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Flow interception on Layer-2

yves.haemmerli
Level 1
Level 1

Hi,

I have a CSS11150 with an SSL Accelerator SCA11000 connected on one of the CSS Ethernet Port. The CSS itself is connected with its GE interface on a Catalyst. Only one VLAN is defined, so the CSS, the SCA and a router are on the same subnet. The default gateway configured in the SCA is the router, not the CSS. I thought first it was a mistake because the return flow from the SCA would pass through the CSS at Layer-2 without interception by the CSS! So I decided to NAT the client address when sending encrypted packets to the SCA to solve this issue.

But, I realized that it works also without NATing the client ! So I concluded that the CSS is able to intercept a packet arriving on one of its interface and associate this packet with a established flow, even if this packet is not destined to the CSS.

Can you confirm this behaviour ? What is the recommendation ?

Thank you ,

Yves

1 Reply 1

seilsz
Level 4
Level 4

Hi Yves -

This behavior is correct. The CSS will check the flow-table first and switch the flow at L2 before any L3 processing takes places.

~Zach

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