Table Of Contents

SIP Configuration Flexibility

Contents

Restrictions for Implementing SIP Configuration Flexibility

Information About SIP Configuration Flexibility

OPTIONS Support

Restrictions for OPTIONS Support

Rewriting From Header on Non-Register Requests

Restrictions for Rewriting From Header on Non-REGISTER Requests

Rewriting To Header on Non-REGISTER Requests

Auto-detecting NAT

Restrictions for Auto-detecting NAT

Routing on Wildcard Domains

Restrictions for Routing on Wildcard Domains

How to Implement SIP Configuration Flexibility

SIP Configuration Flexibility

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Cisco Unified Border Element (SP Edition) offers flexibility in configuring the following features of a Session Initiation Protocol (SIP) adjacency:

•OPTIONS Support

•Rewriting from header on non-REGISTER requests

•Rewriting to header on non-REGISTER requests

•Auto-detecting NAT

•Routing on wildcard domains

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Note For Cisco IOS XE Release 2.4, this feature is supported in the unified model only.

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Cisco Unified Border Element (SP Edition) was formerly known as Integrated Session Border Controller and may be commonly referred to in this document as the session border controller (SBC).

For a complete description of commands used in this chapter, refer to the Cisco Unified Border Element (SP Edition) Command Reference: Unified Model at http://www.cisco.com/en/US/docs/ios/sbc/command/reference/sbcu_book.html.

For information about all Cisco IOS commands, use the Command Lookup Tool at http://tools.cisco.com/Support/CLILookup or a Cisco IOS master commands list.

Feature History for SIP Configuration Flexibility

Release	Modification
Cisco IOS XE Release 2.4	This feature was introduced on the Cisco ASR 1000 Series Aggregation Services Routers along with support for the unified model.

Contents

This module contains the following sections:

•Restrictions for Implementing SIP Configuration Flexibility

•Information About SIP Configuration Flexibility

•How to Implement SIP Configuration Flexibility

Restrictions for Implementing SIP Configuration Flexibility

The restrictions for implementing SIP configuration flexibility are listed per feature in this chapter.

Information About SIP Configuration Flexibility

This section conains the following subsections:

•OPTIONS Support

•Rewriting From Header on Non-Register Requests

OPTIONS Support

By default, Cisco Unified Border Element (SP Edition) blocks the OPTIONS method from passing through, but users can configure Cisco Unified Border Element (SP Edition) on a per-adjacency basis to pass or block the OPTIONS method by using whitelists and blacklists.

Restrictions for OPTIONS Support

•Cisco Unified Border Element (SP Edition) strips out SDP blocks from messages when it allows the OPTIONS method to pass through. This limits what the SIP endpoints can exchange.

•The SBC-SIG does not send the Accept and Allow headers on any methods, including OPTIONS.

•Cisco Unified Border Element (SP Edition) allows only the 100Rel and Replaces tags of the Supported header to pass through, while the other tags of this header are controlled by whitelists and blacklists.

Rewriting From Header on Non-Register Requests

With this feature, users can configure Cisco Unified Border Element (SP Edition) on a per-adjacency basis to control whether it rewrites the hostport section of the From header on Non-Register Requests to the outbound SIP adjacency address or port. If Cisco Unified Border Element (SP Edition) is configured to allow the From header to pass through without it being rewritten, then Cisco Unified Border Element (SP Edition) allows the entire header to pass through without changing it. The only exception occurs with the Tag parameter; Cisco Unified Border Element (SP Edition) assigns a different value to this parameter before passing it through.

Restrictions for Rewriting From Header on Non-REGISTER Requests

•This feature is not applicable for REGISTER requests.

•This feature may only work in a limited way with the Rewrite-Register feature.

•If the From header contains a Tel URI, then Cisco Unified Border Element (SP Edition) does not rewrite the header since it does not have a hostport.

•Depending on the number of headers, options and SIP whitelist profiles, Cisco Unified Border Element (SP Edition) limits the size of the From header that it allows to pass through to approximately 1000 bytes.

Rewriting To Header on Non-REGISTER Requests

The default behavior of Cisco Unified Border Element (SP Edition) is to rewrite the hostport section of the To header on Non-Register Requests to be the outbound SIP adjacency address and port. It also removes any associated parameters. With this feature, users can configure the SBC on a per-adjacency basis to pass the To header through unchanged.

Auto-detecting NAT

With the addition of a new configuration field to the SIP adjacency, it is now possible for users to specify if Cisco Unified Border Element (SP Edition) must auto-detect whether a NAT is in use on that adjacency. If Cisco Unified Border Element (SP Edition) is configured to auto-detect NAT, then for each request that it receives, Cisco Unified Border Element (SP Edition) determines whether a NAT is in use for that endpoint. If Cisco Unified Border Element (SP Edition) determines that NAT is in use, then Cisco Unified Border Element (SP Edition) stores the bindings for that request and uses them when sending a response. Additionally, Cisco Unified Border Element (SP Edition) stores and reuses bindings for REGISTER requests for subsequent Dialog-forming and Out-of-dialog requests.

Restrictions for Auto-detecting NAT

•Cisco Unified Border Element (SP Edition) can auto-detect NAT only by comparing the Sent-by stopper in the Via header with the remote address and port of the message.

•If the stopper contains a domain name, instead of an IP address, Cisco Unified Border Element (SP Edition) cannot auto-detect whether NAT is in use. In this case, Cisco Unified Border Element (SP Edition) assumes that NAT is in use.

•Auto-detecting NAT is applied only to Out-of-dialog requests or Dialog-forming requests.

Routing on Wildcard Domains

Cisco Unified Border Element (SP Edition) routing policy allows you to use the * character in a text domain name match string. This character can match any number of characters in the called address. For example, *domain.com can match both sip1.domain.com and sip2.domain.com.

Restrictions for Routing on Wildcard Domains

•You can only specify one wildcard character in a given match string.

•This feature applies only to text domain name match rules, and not to dialed digit match rules.

How to Implement SIP Configuration Flexibility

This section contains the steps for implementing SIP configuration flexibility.

SUMMARY STEPS

1. configure

2. sbc service-name

3. sbe

4. adjacency sip adjacency-name

5. passthrough from header

6. header-name [contact [add [tls-param]] | from{passthrough} | to{passthrough}]

7. nat force-on

8. exit

DETAILED STEPS

	Command or Action	Purpose
Step 1	configure terminal Example: Router# configure terminal	Enables global configuration mode.
Step 2	sbc service-name Example: Router(config)# sbc mysbc	Enters the mode of an SBC service. •Use the service-name argument to define the name of the service.
Step 3	sbe Example: Router(config-sbc)# sbe	Enters the mode of the signaling border element (SBE) function of the SBC.
Step 4	adjacency sip adjacency-name Example: Router(config-sbc-sbe)# adjacency sip sipadj	Enters the mode of an SBE SIP adjacency. •Use the adjacency-name argument to define the name of the SIP adjacency.
Step 5	passthrough from header Example: Router(config-sbc-sbe-adj-sip)# passthrough from header	Configures the SIP adjacency to disable From rewrite.
Step 6	header-name [contact [add [tls-param]] | from {passthrough} | to {passthrough}] Example: Router(config-sbc-sbe-adj-sip)# header-name to passthrough	Configures the SIP adjacency to disable To rewrite.
Step 7	nat force-on Example: Router(config-sbc-sbe-adj-sip)# nat force-on	Configures the SIP adjacency to assume that all endpoints are behind a NAT device. To configure the SIP adjacency to assume that no endpoints are behind a NAT device, use the nat force-off command. By default, the SBC autodetects whether the endpoints are behind a NAT device.
Step 8	exit Example: Router(config-sbc-sbe-adj-sip)# exit	Exits the adj-sip mode and returns to the SBE mode.