It seems there have been alot of tunnel issues with Cisco and Nortel, But I have not been able to find a resolution. My issue is, during rekey of the vpn tunnel between a Cisco PIX and Nortel Contivity, I incur timeouts and usually require a clearing of the SA's. The PIX ipsec and isakmp timers are set to 28800 seconds. The Nortel is set to 8:00 hours.
I have seen many other people post for the exact same issue, but have never seen any resolution.