Identifying Enable Packets

Identifying Enable Packets
Enable packets
are the missing piece of the flow cache puzzle. Just as the MLS switch watches all
incoming frames destined for the MLS router’s MAC addresses, it also watches all the packets
coming from the MLS router.
It watches these packets, hoping for a match with the candidate packet cache entry. If it can
make the match, the packet is tagged as an enable packet and the remaining elements of the flow
cache are completed in the CAM table. Figure 18.5 depicts the occurrence of an enable packet.
The match is made by using the following criteria:

The source MAC address is from an MLS-RP.

The destination IP address matches the source IP address of a candidate packet.

The source MAC address is associated with the same XTAG value as the candidate packet’s
destination MAC address.
If all three of these criteria are met, the MLS-SE completes the shortcut cache entry.