We currently have multiple sites with ISAKMP/IPSec tunnels between 2800 routers and we need to migrate some of them to GRE tunnels with IPSec. Are there any issues with terminating both GRE and IPsec tunnels on the same router and interface?
I have not seen any issues - apart from the router doing the encryption/decryption & GRE encapsulation/decapsulation, just be mindfull of traffic thru put.
I have seen issues with GRE traffic and MTU problems. Cisco recommend a MTU of 1440 in GRE, I would say configure 1400.