[strongSwan] how to tell charon-nm to use 500/udp and 4500/udp

Tobias Brunner tobias at strongswan.org
Thu Jul 14 16:15:29 CEST 2022

Hi Harald,

> is there some way to tell charon-nm to use 4500/udp for the outgoing
> connection, instead of an arbitrary port, if available? Same for
> 500/udp.

You can explicitly configure the ports via strongswan.conf 
(charon-nm.port and charon-nm.port_nat_t).  Just make sure you don't use 
charon or charon-systemd on the same host to avoid conflicts.

> I assume a problem on the AVM Fritzbox in this context. 500/udp and
> 4500/udp at both ends appears to be more reliable.

That doesn't really make sense as there could always be a NAT in between 
that changes the source ports.

Also, has AVM finally released a version of their system that supports 
IKEv2?  Took them long enough.  But considering their track record 
regarding IKEv1, I guess we have to expect interoperability issues for 
the next 20 years.

> However, I am not
> sure at all where the temporary port comes from.

What are you referring to?


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