at hotmail.com
Thu Apr 14 22:02:49 EDT 2016

Hi Everyone,

Generic question on mtu/fragmentation/drops that Im hoping someone can explain.

Our PE cust Interface "had" MTU set to 9100

Cust CE WAN Interface has MTU set to 1500

If we pinged with anything above 1500bytes (No DF-bit set), packets were dropped.

If we set our PE's Int to 1500, and pinged above 1500bytes, packets would pass (But obviously be fragmented).

My question is why?  i.e. Why would reducing our PE's Ints MTU size to 1500 "allow" packets above 1500bytes to pass fragmented, but at 9100, they were dropped?

Thanks in advance.

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