VLAN MTU problem in 4.9 ?

["." at babolo.ru]

> Hi,
> 
> I have the following setup on a freebsd box acting as a router for multiple 
> LAN's.
> 
> xl0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
>         inet 10.0.0.3 netmask 0xffffffc0 broadcast 10.0.0.63
>         inet6 fe80::260:97ff:fe07:5f4b%xl0 prefixlen 64 scopeid 0x1
>         ether 00:60:97:07:5f:4b
>         media: Ethernet autoselect (100baseTX <full-duplex>)
>         status: active
> xl1: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
>         inet 207.176.232.142 netmask 0xffffffe0 broadcast 207.176.232.159
>         inet6 fe80::2c0:4fff:fe9e:b9c7%xl1 prefixlen 64 scopeid 0x2
>         ether 00:c0:4f:9e:b9:c7
>         media: Ethernet autoselect (100baseTX <full-duplex>)
>         status: active
> vlan0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
>         inet 10.0.1.3 netmask 0xffffffe0 broadcast 10.0.1.31
>         inet6 fe80::260:97ff:fe07:5f4b%vlan0 prefixlen 64 scopeid 0x4
>         ether 00:c0:4f:9e:b9:c7
>         media: Ethernet autoselect (100baseTX <full-duplex>)
>         status: active
>         vlan: 3 parent interface: xl1
> vlan1: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
>         inet 10.0.11.3 netmask 0xffffffe0 broadcast 10.0.11.31
>         inet6 fe80::260:97ff:fe07:5f4b%vlan1 prefixlen 64 scopeid 0x5
>         ether 00:c0:4f:9e:b9:c7
>         media: Ethernet autoselect (100baseTX <full-duplex>)
>         status: active
>         vlan: 4 parent interface: xl1
> 
> 
> The setup is physically connected like this
> 
> Switch 1 <---> (xl0) FreeBSD (xl1) <---> Switch 2
> 
> My Workstation is connected to Switch 1 on the ip network 10.0.0.0/26
> The Server(s) I'm connecting to are on Switch 2 on the ip network 
> 10.0.11.0/27 and/or 10.0.1.0/27
> 
> I seem to have some problems connecting to the above mentioned servers on 
> vlan0 and vlan1.  My SSH session seems to freeze when I type a command that 
> will output quite a bit of data (top, etc...)  I also seem to have some 
> other large data problems between the servers communicating to each other 
> over the VLAN's.
> 
> I had a working setup, but since I upgraded from 4.9-RC2 on the FreeBSD 
> router to 4.9-RELEASE-p1 I've been having the above described problem.  I'm 
> wondering if I left something out in my KERNEL configuration when I upgraded 
> or if I've stumbled onto a bug in 4.9-R ?

ifconfig vlan0 mtu 1496
ifconfig vlan1 mtu 1496 

will restore old behavior.
But I do not know when default mtu for vlan
was changed.