Very slow connection using pfsense to azure vm

  • I am currently experiencing great issues using pfsense ipsec to connect to azure.
    After having worked fine for a few months suddenly the connection is slow (a few kb/s) and unstable. Normal internet access is fine (100mb/s).
    If I use an ipsec vpn from a client pc, the slowness is still an issue.
    The site-to-site vpn also intermittently drops its connection entirely.

    Testing from the same client using another network (e.g. my phone's) the speeds are normal.
    The microsoft helpdesk already ruled out networking issues from their end as well.
    Does anyone have a suggestion to try?

  • Netgate Administrator

    So that's a mobile IPSec server on the same pfSense box that's also slow?

    Check if you have 'Asynchronous Cryptography' enabled in the advanced IPSec settings. Try disabling it and rebooting if you have.
    That would only have applied at an upgrade though.


  • After contact with microsoft helpdesk I found the solution for me.
    For future reference: I had to turn on mss clamping and set it to 1350. This is also in the advanced IPSec settings

    Maybe this settings was defaulted after an update? I wasn't the one who configured it in the first place, so I wouldn't know for sure.

    I made sure to match my settings to this document

    @stephenw10 Thanks for the reply, I had this disabled already, but the pointer was appreciated