Consider the scenario below in which three hosts, with

private IP addresses $10\mathrm{.}0\mathrm{.}1\mathrm{.}13,10\mathrm{.}0\mathrm{.}1\mathrm{.}16,10\mathrm{.}0\mathrm{.}1\mathrm{.}23$ are in

a local network behind a NAT'd router that sits between

these three hosts and the larger Internet. IP datagrams

being sent from, or destined to$,$ these three hosts must

pass through this NAT router. The router$$s interface on the

LAN side has IP address $10\mathrm{.}0\mathrm{.}1\mathrm{.}26,$ while the router$$s

address on the Internet side has IP address

$135\mathrm{.}122\mathrm{.}197\mathrm{.}215$

Before doing this problem, you might want to reread the

section on the NAT protocol in section $4\mathrm{.}3\mathrm{.}4$ in the text.

Suppose that the host with IP address $10\mathrm{.}0\mathrm{.}1\mathrm{.}16$ sends an

IP datagram destined to host $128\mathrm{.}119\mathrm{.}176\mathrm{.}184.$ The

source port is $3468,$ and the destination port is $80.$

Consider the datagram at step $1,$ after the host has sent it but before it has

reached the router. What is the source IP address for this datagram? $10\mathrm{.}0\mathrm{.}1\mathrm{.}16$