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Implementing Carrier Grade NAT on Cisco IOS XR Software
A Stateless XLAT (SL-XLAT) does not create or maintain any per-session or per-flow data structures. It is
an algorithmic operation performed on the IP packet headers that results in the translation of an IPv4 packet
to an IPv6 packet, and vice-versa. SL-XLAT requires Cisco IOS XR Software Release 3.9.3 or 4.0.1 or 4.1.0
or later.
IPv6 Rapid Deployment
IPv6 Rapid Deployment (6RD) is a mechanism that allows service providers to provide a unicast IPv6 service
to customers over their IPv4 network.
Stateful NAT64
The Stateful NAT64 (Network Address Translation 64) feature provides a translation mechanism that translates
IPv6 packets into IPv4 packets and vice versa. NAT64 allows IPv6-only clients to contact IPv4 servers using
unicast UDP, TCP, or ICMP. The public IPv4 address can be shared with several IPv6-only clients. NAT64
supports communication between:
• IPv6 Network and Public IPv4 Internet
• Public IPv6 Internet and IPv4 Network
NAT64 is implemented on the Cisco CRS router CGSE platform. CGSE (Carrier Grade Service Engine) has
four octeons and supports 20 Gbps full duplex traffic. It works on Linux operating system and traffic into
CGSE is forwarded using serviceApp interfaces. SVIs (Service Virtual Interfaces) are configured to enable
traffic to flow in and out of CGSE.
Each NAT64 instance configured is associated with two serviceApps for the following purposes:
• One serviceApp is used to carry traffic from IPv6 side
• Another serviceApp is used to carry traffic from IPv4 side of the NAT64.
NAT64 instance parameters are configured using the CGN CLI. The NAT64 application in the octeons updates
its NAT64 instance and serviceApp databases, which are used to perform the translation between IPv6 and
IPv4 and vice versa.
Active CGN instance configuration is replicated in the standby CGN instance through the XR control plane.
Translations that are established on the Active CGN instance are exported to the Standby CGN instance as
the failure of the Active CGN affects the service until translations are re-established through normal packet
flow. Service interruption is moderate for the given fault detection time and translation learning rate in terms
of seconds or tens of seconds for a large translation database.
Dual Stack Lite
The Dual Stack Lite (DS-Lite) feature enables legacy IPv4 hosts and server communication over both IPv4
and IPv6 networks. Also, IPv4 hosts may need to access IPv4 internet over an IPv6 access network. The IPv4
hosts will have private addresses which need to have network address translation (NAT) completed before
reaching the IPv4 internet. The Dual Stack Lite application has these components:
OL-32659-01
Cisco IOS XR Carrier Grade NAT Configuration Guide for the Cisco CRS Router, Release 5.2.x
IPv6 Rapid Deployment
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