Two tables are used in switch operations, CAM and TCAM. We visited the CAM table in an earlier discussion. In this post we briefly talk about Ternary Content Addressable Memory, or TCAM. Why is it called Ternary? Because it provides three results: 0, 1, and “don’t care”.
The TCAM allows a packet to be evaluated against an entire ACL in a single table lookup. One swoop. This makes lookups ultra-fast. It is done in hardware.
There are two components of TCAM operation:
- Feature Manager (FM)
- Which compiles the access controle entries into the TCAM table.
- Switch Database Manager (SDM) **Not to be confused with Security Device Manager
- Which configures or tunes TCAM partitions, if needed.
Greg Ferro has some good information on TCAM and it’s impact with IPv6.