Table Of Contents

SIP—RFC 2782 Compliance with DNS SRV Queries

Prerequisites SIP—RFC 2782 Compliance with DNS SRV Queries

Information SIP—RFC 2782 Compliance with DNS SRV Queries

How to Configure SIP-RFC 2782 Compliance with DNS SRV Queries

Verifying

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.

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

This section contains the following procedures:

•Configuring DNS Server Query Format RFC 2782 Compliance with DNS SRV Queries (optional)

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.

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Note You do not have to perform this task if you want to use the default RFC 2782 format.

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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)