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6509E 20% speed loss when Router introduced to transfer path


I have an issue that I am trying to track down.  When I have 2 servers on the same VLAN on my AS pair, all is good because nothing leaves the switch.  Where the issue is, is when I have 2 servers on different VLAN's and it requires a hop across the Core router pair.  This hop drops the throughput rate by about 20-25% (from 44M to 35-36M)

I think I know the issue, but want some input to from other to make sure I am not off-base. 

I have a pair of 6509E chassis' running Sup720 (VS-S720-10G) with CEF720 (X6748-GE-TX) modules.  This is my Access Pair running VSS to look as 1 switch.

These tie into the Core pair of 6500E chassis' running Sup720 (Sup720-3B).  This issue I see is that the core has a CEF720 card (6724-SFP), but the AS pair does not connect to the core on that card, they connect on a RJ45 Ethermodule (6148A-GE-TX) card.  Would the fact that the AS pair does not connect to the core on the CEF7220 module on the core, cause the traffic to not make use of the CEF features of the Core and make each packet then have to be processed by the core instead of Express Forwarded?

Any insights would be helpful.



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Re: 6509E 20% speed loss when Router introduced to transfer path

Hello Mflettre,

no it does not mean that packets will be process switched when entering the 6148 linecard.

Actually, this linecard has no connection to the Sup720 720 Gbps switching fabric, but it uses the shared bus that is the legacy interconnection between modules.

The shared bus should be capable of 32 Gbps ( in total) but the speed of single linecard access to bus is 8 Gbps.

see the C6500 architecture white paper for a more detailed explanation

What you need to mind of are the limitations on the C6148 linecard itself that probably has one ASIC every 8 ports with 1GBps shared among 8 ports.

So the linecard is not capable of wire speed on all the ports (if I remember correctly or are 6 ports mapped to a single ASIC that then is connected to the shared bus internally)

Also it is important to note how do you perform the test?

Do you use netperf, iperf or similar?

Is the baseline made using two servers in the same Vlan?

if so you see differences between a simple L2 switched scenario and inter vlan routing.But it should be acceptable.

Hope to help


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