scratch deck

Question 1

How is TCAM different than CAM?

Answer 1

TCAM allows for the matching and evaluation of a packet on more than one field.

Question 2

Architecturally, describe what the TCAM is.

Answer 2

It is an extension of the CAM table but enhanced so that it can do upper-layer processing.

Question 3

Name 3 things TCAM can identify.

Answer 3

• L2 / L3 source/destination address
• Protocol
• QOS markings

Question 4

Name 2 differences between TCAM and CAM.

Answer 4

• TCAM (ternary) provides more flexibility in searching than CAM (binary)
• TCAM does upper-layer processing, CAM does not

Question 5

What are the states TCAM can match on?

Answer 5

1’s, 0’s, and X’s where X is ‘don’t care’

example:

TCAM can search for a value that has 0 1 1 1 X X 1 0 . This will match:

01110010

01110110

01111010

01111110

Question 6

What 3 components make up a TCAM entry?

Answer 6

• Value 172.19.0.0
• Mask 255.255.0.0
• Result Deny

Question 7

What are 3 things that the TCAM Result can be?

Answer 7

• Permit or deny
• Pointer to a next hop in the routing table
• An index to a QOS Policer

Question 8

What 2 factors allow TCAM to be really fast?

Answer 8

• TCAM operates in hardware
• Each of the 5 TCAM partitions can be processing simultaneously allowing multiple operations to be done at the same time