JunOS static-nat and proxy-arp

I’m still relatively new to this JunOS, even though it’s been installed for several months now. Today’s problem was not passing traffic through a new static-nat that I’d setup. I checked the config for static-nats that already existed and couldn’t see the problem.

I needed to look at how the static-nat gets presented on the interface. It’s no good having a NAT rule if you don’t actively acknowledge that you are active on that IP address on an interface. No proxy-arp means nothing gets passed to NAT because the IP doesn’t exist on the network.

To do this make sure you add a proxy-arp address on the interface that you want to access the IP address.

eg.

set security proxy-arp interface reth1.99 address 192.168.99.99/32

Then you’ll have a related rule entry in your security nat static rule-set stanza to handle the translation.

eg.

show rule MyRule   
match {
    destination-address 192.168.99.99/32;
}
then {
    static-nat {
        prefix {
            192.168.0.99/32;
        }
    }
}