Switch model capacity planning

Unanswered Question
Feb 6th, 2008

Hi there. I'm trying to figure what some numbers mean and I'm hoping someone can help. We have a 4507R w/ Supervisor V. The specs on that engine say it will do 96Gbps / 72Mpps. How do you relate the Supervisor throughput with the line cards you want to add. For example, I read that each standard 4500 series line-card supports 6Gbps per slot. (http://www.cisco.com/en/US/prod/collateral/modules/ps2710/ps5494/product_data_sheet0900aecd802109ea.html). So I'm interpreting that to mean that if you put 6 WS-X4306-GB's in a chassis, you would only be using 36Gbps of the available throughput. Is that correct?

Also, how does the 6500 compare? I'm interested in setting up a high-throughput datacenter LAN and I don't want any oversubscription (or very little). As far as I can tell, the 6500 is the way to go, especially with all the flexibility in service modules and line cards, but I need some pretty convincing evidence to sell the idea to management.

Thanks for your help.

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rami_azar Wed, 02/06/2008 - 11:40

Dear branfarm1

i also would like to know the answer.

i have been facing sizing problems as well

Joseph W. Doherty Wed, 02/06/2008 - 17:34

Correct, the "classic" 4500 slots (prior to the recent 45xx-E series), provides 6 Gbps per slot. Also correct the Sup-V is documented as capable of 96 Gbps (fabric) and 72 Mpps, within the 4510R. The smaller chassis, such as your 4507R, don't use the full capacity.

Each line card of 6 Gbps, being full duplex, can push 12 Gbps across the fabric. So for five (believe 4506 or 4507R only support 5 lines cards) and 4 uplinks (dual sups), you need 68 Gbps of fabric bandwidth.

Wire speed, for minimum sized (64 byte) Ethernet frames needs 1.488095 Mpps for each 1 Gbps, so the prior 34 Gbps, equates to 50.59523 Mpps.

See table 1 in http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps4324/product_data_sheet09186a00801fcaba.html

Effectively, the 4507R with sup-V is a line rate capable system.

The 6500, although the chassis is the same, the available bandwidth and pps rates vary based on what's placed in the chassis.

For instance, the 6500 sup-32 offers only a 32 Gbps bus (not fabric) and 15 Mpps. The sup720 offers not only the 32 Gbps bus, but also provides a 720 Gbps fabric with various fabric bandwidths available to each slot: single 8 Gbps, dual 8 Gbps (just one line card?), single 20 Gbps (e.g. some 6513 slots) or dual 20 Gbps. The pps rate for the sup720 is either 15 or 30 Mpps depending on bus or fabric line card connections.

As you might note, the pps rate of the sup720 falls far short of supporting a 720 Gbps fabric. This is made up by using optional, if supported, DFC (distributed function chips) on line cards. The later ones supporting 48 Mpps per slot.

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