[lug] Re: Virtual Hosting

[John Hernandez]

That's usually not a problem because many ISPs assign A/PTR records in a programmatic fashion on dialup subnets, something like:

dailup-192-168-0-1.someisp.com

"Atkinson, Chip" wrote:
> 
> There are (or were) also public ftp servers that do a reverse lookup on the
> domain and if they didn't match you couldn't get in.  I don't know if that's
> the case anymore due to the prevalence of dynamic IPs these days.
> 
> Chip
> 
> > -----Original Message-----
> > From: Justin [mailto:glow at jackmoves.com]
> > Sent: Wednesday, March 14, 2001 6:00 PM
> > To: lug at lug.boulder.co.us
> > Subject: Re: [lug] Re: Virtual Hosting
> >
> >
> > Say one of those records is like a mail server or something.
> > Shouldn't
> > you have the ip resolve back to the mail server hostname? I know BIND
> > will complain about MX address's that are CNAME's and not actual A
> > records for the zone. The dns resolution will still work
> > properly, but
> > I think having the PTR for the mail server hostname is the "correct"
> > way to do things. Or another example that I have experienced setting
> > up , is in the case of irc virtual hosts. The hostname needs to be a
> > PTR record otherwise it won't work.
> >
> > Justin
> >
> > > The alternative is not to have any reverse records (PTR) at all.
> > >
> > > Nate
> > >
> > > Quoting John Hernandez <John.Hernandez at noaa.gov>:
> > >
> > > > Given our hypothetical scenario (where there is not a 1-to-1
> > mapping of
> > > > name-to-address, rather a many-to-1 mapping), you're basically
> > forced to
> > > > pick one of those names for reverse lookup purposes, aren't you?
> > What
> > > > would be the alternative?
> > > >
> > > > A typical client app provides an IP address to the server upon
> > > > connection (in the form of an IP source address).  The order of
> > lookups
> > > > (for a paranoid server) is then address -> name, and then
> > resulting-
> > name
> > > > -> address, not the other way around as you suggested.
> > Servers are
> > > > generally happy when address(in) == address(out), as you correctly
> > > > stated, but that condition is satisfied by setting your PTR RR
> > value to
> > > > any one of the set of valid A RR keys.
> > > >
> > > > rm at mamma.varadinet.de wrote:
> > > > >
> > > > > On Wed, Mar 14, 2001 at 12:18:05PM -0700, John Hernandez wrote:
> > > > > > For the purpose of reverse DNS lookup, you can generally pick
> > any of
> > > > the valid A RR keys for a particular IP address.  As long as a
> > reverse
> > > > -> forward lookup yields a result (IP address) equivalent to your
> > > > initial input, services configured to be paranoid should be
> > satisfied.
> > > > >
> > > > > I would actually advise _against_ picking any A records for
> > setting
> > > > > up reverse lookups. Some services get really upset if
> > the reverse
> > > > > lookup yields strange results (esp. if they do double lookup for
> > > > > security reasons name->address and then address->name. If the
> > address
> > > > > that comes out at the end doens't match the initial one
> > you might
> > > > > have a problem). Most of the java VMs embedded in browsers will
> > > > > only allow an applet to request an URL if the host part of the
> > > > > URL is the same as the hopst part of the applets URL. It's easy
> > > > > to imagine what happens when a cautious security manager starts
> > > > > interacting with strange reverse lookups.
> > > > >
> > > > >  Ralf
> > > > >
> > > > > >
> > > > > > -John
> > > > > >
> > > > > > Justin wrote:
> > > > > > >
> > > > > > > In BIND 8.2.x the only file that relates to what you're
> > talking
> > > > about
> > > > > > > is your reverse zone file. It's the file that maps the ip's
> > back
> > > > to
> > > > > > > specific A record host names. As far as virtual hosting I
> > don't
> > > > believe
> > > > > > > you can have a file like this for virtual use. After all,
> > virtual
> > > > hosts
> > > > > > > don't really have their own ip address, they map back to
> > another
> > > > > > > machines A record ip address. Which, in turn, that
> > ip address
> > must
> > > > > > > reverse lookup to it's respective host as defined by that A
> > > > record. I
> > > > > > > think this stuff is in a BIND RFC somewhere, but
> > I'm sure. I
> > also
> > > > may
> > > > > > > be way off here, but this has been my understanding since I
> > can
> > > > > > > remember...
> > > > > > >
> > > > > > > Justin
> > > > > > >
> > > > > > > > It was my understanding that all the virtual hosts are
> > listed in
> > > > one
> > > > > > > > file and that file is pointed back to the server
> > IP.  Maybe
> > it
> > > > > > > > involves the $INCLUDE directive?
> > > > > > > >
> > > > > > > > Note: When you reply to this message, please include the
> > mailing
> > > > > > > >       list/newsgroup address in Cc: and my email
> > address in
> > To:.
> > > > > > > >
> > > > > > > >
> > > >
> > *********************************************************************
> > > > > > > > Signed,
> > > > > > > > SoloCDM
> > > > > > > > _______________________________________________
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> > > > > > > >
> > > > > > > >
> > > > > > >
> > > > > > > -----
> > > > > > > glow at jackmoves.com
> > > > > > > www.jackmoves.com
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> >
> >
> >
> > --
> > Nate Duehr, nate at natetech.com
> >
> > "Never underestimate the bandwidth of a 747 filled with CD-ROM's."
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> >
> 
> -----
> glow at jackmoves.com
> www.jackmoves.com
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