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
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.
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 STEPSVerifying
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 statusSIP User Agent StatusSIP User Agent for UDP : ENABLEDSIP User Agent for TCP : ENABLEDSIP User Agent bind status(signaling): DISABLEDSIP User Agent bind status(media): DISABLEDSIP max-forwards : 6SIP DNS SRV version: 1 (rfc 2052)