* Fab Siciliano <[EMAIL PROTECTED]> [010913 11:32] wrote:
> Hey everyone. Terrible stuff goin on these days...let's hope we find a
> solution to a all this chaos.
>
> Ok, for the question. (This may be a stupid question BTW.)
>
> Let's say I have a router. Doing NAT. When I send an email to another
> office, the source ip is different from the IP I get when I do a
> traceroute, and it leaves my network.
>
> For instance. I send an email to [EMAIL PROTECTED] In his header, it
> says that the Source address is 204.186.240.123.
> When I do a traceroute to an external domain the address of the device when
> it leaves my network, is 204.186.240.124.
>
> Why would these addresses be different? Thanks
This depends on how NAT is configured on the router (or firewall in
many cases). For instance, it is quite common to have a pool of public
NAT addresses supplied by the router. These addresses are assigned
dynamically and generally expire after a certain interval.
If you make an outbound connection, you might receive the first IP
address in the pool (204.186.240.123.). On your next connection, you
might receive the second IP address in the pool (204.186.240.124). This
is oversimplified, of course. It is also quite common to overload the
pool. Hundreds of users might share 5 public addresses, in which case
you obviously have to reuse the addresses.
It's also quite common to have one IP public IP address in the NAT pool,
so that each person receives the same IP address in their outgoing
connections. The details will vary depending on the implementation of
NAT in your router (or firewall).
--Michael
