I believe you are referring to NAT Overload, which is also know as PAT (Port
Address Translation). I found little information from CCO (most was related
to the cable modem IOS) & it took me quite some time to write my last
config. With PAT you have one (or very few Global IP addresses) & many
Private inside addresses. This is generally the case with a home network or
small business where the user cannot get or does not want to pay for extra
IP addresses. The router is actually ear-marking or mapping the private IP
address (via port spoofing) when leaving the router under the 1 Global IP.
By tagging or earmarking, the router knows what local Private address owns
the TCP session taking place (among many) on the 1 Global IP. The commands
in the config that allow you to do this are:
ip nat pool Circusnuts 24.x.x.1 24.x.x.1 netmask 255.255.255.0
ip nat inside source list 1 pool Circusnuts overload
If you notice, the range given above is one IP (24x.x.1 to 24.x.x.1) address
space in size. The router is instructed to use Overload (to start Port
Spoofing) if that range of the 1 Global IP is ever exceeded by the inside
Private addressing requirements. To watch this take place in your config,
the commands are Show IP NAT Statistics & Show IP NAT Translation.
2621#sh ip nat stat
Total active translations: 3 (0 static, 3 dynamic; 3 extended)
Outside interfaces:
FastEthernet0/1
Inside interfaces:
FastEthernet0/0
Hits: 47215 Misses: 1478
Expired translations: 1475
Dynamic mappings:
-- Inside Source
access-list 1 pool Circusnuts refcount 3
pool Circusnuts: netmask 255.255.255.0
start 24.x.x.1 end 24.x.x.1
type generic, total addresses 1, allocated 1 (100%), misses 2
2621#sh ip nat trans
Pro Inside global Inside local Outside local Outside global
tcp 24.x.x.1:2486 10.1.1.2:2486 207.46.145.36:80 207.46.145.36:80
tcp 24.x.x.1:2483 10.1.1.2:2483 207.46.145.36:80 207.46.145.36:80
tcp 24.x.x.1:2485 10.1.1.2:2485 207.46.179.71:80 207.46.179.71:80
tcp 24.x.x.1:2480 10.1.1.2:2480 207.46.179.71:80 207.46.179.71:80
tcp 24.x.x.1:2484 10.1.1.2:2484 64.232.139.99:80 64.232.139.99:80
udp 24.x.x.1:2481 10.1.1.2:2481 24.5.80.33:53 24.5.80.33:53
udp 24.x.x.1:2482 10.1.1.2:2482 24.5.80.33:53 24.5.80.33:53
udp 24.x.x.1:2479 10.1.1.2:2479 24.5.80.33:53 24.5.80.33:53
Does this makes sense ???
Phil
----- Original Message -----
From: "a. ahmad"
To:
Sent: Saturday, July 07, 2001 8:37 AM
Subject: NAT [7:11245]
> hi,
> can any one describe NAT Function in detail (many-to-one).
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=11252&t=11252
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