[ovs-discuss] SSH over GRE tunnel, MTU 1500 devices in VMs on same physical host

Orabuntu-LXC gilbert at orabuntu-lxc.com
Wed Nov 29 20:12:53 UTC 2017


Hi,

I have what is probably a dumb question so it should be an easy one for
gurus.

I built two VM's on VirtualBox using my Orabuntu-LXC software.  The VM
VNIC's are ports on OvS sw1 on each VM.  The VM's are on the same physical
host.  I have LXC containers on the sw1 switch also.  What has surprised me
with this setup is that I can ssh between containers that are on different
VMs and all the network devices, the VNIC's and the OvS switches, and the
physical interface on the host, are all set to MTU 1500.  Not anywhere in
this setup is MTU 1420 used.  My understanding was, and what I have found
in all previous cases, was that I had to use MTU 1420 for ssh over a GRE
tunnel to allow for encapsulation, so my question is I am wondering how can
ssh be working over this GRE tunnel when all the MTU of all devices is set
to 1500?

TIA

-- 
Gilbert Standen
Creator Orabuntu-LXC
914-261-4594
gilbert at orabuntu-lxc.com
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