6500 Question

Answered Question
Jan 28th, 2010
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Hi,


I'm looking around at various line modules for the 6500 series with Sup 720...

I was reading that the WS-X6748-GE-TX w/ WS-F6700-DFC3 could access 720gb of backplane... does that mean all 48 ports could run at full GB speeds? I don't seem to see anything listed about over subscription. General idea is that i want to replace my pair for 4507R backbone with a 6509-E VSS setup and i'm exploring the various switch fabric cards I could use.

This is what I was thinking about:

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Dual Power supplies 1400w AC
Fan tray
2x WS-X6748-GE-TX w/ WS-F6700-DFC3
1x WS-X6724-SFP
WS-X6716-10G-3C


These would be for my backbone, no PoE required. Provides server access and access-switch aggregation (collapsed core design). Servers are mostly ESX hosts. Will be some iSCSI traffic, so I would like Jumbo Frames, which the WS-6748 supports.

Correct Answer by Jon Marshall about 7 years 1 month ago

rtjensen4 wrote:


Thanks for the information. If the card connects at 40gbps, whats the advantage of having the Sup720 with the DFSC3 card? Where does the 720gbs backplane come in handy? I'm just trying to learn about the platform a bit more and how what advantages this would gain me. Thanks!


720Gbps is the total switch fabric capacity - it's worked out this way


In a 6509 all 9 slots can support 40Gbps connectioin to switch fabric.


So 9 x 40Gbps = 360Gbps


However because the switch fabric is full duplex connectivity Cisco double up the figures so


360 x 2 = 720Gbps


So each WS-X6748-GE-TX module has 40Gbps ( 2 x 20Gbps ) connectivity to the switch fabric.


The WS-X6724-SFP has a single 20Gbps connection to the switch fabric so again there is some oversubscription.


Note that these are physical limitations per slot ie. the 6724-SFP only uses 20Gbps of the switch fabric but that does not mean the other 20Gbps is available to other modules.


Jon

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Jon Marshall Thu, 01/28/2010 - 07:57
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rtjensen4 wrote:


Hi,


I'm looking around at various line modules for the 6500 series with Sup 720...

I was reading that the WS-X6748-GE-TX w/ WS-F6700-DFC3 could access 720gb of backplane... does that mean all 48 ports could run at full GB speeds? I don't seem to see anything listed about over subscription. General idea is that i want to replace my pair for 4507R backbone with a 6509-E VSS setup and i'm exploring the various switch fabric cards I could use.

This is what I was thinking about:

Cisco 6506-E w/ redundant VS-S720-10G-3C
Dual Power supplies 1400w AC
Fan tray
2x WS-X6748-GE-TX w/ WS-F6700-DFC3
1x WS-X6724-SFP
WS-X6716-10G-3C


These would be for my backbone, no PoE required. Provides server access and access-switch aggregation (collapsed core design). Servers are mostly ESX hosts. Will be some iSCSI traffic, so I would like Jumbo Frames, which the WS-6748 supports.


The WS-X6748-GE-TX has 48 ports capable of 1Gbps. The modules has a connection to the switch fabric of 40Gbps so there is some oversubscription but not much and to be honest it would be difficult to get all 48 ports forwarding at 1Gbps at the same time. So you should be fine with this module. If you are really that concerned with oversubscription just populate only 40 of the ports although you need to know how the ports are grouped. If you need to know this info just let me know or you can find it yourself in the 6500 release notes.


Jon

rtjensen4 Thu, 01/28/2010 - 08:01
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Thanks for the information. If the card connects at 40gbps, whats the advantage of having the Sup720 with the DFSC3 card? Where does the 720gbs backplane come in handy? I'm just trying to learn about the platform a bit more and how what advantages this would gain me. Thanks!

Correct Answer
Jon Marshall Thu, 01/28/2010 - 08:09
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rtjensen4 wrote:


Thanks for the information. If the card connects at 40gbps, whats the advantage of having the Sup720 with the DFSC3 card? Where does the 720gbs backplane come in handy? I'm just trying to learn about the platform a bit more and how what advantages this would gain me. Thanks!


720Gbps is the total switch fabric capacity - it's worked out this way


In a 6509 all 9 slots can support 40Gbps connectioin to switch fabric.


So 9 x 40Gbps = 360Gbps


However because the switch fabric is full duplex connectivity Cisco double up the figures so


360 x 2 = 720Gbps


So each WS-X6748-GE-TX module has 40Gbps ( 2 x 20Gbps ) connectivity to the switch fabric.


The WS-X6724-SFP has a single 20Gbps connection to the switch fabric so again there is some oversubscription.


Note that these are physical limitations per slot ie. the 6724-SFP only uses 20Gbps of the switch fabric but that does not mean the other 20Gbps is available to other modules.


Jon

rtjensen4 Thu, 01/28/2010 - 08:13
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O, one last question, if I didn't get the DSFC3 card with the 6748 card.... would that module only connect at 20gbps?

Jon Marshall Thu, 01/28/2010 - 08:55
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rtjensen4 wrote:


O, one last question, if I didn't get the DSFC3 card with the 6748 card.... would that module only connect at 20gbps?


No, you would still get 40Gbps to the switch fabric. Without DFCs all the forwarding and packet rewrite is done by the supervisor. However with DFCs the L2 and L3 forwarding tables are kept locally on the module. So the packet does not have to go to the supervisor to have a L2/L3 lookup and then be forwarded. This increases the overall system performance of the 6500 hugely ie.


without DFCs the 6500 is capable of 30Mpps. A DFC enabled module gets 48Mpps just for that slot.


If you have high throughput requirements you should be looking to utilise DFC cards on your modules.


Edit - you may want to have a read of this doc which covers the benefits of using DFC cards in the 6500 -


6500 DFC


Jon

rtjensen4 Thu, 01/28/2010 - 08:11
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Thanks Jon. Always appreciate your help!

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