TCAM tutorial

liven

Ok just read the TCAM section out of my cisco BCMSN book. I have to say it was a little hard staying really focused on that chapter.

Does anyone know of any other good resources for getting that material into ones head?

Thanks

kryolla

what are you having problems with. The MAC or TCAM table is built on the MAC address (s) that is associated with the port. If the switch doesn't have an entry it floods it to all ports except the port it came in on. The end device will reply and the switch will now have a TCAM entry

liven

Well more on the masks and the lookup process was what I was looking for.

Also how it ties into layer 3 functionality.

Thanks

kryolla

for switches they are no masks with MAC addresses and there is no relation for layer 3 functionality. As for the algorithm it uses for the look up, do they even cover that in the BCMSN book I would think you would need to go to Cisco web site to find that out. I might be wrong, when I get home I will look in that book and see.

liven

Thanks for your replies, and just and FYI the book most certainly goes into this level of TCAM detail.

It also talks about masks in regards to l3 switches (unless I am just remembering it wrong, which is entirely possible!!!!). It is not the most difficult topic, but I did have trouble focusing on it because it was much more low level than I was used to for this type of test/study.


I will post the chapter and page numbers from my book (its the offical cisco book for BCMSN test) when I get home.


Thanks again!!!

kryolla

I was thinking about the CAM table and not TCAM. Here is some info on Switching Database Manager which controls the size and usage of the TCAM tables.

http://blog.ioshints.info/2008/01/tcam-on-catalyst-switches.html

kpjungle

liven wrote:

Thanks for your replies, and just and FYI the book most certainly goes into this level of TCAM detail.

It also talks about masks in regards to l3 switches (unless I am just remembering it wrong, which is entirely possible!!!!). It is not the most difficult topic, but I did have trouble focusing on it because it was much more low level than I was used to for this type of test/study.


I will post the chapter and page numbers from my book (its the offical cisco book for BCMSN test) when I get home.


Thanks again!!!

Without knowing it for sure, I dont think they expect you to explain the functions of the tcam algorithms beyond knowing its a 3 "column" lookup table, compared to the 2 "column" table of regular cam, and it uses masks to ge the most specific match, instead of just a true/false of cam.

liven

Thanks Guys!!!!

_maurice

I too was having trouble understanding the TCAM concept. I had to re-read the section in the BCMSN book near ten times before it made sense to me.

It seems that the TCAM table is made up of unique mask pairs. This way, the switch knows where to look info up once it knows what bits are important. This is much faster than processing an ACL from the top down like a router does. Is this right?