Protocol-Reject for unsupported protocol 'Fujitsu Link Backup and Load Balancing (LBLB)' (0x45)

[triffid]

Freqently while using xl2tpd with "Private Internet Access" VPN provider, I sometimes get floods of

rcvd [LCP ProtRej id=0xbd 00 45 00 00 28 e4 68 40 00 e0 06 9b 4b 0a 0a 01 02 3f 08 08 08 80 93 00 35 f6 f0 87 56 6c 3e 37 ...]
Protocol-Reject for unsupported protocol 'Fujitsu Link Backup and Load Balancing (LBLB)' (0x45)

This is usually accompanied by significant packet loss over the VPN link (while packet loss on the underlying transport seems unaffected), although it always resolves itself after a minute or so.

It most frequently happens immediately after connecting, but reoccurs periodically during a session.

The behaviour looks like some packet id counter or similar is being misinterpreted somewhere, as regular data packets appear to be discarded while this happens.

I've scoured the web, but most posts about this seem to be very old and/or don't match my symptoms.

I haven't tried other l2tp clients, or other l2tp service providers, so I can't conclusively state that it's uniquely an xl2tpd problem - although if I find evidence that it's definitely an issue at PIA's end I'll happily forward the information to them.

If there's anything you'd like me to try to assist in debugging, please let me know.