[c-nsp] Order of Operations for processing a packet (ingress and egress)

[Ian Cox]

I don't believe there is a comprehensive one published on CCO besides
the following document for the 7600.

http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps708/prod_white_paper0900aecd80673385.html

If we just consider LAN modules, then all encapsulation operations are
done by the ingress PFC or DFC responsible for a particular module. The
egress module just performs queuing for the packet. Now egress multicast
replication is an exception to this.

WAN modules essentially behave the same as LAN ports, except they take
an ethernet frame from the fabric and modify it to be ppp etc. The
exception cases are when it comes to VPLS, Selective QinQ, ... where the
 WAN module actually does do the forwarding function. If you ask your
AM/SE you should be able to arrange a presentation on how all forwarding
works, since all the detailed presentations I know of are under NDA.


Ian

Justin Shore wrote:
> Does anyone have any good links to an order of operations for what
> happens in what order on the assorted types of Cisco interfaces in both
> the ingress and egress directions?
> 
> I found one that touchs on the QoS order of operations:
> 
> http://www.cisco.com/en/US/tech/tk543/tk757/technologies_tech_note09186a0080160fc1.shtml
> 
> 
> I'm interested in fairly detailed things like at what point does a
> vanilla IP packet go through the MPLS label imposition process (on
> ingress as it's received or egress onto an MPLS-enabled interface).  Or
> at what point is a packet encapsulated on a GRE interface.  I'm looking
> for a reference that talks about router ports, WAN & LAN ports on a Cat
> routing chassis like the 7600, basic LAN switchports on Cat switches,
> etc.  I've never seen a doc that put it all together and I seldom come
> across docs that even talk about small portions of the order of
> operations.  Any references would be much appreciated.
> 
> Thanks
>  Justin
> 
> 
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