IP Services Intermediate ~8 min

Configure PAT (NAT overload)

Edge router R1 has an inside network on Gi0/0 = 192.168.1.1/24 and an ISP-facing outside interface Gi0/1. Configure PAT so that any host on the inside network gets translated to the outside interface's IP when going to the internet.

Topology

Objectives

○ACL 1 permits 192.168.1.0 0.0.0.255
○Gi0/0 tagged ip nat inside
○Gi0/1 tagged ip nat outside
○PAT bound: ACL 1 → Gi0/1 overload

Hints

Hint 1 — the 4 steps

Define an ACL matching the inside network.
Tag the inside interface: ip nat inside.
Tag the outside interface: ip nat outside.
Bind: ip nat inside source list <acl> interface <out> overload.

Hint 2 — full sequence

enable
configure terminal
 access-list 1 permit 192.168.1.0 0.0.0.255
 interface gi0/0
  ip nat inside
  exit
 interface gi0/1
  ip nat outside
  exit
 ip nat inside source list 1 interface gi0/1 overload
 end

Bonus — PAT with a pool (blueprint 4.1)

Real deployments often overload a small pool of public IPs, not just one. Same ACL, but bind to a named pool:

 ip nat pool INTERNET 203.0.113.10 203.0.113.15 netmask 255.255.255.0
 ip nat inside source list 1 pool INTERNET overload

Bonus — verify

After a flow crosses the router: show ip nat translations shows the mapping; show ip nat statistics summarises hits/misses. And traceroute from an inside host confirms egress via the outside interface.

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