Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 

Cisco 871 IPSec VPN Throughput Speed - SLOW

I have a Cisco 871 Router (AdvIP IOS). I use the 871 in a remote office (connected via Public ISP - 2Mb downstream/10Mb Upstream)to automatically create an EZVPN tunnel back to a Cisco 3000 Concentrator at our HQ.

There is a Cisco 7960 IP phone connected to the 871 and a laptop (new) connected through the IP Phone.

The VPN tunnel comes up fine. The User can log into the network fine and access all network resources (DNS, File Server, Internet, Intranet, etc.).

The problem is that that overall data throughput is very slow. It can take 2-6 minutes to open 60Kb files (e.g., MS-Word, MS-Excel).

I have modified the "IP MTU" on Interface Fa4 (WAN Port) to adjust for overall MTU size (I have not done this on the Concentrator yet). I have configured the "ip tcp adjust-mss" command to change the size of the packets.

I'm looking for any help into any/all things I can should look into to identify how to resolve/alleviate this issue.

I've also had the MTU on the laptop (in the OS) adjusted down to 1270.

Any help you can provide would be appreciated.


Re: Cisco 871 IPSec VPN Throughput Speed - SLOW

Set the MTU size on IPsec tunnel routers to eliminate fragmentation and re-assembly. This is probably a packet fragmentation issue.

Resolve IP Fragmentation, MTU, MSS, and PMTUD Issues with GRE and IPSEC:

CreatePlease to create content