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Date:      Tue, 26 Mar 2002 12:44:38 -0800 (PST)
From:      Archie Cobbs <archie@dellroad.org>
To:        "Cambria, Mike" <mcambria@avaya.com>
Cc:        "'Julian Elischer'" <julian@elischer.org>, "'Archie Cobbs'" <archie@dellroad.org>, "'freebsd-net@freebsd.org'" <freebsd-net@FreeBSD.ORG>
Subject:   Re: Unnumbered IP Interface
Message-ID:  <200203262044.g2QKicE37079@arch20m.dellroad.org>
In-Reply-To: <3A6D367EA1EFD4118C9B00A0C9DD99D70655CE@rerun.avayactc.com> "from Cambria, Mike at Mar 26, 2002 09:59:40 am"

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Cambria, Mike writes:
> example, Archie's answer for unnumbered interfaces isn't in the route
> manpage.  I'm glad I asked.

Quoting route(8):

   "If the destination is directly reachable via an interface requiring no
    intermediary system to act as a gateway, the -interface modifier should
    be specified; the gateway given is the address of this host on the common
    network, indicating the interface to be used for transmission.  Alter-
    nately, if the interface is point to point the name of the interface
    itself may be given, in which case the route remains valid even if the
    local or remote addresses change.

By the way, you can have an "unnumbered" P2P interface that still has
an IP address configured on it -- just configure the same IP address
that's on another interface, e.g.:

    $ ifconfig
    dc0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
	    inet 192.168.0.223 netmask 0xffffff00 broadcast 192.168.0.255
	    ether 00:a0:cc:d6:cc:b1 
	    media: Ethernet autoselect (100baseTX <full-duplex>)
	    status: active
    ng0: flags=88d1<UP,POINTOPOINT,RUNNING,NOARP,SIMPLEX,MULTICAST> mtu 1500
	    inet 192.168.0.223 --> 1.2.3.4 netmask 0xffffff00 

This is sometimes known as "half-routing"..

-Archie

__________________________________________________________________________
Archie Cobbs     *     Packet Design     *     http://www.packetdesign.com

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