Date: Mon, 10 Dec 2001 10:57:42 +1100 (EST) From: Rowan Crowe <rowan@sensation.net.au> To: freebsd-isp@freebsd.org Subject: Re: arplookup Message-ID: <Pine.BSF.4.21.0112101055050.47615-100000@velvet.sensation.net.au> In-Reply-To: <Pine.BSF.4.21.0112091132410.331-100000@veager.jwweeks.com>
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On Sun, 9 Dec 2001, Jim Weeks wrote: > > On Sun, 9 Dec 2001, Rowan Crowe wrote: > > > Just a warning that this will break connectivity to IPs in that block of > > 65535 IPs that are *not* on that LAN. > > > > For example, if your IP is 1.1.100.3 and your netmask is 255.255.255.0, > > your LAN has 255 local hosts, and everything else is routed via the > > gateway. If you change it to 255.255.0.0, then your LAN has 65535 local > > hosts, and everything else is routed via the gateway. > > > > This means that if you try to communicate with (say) 1.1.200.1, it will > > fail, because your machine assumes it's on the LAN, when it's *really* > > outside of that network, and can only be reached via the gateway. > > > > Coming full circle, setting that hostmask may actually cause similar or > > identical ARP errors on other machines, because there will be ARP requests > > coming from your machine for IPs that *are not* on the LAN (but your > > machine thinks they are) > > Full circle indeed! This brings us back to the original problem, why > aren't these requests coming through the gateway in the first place. I > haven't had a strait answer to that question yet. Any enlightenment would > be appreciated. Probably the same fundamental problem - other machines on the same LAN are communicating directly (ether-ether) with IPs that your machine thinks should be routed via the gateway. Your machine says, "hang on, why am I getting an ARP request for an IP which *isn't* on my LAN?" The simple fix is to make sure that your ethernet interface has an IP address in each subnet that is routed in the LAN (so it knows *every* IP that is communicated with directly), but that can be quite wasteful and impractical. I don't know of a more complicated fix, other than hacking the code to disable the error. :) Cheers. -- Rowan Crowe - Melbourne, Australia www.camrecord.com | www.camdiscover.com | www.sensationbot.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-isp" in the body of the message
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