Planning and Configuring HP-UX DCE 1.9

Chapter 8

Notes on Cell Administration

Establishing Intercell Communication

The information in this section supplements the information in the

OSF DCE Administration Guide - Core

Services

, and describes how intercell communication should be conﬁgured in an HP-UX environment.

Communication between DCE cells is facilitated by the gdad daemon, which implements the Global Directory

Agent (GDA). When a client in a local cell wants to access another cell that the local cell does not already

recognize, the request is passed to gdad, which looks up and returns information about how to ﬁnd the remote

cell. This information is cached, so that gdad is not asked repeatedly for the same information.

gdad ﬁnds information about the remote cell by querying a Domain Name Service (DNS) database. DNS is

not part of DCE; it is a widely used distributed naming service, implemented on HP-UX by the named

daemon, and documented in named(1M)manpage and in Internet RFCs 1032, 1033, 1034, and 1035.

These procedures describe conﬁguring GDA so that it can ﬁnd the DNS server or servers where cell

information is stored, creating DNS "resource records" that describe the cells you want GDA to be able to

locate, and establishing peer-to-peer trust between two cells.

Specifying DNS Servers that GDA Should Query

GDA must be told which DNS name servers (such as instances of named) to query for information about

foreign cells. The name server at localhost is usually preferred, as only localhost provides recursive query

service—if localhost doesn't have the requested data, localhost will query other name servers until it either

ﬁnds the requested data or exhausts the list of name servers that it knows about.

Using localhost reduces the requirement to keep GDA informed when name server conﬁgurations change,

and allows GDA to always receive a response with a single query. In some environments, however, you may

want to point GDA at a non-local server or servers, rather than at localhost.

gdad uses the following algorithm to identify which name server or name servers to query:

1. gdad ﬁrst reads the ﬁle /etc/opt/dce/named.ca, which, if present, should contain one or more NS

(NameServer) records and associated A (Address) records. These records specify, in DNS "master" format,

the name server(s) that gdad should query. The master format is described in the named (1M) manpage.

2. If named.ca is not found or does not contain NS records, then gdad looks for name servers in

/etc/resolv.conf. The format of resolv.conf is described in the resolver (4) manpage.

3. If neither /etc/opt/dce/named.ca nor /etc/resolv.conf exists, or if neither ﬁle contains name server

information, then gdad defaults to localhost. Note that if gdad defaults to localhost, named must be

running on the local machine.

If the GDA conﬁguration information is changed, gdad must be stopped and restarted so that it will pick up

the new conﬁguration data.

Choosing DNS Servers for GDA to Query

When choosing DNS Servers for GDA to query, be aware that GDA is not sophisticated enough to obtain part

of the needed data from one name server and part of the data from another name server. The needed data

consists of resource records associated with a cell's domain name and resource records associated with the

domain name(s) of the host(s) on which a cell's CDS servers are running. GDA must be able to obtain all of

this information from a single name server.