CEF - Tunnel interfaces


I have a DMVPN Hub and Spoke setup with a 1721 as the Hub and a few

837's as Spokes.

I have read that CEF switching on the tunnel interfaces will increase performance and reduce CPU overhead, is this true?

The external interfaces on all routers are all ADSL, with Dialer interfaces configured.

I have tried to setup CEF switching on the tunnel interfaces but when I do a "show ip int tunnel 0" it shows that CEF switching is disabled.

Here is the output:

//< Internet address is Broadcast address is Address determined by non-volatile memory MTU is 1468 bytes Helper address is not set Directed broadcast forwarding is enabled Multicast reserved groups joined: Outgoing access list is not set Inbound access list is not set Proxy ARP is enabled Local Proxy ARP is disabled Security level is default Split horizon is enabled ICMP redirects are never sent ICMP unreachables are never sent ICMP mask replies are never sent IP fast switching is disabled IP fast switching on the same interface is disabled IP Flow switching is disabled IP CEF switching is disabled IP Null turbo vector IP multicast fast switching is disabled IP multicast distributed fast switching is disabled IP route-cache flags are Fast, CEF Router Discovery is disabled IP output packet accounting is disabled IP access violation accounting is disabled TCP/IP header compression is disabled RTP/IP header compression is disabled Policy routing is disabled Network address translation is disabled WCCP Redirect outbound is disabled WCCP Redirect inbound is disabled WCCP Redirect exclude is disabled BGP Policy Mapping is disabled //>

What am I doing incorrectly or have I completely lost the plot? I have tried enabling it on the physical interfaces as well...! CEF does show up as enabled on the dialer interfaces. IOS on the 1721 is 12.3(7)T4 IOS on the 837's is 12.3(4)T

Thanks in advance!


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Well one learns new things everyday...... Disabling "tunnel checksumming" has done the trick and enabled CEF switching.


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