why multi-hop icmp redirects to on 13.0 ?

From: Kurt Jaeger <pi_at_freebsd.org>
Date: Sat, 04 Dec 2021 08:59:29 UTC

We (AS12502) recently upgraded one router from 12.2.x to 13.0.x. This
caused some surprising effect, with the router sending out
icmp redirects to over multiple hops:


inet ------ wan:rtr1:lan ------ rtr2 ------ wan:host
                     x.x.x.1                y.y.y.1

host sends a packet to z.z.z.z and receives an icmp redirect from x.x.x.1
like this:

10:20:16.889185 IP x.x.x..1 > y.y.y.1: ICMP redirect z.z.z.z to host, length 48

This has been stopped by net.inet.ip.redirect=0 on rtr1, but my question is:

Why is rtr1 sending those multi-hop icmp redirects at all ?

pi@FreeBSD.org         +49 171 3101372                  Now what ?