I need a router that will have just one FastE interface but will have about 30 GRE/Tunnel interfaces. This router will mainly be routing from FastE to tunnel and vice-versa. I was comparing the 1721 to the 1751 and found something interesting. The 1721 has faster process switching speed than the 1751 but lower Fast/CEF switching numbers. In my case (FastE to Tunnel) which would apply? Process or Fast/CEF? If Fast/CEF is the preferred method, how do I turn this on? How do I apply it to my Tunnel interfaces?
Last question would be: Is CEF used when routing from GRE tunnel interfaces to FastE interfaces? I ask this because I believe there are certain situations where CEF and/or fast switching are not applicable.
You are correct. If there is no valid adjacency to your destination network, for example, the packets would be punted to the processor for switching. CEF is supported on Tunnel interfaces. You can verify your switching patch by "show int stat" to ensure that the correct switching path is being used. Here is a snip from a defect that involved "no adjacency" and the workaround.
When there are no FIB entries for routes via a GRE tunnel
using Policy routing to set the default interface to that GRE tunnel, packets
forwarded through the interface are being punted to the process switch layer this can
be confirmed by looking at the interface switching stats via
'show interface stats'. The reason for this behaviour is that CEF has no adjacency
information for the Tunnel interface 'show adjacency tunnel'
Workaround: Add static route pointing out the GRE tunnel this will force
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...