3750 vs 3750 X TCAM question

[Umesh Shetty]

Hi All,

One of the differences between the 3750 and 3750 X is that the 3750 has external TCAMs whereas 3750 X has TCAMS incorporated in the Port ASIC's. What kind of effect does this have on the forwarding rate or overall switching speed?

Thanks in Advance

Regards

Umesh

[Joseph W. Doherty]

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Posting

Unsure about the impact of TCAM design differences regarding performance of a 3750 vs. 3750-X.  The E/X series have a much higher aggregate PPS rate then the original/G series.  (The also have much higher internal fabric bandwidth too.)

[Umesh Shetty]

Thnx Joseph,

As per my understanding, the older 3750 switches did not have a second tier switch fabric or switch ASIC. The Port ASIC's were directly connected to the Stack Ring which is 32 Gbps and hence even in order to switch a packet locally within the stack member the switch needed to access the stack ring. 

I also had a query about the number of TCAM's in an ASIC, in a 3750 switch with 3 ASIC I can see a total of 6 TCAMS per ASIC. Do you know what role these 6 TCAM's play is it that one TCAM is used for one individual feature , ex IPV4 ACES, IPV4 Routes, QOS Aces etc. If it is this way why would be need SDM template if it is one TCAM per feature on an ASIC.

Attached is the TCAM and ASIC count that I am querying about.

Regards

Umesh

[Joseph W. Doherty · Accepted solution]

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The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

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In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

I really cannot comment much more on the architecuture of the 3750s.  Haven't seen much published by Cisco.

Regarding whether the original series have a switch fabric different from their stack ring, the sibling 3560 is described as having a 32 Gbps fabric and it doesn't have (visible) stack ports.  I believe the original 3750 stack ports are 8 Gbps, duplex.  The original 3750's ASICs appear to be limited to 8 Gbps, as the rare 3750G-10g's single 10g port is noted as being able to only sustain 8 Gbps.

Also, although the original stack ring has all the traffic on it from each 3750, I suspect that's due to replication between the fabric and the stack ring, not that they are one and the same.  I suspect this, because I believe the stack ring tries to, I believe, load balance between its two stack ports, and a fabric is a switch fabric if all traffic is flooded to everything, then its a bus.

Again, though, don't know for sure.  We really need someone from Cisco that "knows" the actual architecure of the different 3750 series switches.