netdev - Re: "ip route show dev enp0s9" does not show all routes for enp0s9

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Date: Thu, 27 Jun 2024 19:36:32 -0700
From: Stephen Hemminger <stephen@...workplumber.org>
To: "Muggeridge, Matt" <matt.muggeridge2@....com>
Cc: "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: "ip route show dev enp0s9" does not show all routes for enp0s9

On Fri, 28 Jun 2024 00:01:47 +0000
"Muggeridge, Matt" <matt.muggeridge2@....com> wrote:

> Hi,
> 
> This looks like a problem in "iproute2".  This was observed on a fresh install of Ubuntu 24.04, with Linux 6.8.0-36-generic.
> 
> NOTE: I first raised this in https://bugs.launchpad.net/ubuntu/+source/iproute2/+bug/2070412, then later found https://github.com/iproute2/iproute2/blob/main/README.devel.
> 
> * PROBLEM
> Compare the outputs:
> 
> $ ip -6 route show dev enp0s9
> 2001:2:0:1000::/64 proto ra metric 1024 expires 65518sec pref medium
> fe80::/64 proto kernel metric 256 pref medium
> 
> $ ip -6 route
> 2001:2:0:1000::/64 dev enp0s9 proto ra metric 1024 expires 65525sec pref medium
> fe80::/64 dev enp0s3 proto kernel metric 256 pref medium
> fe80::/64 dev enp0s9 proto kernel metric 256 pref medium
> default proto ra metric 1024 expires 589sec pref medium
>  nexthop via fe80::200:10ff:fe10:1060 dev enp0s9 weight 1
>  nexthop via fe80::200:10ff:fe10:1061 dev enp0s9 weight 1
> 
> The default route is associated with enp0s9, yet the first command above does not show it.
> 
> FWIW, the two default route entries were created by two separate routers on the network, each sending their RA.
> 
> * REPRODUCER
> Statically Configure systemd-networkd with two route entries, similar to the following:
> 
> $ networkctl cat 10-enp0s9.network
> # /etc/systemd/network/10-enp0s9.network
> [Match]
> Name=enp0s9
> 
> [Link]
> RequiredForOnline=no
> 
> [Network]
> Description="Internal Network: Private VM-to-VM IPv6 interface"
> DHCP=no
> LLDP=no
> EmitLLDP=no
> 
> 
> # /etc/systemd/network/10-enp0s9.network.d/address.conf
> [Network]
> Address=2001:2:0:1000:a00:27ff:fe5f:f72d/64
> 
> 
> # /etc/systemd/network/10-enp0s9.network.d/route-1060.conf
> [Route]
> Gateway=fe80::200:10ff:fe10:1060
> GatewayOnLink=true
> 
> 
> # /etc/systemd/network/10-enp0s9.network.d/route-1061.conf
> [Route]
> Gateway=fe80::200:10ff:fe10:1061
> GatewayOnLink=true
> 
> 
> 
> Now reload and reconfigure the interface and you will see two routes.
> 
> $ networkctl reload
> $ networkctl reconfigure enp0s9
> $ ip -6 r
> $ ip -6 r show dev enp0s9 # the routes are not shown
> 

"Don't blame the messenger", the ip command only reports what the kernel
sends. So it is likely a route semantics issue in the kernel.