Firewalling jails and lo0

Niklaas Baudet von Gersdorff stdin at
Sat Aug 6 15:54:39 UTC 2016


In the manual I read the advice to disable the firewall on the
loopback interface (`set skip on lo0`) It makes sense to me: Why
would I want to firewall traffic on the loopback interface?

I have jails with IPs assigned on lo1. Intentionally I do /not/
`set skip on lo1` because I also want to restrict traffic (in and
out) from and to the jails. (In case one of them becomes

However, today I realised that some connections originating from
these jails use the loopback interface lo0. That said, they
"circumvent" the firewall I set on lo1. `tcpdump` shows
connections on lo0 from and to jails' IPs (especially IPv6s)
although these IPs are solely assigned to lo1.

I was quite surprised by that behaviour. So, if I want to isolate
the jails and restrict traffic from an to them, will I need to
remove skipping on lo0 and block there too?

Any advice and explanation is very much appreciated.


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