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Simple Cisco NAT Concepts – Nat Pools and Static Nat — 2015-12-09 I thought I’d go over these two concepts really quickly. NAT Pools – When you are overloading a single IP, the truth is that you are using the ports available on that IP to send and recieve traffic and that’s translating to IP’s on the inside. Once you have even a few pc’s you can see from the translation table that many many ports are used, and while these connections tend to get torn down quickly, it’s still quite possible to run out. It really just depends on how many active clients you have to nat. To overcome this, you can create a pool of external IP’s to overload. The router will simply move to the next IP when the first has too many ports full. Lets use the same lab as our last NAT example. Router0 is using 128.128.129.2 as it’s interface. It’s gateway is 128.128.129.1, which is on Router1. If we are using that same lab.. we need to remove the nat command we issued earlier. WORKRTR(config)#no ip nat inside source list INSIDE_NAT_ADDRESSES interface GigabitEthernet0/1 overload if you have active connections you will be asked to kill those connections, and nat will of course.. stop. to nat overload, first we need to create a nat pool. In this example, I want to make ip’s 128.128.129.50 thru 128.128.129.100 available in my pool. WORKRTR(config)#ip nat pool OUTSIDE_PUBLIC 128.128.129.50 128.128.129.100 netmask 255.255.255.0 and now we simply create our nat using the same ACL we made in our last example. WORKRTR(config)#ip nat inside source list INSIDE_NAT_ADDRESSES pool OUTSIDE_PUBLIC overload We can now see in in the translations tables the nats being created. WORKRTR#sho ip nat translations Pro Inside global Inside local Outside local Outside global icmp 128.128.129.50:102410.0.0.101:7 128.128.128.10:7 128.128.128.10:1024 icmp 128.128.129.50:102510.0.0.101:8 128.128.128.10:8 128.128.128.10:1025 icmp 128.128.129.50:102610.0.0.101:9 128.128.128.10:9 128.128.128.10:1026 icmp 128.128.129.50:102710.0.0.101:10 128.128.128.10:10 128.128.128.10:1027 icmp 128.128.129.50:102810.0.0.101:11 128.128.128.10:11 128.128.128.10:1028 icmp 128.128.129.50:102910.0.0.101:12 128.128.128.10:12 128.128.128.10:1029 icmp 128.128.129.50:103010.0.0.101:13 128.128.128.10:13 128.128.128.10:1030 icmp 128.128.129.50:103110.0.0.101:14 128.128.128.10:14 128.128.128.10:1031 icmp 128.128.129.50:103210.0.0.101:15 128.128.128.10:15 128.128.128.10:1032 icmp 128.128.129.50:103310.0.0.101:16 128.128.128.10:16 128.128.128.10:1033 icmp 128.128.129.50:103410.0.0.101:17 128.128.128.10:17 128.128.128.10:1034 icmp 128.128.129.50:103510.0.0.101:18 128.128.128.10:18 128.128.128.10:1035 icmp 128.128.129.50:103610.0.0.101:19 128.128.128.10:19 128.128.128.10:1036 icmp 128.128.129.50:103710.0.0.101:20 128.128.128.10:20 128.128.128.10:1037 icmp 128.128.129.50:103810.0.0.101:21 128.128.128.10:21 128.128.128.10:1038 icmp 128.128.129.50:103910.0.0.101:22 128.128.128.10:22 128.128.128.10:1039 icmp 128.128.129.50:104010.0.0.101:23 128.128.128.10:23 128.128.128.10:1040 icmp 128.128.129.50:104110.0.0.101:24 128.128.128.10:24 128.128.128.10:1041 icmp 128.128.129.50:104210.0.0.101:25 128.128.128.10:25 128.128.128.10:1042 icmp 128.128.129.50:104310.0.0.101:26 128.128.128.10:26 128.128.128.10:1043 I can’t really create the traffic in my lab to make this jump to the next IP however ...