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_sip._udp.example.com 86400 IN SRV 10 100 5060 examplecorp.dyndns.net _sip._tcp.example.com 86400 IN SRV 10 100 5060 examplecorp.dyndns.net |
Notes on DNS & SRV Records
A flaw in Polycom's SRV record use has been identified. Polycom phones don't honor the DNS SRV weight, but they do honor the priority. What this means is that they don't resort the list of records when they get it from DNS. Most DNS servers by default produce the SRV records in cyclical order. This means that there are only 3 combinations that the records will show up in.
A suggested work-around for this problem is to use the bind (9.6 & later) command rrset-order.
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rrset-order
rrset-order { order_spec ; [ order_spec ; ... ]
rrset-order defines the order in which multiple records of the same type are returned. This works for any record type in which the records are similar not just A or AAAA RRs and covers results in the ANSWER SECTION and the ADDITIONAL SECTION. The default is cyclic (round-robin).
The full specification of rrset-order is shown below. An 'order_spec' is defined as:
class class_name ][ type type_name ][ name "domain_name"] order ordering;
Where 'class_name' is the record class, for example, IN (default is 'any'), type is the Resource Record type (if none specified defaults to 'any'), domain_name limits the statement to a specific domain suffix and defaults to root (all domains), order is a key word and ordering may take one of the following values:
fixed - records are returned in the order they are defined in the zone file
random - records are returned in a random order
cyclic - records are returned in a round-robin fashion
Note: For reasons best known to the ISC (BIND's author) the fixed value is now (BIND 9.6+) only available if the configure option --with-fixed-rrset is used in the build. Neither BSD nor Debian standard packages use this option. This is likely to be true for Fedora and other RPMs but has not been verified (use named -V to check). For practical purposes only cyclic and random are the available choices.
Examples
Defines that all equal records for all domains will be returned in random order.
rrset-order {order random;};
Defines that all equal MX records for example.com will be returned in random order all others in cyclic order.
rrset-order {type MX name "example.com" order random; order cyclic};
This statement may be used in a view or a global options clause.
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Advanced DNS configuration
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