How to deny getting static ip address via pf ?
repcsike at gmail.com
Tue Jul 26 13:05:47 UTC 2011
2011/7/26 Matthew Seaman <m.seaman at infracaninophile.co.uk>
> On 26/07/2011 11:44, Yavuz Maşlak wrote:
> > I use pf on freebsd as packet filter.
> > I have a wireless area. The users get to the internet using automatic ip
> > from the dhcp server.
> > I wish to deny to assign a static ip address by manual.
> > How can I do that with pf or ipfw or another thing?
> Interesting problem. Do you control the DHCP server and is it running
> ISC dhcpd? If so, you can parse the dhcpd.leases file to find all of
> the addresses the DHCP server has allocated. Then you could create
> firewall rules that default to blocking the DHCP address range, but are
> overridden to allow the allocated addresses. The table feature in pf
> would be a good way of implementing something like that. (I think ipfw
> has an equivalent feature nowadays too.)
> It's not going to be pretty, and you'll need to update the table of
> allowed addresses quite frequently, or legitimate users will find
> themselves locked out of internet access. Also it won't stop someone
> who has hijacked an IP from someone else's lease.
> Wondering why your users would prefer manually setting addresses rather
> than using DHCP, since using DHCP takes away virtually all the effort
> involved? If it's because almost all the addresses are already assigned
> to leases and it takes ages to get on-line, then two courses of action
> suggest themselves:
> 1) Serve a larger address range through DHCP and/or make the lease
> times shorter. Assuming you're behind a NAT gateway, this
> shouldn't be particularly hard to set up.
> 2) Look at the 'adaptive-lease-time-threshold' setting in dhcpd.conf
> -- this says to dynamically shorten lease times once address pool
> usage goes above a threshold percentage.
> Dr Matthew J Seaman MA, D.Phil. 7 Priory Courtyard
> Flat 3
> PGP: http://www.infracaninophile.co.uk/pgpkey Ramsgate
> JID: matthew at infracaninophile.co.uk Kent, CT11 9PW
I would run a perl program as a daemon that would parse the dhcp logs for
given IPs, then I would load those IPs to a PF table, which that way could
contain the trusted hosts, which you would then pass packets from and to.
This could work IMHO. But this aproach to the problem can contain serious
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