Yealink T21PE2 User Manual

Administrator’s Guide for SIP-T2 Series/T4 Series/T5 Series/CP920 IP Phones
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Support for negative caching of DNS queries as described in RFC 2308 is also provided to allow faster failover when
prior DNS queries have returned no results from the DNS server.
Topics
Behave with a Configured DNS Server
Static DNS Cache Configuration
Behave with a Configured DNS Server
When the IP phone is configured with a DNS server, it will behave as follows to resolve the domain name of the server:
l The IP phone performs a DNS query to resolve the domain name from the DNS server.
l If the DNS query returns no results for the domain name, or the returned record cannot be contacted, the values in
the static DNS cache (if configured) are used when their configured time intervals are not elapsed.
l If the configured time interval is elapsed, the IP phone will attempt to perform a DNS query again.
l If the DNS query returns a result, the IP phone will use the returned record from the DNS server and ignore the stat-
ically configured cache values.
When the IP phone is not configured with a DNS server, it will behave as follows:
l The IP phone attempts to resolve the domain name within the static DNS cache.
l The IP phone will always use the results returned from the static DNS cache.
Static DNS Cache Configuration
The following table lists the parameters you can use to configure static DNS cache.
Parameter
account.X.dns_cache_type
[1]
<MAC>.cfg
Description
It configures whether the IP phone uses the DNS cache for domain name resolution of the SIP server and
caches the additional DNS records.
Permitted
Values
0-Perform real-time DNS query rather than using DNS cache.
1-Use DNS cache, but do not record the additional records.
2-Use DNS cache and cache the additional DNS records.
Default 1
Parameter
account.X.static_cache_pri
[1]
<MAC>.cfg
Description
It configures whether preferentially to use the static DNS cache for domain name resolution of the SIP
server.
Permitted
Values
0-Use domain name resolution from server preferentially
1-Use static DNS cache preferentially
Default 0
Parameter
dns_cache_naptr.X.name
[2]
<y0000000000xx>.cfg
Description
It configures the domain name to which NAPTR record X refers.
Example:
dns_cache_naptr.1.name = yealink.pbx.com
Permitted
Values
Domain name

Yealink T21PE2 Specifications

General

Brand	Yealink
Model	T21PE2
Category	IP Phone
Language	English