Re: NAT and DNS/NTP servers

["Andrew E. Mileski" <andrewm@isoar.ca>]

Andrew E. Mileski wrote:
> When a private client (192.168.1.2) sends a packet to the same place,
> the packet arriving on the LAN_IFC has:
>   source address: private client = 192.168.1.2
>   source port: 123
>   destination address: time.nist.gov = 192.43.244.18
>   destination port: 123
> This gets SNAT'ed by the gateway and sent out the WAN_IFC to the
> internet looking like this:
>   source address: WAN_IP = 209.217.118.226
>   source port: 123
>   destination address: time.nist.gov = 192.43.244.18
>   destination port: 123
> A reply packet from time.nist.gov arrives on WAN_IFC with:
>   source address: time.nist.gov = 192.43.244.18
>   source port: 123
>   destination address: WAN_IP = 66.11.173.24
>   destination port: 123
> Because the port wasn't remapped, there appears to be ambiguity
> in whether the reply packet should be routed to the private host
> (192.168.1.2) or the NTP server process on the router.

Doh! made a mistake the WAN_IP in the reply above should
be 209.217.118.226 not 66.11.173.24.  Sorry.  [That's why
I tried to avoid typing numbers originally; to avoid mistakes.]

-- 
Andrew E. Mileski