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

ISL and card capacity question.


When using ISL's on 16 port 2 Gb cards, you can use one port for an ISL but when using 32 port cards, you must use only one port in the port group (four ports). So the other three ports are useless (turned off).

With the new 4 Gb cards, port groups are no longer composed of four ports. The DS-X9124 is composed of six ports and the DS-X9148 is composed of twelve ports in a port group.

So, what exactly does that mean? Will an ISL require 5 ports and 11 ports to be wasted in the 24 and 48 port 4 Gb cards respectively? If so, thats a huge waste of ports.

The reason I ask is that my edge 9216's will have the 16 port 2 Gb ports (the second card will be a DS-X9148) for Port Channel ISL's to my 9509 core.

Our project manager has gotten carried away with the new 4 Gb ports but has not done much research. So if I had a 8 port Port Channel ISL from the 9216, can I use a 24 port 4 Gb card in the 9509 or do I need another 16 port 2 Gb card?

The Cisco doco on the 4 Gb cards sort of suggests that the 24 port 4 Gb card can be used for ISL's but it does not state if port groups have restrictions like the 32 port 2 Gb cards.

Clear as mud isn't it? Any help would be appreciated.


Cisco Employee

Re: ISL and card capacity question.

No restrictions like on the 32-port card.

With the new 24 and 48 port cards you have 12.8 Gbps of bandwidth available per port group and you can dedicate bandwidth per port from that. ISLs require dedicated bandwidth. As long as you do not overbook the port group by dedicating more bandwidth than available you're fine and do not need to put any ports out of service.

E.g. on a 24 port card you have 4 port groups of 6 ports each. You could dedicate 2 ports @ 4G in the port group for two ISLs and have the other four ports in the group share the rest of 4 Gbps (running 4:1 oversubscribed). Or you could just use one ISL per port group and have five ports share the rest of 8.8 Gbps.

All that is described in detail here:


CreatePlease to create content