I’ve a VPN server running on a draytek modem.
If I connect through the modem from an Android mobile phone, everything works fine.
Whereas if I connect from NetworkManager using pptp, it works for a bit:
- Connection is OK
- I can use ssh to connect to a machine at the other end of the pptp link
- I can ‘ls’ and get an OK response
- However, when I ‘ls -la’, the connection freezes
- Additionally, any http session that has images on the page also freeze
I’ve managed to get this working OK by adjusting the MTU at the remote end, i.e.:
- Connect VPN – OK
- Check the MTU at the local end with ifconfig (it is 1400)
- ssh to a machine at the other end of the pptp link
- check the MTU at the remote end with ifconfig (it is 1500)
- Adjust the MTU at the remote end to 1300 (ifconfig eth0 mtu 1300)
- ls -la (and everything else) works fine
Unfortunately, I can’t go about adjusting the MTU of any other machines I may connect to over the VPN (e.g. google).
I’ve also used wireshark to capture the transactions, and it looks like one of the last things that is done before the connection freezes is to send a [TCP Window Update] from the client to the other end (in this case … 192.168.11.200).
Wireshark Capture of ‘ls -la’ over ssh connection over vpn
Remember that all of this works fine from an Android client, so everything points to the Ubuntu client.
Q: Has Anyone got any pointers or ideas?
pptp version: 1.9.0
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