Problem solve Get help with specific problems with your technologies, process and projects.

Reduce MTU for VPN connecting to ADSL

I have a customer with a Checkpoint 650 VPN concentrator and Checkpoint client VPN on a PC. The Client VPN PC is connected to Verizon's ADSL Line that runs PPPoE. We can establish the VPN tunnel, but then we cannot do anything but ping the devices across the tunnel. I read about MTU issues with PPPoE, so I assume the IPSec Header plus the PPPoE header are making the packets larger than the default 1500 and they are getting dropped somewhere in the Verizon ATM cloud. Is there a way I can make the VPN client negotiate a smaller MTU size with the host on the other end of the VPN tunnel (email servers, file servers etc.)? Or is there another solution?
I ran into this problem with Pacific Bell's DSL service. Try reducing the MTU to 1492 bytes or less. The instructions for doing this are on the RASPPPOE site. Here is the link: http://user.cs.tu-berlin.de/~normanb/ (search for MTU on the page).

DSL Reports also has more info on this topic: www.dslresports.com (search for PPPOE and MTU).
This was last published in January 2002

Dig Deeper on Network Security Best Practices and Products

Have a question for an expert?

Please add a title for your question

Get answers from a TechTarget expert on whatever's puzzling you.

You will be able to add details on the next page.

Start the conversation

Send me notifications when other members comment.

By submitting you agree to receive email from TechTarget and its partners. If you reside outside of the United States, you consent to having your personal data transferred to and processed in the United States. Privacy

Please create a username to comment.