My setup is as follows:
Cisco PIX 515
Cisco 1841 router with Advanced Security feature set
My HQ also has other branch offices connected via MPLS.
I have onfigured IPSEC VPN connectivity between the PIX and the 1841 router.
Initially, I configured the PIX and 1841 to only route the connected subnets (172.20.0.0/16 & 172.22.0.0/16) across the runnel and everything was working fine.
Second step, I added 172.19.0.0/16 to also be available across the VPN from my branch office. Everything was still working fine.
Next step, I also added 172.21.0.0/16 to be available from the branch office. That's when my problems started.
Immediately, the VPN tunnel became very unstable. Frequently, the tunnel would go down and no traffic would be routed across.
As soon as I removed 172.21.0.0/16 from the tunnel, it stabilized again.
Are there any limitations in how much traffic the 1841 router can handle, or am I missing something on the configuration?