Showing results for 
Search instead for 
Did you mean: 

Why do flexwan and shared interface processors (SIP) for 7600 have memory?

Hi all,

I am trying to understand the 7600 hardware and just noticed the flexwan and sip datasheets mention memory for "large routing tables". Why? Isn't this responsability of a card like RSP720 / supervisor cards?

Going a bit further... whats the difference between a gigabit spa (shared port adapter) and a gigabit linecard (besides the number of ports)?


Giuseppe Larosa
Hall of Fame Master

Hello Mario,

the roots of the flexwan module are in the VIP linecards for cisco C7500 the first Cisco router to deploy a CEF distributed model ( not totally).

in a distributed multi layer device the main route processor, the PFC component more exactly, builds the master copy of the CEF table that is sent to all the intelligent linecards that need memory to host a read only copy of the CEF table.

if all linecards are intelligent and have a copy of the whole CEF table, the main RSP is not consulted not even for the first packet of a flow but the linecards can use the CEF table to perform packet rewrite.

There is also another reason for cpu and memory on flexwan and on SIP linecards: they need to be smart enough to handle WAN interfaces of various types and this is not possible on the RSP 720 because the C7600 and the C6500 are multilayer switches.

Flexwan modules use port adapters that can be used in VIP linecards for C7500. SIP linecards host SPA that are the next generation of port adapters.

>> whats the difference between a gigabit spa (shared port adapter) and a gigabit linecard (besides the number of ports)?

the GE port on the SPA has much more feature like more complex QoS similar to ISR routers , support for features like VPLS or other.

a normal linecard provides low cost per port but far less features

Hope to help


Hi Giuseppe,

thanks very much for the explanation. I was beginning to think that a flexwan or SIP was able to function even without an RSP or supervisor. What I understood is this is similar to linecards with DFC. I am correct?

Now I understand why when choosing a SIP I must look carefully at memory if I want to work with full internet routing and BGP.

thanks again.