On Sat, 23 Nov 2024 15:25:15 +0100, Pascal Stumpf wrote:
> On Sat, 23 Nov 2024 13:42:45 -0000 (UTC), Stuart Henderson wrote:
> > On 2024-11-23, Pascal Stumpf <pas...@stumpf.co> wrote:
> > > Scenario: 7.6-stable running on a gateway, connected to the internet via
> > > pppoe0 over vlan7, several downstream /24 network segments. iked(8) is
> > > serving several clients, running mostly Mac OS, with policies like this:
> > >
> > > ikev2 "foo" esp \
> > > from 192.168.100.1 to dynamic \
> > > from 192.168.5.0/24 to dynamic \
> > > from 192.168.50.0/24 to dynamic \
> > > [...]
> > > peer any \
> > > srcid bar dstid foo \
> > > config address 192.168.100.0/24
> > >
> > > where we have vlanN interfaces carrying the 192.168.5.1/24 etc. etc. atop
> > > an igc(4) interface and 192.168.100.1/24 is on lo1 for debugging purposes.
> > >
> > > There is a relayd running on the gateway itself, with relays listening
> > > on both the pppoe0 address and 192.168.5.1 (vlan5).
> > >
> > > Mac OS sets the MTU on its ipsec0 interface to 1280, so the scrub rules
> > > in pf.conf look like this:
> > >
> > > [...]
> > > match in on pppoe0 scrub (max-mss 1440, no-df, random-id, reassemble tcp)
> > > match out on pppoe0 scrub (max-mss 1440)
> > > match on enc0 all scrub (max-mss 1280)
> > > [...]
> >
> > MSS should be capped at (MTU - IP header size - TCP header size).
> >
> > IPv4 headers are 20 bytes, TCP between 20 and 60 bytes (20 is quite
> > common, but 32 is also quite common if TCP timestamps are used).
> >
> > https://lostintransit.se/2024/09/05/mss-mss-clamping-pmtud-and-mtu/
>
> Tested with (max-mss 1228). Still, the same fragmentation.
>
> > > This works fine for all downstream hosts, with tcpdump showing
> > > consistent packet sizes of 1356 on pppoe0. But max-mss seems to be
> > > ignored for all connections to the gateway host itself, including the
> > > ones to relayd at 192.168.5.1, resulting in heavy fragmentation:
> >
> > Do you have a "set skip" line?
>
> set skip on enc? No.
>
> And as I said, the setup works just fine for any host on any of the /24
> segments behind the gateway.
>
> So I really think this is about 192.168.5.1 being a locally assigned address.
Some more observations:
On a very similar setup on my home router, I have:
iked.conf:
ikev2 "roadwarrior" esp \
from 192.168.2.0/24 to dynamic \
from 192.168.100.0/24 to dynamic \
peer any \
[...]
with 192.168.2.1/24 assigned to a vport(4) and the same scrub rule in
pf.conf:
match on enc0 all scrub (max-mss 1228)
Connections to the machines on the 192.168.2.0/24 net are fine, however
there is heavy fragmentation going on for TCP connections to 192.168.2.1
over the tunnel.
Playing around with the max-mss value, I can observe that it is being
applied to inbound packets, but answers are still huge. It looks like
something is relying on them being segmented later (but they aren't).
> > --
> > Please keep replies on the mailing list.
> >
