netdev - Re: PMTUD broken inside network namespace with multipath routing

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Date:   Fri, 14 Aug 2020 10:08:30 +0300
From:   mastertheknife <mastertheknife@...il.com>
To:     David Ahern <dsahern@...il.com>
Cc:     netdev@...r.kernel.org
Subject: Re: PMTUD broken inside network namespace with multipath routing

Hello David,

It's on a production system, vmbr2 is a bridge with eth.X VLAN
interface inside for the connectivity on that 252.0/24 network. vmbr2
has address 192.168.252.5 in that case
192.168.252.250 and 192.168.252.252 are CentOS8 LXCs on another host,
with libreswan inside for any/any IPSECs with VTi interfaces.

Everything is kernel 5.4.44 LTS

I wish i could fully reproduce all of it in a script, but i am not
sure how to create such hops that return this ICMP

Thank you,
Kfir


On Wed, Aug 12, 2020 at 10:21 PM David Ahern <dsahern@...il.com> wrote:
>
> On 8/12/20 6:37 AM, mastertheknife wrote:
> > Hello David,
> >
> > I tried and it seems i can reproduce it:
> >
> > # Create test NS
> > root@...t:~# ip netns add testns
> > # Create veth pair, veth0 in host, veth1 in NS
> > root@...t:~# ip link add veth0 type veth peer name veth1
> > root@...t:~# ip link set veth1 netns testns
> > # Configure veth1 (NS)
> > root@...t:~# ip netns exec testns ip addr add 192.168.252.209/24 dev veth1
> > root@...t:~# ip netns exec testns ip link set dev veth1 up
> > root@...t:~# ip netns exec testns ip route add default via 192.168.252.100
> > root@...t:~# ip netns exec testns ip route add 192.168.249.0/24
> > nexthop via 192.168.252.250 nexthop via 192.168.252.252
> > # Configure veth0 (host)
> > root@...t:~# brctl addif vmbr2 veth0
>
> vmbr2's config is not defined.
>
> ip li add vmbr2 type bridge
> ip li set veth0 master vmbr2
> ip link set veth0 up
>
> anything else? e.g., address for vmbr2? What holds 192.168.252.250 and
> 192.168.252.252