This is my problem:
-Ive a lmds 4 simetric connection attached to my cisco 1721 with wic 1enet. Downloading from internet and uploading to internet work properly uo tu 450 KB/s, but using a vpn 3des the upload is only up to 50 or 60 KB
As earlier wrote "With VPN module you will be able to encrypt at E1 speed (2Mbps) and establish roughly 100 ipsec tunnels". The ISR routers (850, 870, 1800, 2800, 3800 series) are different things in respect to the IPS/SSL performance since they have totally different hardware architecture. For instance the 870 series maximum 3DES throughput is 30Mbps. I'm afraid you won't be able to take advantage of the 4Mbps line unless you upgrading to new, stronger platform.
Try from these ones:
12.4(5a), 12.4(5.13) and 12.4(5.13)T
You have 12.4.5 image and the first release where this bug fixed is 12.4.5a so you have to upgrade to that at least (or later image listed earlier).
Hope it helps,
If it doesn't have a VPN Hardware Accelerator, it will perform encryption using the router's CPU.
If you are using 3DES, I recommend scaling down the DES and see if it helps.
If it doesn't, I recommend getting a router with a VPN Hardware Accelerator.
Can you post a show ver from this router ?