VPN over slow Internet connections

William Herrin bill at herrin.us
Thu Apr 21 17:24:10 UTC 2011

On Thu, Apr 21, 2011 at 12:55 PM, Ben Whorwood <bw-ml at mube.co.uk> wrote:
> Can anyone share any thoughts or experiences for VPN links running over slow
> Internet connections, typically 2kB/s - 3kB/s (think 33.6k modem)?
> We are looking into utilising OpenVPN for out-of-office workers who would be
> running mobile broadband in rural areas. Typical data across the wire would
> be SQL queries for custom applications and not much else.
> Some initial thoughts include...
>  * How well would the connection handle certificate (>= 2048 bit key) based
> authentication?

Fine. The certificate isn't sent very often and is only 256 bytes when
it is sent.

>  * Is UDP or TCP better considering the speed and possibility of packet loss
> (no figures to hand)?

TCP is more likely to pass firewalls at the user's end, especially if
you put your VPN server on port 443. UDP will allow the user's various
sessions to recover from packet loss independently (i.e. faster). I
would pick UDP and provide an alternate TCP configuration for users
who experience trouble.

>  * Is VPN over this type of connection simply a bad idea?

No worse than using this slow a connection in the first place. VPN
overhead is 5% to 10% tops. I would use a split tunnel though; let
general internet destinations go directly through the Internet
connection rather than through the VPN.

Bill Herrin

William D. Herrin ................ herrin at dirtside.com  bill at herrin.us
3005 Crane Dr. ...................... Web: <http://bill.herrin.us/>
Falls Church, VA 22042-3004

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