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gkuzmowycz
Beginner

4507 backplane data rate - what counts?

I know the 4507 (non-E) is advertised as having a backplane data rate max of 48Gbps, and that each line card has a maximum of 6Gbps. This ends up meaning that a 48-port line card has 6 groups of 8 ports, with each group "allowed" 1Gbps. But my question is whether two devices in physically adjacent ports, let's say ports 1 and 3, which are belong to the same VLAN and are on the same IP subnet can each talk to the other at 1Gb, since that's one flow? Extrapolating a switch mostly filled in that manner, does the 48Gb limit come into play if the packets/frames don't have to go to the backplane?

1 ACCEPTED SOLUTION

Accepted Solutions
Giuseppe Larosa
Hall of Fame Master

Hello George,

we had performed performance tests some days ago.

There is a limit of 1Gbps per 8 port group.

There is not local switching capacity that can provide a performance gain in switching traffic between two ports served by the same ASIC chip.

see also

http://www.cisco.com/en/US/products/hw/switches/ps700/products_tech_note09186a008015bfd6.shtml#giga

and the following paragraph

If the frames received on any group exceeds the bandwidth of 1 Gbps, the device starts to drop the frames. These drops are not obvious as they are dropped at the internal ASIC rather than the actual interfaces. This can lead to slow throughput of packets across the device.

in our tests we have seen that with one port handling 450 Mbps of traffic another port in the same 8ports group could reach 550 Mbps with exceeding traffic (all coming from other linecards) being dropped and counted as output drops

Hope to help

Giuseppe

View solution in original post

2 REPLIES 2
Giuseppe Larosa
Hall of Fame Master

Hello George,

we had performed performance tests some days ago.

There is a limit of 1Gbps per 8 port group.

There is not local switching capacity that can provide a performance gain in switching traffic between two ports served by the same ASIC chip.

see also

http://www.cisco.com/en/US/products/hw/switches/ps700/products_tech_note09186a008015bfd6.shtml#giga

and the following paragraph

If the frames received on any group exceeds the bandwidth of 1 Gbps, the device starts to drop the frames. These drops are not obvious as they are dropped at the internal ASIC rather than the actual interfaces. This can lead to slow throughput of packets across the device.

in our tests we have seen that with one port handling 450 Mbps of traffic another port in the same 8ports group could reach 550 Mbps with exceeding traffic (all coming from other linecards) being dropped and counted as output drops

Hope to help

Giuseppe

View solution in original post

Thank, Giuseppe. Not the answer I wanted to hear, but precisely the info I was looking for.