"set skip on lo" on 12.x and 13.0

Marek Zarychta zarychtam at plan-b.pwste.edu.pl
Tue Feb 9 14:50:59 UTC 2021

Dear list,

I am observing changed behaviour of the rule "set skip on lo". This rule 
previously allowed for communication between the host and the jail no 
only on loopback interfaces, but also on shared network interfaces, for 
example, if a host had address x.x.x.x/24 and jail had address 
x.x.x.y/32 on the same NIC, the rule above allowed for communication 
between the host and jail using x.x.x.x and x.x.x.y addresses. I am 
considering jails without VNET enabled and using the same fib number. 
Now to allow this kind of communication I had to add "pass quick on lo", 
but I went out of free states rather quickly, so instead of increasing 
the state limit, I have changed the method of communication between the 
host and the jails to utilize only loopback addresses.

It's rather not a regression but a change, some people might consider it 
POLA violation, but probably won't if it gets widely announced.


Marek Zarychta

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