- Bronze, 100 points or more
hi every body!
I have few questions about acef:
A cisco press book says"Line cards send initial packet of a flow to supervisor engine,where packet is switched in hardware using the master cef table.The forwarding decision made, is then stored in local scaled-down cef table on linecard where the flow enters the switch,with local linecard making subsequent forwarding decision for packets asssocitaed with the flow"
My question is when we consider packet belong to same flow?
For example in case of net flow switching, packets containing similar source ip,destination ip, port and ingress interface are considered belonging to same flow.
What do we consider in acef for a packet to belong to same flow?
thanks a lot!
my understanding is that CEF is topology driven and even first packet of a flow is switched and not process swichted.
This makes the difference between CEF and its predecessors like Fast switching.
In a C5500 MLS is traffic driven by using the Netflow feature card and can be combined even with an external router.
In C550 or C6500 sup1 the first packet of a flow needs to be sent to the processor and the NFFC is able to store the shortcut of the RSM action on the packet: subsequent packets are then multilayer switched as the first: the NFFC is able to perform the packet rewrite.
What can change in modern C6500 is the combination of centralized forwarding and distributed forwarding: each linecard / module able to perform in a distributed manner has a complete copy of the CEF table that is built and maintained by the supervisor
Hope to help
6500 switches use MLS with CEF to forward packets so it is not just the CEF you see on routers.
MLS is flow based and records the extra information that you mention.
Does this make sense ?
To be honest i thought it was a typo at first as i have never come across acef before, dcef (distributed CEF) yes but not acef. It sounds like acef may have been a forerunner of dcef. Guess that's one of the reasons i still do NetPro, i'm always learning :-)
From the 6500 CatOS configuration document on guidelines/restrictions for acef
The only MLS flow mask supported is full flow. Full flow is the most-specific flow mask. A full flow entry includes the destination/source IP address, destination/source Layer 4 port number, protocol type, and Layer 2 header.
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