WS-X4448 uplink trunk

As far I read on official Cisco website, the 48 ports 10.100.1000 line card WS-X4606-X2-E is made of 6 groups of 8 ports each connected to 1Gbits trunk to Supervisor.

What if I have 4 servers, so 4 ports, in the same vlan, same subnet, connected to the same group of 8 ports. Those 4 servers need to communicate at 1Gbits rate between eachother. Does the traffic goes up to the supervisor, so I would have 250mbits per server ? or the local traffic stays in the group on the local card and everybody got 1gbits ?

The solution:

When you have devices in the same subnet, the switch only needs to use the CAM table to forward the traffic.  The CAM table contains the MAC address and associated port in which the MAC address is attached. So basically only L2 is used. 

6500 and 4500 series switches use centralized switching, "With centralized switching, routing, ACL, QoS, and forwarding decisions are made on the Supervisor Engine in a modular chassis"

Forwarding architecture: These modules use the central Cisco Express Forwarding engine located on the supervisor engine.

• Forwarding performance: These modules forward packets up to 30 Mpps per system and up to 15 Mpps per slot if upgraded to support distributed forwarding.

You are correct in your assumption - there is no "local switching" on that linecard, so every packet must go through the oversubscrbied 1GigE backplane connection.

If you have a 4500 and any Sup before the Sup6, and have servers that must communicate at 1GigE, then you need to put the servers into different port groups.  For example, server #1 in port 1, then shut down ports 2 through 8 with description "OVERSUBSCRIBED."  Server #2 would go into port 9, then shut down ports 10 through 16, etc.

This is a limitation of the 4500...  For the newer 4500-E and the Sup6-E, the backplane has increased from 6GigE to 24GigE.  You have a couple options:

  WS-X4624-SFP-E: 24-port SFP (pluggable) with full line-rate.  For typical server connectivity you would have to get a TX SFP (GLC-T)

  WS-X4648-RJ45-E: 24-port 10/100/1000 with 2:1 oversubscription.  For a high-traffic server, you would just connect on every other port.