Date: Tue, 06 Aug 2002 00:48:31 -0700 From: Terry Lambert <tlambert2@mindspring.com> To: Brad Laue <brad@brad-x.com> Cc: freebsd-hackers@freebsd.org Subject: Re: ifconfig alias and the 0xffffffff netmask Message-ID: <3D4F7F4F.97609D75@mindspring.com> References: <3D4F7539.2090201@brad-x.com>
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Brad Laue wrote: > Minor question regarding this; to recap: > > Creating an IP alias on the same subnet as the original seems under > FreeBSD to require setting the netmask of the alias to 255.255.255.255, > or at least a subnet of the original. > > What impact, if any, will having a /32 netmask on an aliased IP have? > > It seems inconsistent with networking practice regarding interface > aliases, which typically view the aliased IP's simply as distinct hosts > on the same physical network, allowing them to have the same netmask. > This method is used with Cisco IOS and other Unix-like operating > systems. Is it incorrect? 255.255.255.255 means "This is an alias IP address". The actual netmask in effect is the same netmask as the real IP address. The thing that's broken is that you can't have a different netmask from that of the real IP address. Really, this comes down to interfaces and driver structure, and the inability to associate a send-from address with a route entry (route is "out", not "from", so the from address you get is the outbound address). This causes problems with NFS in some cases, since it looks like an aliased server is trying to spoof a response to a client, which expect the response to come from the same IP the request was sent on. I believe this is a FAQ, and it has two paragraphs in the Handbook. -- Terry To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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