Differences between version 3 and previous revision of CiscoExpressForwarding.
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| Newer page: | version 3 | Last edited on Friday, November 14, 2003 4:52:03 pm | by LindsayDruett | Revert |
| Older page: | version 2 | Last edited on Friday, November 14, 2003 1:56:14 pm | by PerryLorier | Revert |
@@ -2,5 +2,11 @@
Although you can use CEF in any part of a network, it is designed for high-performance, highly resilient Layer 3 IP backbone switching.
----
-While this
is a good BuzzWordCompliant answer, what does it ''actually'' mean?
My understanding
of CEF was
that all the routing was done on the
line card
(not on
the host CPU
), so some advantaced features weren
't available with CEF.
+Basically Cisco Express Forwarding
is another method of passing packets from one interface to another on
a router.
This is the method
of switching
that Cisco are implementing right across their product
line (apart from
the SOHO routers
)%%%
+%%%
+Unlike other methods of switching in a router (for example
, Fast Switching) where the first packet hits the processor
so that the destination of the packet is found and any subsequent packet is switched as the source and destination of the packet is stored in a cache therefore the processor doesn
't need to be involved for the rest of that traffic flow, this method is also known as "route first, switch many".%%%
+%%%
+With CEF, no packets hit the processor, every packet is switched. Instead a Forwarding Information Base (FIB) is created using information created from the route table, IP Interfaces, etc and taking in account things like access-lists, and later realising that
available bandwidth needed to be considered when creating the FIB. All the packets are then switched from one port to another using the information created from the FIB.%%%
+%%%
+There are variants of CEF, for example Dialer CEF, where you may have a branch office router
with a modem card built in and therefore have varying speeds ranging from dial-up modem speeds to Local Area Network speeds. Another variant is Distributed
CEF (dCEF) which is implemented on a switch with more than one line card (Catalyst 4000 upwards) so that traffic flows will only hit the backpane if the traffic is going from a port on one card to a port on another card. To support dCEF, there has to be processing capability on each line card in order to build and share a FIB on each line card
.%%%
