IOS XE 3.6S was released recently introducing Carrier Grade NAT to ASR 1000 platform. CGN translates IPv4 addresses into IPv6 addresses and vice versa and is one of the most critical feature while world is slowly moving into IPv6 addressing. It can also be used for NAT44 (IPv4 private to IPv4 public) translation. What differs CGN from traditional NAT? CGN increases the scalability of the number of NAT translations that can be supported because destination information is not stored and works good with carrier services like broadband access aggregation (ie. PPPoE, DSL)
Carrier Grade NAT differs a little from traditional NAT. It does not support outside mappings, because it does not store destination IP address. There are also few other limitations on ASR1000 platform – IP Sessions are not supported nor box-to-box redundancy. Other features important for service providers, including Lawful Intercept, high-speed logging using NetFlow, vrf-awareness or multihoming, are supported.
CGN is enabled globally – you can’t have carrier grade and traditional NAT working together on same box. Old NAT configuration have to be removed prior to enabling CGN. Feature is enabled using command
ASR1000(config)# ip nat settings mode cgn