Chapter 42: Fully-Qualified Domain Name (FQDN)
STANDARD Revision 1.0
C4® CMTS Release 8.3 User Guide
© 2016 ARRIS Enterprises LLC. All Rights Reserved.
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If the C4 CMTS polling reveals that the FQDN-to-IP binding has changed, then any DSG or IGMP data forwarding based
on that binding must be stopped. This happens when the polling response does not indicate a binding or when it
indicates that the FQDN is bound to something other than an IPv4 unicast address.
When an FQDN to IP address binding is removed, dependent DCD messages will be modified according to the following
conditions:
If affected DSG tunnel classifier(s) are currently included in the DCD, the classifier(s) will be removed from the DCD.
If affected DSG tunnel classifier(s) are the sole classifier(s) for tunnel(s) that are currently included in the DCD, the
tunnel(s) will be removed from the DCD.
When an FQDN to IP address binding is regained, dependent DCD messages will be modified according to the following
conditions:
If affected DSG tunnel classifier(s) were removed from the DCD, the classifier(s) will be re-established in the DCD to
reflect the IP address.
If affected DSG tunnel classifier(s) were the sole classifier(s) for tunnel(s) previously removed from the DCD, the
tunnel(s) will be reestablished in the DCD.
If for whatever reason the DNS server does not respond to queries from the CMTS, then at some point the FQDNs go
into a timeout state. The C4/C4c maintains FQDNs in this state and assumes that the IP addresses of these FQDNs are
still valid until the DNS server comes back online and changes them.
The CMTS permits FQDN and Partially Qualified Domain Name (PQDN) names to be up to 154 characters in length:
The default domain name may be up to 96 characters in length.
Domain names consist of one or more parts called labels. Each such label cannot exceed 63 characters in length.
The C4 CMTS enforces RFC 3696 and RFC 1035 rules for domain naming. These rules are also called the LDH (Letter-
Digit-Hyphen) rules:
"The LDH rule, as updated, provides that the labels (words or strings separated by periods) that make up a domain
name must consist of only the ASCII alphabetic and numeric characters, plus the hyphen. No other symbols or
punctuation characters are permitted, nor is blank space. If the hyphen is used, it is not permitted to appear at
either the beginning or end of a label. There is an additional rule that essentially requires that top-level domain
names not be all-numeric." (From RFC 3696.)
"The labels must follow the rules for ARPANET host names. They must start with a letter, end with a letter or digit,
and have as interior characters only letters, digits, and hyphen." (From RFC 1035.)
