Cisco Unified Border Element (Enterprise) Standards Compliance Configuration Guide, Cisco IOS XE Release 3S
SIP RFC 2782 Compliance with DNS SRV Queries
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SIP RFC 2782 Compliance with DNS SRV Queries

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 caveats and feature information, see Bug Search Tool and 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 module.

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.


SUMMARY STEPS

    1.    enable

    2.    configure terminal

    3.    interface type number

    4.    sip-ua

    5.    srv version {1 | 2}

    6.    exit


DETAILED STEPS
      Command or Action Purpose
    Step 1 enable


    Example:
    Router> enable
     

    Enables privileged EXEC mode.

    • Enter your password if prompted.
     
    Step 2 configure terminal


    Example:
    Router# configure terminal
     

    Enters global configuration mode.

     
    Step 3 interface type number


    Example:
    Router(config)# interface gigabitethernet 0/0/0
     

    Configures an interface type and enters interface configuration mode

     
    Step 4 sip-ua


    Example:
    Router(config-if)# sip-ua 
     

    Enters SIP UA configuration mode.

     
    Step 5 srv version {1 | 2}


    Example:
    Router(config-sip-ua)# srv version 2
     

    Generates DNS SRV queries in either RFC 2782 or RFC 2052 format.

    • 1 --The query is set to the domain name prefix of protocol.transport. (RFC 2052 style).
    • 2 --The query is set to the domain name prefix of _protocol._transport. (RFC 2782 style). This is the default.
     
    Step 6 exit


    Example:
    Router(config-sip-ua)# exit
     

    Exits the current configuration mode.

     

    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.