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

From: Lutz Donnerhacke <>
Date: Sun, 05 Dec 2021 20:53:33 UTC
On Sun, Dec 05, 2021 at 08:20:08PM +0200, John Hay wrote:
> Something I have observed is that if you use FreeBSD 13 as a router with 2
> subnets on the same interface, it will generate redirects when hosts send
> packets to the other subnet via the FreeBSD router. I think it is wrong.

No, it's correct.

> The host does not have a more direct way to get to the other subnet.

The other host can arp for an address in a non-connected network on the
interface because it's the same L2 domain. Hence the ICMP redirect is send
out to provide the shortcut (skipping the router).

> RFC792
> on page 13 does not talk about interfaces, but networks, "If G2 and the
> host identified by the internet source address of the datagram are on the
> same network...".

"network" == "layer 2 domain".