L2TP client works from remote LAN but not from 4G network

[Lucardo]

Hello,

I have a really strange issue. Having set up an L2TP server on a mikrotik router, I can sucessfully connect from my iPhone when inside a remote LAN (home) but cannot connect from the 4g network…

Any ideas? Thank you!

[pe1chl]

That could be several things:

• your firewall is dropping the incoming requests from internet (as it should, until you change it to pass this particular traffic)
• your 4G provider is not transparently passing all packets (they have a firewall you cannot modify)
• you are trying to make multiple connections. the first one works, others do not.

The latter is a limitation of L2TP. You can have only a single user behind the same NAT.

[Steveocee]

@pe1chl

That could be several things:

• your firewall is dropping the incoming requests from internet (as it should, until you change it to pass this particular traffic)
• your 4G provider is not transparently passing all packets (they have a firewall you cannot modify)
• you are trying to make multiple connections. the first one works, others do not.

The latter is a limitation of L2TP. You can have only a single user behind the same NAT.

Literally this.