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Re: IPv6 TCP sessions hangs when using PF keep state

Anthony Mallet <> writes:

> On Monday, at 12:28, Greg Troxel wrote:
> | But, the default mtu on gif(4) is 1280.   So you should not be seeing
> | IPv6 fragmentation.
> However, I do see it... Not even talking about UDP, I see
> fragmentation between a netbsd and solaris 10 host through a gif
> tunnel. For some reason the MSS of my outgoing packets is set to 1440
> initially. I'm currently investigating :)

I am seeing fragmentation too (from doing an ftp from from a
host on a lan behind a tunneling gateway).  I thought that v6 by default
limited itself to 1280, but now I can't remember why I think that.

> Also, if you are on a host on the LAN behind the gateway, is it
> possible that the host starts tcp with the correct MSS?

I don't follow what you are asking.  I saw outgoing SYN packets with mss
1440.  That's ok, except that it's too high for the tunnel.

What I don't understand is why the far side doesn't drop when it gets
the packet-too-big messsage.

> I have a related question: ifconfig gif0 does not show any MTU
> value. Is this a bug? I can do "ifconfig gif0 mtu 1480" without error,
> but I'm not sure if this is silently ignored or not.

On what system/version?  On a netbsd-5 system, where I did not try to
set the MTU, 'ifconfig -a' included the line:
  gif0: flags=8051<UP,POINTOPOINT,RUNNING,MULTICAST> mtu 1280

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