Date: Tue, 13 Jul 1999 08:29:29 -0500 From: Jon Hamilton <hamilton@pobox.com> To: Kris Kennaway <kkennawa@physics.adelaide.edu.au> Cc: Stephen Hocking-Senior Programmer PGS Tensor Perth <shocking@prth.pgs.com>, hackers@freebsd.org Subject: Re: Setting up a firewall with dynamic IPs Message-ID: <19990713132930.342EF200@woodstock.monkey.net> In-Reply-To: Your message of "Tue, 13 Jul 1999 22:16:32 %2B0930." <Pine.OSF.4.10.9907132210380.2013-100000@bragg>
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In message <Pine.OSF.4.10.9907132210380.2013-100000@bragg>, Kris Kennaway wrote : } On Tue, 13 Jul 1999, Stephen Hocking-Senior Programmer PGS Tensor Perth wrote } : } } > I was checking out the firewall setup in /etc/rc.firewall, and noticed } > that the simple example relied on a fixed IP address for the external } > interface. I don't know ahead of time what IP address is going to be } > allocated to me before I dial up. Would it be possible to specify an } > interface (tun0) rather than an IP address? } } You could probably do it from /etc/ppp/ppp.linkup, which knows your IP } address as MYADDR. But if you just have asingle machine on the end of the } dialup then You can do it as the original poster was thinking as well by specifying the "recv $interface" parameter. See ipfw(8) for details. } I find I can get away with just specifying the netmask from which the dialup } IPs are assigned in place of a single address - all that can happen is that } packets get through your firewall destined to a nonexistent address (i.e. if } you allow incoming port Y traffic then people can send to port Y on } nonexistent IP addresses (i.e. your peer addresses) which will be dropped by } the kernel). That approach will lose if you change ISPs or if your ISP changes or expands its dynamic IP pool. There's also a small window between the time your ppp connection is established and the time ppp.linkup is executed; better to do this based on interface. -- Jon Hamilton hamilton@pobox.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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