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.
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. Networking Equipment in UK
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