netdev - RE: IP routing sending local packet to gateway.

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Date:   Fri, 27 Aug 2021 16:39:27 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     David Laight <David.Laight@...LAB.COM>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: IP routing sending local packet to gateway.

From: David Laight
> Sent: 27 August 2021 15:12
> 
> I've an odd IP routing issue.
> A packet that should be sent on the local subnet (to an ARPed address)
> is being send to the default gateway instead.

I've done some tests on a different network where it all appears to work.

But running 'tcpdump -pen' shows that all the outbound packets for the
TCP connections are being sent to the default gateway.

5.10.30, 5.10.61 and 5.14.0-rc7 all behave the same way.

If do a ping (in either direction) I get an ARP table entry.
But TCP connections (in or out) always use the default gateway.

I'm now getting more confused.
I noticed that the 'default route' was missing the 'metric 100' bit.
That might give the behaviour I'm seeing if the netmask width is ignored.

But if I delete the default route (neither netstat -r or ip route show
it) then packets are still being sent to the deleted gateway.
If I delete the arp/neigh entry for the deleted default gateway an
outward connection recreates the entry - leaving the one for the actual
address 'STALE'.

Something very odd is going on.

	David

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