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Community Manager

Ask the Expert: Catalyst 6500 Switch Architecture

With Akshay Balaganur

Welcome to the Cisco Support Community Ask the Expert conversation. This is an opportunity to learn from Cisco expert Akshay Balaganur about Cisco Catalyst 6500, one of the most widely deployed switches in the world. The "Swiss Army knife of network", can do routing, switching, security, wireless and almost everything that you would want your core switch to do.

Remember to use the rating system to let Akshay know if you have received an adequate response. 

Akshay might not be able to answer each question due to the volume expected during this event. Remember that you can continue the conversation on the Network Infrastructure sub-community discussion forum shortly after the event.  This event lasts through July 27, 2012. Visit this forum often to view responses to your questions and the questions of other community members.


Hello Kevin,

Unfortunatley the port-asic mapping architecture documents for Line cards of 6500 are only internal.

But I can answer your query about 6748s and 6724s.

In WS-X6748-GE-TX ,  12 ports are mapped to one port Asic. And all tweleve ports are serialy placed eg ports 1-12 map to one asic, port 13-24 map to next asic.

In WS-X6748-SFP ,  again 12 ports are mapped to one port Asic like before. But they are not serially placed. The aricheture is like this.  First two asics have all odd ports. Next two asics have all even ports. So fisrts asic has ports form 1,3,5 so on til 23. Second asic has 25, 27 ,29 so on 47 . Third asic has even ports starting from 2 till 24. Fourth asic starts from 26 and ends at 48. You got it right !

In WS-X6724-SFP , 12 ports are mapped to each asic. Ports are placed in sequence.

Hope it helps. Please rate if you find it useful.




hi Akshay,

A few more questions:

1. Is there any document that shows what functions are performed in hardware, and what are performed in software on the Cat 6K's?

We'd like to utilize things like NBAR & WCCP, but wanted to make sure we don't over run the CPU, if they're done in software.

I suppose wccp L2 redirect/return is hardware accelerated, but what about wccp GRE method?

Also, when we do "show policy-map interface", many counters remain zero.

Why is that? Does it mean QoS is done in hardware?

These are just some of the examples...we'd love to get a full list of the services performed in hardware vs software.

2. Is there an FAQ page for the WiSM2 blade like this one (for WiSM1):

We'd like to know how many WiSM2 blades we can populate in a 6500 chassis, and if there's the same limitation as WiSM1 blades.

How come there can be only four WiSM's in a 6509E, if there are two other service modules present?

What happens to the remaining two available slots? (9 total - 1 sup - 4 WiSM's - 2 = 2)

There is no exhaustice list of features performed in software.

You can refer teh data sheet of the supervisor enginer and it lists all the features supported in the hardware for that superviosr. For example here is a datasheet of SUP720.

    WCCP GRE is supported in hardware.

      Please note that the wccp egress mode is NOT supported in hardware and will cause High CPU.

     Please refer the following document for wccp configurations supported in hardware for Cisco catalyst 6500.

Some of the reasons for switching traffic in software ( CPU) are following.


•Same interface forwarding (to generate ICMP redirects)
•ACL log
•ACL deny – no route packet (to generate ICMP unreachable)
•Forwarding exception (out of TCAM/adj space)
•Feature exception (out of TCAM space / conflict)
•SW-supported feature (crypto, nbar, GRE)


•IP options
•Multicast path setup
•Multicast RPF drops
•Platform-specific traffic handling
•Forwarding path issues – requires troubleshooting
•Glean (Packets requiring ARP resolution) /

     Receive(Packets falling in the Receive case)

Here are few links to troublehooting high cpu issue on 6500. These documents all list some of the feature that are not supported in hardware and punt it to CPU.

2. show policy-map interface

3. I have not worked with wireless, so do not have much idea about WISMs . I will get back to you on this.



This is the document I could find for the WISM2.

Regarding the number of WISMs you can have the points mentioned in the document are correct.

There is cap on the mixed number of service modules you can have in the 6500. And that cap is 6 (including WISMs).

So anypoint if you are using multiiple service modules , then the max you can go is till 6 .




Hi, I require some clarifications regarding deployment of Control plane policy in Cat-6500 switch. In a 6500 switch which is functioning normal in a production environment, are there any way to measure the traffic rates (bps) of different types of packets (BGP, HSRP, PIM etc.,) going to control plane. This will help in determining a holistic traffic rates for control plane policy. Also please explain the right way to calculate conform and excess burst values (be & bc).

Hi ,

No such commands that I am aware of.  It is mostly trail and error. Start with a high limit rate and go down till you find the threshold that fits your network.

Here is a document which explains greatly.



Just to add some extra information, you can configure a Span session for the CPU and monitor it during the peak ours.

Do this for a weeks time. After comparing all the captures , you will get a rough estimate of the different control plane trafffic coming to CPU and their rates. You could also use " show ip traffic " but then its not purely control plane. It will show you all the software switched traffic.


Hi Akshay,

My query is regarding the control plane policing in 6500 switch. I have implemented CoPP in 65500 with different rate limits higher than the actual required for different classes of control plane traffic. I wish to tune this value for a near realistic one.

The show policy-map control-plane detail gives me the peak bps for each class for hardware counters (Hardware CoPP).

Whereas the software counters are displaying only the total number of bytes forwarded till now and last 5 minutes rate for each class of traffic.

Is there anyway to find out the peak bps of the traffic forwarded by software CoPP for each class?

Can we be able to find/calculate the peak bps using the statistics available in the software counter display?

Frequent Contributor

You don't ugrade a 6513 IOS (they are not being used in actual VSS infrastructure)  the same way as let's say a 2960 switch. Basically I have a 6513 running dual SUPs in SSO mode. I see that in Cisco instructions there are different procedures for upgrading IOS of a 6513 with redundant Supervisor Engines and MSFC that runs in Hybrid mode, upgrading in Native mode, etc.

How do I know if my 6513 switches (x2) are in these modes?

What else should I be cautios of before doing the updrade (I already know SUPs have enough RAM, config is backed up, etc.)?