SIP RFC 2782 Compliance with DNS SRV Queries
Effective with Cisco IOS XE Release 2.5, the Domain Name System Server (DNS SRV) query used to determine the IP address of the user endpoint is modified in compliance with RFC 2782 (which supersedes RFC 2052). The DNS SRV query prepends the protocol label with an underscore "_" character to reduce the risk of duplicate names being used for unrelated purposes. The form compliant with RFC 2782 is the default style.
Finding Feature Information
Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the Feature Information Table at the end of this document.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Prerequisites SIP RFC 2782 Compliance with DNS SRV Queries
Cisco Unified Border Element
- Cisco IOS Release 12.2(8)T or a later release must be installed and running on your Cisco Unified Border Element.
Cisco Unified Border Element (Enterprise)
- Cisco IOS XE Release 2.5 or a later release must be installed and running on your Cisco ASR 1000 Series Router.
Information SIP RFC 2782 Compliance with DNS SRV Queries
Session Initiation Protocol (SIP) on Cisco VoIP gateways uses the DNS SRV query to determine the IP address of the user endpoint. The query string has a prefix in the form of "protocol.transport." and is attached to the fully qualified domain name (FQDN) of the next hop SIP server. This prefix style originated in RFC 2052. Beginning with Cisco IOS XE Release 2.5, a second style, in compliance with RFC 2782, prepends the protocol label with an underscore "_"; for example, "_protocol._transport." The addition of the underscore reduces the risk of the same name being used for unrelated purposes. The form compliant with RFC 2782 is the default style.
How to Configure SIP-RFC 2782 Compliance with DNS SRV Queries
Configuring DNS Server Query Format RFC 2782 Compliance with DNS SRV Queries
Compliance with RFC 2782 changes the DNS SVR protocol label style. RFC 2782 updates RFC 2052 by prepending the protocol label with an underscore character. The prefix format compliant with RFC 2782 is the default format. However, backward compatibility is available, allowing newer versions of Cisco IOS software to work with older networks that support only RFC 2052 DNS SVR prefix style.
To configure the format of DNS SRV queries to comply with RFC 2782, complete this task.
 Note |
You do not have to perform this task if you want to use the default RFC 2782 format. |
DETAILED STEPS
Verifying
The following example shows sample is output from the show sip-ua status command used to verify the style of DNS server queries:
Router# show sip-ua status
SIP User Agent Status
SIP User Agent for UDP : ENABLED
SIP User Agent for TCP : ENABLED
SIP User Agent bind status(signaling): DISABLED
SIP User Agent bind status(media): DISABLED
SIP max-forwards : 6
SIP DNS SRV version: 1 (rfc 2052)
Feature Information for SIP RFC 2782 Compliance with DNS SRV Queries
The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
ISR feature history table entry
| Table 1 | Feature Information for SIP: RFC 2782 Compliance with DNS SRV Queries |
| Feature Name |
Releases |
Feature Information |
|---|---|---|
| SIP: RFC 2782 Compliance of DNS SRV Queries |
12.2(8)T, 12.2(11)T, 12.2(15)T |
Effective with Cisco IOS XE Release 2.5, the DNS SRV query used to determine the IP address of the user endpoint is modified in compliance with RFC 2782 (which supersedes RFC 2052). The DNS SRV query prepends the protocol label with an underscore "_" character to reduce the risk of duplicate names being used for unrelated purposes. The form compliant with RFC 2782 is the default style. The following command was introduced or modified: srv version. |
ASR feature history table entry
| Table 2 | Feature Information for SIP: RFC 2782 Compliance with DNS SRV Queries |
| Feature Name |
Releases |
Feature Information |
|---|---|---|
| SIP: RFC 2782 Compliance of DNS SRV Queries |
Cisco IOS XE Release 2.5 |
Effective with Cisco IOS XE Release 2.5, the DNS SRV query used to determine the IP address of the user endpoint is modified in compliance with RFC 2782 (which supersedes RFC 2052). The DNS SRV query prepends the protocol label with an underscore "_" character to reduce the risk of duplicate names being used for unrelated purposes. The form compliant with RFC 2782 is the default style. The following command was introduced or modified: srv version. |
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