netdev - iproute2 ECMP should display expiry for each nexthop

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Message-ID: <SJ0PR84MB2088CF4614829F0A130DDE60D8DE2@SJ0PR84MB2088.NAMPRD84.PROD.OUTLOOK.COM>
Date: Thu, 4 Jul 2024 23:50:59 +0000
From: "Muggeridge, Matt" <matt.muggeridge2@....com>
To: "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: iproute2 ECMP should display expiry for each nexthop

The output from iproute2 is misleading. It shows an expiry time in the header
of the nexthop list, which suggests all nexthops are goverened by the same
expiry time. However, my testing proves that is not the case. Each nexthop
expires according to its own expiration.

E.g. imagine a host receives an RA with lifetime=10s from TR1. Then 5 seconds
later, it receives an RA with lifetime=10s from TR2. iproute2 displays them as:

$ ip -6 route
default proto ra metric 2048 expires 6sec pref medium
        nexthop via fe80::200:10ff:fe10:1061 dev enp0s9 weight 1
        nexthop via fe80::200:10ff:fe10:1060 dev enp0s9 weight 1

>From the output, you would be forgiven for thinking that both nexthops will
expire in 6 seconds. However, they expire according to their own lifetimes.
In this example, TR2 expires 5s after TR1, since that's when they were received.

FWIW, my Ubuntu 24.04 system uses networkd, which configures routes via NetLink.

Matt.