Cisco IOS Firewall Support for Skinny Local Traffic and CME

First Published: July 11, 2008
Last Updated: July 21, 2010

The Cisco IOS Firewall Support for Skinny Local Traffic and CME feature enhances the Context-Based Access Control (CBAC) functionality to support Skinny traffic that is either generated by or destined to the router. When Cisco Call Manager Express (CME) is enabled on the Cisco IOS firewall router, the CME manages both VoIP and analog phones using Skinny Client Control Protocol (SCCP) over either an intranet or the Internet with flow-around and flow-through modes of CME.

In addition,the Firewall Support of Skinny Client Control Protocol feature extends the support of SCCP to accommodate video channels.

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 for Cisco IOS Firewall Support for Skinny Local Traffic and CME" section.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

Contents

•Prerequisites for Cisco IOS Firewall Support for Skinny Local Traffic and CME

•Restrictions for Cisco IOS Firewall Support for Skinny Local Traffic and CME

•Information About Cisco IOS Firewall Support for Skinny Local Traffic and CME

•How to Configure Cisco IOS Firewall Support for Skinny Local Traffic and CME

•Additional References

•Feature Information for Cisco IOS Firewall Support for Skinny Local Traffic and CME

Prerequisites for Cisco IOS Firewall Support for Skinny Local Traffic and CME

The Skinny inspection module is part of the inspection subsystem; thus, your router must be running an image that has firewall support.

Restrictions for Cisco IOS Firewall Support for Skinny Local Traffic and CME

This feature has the following restrictions:

•Skinny inspection will inspect only the SCCP sessions that have been established after the firewall is configured with Skinny inspection. That is, any SCCP sessions that were established through the firewall before the Skinny inspection was configured will not be inspected.

•This feature does not support Music on Hold (MOH) when a device other than the Call Manager (CM) is the music server. (This feature does support MOH when the CM is the music server.)

•This feature does not address either the multicast functionality of SCCP or the functionality of multiple active calls on a single Skinny client.

This feature does not support the following Skinny and firewall configurations.

The CM and the Skinny client cannot be on three different networks that are separated at the firewall. The firewall implementation does not inspect sessions that have devices residing on more than two distinct networks that are segregated at the firewall. That is, if more than two interfaces at the firewall, session inspection is not supported.

Information About Cisco IOS Firewall Support for Skinny Local Traffic and CME

•Skinny Inspection Overview

•Pregenerated Session Handling

•NAT with CME and the Cisco IOS Firewall

•New Registry for Locally Generated Traffic

Skinny Inspection Overview

Skinny inspection enables voice communication between two Skinny clients by using a CM. Typically, the CM provides service to the Skinny clients on TCP Port 2000. Initially, a Skinny client connects to the CM by establishing a TCP connection; the client will also establish a TCP connection with a secondary CM, if available. After the TCP connection is established, the client will register with the primary CM, which will be used as the controlling CM until the CM reboots or there is a keepalive failure. Thus, the Skinny TCP connection between the client and the CM exists forever and is used to establish calls coming to or from the client. If a TCP connection failure is detected, the secondary CM is used. All data channels established with the previous CM remain active and will be closed after the end parties hang up the call.

The Skinny module inspects the locally generated or terminated Skinny control channel and to open or close pin-holes for the media channels that are originated from or destined to the Cisco IOS firewall.

Pass-through Skinny traffic and locally generated or terminated Skinny traffic is treated in the same way at the firewall. Both the control channels are inspected in the same way and the same set of Skinny messages are interpreted to obtain information about the possible media channels.

Table 1 lists the set of messages that are necessary for the data sessions to open and close. Skinny inspection will examine the data sessions that are deemed for opening and closing the access list pinholes.

Table 1 Skinny Data Session Messages

Skinny Inspection Message
Description

StationCloseReceiveChannelMessage

CM instructs the Skinny client (on the basis of the information in this message) to close the receiving channel.

StationOpenReceiveChannelAckMessage

Contains the IP address and port information of the Skinny client sending this message. This message also contains the status of whether or not the client is willing to receive the voice traffic.

StationStartMediaTransmissionMessage

Contains the IP address and port information of the remote Skinny client.

StationStopMediaTransmissionMessage

CM instructs the Skinny client (on the basis of the information in this message) to stop transmitting voice traffic.

StationStopSessionTransmissionMessage

CM instructs the Skinny client (on the basis of the information in this message) to end an indicated session.

StationOpenMultiMediaReceiveChannelAckMessage

Contains the IP address and port information of the skinny client sending this message. It also contains the status of whether the client is willing to receive the video and data channels.

StationCloseMultiMediaReceiveChannel

This message is sent from the Cisco Unified Communications Manager to the Skinny endpoint to request closing the receiving video or data channel.

StationStartMultiMediaTransmitMessage

This message is sent from Cisco Unified Communications Manager to the Skinny endpoint whenever Cisco Unified Communications Manager gets back OpenLogicalChannelAck for the video or data channel.

StationStopMultiMediaTransmission

This message is sent to Skinny endpoints to request transmission of video or data channel to stop.


Pregenerated Session Handling

When two phones register with the CME running on Cisco IOS firewall, two control channels terminated on the CME box. These two control channels are TCP connections and are inspected by the Firewall Skinny module. When pinholes are opened for the media traffic, a total of four pre-gen sessions are created, two for each control session.

With the flow-through mode of operation of CME, the four pregenerated sessions are converted to two active sessions. The same number of active sessions is retained because there are two media sessions, one from each phone terminating on CME.

With the flow-around mode of operation of CME, the CME is bypassed as there is a direct connection between the two phones. In this mode, there are two possible scenarios:

•When both phones are on the same side of the CME, there is no exchange of media packets between the two phones. However, exchange of media packets is possible with pass-through traffic. In this case, the pre-gen sessions will timeout because the media traffic will not reach the router itself.

•When both phones are located on either side of the CME, the media traffic goes through the CME box. The four pre-gen sessions that are created are converted to one active session. Instead of creating four pre-gen sessions, only two pre-gen sessions are created. These two pre-gen sessions are converted to one active session when you see the media traffic.

NAT with CME and the Cisco IOS Firewall

In typical deployments, both Cisco IOS firewall and Network Address Translator (NAT) will be running on the same router. When CME is also running, typically in the case of an Integrated Services Router (ISR), some complexities and limitations exist.

•If two Skinny phones are registered to CME that is on the Cisco IOS firewall with NAT. When Phone 1 attempts to communicate with Phone 2, the IP and port (mostly private IP) of Phone 1 will be exchanged with Phone 2 over the already established TCP connection.

•If NAT is configured on the outside interface to translate all the private addresses to the router's global address. Some private addresses are exchanged over a TCP connection between the router and the remote phone. If NAT is able to translate the addresses in such flows where one endpoint is the router itself, then NAT and CME running on the same box will not cause any problems. If not, the following scenarios are possible:

•In flow-through mode of operation, the voice data channels, Real-time Transport Protocol (RTP) stream over User Datagram Protocol (UDP), from Phone 1 and Phone 2, both terminate on CME. So, there will be one RTP over UDP connection from Phone 1 to the CME and a second from Phone 2 to the CME. The CME relays the voice data over the two channels. In this case, there should not be any problem with NAT running on the CME box, as the connection is terminated on the router from Phone 2 and the address used for that connection is the global address of the router.

•In flow-around mode of operation, there is a direct connection (RTP over UDP) between Phone1 and Phone 2 for carrying voice data traffic. If NAT does not translate the private IP of Phone 1, then the voice data channel will not be established successfully because the private IP of Phone 1 is shared in the control channel. In such a scenario, the running of CME with NAT breaks down.

New Registry for Locally Generated Traffic

A new registry is created in the Skinny local media traffic path. This path differs from the regular switching path code, where all the controlling and pass-through media traffic is inspected. The Skinny module sends the locally generated traffic using the "fastsend" application program interface (API) which does not put the packet in the regular switching path, but sends it directly (to Layer 2 drivers). This new registry resets the timeouts for the media channels and also reports the number of Skinny media sessions that are established such as the output of show commands.

Note The above API is used to update the Firewall sessions when the media channel is active. Firewall will not attempt to protect the CME box based on the nonexistence of pregen. Therefore, the firewall will not drop media packets for which there is no pre-gen/active session. The MTP module in CME protects itself by dropping the packets that do not match the source IP and source port numbers.

How to Configure Cisco IOS Firewall Support for Skinny Local Traffic and CME

•Creating a ZonePair Between a Zone and the Self Zone (required)

Creating a ZonePair Between a Zone and the Self Zone

To inspect the traffic that is destined to the router or the traffic originating from the router, you need to create a zonepair between a zone (containing the incoming/outgoing interface) and the self zone.

SUMMARY STEPS

1. enable

2. configure terminal

3. parameter-map type inspect parameter-map-name

4. alert {on | off}

5. audit-trail {on | off}

6. class-map type inspect protocol-name [match-any | match-all] class-map-name

7. policy-map type inspect policy-map-name

8. class type inspect class-map-name

9. zone security name

10. zone security name

11. zone-pair security zone-pair-name {source source-zone-name | self} destination [self | destination-zone-name]

12. service-policy type inspect policy-map-name

13. interface type number

14. zone-member security zone-name

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 

parameter-map type inspect parameter-map-name

Example:

Router(config)# parameter-map type inspect insp-pmap

Configures an inspect parameter map for connecting thresholds, timeouts, and other parameters pertaining to the inspect action.

•Enters parameter-map type inspect configuration mode.

Step 4 

alert {on | off}

Example:

Router(config-profile)# alert on

(Optional) Turns on and off Cisco IOS stateful packet inspection alert messages that are displayed on the console.

Step 5 

audit-trail {on | off}

Example:

Router(config-profile)# audit-trail on

(Optional) Turns audit trail messages on or off.

Step 6 

class-map type inspect protocol-name [match-any | match-all] class-map-name

Example:

Router(config-profile)# class-map type inspect skinnycmap match-any protocol skinny

Creates a class map for the Skinny protocol so that you can enter match criteria.

•Enters class-map configuration mode.

Step 7 

policy-map type inspect policy-map-name

Example:

Router(config-profile)# policy-map type inspect skinnypmap

Creates a policy map so that you can enter match criteria.

•Enters policy map configuration mode.

Step 8 

class type inspect class-map-name

Example:

Router(config-profile)# class type inspect skinnycmap

Specifies the name of the class on which an action is to be performed.

•The value of the class-map-name argument must match the appropriate class name specified via the class-map type inspect command.

Step 9 

zone security name

Example:

Router(config-profile)# zone security z1

Creates a zone for phone 1.

•Enters global configuration mode.

Step 10 

zone security name

Example:

Router(config-profile)# zone security z2

Creates a zone for phone 2.

Step 11 

exit

Example:

Router(config-profile)#exit

Exits profile configuration mode.

Step 12 

zone-pair security zone-pair-name {source source-zone-name | self} destination [self | destination-zone-name]

Example:

Router(config)# zone-pair security z1-self source z1 destination self

Creates a zone-pair.

•Enters security zone-pair configuration mode.

Step 13 

service-policy type inspect policy-map-name

Example:

Router(config-sec-zone-pair)# service-policy type inspect skinnypmap

Attaches a firewall policy map to the destination zone-pair.

•If a policy is not configured between a pair of zones, traffic is dropped by default.

•Enters global configuration mode.

Step 14 

interface type number

Example:

Router(config)# interface FastEthernet4/1

Specifies the type of interface to be configured and the port, connector, or interface card number.

Step 15 

zone-member security zone-name

Example:

Router(config-sec-zone-pair)# zone-member security z1

Specifies the name of the security zone to which an interface is attached.

Additional References

Related Documents

Related Topic
Document Title

Cisco IOS commands

Cisco IOS Master Commands List, All Releases

Firewall support of SCCP

"Firewall Support of Skinny Client Control Protocol (SCCP)" chapter in the Cisco IOS Security Configuration Guide

Firewall commands

Cisco IOS Security Command Reference


Standards

Standard
Title

None

—


MIBs

MIB
MIBs Link

None

To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:

http://www.cisco.com/go/mibs


RFCs

RFC
Title

None

—


Technical Assistance

Description
Link

The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password.

http://www.cisco.com/cisco/web/support/index.html


Feature Information for Cisco IOS Firewall Support for Skinny Local Traffic and CME

Table 2 lists the features in this module and provides links to specific configuration information.

Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

Note Table 2 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.

Table 2 Feature Information for Cisco IOS Firewall Support for Skinny Local Traffic and CME

Feature Name
Releases
Feature Information

IOS Firewall Support for Skinny Local Traffic and CME

12.4(20)T

The Cisco IOS Firewall Support for Skinny Local Traffic and CME feature enhances the Context-Based Access Control (CBAC) functionality to support `router generated/destined to router' Skinny traffic. When CME is enabled on the IOS firewall router, it manages both VoIP and analog phones using Skinny Client Control Protocol (SCCP) over intranet or internet with flow-around and flow-through modes of CME.

The following commands were introduced or modified:

class-map type inspect, class type inspect, interface, parameter-map type inspect, policy-map type inspect, service-policy type inspect, zone-member security, zone-pair security.

IOS Zone-Based Firewall SCCP Video Support

15.1(2)T

The IOS Zone-Based Firewall SCCP Video Support (SCCP) feature extends support to accommodate video channels.


Cisco and the Cisco Logo are trademarks of Cisco Systems, Inc. and/or its affiliates in the U.S. and other countries. A listing of Cisco's trademarks can be found at www.cisco.com/go/trademarks. Third party trademarks mentioned are the property of their respective owners. The use of the word partner does not imply a partnership relationship between Cisco and any other company. (1005R)

Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental.

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