6807-XL with Sup 2T

[som3awy]

Let's say I install a linecard with either a DFC or CFC in the chassis. The sup 2T has a PFC which makes all the forwarding decisions. Then what's the use of the DFC/CFC on the linecard?

[Jon Marshall]

If the module has DFC then the forwarding tables on the PFC are downloaded to the DFC so the module can make forwarding decisions locally ie. no need to send the header to the supervisor. 

Jon

[Joseph W. Doherty]

Just to add to what Jon has already noted, a sup2T forwarding capacity of 60 Mpps (IPv4) would, for minimal sized packets, only support 40 Gbps (for the whole chassis). You need DFCs on line cards to provide the additional forwarding capacity needed by many gig and/or 10g ports. Each DFC4 provides another 60 Mpps. (As Jon also noted, the DFC forwarding only applies to that line card's forwarding [from ingress on the line card's ports].)

If even with DFCs, overall Mpps appears insufficient, it is, if all the traffic was minimal size, but as the generally that's not the case, with DFC line cards, you can usually push all ports, concurrently, at line rate.

[som3awy]

Thank you both! So the DFCs are used to forward traffic between ingress and egress ports on the same line card? Is it the same for CFCs?

[Jon Marshall · Accepted solution]

No, CFCs are Centralised Forwarding Cards which means they have to ask the supervisor for a forwarding decision. 

Jon

[Joseph W. Doherty · Accepted solution]

"Is it the same for CFCs?"

No, as already also answered by Jon.

"So the DFCs are used to forward traffic between ingress and egress ports on the same line card?"

Yes but (if I remember correcly) the DFC can forward traffic from DFC's line card's ingress port to any other port. I.e. the egress port does not need to be on the same line card.

[som3awy]

Thank you both for your help. Really appreciate it.