[ofa-general] What causes "ib0: packet len 65520 (> 2048) too long to send, dropping" messages?

[Or Gerlitz]

Scott Weitzenkamp (sweitzen) wrote:
> I see a small number of these types of messages, when I send large 
> messages via IP multicast.
>  
> Why do I only see a few of the messages?

b/c IPoIB CM makes the stack to learn that for this neighbour the MTU is 
2K (2044) and not the 64K (65520) device MTU published to the stack.

The IPoIB code uses the update_pmtu callback of the neighbour for that 
matter, emulating the case where "path mtu" icmp packet has been 
received from a router.

Or.