| ### Defining a Cell in the Domain Name System Names in DNS are associated with one or more data structures called resource records. The resource records are stored in a data file whose name and location are implementation specific. To create a cell entry, you must edit the data file and create two resource records for each CDS server that maintains a replica of the cell namespace root. The first resource record, whose type can be AFSDB or MX, contains the hostname of the system where the CDS server resides. You can use MX as an alternative to using AFSDB. The second record, of type TXT, contains the following information about the replica of the root directory that the server maintains: · The Universal Unique Identifier (UUID) of the cell namespace, in hexadecimal notation · The type of the replica (master or read-only) · The global CDS name of the clearinghouse where the replica resides · The UUID of the clearinghouse, in hexadecimal notation · The DNS name of the host where the clearinghouse resides The following example shows a set of AFSDB resource records for a cell that is named cs.tech.edu, in which two replicas of the root directory exist. Note that only the first resource record contains the cell name; the second, third, and fourth records are assumed to be associated with the same cell because they do not contain a cell name. The TTL heading stands for time-to-live, a value, in seconds, after which the data is no longer considered valid in a DNS cache. (The value shown specifies a default value of 1 week.) The IN class indicates that the protocol is Internet, and the subtype of 2 indicates that a name server exists on the host named in the record. ;First Replica: ;Name TTL Class Type Subtype Host cs.tech.edu 604800 IN AFSDB 2 fox.cs.tech.edu ;Name TTL Class Type Rdata 604800 IN TXT (1 ;version fd3328c4-2a4b-11ca-af85-09002b1c89bb ;ns uuid Master ;Replica1 type /.../cs.tech.edu/cs1_ch ;ch name fd3328c5-2a4b-11ca-af85-09002b1c89bb ;ch uuid fox.cs.tech.edu) ;host ;Second Replica: 604800 IN AFSDB 2 rox.cs.tech.edu 604800 IN TXT (1 ;version fd3328c4-2a4b-11ca-af85-09002b1c89bb ;ns uuid Read-only ;Replica2 type /.../cs.tech.edu/cs2_ch ;ch name fd3429c4-2a4b-11ca-af87-09002b1c89bb ;ch uuid rox.cs.tech.edu) ;host You can use MX as an alternative to using AFSDB. The following example shows a set of MX resource records for the same cell, cs.tech.edu , in which two replicas of the root directory exist. ;First Replica: ;Name TTL Class Type Preference Exchange cs.tech.edu. 604800 IN MX 1 fox.cs.tech.edu. ;Name TTL Class Type Rdata 604800 IN TXT (1 ;version fd3328c4-2a4b-11ca-af85-09002b1c89bb ;ns uuid Master ;Replica1 type /.../cs.tech.edu/cs1_ch ;ch name fd3328c5-2a4b-11ca-af85-09002b1c89bb ;ch uuid fox.cs.tech.edu) ;host ;Second Replica: 604800 IN MX 2 rox.cs.tech.edu. 604800 IN TXT (1 ;version fd3328c4-2a4b-11ca-af85-09002b1c89bb ;ns uuid Read-only ;Replica2 type /.../cs.tech.edu/cs2_ch ;ch name fd3429c4-2a4b-11ca-af87-09002b1c89bb ;ch uuid rox.cs.tech.edu) ;host After you configure a cell, you can use the dcecp directory show command to display the information that is required to construct resource records like those shown in the previous example. The following is an example directory show command that displays the DNS-formatted output for a cell named /.../cs.tech.edu. Note that the show cell command does not display the host name (including domain) at the end of the TXT record. dcecp> directory show /.../cs.tech.edu dcecp> To create a new resource record in the DNS namespace, use the information from the directory show command and place the properly formatted data into the DNS data file. ###