pf: redirect a packet's port but not its address?

[Andrey V. Elsukov]

On 23.01.2018 19:17, Alan Somers wrote:
>>> Unfortunately, pf currently lacks this capability.  But it looks like it
>>> could be added without breaking existing pf.conf syntax.  Would this be a
>>> good idea?
>>>
>>> I don't use ipfw, but from reading the man page I believe that it has the
>>> same problem.
>>
>> I think ipfw should work with such configuration using "fwd" action,
>> since TCP/UDP has special handling for this.
> 
> 
> The man page says that the fwd directive always takes an IP address.  What
> I need is a way to forward the port without changing the IP address.  Is
> that possible in ipfw?

"fwd" rule does not changing nor IP address, nor port. It uses some
magic with PCB lookup in the TCP/UDP code.
Just tried this:

# ipfw add fwd ::1,5678 tcp from any to any 4000
# nc -6 -l ::1 5678

And from another host tried:
# telnet -6 fc00::1 4000

And this works.

-- 
WBR, Andrey V. Elsukov

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