Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. And see here for current known issues.

New Member

6500 module options

I'm in the process of upgrading my 6500 with old modules to a SUP720. I know the latest 67xx and 68xx modules offer 40gbs connections to the backplane. How about these I currently have? What kind of connectivity do they have to the backplane? If it's something in the range of 8gbps and the module has 48 gigabit ports, then each port really has a capacity of 166mbps which concerns me.

WS-X6548-GE-TX (48 port gigabit ethernet)

WS-X6408A-GBIC (8 port mixed media gigabit slots)

Thank you!


Re: 6500 module options

Hi there,

The WS-6548-GE-TX cards were designed to extend gigabit connectivity to the desktop and as such use oversubscription.

The card is broken up into 6 groups (ports 1 - 8, 9 - 16, 17 - 24, 25 - 32, 33 - 40 and 41 - 48) with each group having a single 1Gbps ASIC uplink and 1Mb shared buffer. Due to the single 1Gbps uplink serving 8 ports, the total aggregate bandwidth of all 8 ports in a group cannot exceed 1Gbps.

This gives the card an oversubscription ratio of 8:1, so if you were using maximum speed on each interface equally, it would restrict each interface individually to around 125Mbps throughput. As the card was designed as high density gigabit for workstations, it would be rare that you would see a group using the full 1Gbps uplink capability in its intended medium (workstations). So while its oversubscribed, workstations are usually doing so little traffic that should one port need the bandwidth, most if it will be availible at all times for use.

Hope this helps.


New Member

Re: 6500 module options

Nik, thanks for the quick response. I'm going to need a 48-port gigabit blade for servers hence going by your response, it seems I should buy the Cisco Express Forwarding 720 Copper 10/100/1000 Ethernet Interface Module (WS-X6748-GE-TX). Will this blade give me 1gbps for each port? I think it connects to the backplane at 40gbps

Also, any comments on the WS-X6408A-GBIC?



Re: 6500 module options


The WS-X6748 has two 20Gbps connections to the Sup720 fabric giving it a total of 40Gbps. Using CEF you will get up to 30 Mpps per system, or you can install the dCEF upgrade to support 48 Mpps. Whilst it is considered a true line rate card, if being fully utilised it will have an oversubscription rate of approximately 1.2:1, giving you a total of ~830Mbps per port at 100% utilisation for the entire card. If you are pumping 40Gbps through a single line card then I think its time to add another =)

I believe the WS-6408A is a 1:1 card with full line rate for each port. Having never used them (or looked into them) I could be wrong though, so if youre going to use these in a production environment I would double check with Cisco.

Hope that helps and please remember to rate posts that do.