CCNA Foundations: PAT (NAT Overload) — Many Hosts, One IP

Today's daily lab

Deploy Port Address Translation (NAT overload) on an enterprise edge so two inside clients share a single public IPv4 address to reach an external HTTP service on an ISP router. You will designate inside/outside, build the NAT selection ACL, configure the overload rule, and verify simultaneous flows and translations from the end hosts.

Learning objectives

• Configure inside and outside interfaces for NAT on a Cisco IOS edge router
• Author a standard ACL that selects the inside subnet for PAT
• Apply ip nat inside source list <acl> interface <wan> overload using the WAN's public IP
• Verify simultaneous connections from multiple inside hosts to an outside server
• Interpret show ip nat translations and statistics outputs to confirm port multiplexing

Troubleshooting focus

• If hosts cannot reach 203.0.113.1, verify the default route on the edge points at 203.0.113.1 and that the WAN interface is up/up.
• If pings work but HTTP fails, confirm the ISP router's HTTP server is running and reachable (ip http server enabled) and that the NAT ACL actually matches 10.10.10.0/24.
• If show ip nat translations is empty during traffic, check that ip nat inside is on the LAN-facing interface and ip nat outside is on the WAN-facing interface (not reversed).
• If only one host is translated, ensure both clients have the correct default gateway (10.10.10.1) and are in VLAN 10 on the switch access ports.
• For intermittent success, confirm there is no overlapping or wrong subnet mask on the LAN or transit /30; mismatched masks can ARP or route incorrectly.