One Question

[sharma . tarun]

Title: One Question

Hi,
First of all sorry for asking non relevent question but somehow it belongs to
IP. So hopefully I will get a reply for this question.
Actually long back when I just started the work on IP then i came across one
problem. As for my company we have IP addresses in our LAN and we have one entry
for default IP address which is used if our destination IP address doesnt match
with anyone in our ARP cache. Now router decides whether this IP address belongs
to outer world or not based upon its net address and routes it accordingly.
Now the question was if the source IP address remains same as my host address in
LAN or it is replaced by router's IP address. If it remains the same then it
gives a logical picture and packet can travel from destination to source(reverse
path). But if it is replaced by router's address then how can packets come to
source address. According to my understanding source IP address doesnt change
and it works in a unique fashion. But it this is the case then why we give only
one IP address to corporates. We give it because we dont want to use so many
IP addresses for a corporate and IP addresses are limited.
Even this is one of the reason we are going towards IPv6.

Please give me some clear picture of this.
Thanks and excuse me of non relevent question. But this is the place where I can
get best answer.

Regards
Tarun Sharma