On Thu, Oct 02, 2025 at 08:34:12PM -0400, Jon Maloy wrote:
> Even ICMP needs to be updated to use the external MAC address instead
> of just the own tap address when applicable. We do that here.
> 
> Signed-off-by: Jon Maloy <jmaloy@redhat.com>
> Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
> 
> ---
> v3: - Adapted to the move of external MAC address from struct flowside
>       to struct flow_common
> v4: - Adapted to name changes in previous commits in this series
> v5: - Added conditional lookup in ARP/NDP if the flow's tap_omac is
>       undefined
> v6: - Looking up MAC of ICMP generating node in udp_send_tap_icmp4/6()
>       when available, instead trusting the contents of flow->tap_omac.
> v12: - Using MAC_IS_UNDEF() instead of MAC_IS_ZERO()
>      - Comment update after feedback from Stefano
> ---
>  icmp.c |  8 ++++++--
>  ndp.c  |  2 +-
>  tap.c  | 10 ++++++----
>  tap.h  |  4 ++--
>  udp.c  | 12 ++++++++++--
>  5 files changed, 25 insertions(+), 11 deletions(-)
> 
> diff --git a/icmp.c b/icmp.c
> index 6dffafb..93b394a 100644
> --- a/icmp.c
> +++ b/icmp.c
> @@ -125,17 +125,21 @@ void icmp_sock_handler(const struct ctx *c, union epoll_ref ref)
>  	flow_dbg(pingf, "echo reply to tap, ID: %"PRIu16", seq: %"PRIu16,
>  		 ini->eport, seq);
>  
> +	/* Find if neighbour table has a recorded MAC address */
> +	if (MAC_IS_UNDEF(pingf->f.tap_omac))
> +		fwd_neigh_mac_get(c, &ini->oaddr, pingf->f.tap_omac);

Again a lookup by guest address.  Actually looking at these later
patches, having the table stored in terms of guest address probably
makes more sense than my earlier suggestions.

That means the NAT needs to move where you populate the table from
host updates.

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson