blank.gif (43 bytes)

Church Of The
Swimming Elephant

Search:
3.6.2. Aliases and canonical names Connected: An Internet Encyclopedia
3.6.2. Aliases and canonical names

Up: Connected: An Internet Encyclopedia
Up: Requests For Comments
Up: RFC 1034
Up: 3. DOMAIN NAME SPACE and RESOURCE RECORDS
Up: 3.6. Resource Records
Prev: 3.6.1. Textual expression of RRs
Next: 3.7. Queries

3.6.2. Aliases and canonical names

3.6.2. Aliases and canonical names

In existing systems, hosts and other resources often have several names that identify the same resource. For example, the names C.ISI.EDU and USC-ISIC.ARPA both identify the same host. Similarly, in the case of mailboxes, many organizations provide many names that actually go to the same mailbox; for example Mockapetris@C.ISI.EDU, Mockapetris@B.ISI.EDU, and PVM@ISI.EDU all go to the same mailbox (although the mechanism behind this is somewhat complicated).

Most of these systems have a notion that one of the equivalent set of names is the canonical or primary name and all others are aliases.

The domain system provides such a feature using the canonical name (CNAME) RR. A CNAME RR identifies its owner name as an alias, and specifies the corresponding canonical name in the RDATA section of the RR. If a CNAME RR is present at a node, no other data should be present; this ensures that the data for a canonical name and its aliases cannot be different. This rule also insures that a cached CNAME can be used without checking with an authoritative server for other RR types.

CNAME RRs cause special action in DNS software. When a name server fails to find a desired RR in the resource set associated with the domain name, it checks to see if the resource set consists of a CNAME record with a matching class. If so, the name server includes the CNAME record in the response and restarts the query at the domain name specified in the data field of the CNAME record. The one exception to this rule is that queries which match the CNAME type are not restarted.

For example, suppose a name server was processing a query with for USC- ISIC.ARPA, asking for type A information, and had the following resource records:

    USC-ISIC.ARPA   IN      CNAME   C.ISI.EDU

    C.ISI.EDU       IN      A       10.0.0.52

Both of these RRs would be returned in the response to the type A query, while a type CNAME or * query should return just the CNAME.

Domain names in RRs which point at another name should always point at the primary name and not the alias. This avoids extra indirections in accessing information. For example, the address to name RR for the above host should be:

    52.0.0.10.IN-ADDR.ARPA  IN      PTR     C.ISI.EDU

rather than pointing at USC-ISIC.ARPA. Of course, by the robustness principle, domain software should not fail when presented with CNAME chains or loops; CNAME chains should be followed and CNAME loops signalled as an error.


Next: 3.7. Queries

Connected: An Internet Encyclopedia
3.6.2. Aliases and canonical names

Cotse.Net

Protect yourself from cyberstalkers, identity thieves, and those who would snoop on you.
Stop spam from invading your inbox without losing the mail you want. We give you more control over your e-mail than any other service.
Block popups, ads, and malicious scripts while you surf the net through our anonymous proxies.
Participate in Usenet, host your web files, easily send anonymous messages, and more, much more.
All private, all encrypted, all secure, all in an easy to use service, and all for only $5.95 a month!

Service Details

 
.
www.cotse.com
Have you gone to church today?
.
All pages ©1999, 2000, 2001, 2002, 2003 Church of the Swimming Elephant unless otherwise stated
Church of the Swimming Elephant©1999, 2000, 2001, 2002, 2003 Cotse.com.
Cotse.com is a wholly owned subsidiary of Packetderm, LLC.

Packetderm, LLC
210 Park Ave #308
Worcester, MA 01609