Re: why multi-hop icmp redirects to on 13.0 ?

From: Bjoern A. Zeeb <>
Date: Sat, 04 Dec 2021 16:19:41 UTC
On Sat, 4 Dec 2021, Kurt Jaeger wrote:

> Hi!
> 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:
> Example:
> 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 ?

Could you elaborate on:

(a) Do rtr1 or rtr2 have a default route or are they carrying a full DFZ
     without default route?

     Assumption: if both rtr2 and rtr1 are running 13 and not 12, rtr2
     does have a default route and rtr1 has a full DFZ only and no
     default route?

(b) At the time this happens does rtr1 have a route to z.z.z.z ?
     route -4 get z.z.z.z


Bjoern A. Zeeb                                                     r15:7