VLAN MTU problem in 4.9 ?

[Stephane Raimbault]

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 ?

I looked at some previous posts in the mailing lists and found some that 
indicated a problem with MTU's so I've provided some pings from servers on 
the same vlan as the freebsd router pinging it and discovered something, 
that I'm not so sure is strange behaviour for a vlan or not.

No problems ssh'ng to the servers hanging off of Switch 2 on the xl1 
interface (untagged vlan) from the workstations, and no problems with pings

(From the 207.176.232.128/27 Network)
# ping -c 1 -s 1500 207.176.232.142
PING 207.176.232.142 (207.176.232.142): 1500 data bytes
1508 bytes from 207.176.232.142: icmp_seq=0 ttl=64 time=1.169 ms

--- 207.176.232.142 ping statistics ---
1 packets transmitted, 1 packets received, 0% packet loss
round-trip min/avg/max/stddev = 1.169/1.169/1.169/0.000 ms


However I do have problem's ssh'ng to servers on the following 2 VLAN's.

(From the 10.0.1.0/27 Network)
# ping -c 1 -s 1468 10.0.1.3
PING 10.0.1.3 (10.0.1.3): 1468 data bytes
1476 bytes from 10.0.1.3: icmp_seq=0 ttl=64 time=0.758 ms

--- 10.0.1.3 ping statistics ---
1 packets transmitted, 1 packets received, 0% packet loss
round-trip min/avg/max/stddev = 0.758/0.758/0.758/0.000 ms
# ping -c 1 -s 1469 10.0.1.3
PING 10.0.1.3 (10.0.1.3): 1469 data bytes

--- 10.0.1.3 ping statistics ---
1 packets transmitted, 0 packets received, 100% packet loss


(From the 10.0.11.0/27 Network)
# ping -c 1 -s 1468 10.0.11.3
PING 10.0.11.3 (10.0.11.3): 1468 data bytes
1476 bytes from 10.0.11.3: icmp_seq=0 ttl=64 time=1.039 ms

--- 10.0.11.3 ping statistics ---
1 packets transmitted, 1 packets received, 0% packet loss
round-trip min/avg/max/stddev = 1.039/1.039/1.039/0.000 ms
# ping -c 1 -s 1469 10.0.11.3
PING 10.0.11.3 (10.0.11.3): 1469 data bytes

--- 10.0.11.3 ping statistics ---
1 packets transmitted, 0 packets received, 100% packet loss




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?

Thank you for your time,
Stephane.

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