GMILIEFS@MITVMA.MIT.EDU ("Gary S. Miliefsky") (10/11/89)
Is it valid for a multi-homed host to have a unique name for each ip address, or is it required/implied that a multi-homed host have a single node name and more than one ip address?
ug051@crayamid.cray.com (Michael Nittmann) (10/11/89)
So, even on a multihomed host, the hostname command gives you the let's say generic name under which the hosts identifies itself. BUT: names have no significiance, it is the internet addresses that count, the allocated names (via hosts file) only have to be unique. Ergo: multihomed host had different names for every internet address it hosts. michael
kasten@interlan.interlan.COM (Frank Kastenholz) (10/11/89)
Gary, A node name is just something to make it easy for us human types to enter commands. The node name/IP address mapping is a function of your local directory system. Most, if not all, such directory systems basically do one-to-one mapping - one host name per IP address and vice versa. A directory system _could_ return >1 IP address for a given node name, but then the problem of choosing which IP address to use comes up - if I say FTP FOO and I get back 2 IP addresses - 1.1.1.1 and 2.2.2.2, which one should I use? There are all kinds of heuristics that one could use (I am "closer" to net 1.x.x.x than I am to 2.x.x.x, etc, etc, etc) but no one does. Having a unique name for each IP address solves these problems, but introduces some human problems. A machine would have multiple equally valid names - "You can call me Ray, or You can call me Jay...." So, to summarize - having one name and multiple IP addresses is theoretically possible, but there does not seem to be any support for it in the name/address resolution systems so the tacit implementors agreement is one address/one name. Cheers Frank Kastenholz Racal InterLan
mcc@WLV.IMSD.CONTEL.COM (Merton Campbell Crockett) (10/12/89)
Is there an RFC that defines a multihomed system? In an AUTODIN environment a multihomed system has a single name but multiple mutually exclusive routes to the system. Within the AUTODIN concept, NIC.DDN.MIL would be a multihomed system as it is accessible from the ARPANET and the MILNET. A system on a regional network might be considered multihomed if it can be accessed direct- ly from the Internet as well as the regional net. Torben's workstation may be considered multihomed in its local environment but would not be from my perspective if there is only one route to his LAN. Now is a system really multihomed if the PSNs are co-located? Merton
craig@NNSC.NSF.NET (Craig Partridge) (10/12/89)
> A node name is just something to make it easy for us human types to enter > commands. The node name/IP address mapping is a function of your local > directory system. Most, if not all, such directory systems basically > do one-to-one mapping - one host name per IP address and vice versa. > > ... > > So, to summarize - having one name and multiple IP addresses is theoretically > possible, but there does not seem to be any support for it in the name/address > resolution systems so the tacit implementors agreement is one address/one name. Frank: I think the tide is moving the other way. People will use one name which maps to multiple addresses. The Host Requirements states that applications have to be able to handle a case where a name maps to multiple addresses, and if one fails, try to connect to the other. Craig
stine@SPARTA.COM (Robert Havens Stine) (10/12/89)
Enough of this practical, reality-based stuff! :-) Addresses are identifiers that are used to label where messages can be sent or received. An IP address identifies a host's network interface. A host may have several network interfaces. Like IP addresses, host names are identifiers. They are used to label (surprise!) hosts. A host may have several host names. To use a network, a mapping must be made from host name to IP address(es). Hence the DNS. But, as has been amply testified, there is no need for a one-to-one mapping between the names of a host and the IP addresses of its interfaces. - Bob Stine
stine@SPARTA.COM (Robert Havens Stine) (10/13/89)
>>Addresses are identifiers that are used to label where messages can be >>sent or received. An IP address identifies a host's network >>interface. A host may have several network interfaces. >And it could even have several IP addresses on the *same* network interface.... Right. There's a mapping between the subnet and the internet layers. IP addresses still, in some sense, are handles for identifying datagram sources and sinks for users of the internet service. >>Like IP addresses, host names are identifiers. They are used to label >>(surprise!) hosts. A host may have several host names. >> >>To use a network, a mapping must be made from host name to IP >>address(es). Hence the DNS. >This is news to me at least. It is my understanding that if you use the >DNS, there can only be one host name. CNAMES records of course, but only >one ``true" name... Jeez! What are the other "untrue" names? Meaningless scribbles? Mispronunciations? Of course there are varieties of names, some of which may be special in some way. DNS provides a mapping between names and addresses. - Bob