VLAN MTU problem in 4.9 ?

[Michael Sierchio]

Stephane Raimbault wrote:

> So it seems that when I specify a ping of greater then 1468 the pings 
> stop responding to the vlan interface on the freebsd router?
> 
> I also did a tcpdump while doing these pings from the freebsd router and 
> it doesn't see any packets when specifying a ping of 1469, but it sees 
> the ping with pkt size specified to 1468.
> 
> Any thoughts on this problem that I'm having?  Any other data I can 
> provider perhaps?

DF?  Size of tagged frames?  Recall that "packet size" perhaps not
what you think, also.

Have you read the vlan man page, specifically:

      Note: Unless marked as having native support for vlan, the above drivers
      don't inform the vlan driver about their long frame handling capability.
      Just increase the MTU of a vlan interface if it appears to be lower than
      1500 bytes after attaching to a parent known to support long frames.

But you invite speculation -- a raw tcpdump (-nqvv or so) would
be nice.