Carrier grade NAT

LI for NAT is supported to mirror configured subscriber’s traffic to a mirror destination. When active, packets are mirrored from the perspective of the NAT outside interface (after NAT translations have occurred). All traffic for the specified subscriber, including traffic associated with static port-forwards, is mirrored. This feature is supported for 7450 ESS and 7750 SR only.

A simplified Ethernet encapsulation (with an optional Intercept ID) is used for all NAT traffic. When mirroring NAT traffic, the mirror destination must be of type ether. The customer packet from the (outside) IP header onwards (including the IP header) is mirrored. The operator has the configuration option of embedding the intercept ID into the LI packet using an explicit intercept-id command. Both packet formats are described below:

Figure: Ethernet mirror examples

The contents of the highlighted fields are configurable using the following CLI:

li
    li-source service-id
         nat
             classic-lsn-sub router name ip address 
                 intercept-id id
             dslite-lsn-sub router name b4 ipv6-address
                 intercept-id id
             l2-aware-sub sub-ident 
                 intercept-id id

The default Ethernet-header is to use etype 0x600 and system MAC address for both the source and destination addresses. The configurable Ethertype and Intercept ID is only added when an intercept ID is present for the subscriber in the NAT configuration.