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Gratuitous ARP static NAT, 1450-Appliance


Today I migrated a firewall-configuration from a SG80-Appliance to a 1450er-Appliance (configured everything manually, installed the latest firmware 07/2017). We have a lot of auto-static-nats configured there (are terminateing in the WAN-Interface). Just for clarification, the WAN-Inteface is configured with internal-ips (MPLS-Connection).

After activating the new appliance (same  ips and static-nat-ips taken from the old SG80-Appliance) the static-nats did not work, because the old MAC-Addresses of the old SG80-Appliance were stored on the router's arp-table.

But the new MAC of the WAN-Interface was updated immediately. So it seems, that the Firewall does not send out gratuitous arp for static-nat-ips but only for its own IP on the WAN-Interface.

As I said, it was not a problem, but I only want to know, if this is a standard behaviour because today it was the very first time, I did not delete the arp-table for the nat-ips, do not know why. Smiley Happy

Best regards


2 Replies

Hello Martin.

From the tests I made with a 1470 it seems it does not send gratuitous ARP. It will only respond to ARP requests.

This seems to be the standard behavior.



Thank you for the test! I found a great command. With this command you can force the appliance to send out g-arps:

echo 1 > /proc/sys/net/ipv4/ip_nonlocal_bind --> enable this "feature in the kernel"

arping -c 4 -A -I WAN --> here the g-arp will be done for the WAN-Interface and for the IP

 echo 0 > /proc/sys/net/ipv4/ip_nonlocal_bind --> disable this "feature in the kernel"

This works great



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