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Date:      Thu, 28 Dec 1995 08:18:22 -0600
From:      "Greg Rowe" <greg@uswest.net>
To:        "Julian H. Stacey" <jhs@freebsd.org>, hackers@freebsd.org
Subject:   Re: Faking the IP address for a temporarily dead host
Message-ID:  <9512280818.ZM25711@nevis.oss.uswest.net>
In-Reply-To: "Julian Stacey jhs@freebsd.org" <jhs@vector.enet> "Faking the IP address for a temporarily dead host" (Dec 26,  2:37pm)
References:  <199512261337.OAA09011@vector.enet>

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If both systems are connected to the same network provider, you should be able
to do an ifconfig alias for your friends IP address/host name on your box and
add your friends host name to the sendmail.cf "Cw" record.(add
usernames/alaises to your box as well) You can then run your system as both
systems and continue recieving mail to both. We "hot backup" systems this way.

If the two systems are connected to different providers, I think your gonna run
into routing problems though.

Greg
On Dec 26,  2:37pm, Julian Stacey jhs@freebsd.org wrote:
> Subject: Faking the IP address for a temporarily dead host
> --------
>
> Hi FreeBSD people,
>
> What would be the technical ramifications of faking an IP address to be
> that of a friend's FreeBSD system that has temporarily died ?
> ( presumably mail for the users on that box is currently piling up in
> sendmail queues around the world (inc. freefall)).
>
> Background:
>   The friend's host died before 17:30 GMT+01:00 21 or 22 Dec.
>   All my mail between then & ~20:00 GMT+01:00 25 Dec. was forwarded to
>   that host from freefall (I removed freefall .forward then ),
>   I don't know yet if the dead hosts's /var/mail/jhs died with system,
>   (ie dont know if it was a disc crash, or mere power failure)
>   Friend's message on my answerphone got only truncated details.
>   I can't ping the dead host (of course).
>
> The dead host was not a web server or ftp server etc,  so I don't think
> anything too dramatic would occur.
>
> Whilst I don't want to do this without the dead host's administrator's
> permission
> 	(by phone I guess, he's not back till next week, & not at his host
> 	till 8th Jan),
> I am wondering what would be the ramifications of me resetting my IP
> to his host, rebooting, & connecting to the net for a few hours,
> & sending short dummy mails to jhs@freefall etc, to trigger
> the sendmail daemons to flush their spool queues of all mail piling up
> for all users @dead-host ?
>
> Obviously I'd have to check my .forwards & /etc/aliases here so no loops
> started, & create passwd & alias entries to accept mail destined for users
> @dead-host, also I should make sure not to collide with dead box's IP address
> when it comes back to life 8th Jan or after.
>
> Another (unconnected) friend reckons DNS would prevent me doing this,
> but I'm not clear why (I admit I still need to read my DNS & Bind Nutshell
:-)
> I thought most of the routing tables on the net were automatically maintained
> these days, not hand maintained, I would guess if I ftp freefall,
> I would appear in its route state tables, even if I hadnt config my routed
> to boradcast my hosts availability ?.
>
> It's not something I want to rush into, and not without dead-host's
> administrator's permission but if he's got serious hardware problems,
> I'd like to be able to offer help, if viable, to the extent of host
> masquerading, (& then loaning him my spare machine after the masquerade,
> 'till he fixes his host).
>
> Comments on viability or otherwise appreciated, Thanks :-)
>
> Julian
> --
> Julian H. Stacey	jhs@freebsd.org  	http://www.freebsd.org/~jhs/
>-- End of excerpt from Julian Stacey jhs@freebsd.org



-- 
Greg Rowe                           | 
U S West - Interact Services        | INTERNET greg@uswest.net
111 Washington Ave. South           | Fax:      (612) 672-8537
Minneapolis, MN USA 55401           | Voice:    (612) 672-8535

    Never trust an operating system you don't have source for....




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