Non-blocking operation on Catalyst 6500

[moabdallah]

I have Catalyst 6506-E with :

Dual SUP-720-3B

One WS-X6748-SFP ( 48 SFP ports )

One WS-X6748-GE-TX ( 48 100/1000Base-T ports)

Do I have non blocking, Full duplex, operation at maximum port speed ?

Please note that :

I am using only 24 ports on WS-X6748-SFP module & 24 ports on WS-X6748-GE-TX and I don't have any DFC installed

Regards

Mohamed

[ankurbhasin]

Hi Mohamed,

As you have sup 720 which has integrated SFM and also the line cards (WS-X6748-SFP & WS-X6748-GE-TX) which you are having is fabric enabled which means you have non blocking architecture setup and it will be operational at maximum port speed.

HTH, if yes please rate the post.

Ankur

[moabdallah]

Hi Ankur,

Thanks for your reply

The point here the Switch performance is 30 Mpps

Two moudles installed (WS-X6748-SFP & WS-X6748-GE-TX), so that throughput is 15Mpps per slot.

Using 24 ports 1000Base-Sx only (WS-X6748-SFP ) full duplex operation with 15 Mpps performance

Using 24 ports 1000Base-Sx only (WS-X6748-GE-TX) full duplex operation with 15 Mpps performance

Does this mean blocking OR non-blocking with full duplex operation at maximum port speed?

Regards

Mohamed

[jv]

Actually, that is not correct. All of the 48 port Gig-E line cards for the 6500 are oversubscribed; it does vary by the degree of oversubscription.

In a 6506 or a 6509 (with a Sup720) you have (2) 20 Gbps connections (per slot) to the fabric. With a WS-X6748-GE-TX you have a potential for 48 (Full Duplex) Gbps of traffic, but only 2 connections to the fabric. This yields an oversubscription rate of 1.2:1 (or 48:40) assuming a worst case scenario.

It should be noted that the 24 port 67xx cards are still oversubscribed as well, because they only have one connection to the fabric. There is a potential for 24 Gbps of traffic and only (1) 20 Gbps fabric connection, so it has an identical oversubscription rate.

By using only 24 of the 48 possible ports, depending on which ones you choose, you should be OK. But I do not know which ports use which fabric connection on the backplane, so I can't assist you in picking them.

It should be noted that in most environments it is unlikely every port will be a 100% utilized so the risk of dropping packets because of oversubscription is low.

[moabdallah]

What about the throughput ?

Without DFC3B, thourput is 30 Mpps only per system

if I am using 24 ports from 6748-SFP and 24 ports from 6748-SFP modules ( total of 48 ports 1000BaseX )

If you calculate with packet = 64 byte

30 Mpps is not enough for 48 1000BasX full duplex operation

Is this correct ?

Regards

Mohamed Abdallah

[jv]

With 64 byte packets a Gig-E connection can push 1,488,000 in each direction, so Full Duplex would be 2,976,000. That is a per port number. Just multiply that times the number of ports and you'll reach your 30Mpps pretty fast. Keep in mind that those numbers are a worst case scenario. You need to consider what your real world traffic is going to look like and run the numbers. Is it likely that your average packet size will be the smallest packet size? 30Mpps is a lot of traffic.

This may help with some of your calculations.

http://www.erg.abdn.ac.uk/users/gorry/course/lan-pages/enet-calc.html

I hope this has helped.

James

[moabdallah]

Hi James,

Thanks for your help

That mean 30 Mpps is not enough ( blocking) to handle the total of 48 1000Base-X full duplex operation ( in the worest case scenario 64 byte packet )

Please confim

Regards

Mohamed

[jv]

Confirmed. The calculation would be as follows:

2,976,000 * 48 = 142,848,000 pps.

~143 Mpps.

Nearly 4.7x the rating of 30Mpps

James