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IPv6 NAT PT Overview

Starting in Junos OS Release 20.2R1 you can run IPv6 NAT-PT Next Gen Services on MX240, MX480, and MX960 routers.

IPv6 Network Address Translation-Protocol Translation (NAT-PT) provides address allocation and protocol translation between IPv4 and IPv6 addressed network devices. The translation process is based on the Stateless IP/ICMP Translation (SIIT) method; however, the state and the context of each communication are retained during the session lifetime. IPv6 NAT-PT supports Internet Control Message Protocol (ICMP), TCP, and UDP packets.

IPv6 NAT-PT supports the following types of NAT-PT:

  • Traditional NAT-PT—In traditional NAT-PT, the sessions are unidirectional and outbound from the IPv6 network . Traditional NAT-PT allows hosts within an IPv6 network to access hosts in an IPv4 network. There are two variations to traditional NAT-PT: basic NAT-PT and NAPT-PT.

    In basic NAT-PT, a block of IPv4 addresses at an IPv4 interface is set aside for translating addresses as IPv6 hosts as they initiate sessions to the IPv4 hosts. The basic NAT-PT translates the source IP address and related fields such as IP, TCP, UDP, and ICMP header checksums for packets outbound from the IPv6 domain . For inbound packets, it translates the the destination IP address and the checksums.

    Network Address Port Translation-Protocol Translation (NAPT-PT) can be combined with basic NAT-PT so that a pool of external addresses is used in conjunction with port translation. NAPT-PT allows a set of IPv6 hosts to share a single IPv4 address. NAPT-PT translates the source IP address, source transport identifier, and related fields such as IP, TCP, UDP, and ICMP header checksums, for packets outbound from the IPv6 network. The transport identifier can be a TCP/UDP port or an ICMP query ID. For inbound packets, it translates the destination IP address, destination transport identifier, and the IP and the transport header checksums.

  • Bidirectional NAT-PT—In bidirectional NAT-PT, sessions can be initiated from hosts in the IPv4 network as well as the IPv6 network. IPv6 network addresses are bound to IPv4 addresses, either statically or dynamically as connections are established in either direction. The static configuration is similar to static NAT translation. Hosts in IPv4 realm access hosts in the IPv6 realm using DNS for address resolution. A DNS ALG must be employed in conjunction with bidirectional NAT-PT to facilitate name-to-address mapping. Specifically, the DNS ALG must be capable of translating IPv6 addresses in DNS queries and responses into their IPv4 address bindings, and vice versa, as DNS packets traverse between IPv6 and IPv4 realms.


    The devices partially support the bidirectional NAT-PT specification. It supports flow of bidirectional traffic assuming that there are other ways to convey the mapping between the IPv6 address and the dynamically allocated IPv4 address. For example, a local DNS can be configured with the mapped entries for IPv4 nodes to identify the addresses.

NAT- PT Operation—The devices support the traditional NAT-PT and allow static mapping for the user to communicate from IPv4 to IPv6 . The user needs to statically configure the DNS server with an IPv4 address for the hostname and then create a static NAT on the device for the IPv6-only node to communicate from an IPv4-only node to an IPv6-only node based on the DNS.

Release History Table
Starting in Junos OS Release 20.2R1 you can run IPv6 NAT-PT Next Gen Services on MX240, MX480, and MX960 routers.