Table Of Contents
Source Specific Multicast with IGMPv3,
IGMP v3lite, and URDHow SSM Differs from Internet Standard Multicast
Supported Standards, MIBs, and RFCs
SSM with IGMP v3lite and URD Example
Source Specific Multicast with IGMPv3,
IGMP v3lite, and URD
This feature module describes the Source Specific Multicast feature and includes the following sections:
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Supported Standards, MIBs, and RFCs
Feature Overview
The Source Specific Multicast feature is an extension of IP multicast where datagram traffic is forwarded to receivers from only those multicast sources to which the receivers have explicitly joined. For multicast groups configured for SSM, only source-specific multicast distribution trees (no shared trees) are created.
SSM Components Overview
Source Specific Multicast (SSM) is a datagram delivery model that best supports one-to-many applications, also known as broadcast applications. SSM is a core networking technology for the Cisco implementation of IP multicast solutions targeted for audio and video broadcast application environments. This feature module discusses the following Cisco IOS components that support the implementation of SSM:
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PIM-SSM is the routing protocol that supports the implementation of SSM and is derived from PIM sparse mode (PIM-SM). IGMP is the Internet Engineering Task Force (IETF) standards track protocol used for hosts to signal multicast group membership to routers. Version 3 of this protocol supports source filtering, which is required for SSM. To run SSM with IGMPv3, SSM must be supported in the Cisco IOS router, the host where the application is running, and the application itself. IGMP v3lite and URD are two Cisco-developed transition solutions that enable the immediate development and deployment of SSM services, without the need to wait for the availability of full IGMPv3 support in host operating systems and SSM receiver applications. IGMP v3lite is a solution for application developers that allows immediate development of SSM receiver applications switching to IGMPv3 as soon as it becomes available. URD is a solution for content providers and content aggregators that enables them to deploy receiver applications that are not yet SSM enabled (through support for IGMPv3). IGMPv3, IGMP v3lite, and URD interoperate with each other, so that both IGMP v3lite and URD can easily be used as transitional solutions toward full IGMPv3 support in hosts.
How SSM Differs from Internet Standard Multicast
The current IP multicast infrastructure in the Internet and many enterprise intranets is based on the PIM-SM protocol and Multicast Source Discovery Protocol (MSDP). These protocols have proven to be reliable, extensive, and efficient. However, they are bound to the complexity and functionality limitations of the Internet Standard Multicast (ISM) service model. For example, with ISM, the network must maintain knowledge about which hosts in the network are actively sending multicast traffic. With SSM, this information is provided by receivers through the source address(es) relayed to the last hop routers by IGMPv3, IGMP v3lite, or URD. SSM is an incremental response to the issues associated with ISM and is intended to coexist in the network with the protocols developed for ISM. In general, SSM provides a more advantageous IP multicast service for applications that utilize SSM.
ISM service is described in RFC 1112. This service consists of the delivery of IP datagrams from any source to a group of receivers called the multicast host group. The datagram traffic for the multicast host group consists of datagrams with an arbitrary IP unicast source address S and the multicast group address G as the IP destination address. Systems will receive this traffic by becoming members of the host group. Membership to a host group simply requires signalling the host group through IGMP Version 1, 2, or 3.
In SSM, delivery of datagrams is based on (S, G) channels. Traffic for one (S, G) channel consists of datagrams with an IP unicast source address S and the multicast group address G as the IP destination address. Systems will receive this traffic by becoming members of the (S, G) channel. In both SSM and ISM, no signalling is required to become a source. However, in SSM, receivers must subscribe or unsubscribe to (S, G) channels to receive or not receive traffic from specific sources. In other words, receivers can receive traffic only from (S, G) channels to which they are subscribed, whereas in ISM, receivers need not know the IP addresses of sources from which they receive their traffic. The proposed standard approach for channel subscription signalling utilizes IGMP INCLUDE mode membership reports, which are supported only in Version 3 of IGMP.
SSM IP Address Range
SSM can coexist with the ISM service by applying the SSM delivery model to a configured subset of the IP multicast group address range. The Internet Assigned Numbers Authority (IANA) has reserved the address range 232.0.0.0 through 232.255.255.255 for SSM applications and protocols. Cisco IOS software allows SSM configuration for an arbitrary subset of the IP multicast address range 224.0.0.0 through 239.255.255.255. When an SSM range is defined, existing IP multicast receiver applications will not receive any traffic when they try to use addresses in the SSM range (unless the application is modified to use explicit (S, G) channel subscription or is SSM enabled through URD).
SSM Operations
An established network, in which IP multicast service is based on PIM-SM, can support SSM services. SSM can also be deployed alone in a network without the full range of protocols that are required for interdomain PIM-SM (for example, MSDP, Auto-RP, or bootstrap router [BSR]) if only SSM service is needed.
If SSM is deployed in a network already configured for PIM-SM (Cisco IOS Release 12.0 or later releases is recommended), then only the last hop routers must be upgraded to a Cisco IOS Release 12.1(5)T or later release image that supports SSM. Routers that are not directly connected to receivers can run Cisco IOS Release 12.0 or later releases. In general, these nonlast hop routers must only run PIM-SM in the SSM range, and may need additional access control configuration to suppress MSDP signalling, registering, or PIM-SM shared tree operations from occurring within the SSM range.
In Cisco IOS Release 12.1(3)T and later releases, the SSM mode of operation is enabled by configuring the SSM range through the ip pim ssm command. This configuration has the following effects:
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Both IGMP v3lite and URD are based on utilizing existing application IGMP group membership and extending it with their respective (S, G) channel subscription mechanism, which is ignored by Cisco IOS software outside the SSM range of addresses. Within the SSM range, IGMP Version 1 (IGMPv1) or Version 2 (IGMPv2) group membership reports or IGMPv3 EXCLUDE mode membership reports are acted upon only in conjunction with an (S, G) specific membership report from URD or IGMP v3lite.
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IGMPv3 Host Signalling
IGMPv3 is the third version of the IETF standards track protocol in which hosts signal membership to last hop routers of multicast groups. IGMPv3 introduces the ability for hosts to signal group membership with filtering capabilities with respect to sources. A host can either signal that it wants to receive traffic from all sources sending to a group except for some specific sources (called EXCLUDE mode), or that it wants to receive traffic only from some specific sources sending to the group (called INCLUDE mode).
IGMPv3 can operate with both ISM and SSM. In ISM, both EXCLUDE and INCLUDE mode reports are applicable. In SSM, only INCLUDE mode reports are accepted by the last hop router. EXCLUDE mode reports are ignored.
IGMPv3 is described in more detail in the Cisco IOS Release 12.1(5)T IGMP Version 3 feature module.
IGMP v3lite Host Signalling
IGMP v3lite is a Cisco-developed transitional solution for application developers to immediately start programming SSM applications. It allows you to write and run SSM applications on hosts that do not yet support IGMPv3 in their operating system kernel.
Applications must be compiled with the Host Side IGMP Library (HSIL) for IGMP v3lite. This software provides applications with a subset of the IGMPv3 applications programming interface (API) that is required to write SSM applications. HSIL was developed for Cisco by Talarian and is available from the following web page:
http://www.talarianmulticast.com/cgi-bin/igmpdownld
One part of the HSIL is a client library linked to the SSM application. It provides the SSM subset of the IGMPv3 API to the SSM application. If possible, the library checks whether the operating system kernel supports IGMPv3. If it does, then the API calls simply are passed through to the kernel. If the kernel does not support IGMPv3, then the library uses the IGMP v3lite mechanism.
When using the IGMP v3lite mechanism, the library tells the operating system kernel to join to the whole multicast group, because joining to the whole group is the only method for the application to receive traffic for that multicast group (if the operating system kernel only supports IGMPv1 or IGMPv2). In addition, the library signals the (S, G) channel subscriptions to an IGMP v3lite server process, which is also part of the HSIL. A server process is needed because multiple SSM applications may be on the same host. This server process will then send IGMP v3lite-specific (S, G) channel subscriptions to the last hop Cisco IOS router, which needs to be enabled for IGMP v3lite. This Cisco IOS router will then see both the IGMPv1 or IGMPv2 group membership report from the operating system kernel and the (S, G) channel subscription from the HSIL daemon. If the router sees both of these messages, it will interpret them as an SSM (S, G) channel subscription and join to the channel through PIM-SSM. We recommend referring to the documentation accompanying the HSIL software for further information on how to utilize IGMP v3lite with your application.
IGMP v3lite is supported by Cisco only through the API provided by the HSIL, not as a function of the router independent of the HSIL. By default, IGMP v3lite is disabled. When IGMP v3lite is configured through the ip igmp v3lite command on an interface, it will be active only for IP multicast addresses in the SSM range.
URD Host Signalling
URD is a Cisco-developed transitional solution that allows existing IP multicast receiver applications to be used with SSM without the need to modify the application and change or add any software on the receiver host running the application. URD is a content provider solution in which the receiver applications can be started or controlled through a web browser.
URD operates by passing a special URL from the web browser to the last hop router. This URL is called a URD intercept URL. A URD intercept URL is encoded with the (S, G) channel subscription and has a format that allows the last hop router to easily intercept it.
As soon as the last hop router intercepts both an (S, G) channel subscription encoded in a URD intercept URL and sees an IGMP group membership report for the same multicast group from the receiver application, the last hop router will use PIM-SSM to join toward the (S, G) channel as long as the application maintains the membership for the multicast group G. The URD intercept URL is thus only needed initially to provide the last hop router with the address of the source(s) to join to.
A URD intercept URL has the following syntax:
http://webserver:465/path?group=group&source=source1&...source=sourceN&The webserver string is the name or IP address to which the URL is targeted. This target need not be the IP address of an existing web server, except for situations where the web server wants to recognize that the last hop router failed to support the URD mechanism. The number 465 indicates the URD port. Port 465 is reserved for Cisco by the IANA for the URD mechanism so that no other applications can use this port.
When the browser of a host encounters a URD intercept URL, it will try to open a TCP connection to the web server on port 465. If the last hop router is enabled for URD on the interface where the router receives the TCP packets from the host, it will intercept all packets for TCP connections destined to port 465 independent of the actual destination address of the TCP connection (independent of the address of the web server). Once intercepted, the last hop router will "speak" a very simple subset of HTTP on this TCP connection, emulating a web server. The only HTTP request that the last hop router will understand and reply to is the following GET request:
GET argument HTTP/1.0argument = /path?group=group&source=source1&...source=sourceN&When it receives a GET command, the router tries to parse the argument according to this syntax to derive one or more (S, G) channel memberships. The path string of the argument is anything up to, but not including, the first question mark, and is ignored. The group and source1 through sourceN strings are the IP addresses fully qualified domain names of the channels for which this argument is a subscription request. If the argument matches the syntax shown, the router interprets the argument to be subscriptions for the channels (source1, group) through (sourceN, group).
The router will accept the channel subscription(s) if the following conditions are met:
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If the channel subscription is accepted, the router will respond to the TCP connection with the following HTML page format:
HTTP/1.1 200 OKServer:cisco IOSContent-Type:text/html<html><body>Retrieved URL string successfully</body></html>If an error condition occurs, the <body> part of the returned HTML page will carry an appropriate error message. The HTML page is a by-product of the URD mechanism. This returned text may, depending on how the web pages carrying a URD intercept URL are designed, be displayed to the user or be sized so that the actual returned HTML page is invisible.
The primary effect of the URD mechanism is that the router will remember received channel subscriptions and will match them against IGMP group membership reports received by the host. The router will "remember" a URD (S, G) channel subscription for up to 3 minutes without a matching IGMP group membership report. As soon as the router sees that it has received both an IGMP group membership report for a multicast group G and a URD (S, G) channel subscription for the same group G, it will join the (S, G) channel through PIM-SSM. The router will then continue to join to the (S, G) channel based only on the presence of a continuing IGMP membership from the host. Thus, one initial URD channel subscription is all that is needed to be added through a web page to enable SSM with URD.
If the last hop router from the receiver host is not enabled for URD, then it will not intercept the HTTP connection toward the web server on port 465. This situation will result in a TCP connection to port 465 on the web server. If no further provisions on the web server are taken, then the user may see a notice (for example, "Connection refused") in the area of the web page reserved for displaying the URD intercept URL (if the web page was designed to show this output). It is also possible to let the web server "listen" to requests on port 465 and install a Common Gateway Interface (CGI) script that would allow the web server to know if a channel subscription failed (for example, to subsequently return more complex error descriptions to the user).
Because the router returns a Content-Type of text and HTML, the best way to include the URD intercept URL into a web page is to use a frame. By defining the size of the frame, you can also hide the URD intercept URL on the displayed page.
By default, URD is disabled on all interfaces. When URD is configured through the ip urd command on an interface, it will be active only for IP multicast addresses in the SSM range.
Benefits
IP Multicast Address Management Not Required
In the ISM service, applications must acquire a unique IP multicast group address because traffic distribution is based only on the IP multicast group address used. If two applications with different sources and receivers use the same IP multicast group address, then receivers of both applications will receive traffic from the senders of both applications. Even though the receivers, if programmed appropriately, can filter out the unwanted traffic, this situation would cause generally unacceptable levels of unwanted traffic.
Allocating a unique IP multicast group address for an application is still a problem. Most short-lived applications use mechanisms like Session Description Protocol (SDP) and Session Announcement Protocol (SAP) to get a random address, a solution that does not work well with a rising number of applications in the Internet. The best current solution for long-lived applications is described in RFC 2770, but this solution suffers from the restriction that each autonomous system is limited to only 255 usable IP multicast addresses.
In SSM, traffic from each source is forwarded between routers in the network independent of traffic from other sources. Thus different sources can reuse multicast group addresses in the SSM range.
Denial of Service Attacks from Unwanted Sources Inhibited
In SSM, multicast traffic from each individual source will be transported across the network only if it was requested (through IGMPv3, IGMP v3lite, or URD memberships) from a receiver. In contrast, ISM forwards traffic from any active source sending to a multicast group to all receivers requesting that multicast group. In Internet broadcast applications, this ISM behavior is highly undesirable because it allows unwanted sources to easily disturb the actual Internet broadcast source by simply sending traffic to the same multicast group. This situation depletes bandwidth at the receiver side with unwanted traffic and thus disrupts the undisturbed reception of the Internet broadcast. In SSM, this type of denial of service (DoS) attack cannot be made by simply sending traffic to a multicast group.
Easy to Install and Manage
SSM is easy to install and provision in a network because it does not require the network to maintain which active sources are sending to multicast groups. This requirement exists in ISM (with IGMPv1, IGMPv2, or IGMPv3).
The current standard solutions for ISM service are PIM-SM and MSDP. Rendezvous point (RP) management in PIM-SM (including the necessity for Auto-RP or BSR) and MSDP is required only for the network to learn about active sources. This management is not necessary in SSM, which makes SSM easier to install and manage, and therefore easier to operationally scale in deployment. Another factor that contributes to the ease of installation of SSM is the fact that it can leverage preexisting PIM-SM networks and requires only the upgrade of last hop routers to support IGMPv3, IGMP v3lite, or URD.
Ideal for Internet Broadcast Applications
The three benefits previously described make SSM ideal for Internet broadcast-style applications for the following reasons:
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Restrictions
Legacy Applications Within the SSM Range Restrictions
Existing applications in a network predating SSM will not work within the SSM range, unless they are modified to support (S, G) channel subscriptions or are enabled through URD. Therefore, enabling SSM in a network may cause problems for existing applications if they use addresses within the designated SSM range.
IGMP v3lite and URD Require a Cisco IOS Last Hop Router
SSM and IGMPv3 are solutions that are being standardized in the IETF. However, IGMP v3lite and URD are Cisco-developed solutions. For IGMP v3lite and URD to operate properly for a host, the last hop router toward that host must be a Cisco IOS router with IGMP v3lite or URD enabled.
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Address Management Restrictions
Address management is still necessary to some degree when SSM is used with Layer 2 switching mechanisms. Cisco Group Management Protocol (CGMP), IGMP snooping, or Router-Port Group Management Protocol (RGMP) currently support only group-specific filtering, not (S, G) channel-specific filtering. If different receivers in a switched network request different (S, G) channels sharing the same group, then they will not benefit from these existing mechanisms. Instead, both receivers will receive all (S, G) channel traffic (and filter out the unwanted traffic on input). Because of the ability of SSM to reuse the group addresses in the SSM range for many independent applications, this situation can lead to less than expected traffic filtering in a switched network. For this reason it is important to follow the recommendations set forth in the IETF drafts for SSM to use random IP addresses out of the SSM range for an application to minimize the chance for reuse of a single address within the SSM range between different applications. For example, an application service providing a set of television channels should, even with SSM, use a different group for each television (S, G) channel. This setup will guarantee that multiple receivers to different channels within the same application service will never experience traffic aliasing in networks that include Layer 2 switches.
IGMP Snooping and CGMP Limitations
IGMPv3 uses new membership report messages that may not be recognized correctly by older IGMP Snooping switches, in which case hosts will not properly receive traffic. This situation is not an issue if URD or IGMP v3lite is used with hosts where the operating system is not upgraded for IGMPv3, because IGMP v3lite and URD rely only on IGMPv1 or IGMPv2 membership reports. For more information about switching issues related to IGMP (especially with CGMP), refer to the Cisco IOS Release 12.1(5)T IGMP Version 3 feature module.
URD Intercept URL Limitations
A URD intercept URL string must be fewer than 256 bytes in length, starting from the /path argument. In the HTTP/TCP connection, this string must also be contained within a single TCP/IP packet. For example, for a 256-byte string, a link maximum transmission unit (MTU) of 128 bytes between the host and intercepting router would cause incorrect operation of URD.
State Maintenance Limitations
In PIM-SSM, the last hop router will continue to periodically send (S, G) join messages if appropriate (S, G) subscriptions are on the interfaces. Therefore, as long as receivers send (S, G) subscriptions, the shortest path tree (SPT) state from the receivers to the source will be maintained, even if the source is not sending traffic for longer periods of time (or even never).
This case is opposite to PIM-SM, where (S, G) state is maintained only if the source is sending traffic and receivers are joining the group. If a source stops sending traffic for more than 3 minutes in PIM-SM, the (S, G) state will be deleted and only reestablished after packets from the source arrive again through the RPT. Because no mechanism in PIM-SSM notifies a receiver that a source is active, the network must maintain the (S, G) state in PIM-SSM as long as receivers are requesting receipt of that channel.
HSIL Limitations
As explained in the "IGMP v3lite Host Signalling" section, the HSIL tries to determine if the host operating system supports IGMPv3. This check is made so that a single application can be used both on hosts where the operating system has been upgraded to IGMPv3 and on hosts where the operating system only supports IGMPv1 or IGMPv2. Checking for the availability of IGMPv3 in the host operating system can only be made by the HSIL if IGMPv3 kernel support exists for at least one version of this operating system at the time when the HSIL was provided. If such an IGMPv3 kernel implementation has become available only recently, then users may need to also upgrade the HSIL on their hosts so that applications compiled with the HSIL will then dynamically bind to the newest version of the HSIL, which should support the check for IGMPv3 in the operating system kernel. Upgrading the HSIL can be done independently of upgrading the application itself.
Related Documents
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This draft describes the SSM model, its default usage with the 232/8 address range, and how IGMPv3 applies to SSM.
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This draft describes PIM-SSM mode as used with Cisco IOS SSM.
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This draft describes IGMPv3 on which the host signalling of IGMP v3lite is based.
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This draft describes the proposed API for IGMPv3 on hosts. A subset of this API is provided by the HSIL for implementation of IGMP v3lite.
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This draft describes PIM-SM on which PIM-SSM mode is based.
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This draft describes the Best Current Practices (BCP) for using PIM-SM within the SSM range.
Supported Platforms
SSM with IGMPv3, IGMP v3lite, and URD is supported on all Cisco IOS Release 12.1(5)T platforms and later releases.
Supported Standards, MIBs, and RFCs
Standards
No new or modified standards are supported by this feature.
MIBs
No new or modified MIBs are supported by this feature.
To obtain lists of MIBs supported by platform and Cisco IOS release and to download MIB modules, go to the Cisco web site on Cisco Connection Online (CCO) at http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml.
RFCs
No new or modified RFCs are supported by this feature.
Configuration Tasks
See the following sections for configuration tasks for SSM. Each task in the list is identified as either optional or required.
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Configuring SSM
Verifying SSM
To verify configuration of multicast groups supporting SSM, use the following show commands:
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Configuration Examples
This section provides the following SSM configuration examples:
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SSM with IGMPv3 Example
The following example shows how to configure a router (running IGMPv3) for SSM:
ip multicast-routing!interface Ethernet3/1ip address 172.21.200.203 255.255.255.0description backbone interfaceip pim sparse-dense-mode!interface Ethernet3/2ip address 131.108.1.2 255.255.255.0ip pim sparse-dense-modedescription ethernet connected to hostsip igmp version 3!ip pim ssm defaultSSM with IGMP v3lite and URD Example
The following example shows how to configure IGMP v3lite and URD on interfaces connected to hosts for SSM. Configuring IGMP v3lite and URD is not required or recommended on backbone interfaces.
interface ethernet 3/1ip address 172.21.200.203 255.255.255.0ip pim sparse-dense-modedescription ethernet connected to hosts!interface ethernet 1description ethernet connected to hostsip address 131.108.1.2 255.255.255.0ip pim sparse-dense-modeip urdip igmp v3liteSSM Filtering Example
The following example shows how to configure filtering on a legacy RP router running Cisco IOS releases earlier than Release 12.1(3)T for SSM routing. This filtering will suppress all unwanted PIM-SM and MSDP traffic in the SSM range. Without this filtering, SSM will still operate, but there may be additional RPT traffic if legacy first hop and last hop routers exist in the network.
ip access-list extended no-ssm-rangedeny ip any 232.0.0.0 0.255.255.255 ! SSM rangepermit ip any any! Deny registering in SSM rangeip pim accept-register list no-ssm-rangeip access-list extended msdp-nono-listdeny ip any 232.0.0.0 0.255.255.255 ! SSM Range! .! .! .! See ftp://ftpeng.cisco.com/ipmulticast/config-notes/msdp-sa-filter.txt for other SA! messages that typically need to be filtered.permit ip any any! Filter generated SA messages in SSM range. This configuration is only needed if there! are directly connected sources to this router. The "ip pim accept-register" command! filters remote sources.ip msdp redistribute list msdp-nono-list! Filter received SA messages in SSM range. "Filtered on receipt" means messages are! neither processed or forwarded. Needs to be configured for each MSDP peer.ip msdp sa-filter in msdp-peer1 list msdp-nono-list! .! .! .ip msdp sa-filter in msdp-peerN list msdp-nono-listCommand Reference
This section documents the following new or modified commands. For other commands related to IGMPv3, refer to the Cisco IOS Release 12.1(5)T IGMP Version 3 feature module. All other commands used with this feature are documented in the Cisco IOS Release 12.1 command reference publications.
ip igmp v3lite
To enable acceptance and processing of Internet Group Management Protocol Version 3 lite (IGMP v3lite) membership reports on an interface, use the ip igmp v3lite interface configuration command. To disable IGMP v3lite, use the no form of this command.
ip igmp v3lite
no ip igmp v3lite
Syntax Description
This command has no arguments or keywords.
Defaults
Disabled
Command Modes
Interface configuration
Command History
Usage Guidelines
To use this command, you must define a Source Specific Multicast (SSM) range of IP addresses using the ip pim ssm global configuration command. When IGMP v3lite is enabled, it is supported in the SSM range of addresses only.
Examples
The following example shows how to configure IGMP v3lite on Ethernet interface 3/1:
Router(config)# interface ethernet 3/1Router(config-if)# ip igmp v3liteRelated Commands
ip pim ssm
To define the Source Specific Multicast (SSM) range of IP multicast addresses, use the ip pim ssm global configuration command. To disable the SSM range, use the no form of this command.
ip pim ssm {default | range access-list}
no ip pim ssm
Syntax Description
default
(Optional) Defines the SSM range access list to 232/8.
range access-list
(Optional) Standard IP access list defining the SSM range.
Defaults
Disabled
Command Modes
Global configuration
Command History
Usage Guidelines
When an SSM range of IP multicast addresses is defined by the ip pim ssm command, no Multicast Source Discovery Protocol (MSDP) Source-Active (SA) messages will be accepted or originated in the SSM range.
Examples
The following example shows how to configure SSM service for the IP address range defined by access list 4:
Router(config)# access-list 4 permit 224.2.151.141Router(config)# ip pim ssm range 4Related Commands
ip urd
To enable interception of TCP packets sent to the reserved URL Rendezvous Directory (URD) port 465 on an interface and processing of URD channel subscription reports, use the ip urd command in interface configuration mode. To disable URD on an interface, use the no form of this command.
ip urd [proxy]
no ip urd [proxy]
Syntax Description
Defaults
Disabled
Command Modes
Interface configuration
Command History
Usage Guidelines
To use this command, you must first define a Source Specific Multicast (SSM) range of IP addresses using the ip pim ssm global configuration command. When URD is enabled, it is supported in the SSM range of addresses only. We recommend that you not enable URD on backbone interfaces, but only on interfaces connecting to hosts.
URD functionality is available for multicast process switching, fast switching, and distributed fast-switching paths.
Examples
The following example shows how to configure URD on Ethernet interface 3/3:
interface ethernet 3/3ip urdRelated Commands
show ip igmp groups
To display the multicast groups with receivers that are directly connected to the router and that were learned through Internet Group Management Protocol (IGMP), use the show ip igmp groups EXEC command.
show ip igmp groups [group-name | group-address | type number] [detail]
Syntax Description
Command Modes
EXEC
Command History
Usage Guidelines
If you omit all optional arguments and keywords, the show ip igmp groups command displays by group address, interface type, and interface number all directly connected multicast groups.
Examples
The following is sample output from the show ip igmp groups command:
Router# show ip igmp groupsIGMP Connected Group MembershipGroup Address Interface Uptime Expires Last Reporter239.255.255.254 Ethernet3/1 1w0d 00:02:19 172.21.200.159224.0.1.40 Ethernet3/1 1w0d 00:02:15 172.21.200.1224.0.1.40 Ethernet3/3 1w0d never 171.69.214.251224.0.1.1 Ethernet3/1 1w0d 00:02:11 172.21.200.11224.9.9.2 Ethernet3/1 1w0d 00:02:10 172.21.200.155232.1.1.1 Ethernet3/1 5d21h stopped 172.21.200.206The following is sample output from the show ip igmp groups command with the group-address argument and detail keyword:
Router# show ip igmp groups 232.1.1.1 detailInterface: Ethernet3/2Group: 232.1.1.1Uptime: 01:58:28Group mode: INCLUDELast reporter: 10.0.119.133CSR Grp Exp: 00:02:38Group source list: (C - Cisco Src Report, U - URD, R - Remote)Source Address Uptime v3 Exp CSR Exp Fwd Flags171.69.214.1 01:58:28 stopped 00:02:31 Yes CTable 1 describes the significant fields shown in the output.
Related Commands
ip igmp query-interval
Configures the frequency at which the Cisco IOS software sends IGMP host-query messages.
show ip mroute
To display the contents of the IP multicast routing table, use the show ip mroute EXEC command.
show ip mroute [group-name | group-address] [source] [summary] [count] [active kbps]
Syntax Description
Defaults
The show ip mroute command displays all groups and sources.
The show ip mroute active command displays all sources sending at a rate greater than or equal to 4 kbps.
Command Modes
EXEC
Command History
10.0
This command was introduced.
12.1(3)T
The U, s, and I flags for Source Specific Multicast (SSM) were introduced.
Usage Guidelines
If you omit all optional arguments and keywords, the show ip mroute command displays all entries in the IP multicast routing table.
The Cisco IOS software populates the multicast routing table by creating (S, G) entries from (*, G) entries. The star refers to all source addresses, the "S" refers to a single source address, and the "G" is the destination multicast group address. In creating (S, G) entries, the software uses the best path to that destination group found in the unicast routing table (that is, through Reverse Path Forwarding [RPF]).
Examples
The following is sample output from the show ip mroute command for a router operating in dense mode. This command displays the contents of the IP multicast routing table for the multicast group named cbone-audio.
Router# show ip mroute cbone-audioIP Multicast Routing TableFlags: D - Dense, S - Sparse, C - Connected, L - Local, P - PrunedR - RP-bit set, F - Register flag, T - SPT-bit setTimers: Uptime/ExpiresInterface state: Interface, Next-Hop, State/Mode(*, 224.0.255.1), uptime 0:57:31, expires 0:02:59, RP is 0.0.0.0, flags: DCIncoming interface: Null, RPF neighbor 0.0.0.0, DvmrpOutgoing interface list:Ethernet0, Forward/Dense, 0:57:31/0:02:52Tunnel0, Forward/Dense, 0:56:55/0:01:28(198.92.37.100/32, 224.0.255.1), uptime 20:20:00, expires 0:02:55, flags: CIncoming interface: Tunnel0, RPF neighbor 10.20.37.33, DvmrpOutgoing interface list:Ethernet0, Forward/Dense, 20:20:00/0:02:52The following is sample output from the show ip mroute command for a router operating in sparse mode:
Router# show ip mrouteIP Multicast Routing TableFlags: D - Dense, S - Sparse, C - Connected, L - Local, P - PrunedR - RP-bit set, F - Register flag, T - SPT-bit setTimers: Uptime/ExpiresInterface state: Interface, Next-Hop, State/Mode(*, 224.0.255.3), uptime 5:29:15, RP is 198.92.37.2, flags: SCIncoming interface: Tunnel0, RPF neighbor 10.3.35.1, DvmrpOutgoing interface list:Ethernet0, Forward/Sparse, 5:29:15/0:02:57(198.92.46.0/24, 224.0.255.3), uptime 5:29:15, expires 0:02:59, flags: CIncoming interface: Tunnel0, RPF neighbor 10.3.35.1Outgoing interface list:Ethernet0, Forward/Sparse, 5:29:15/0:02:57The following is sample output from the show ip mroute command that shows the virtual circuit descriptor (VCD) value, because an ATM interface with PIM multipoint signalling is enabled:
Router# show ip mroute 224.1.1.1IP Multicast Routing TableFlags: D - Dense, S - Sparse, C - Connected, L - Local, P - PrunedR - RP-bit set, F - Register flag, T - SPT-bit set, J - Join SPTTimers: Uptime/ExpiresInterface state: Interface, Next-Hop or VCD, State/Mode(*, 224.1.1.1), 00:03:57/00:02:54, RP 130.4.101.1, flags: SJIncoming interface: Null, RPF nbr 0.0.0.0Outgoing interface list:ATM0/0, VCD 14, Forward/Sparse, 00:03:57/00:02:53The following is sample output from the show ip mroute command with the summary keyword:
Router# show ip mroute summaryIP Multicast Routing TableFlags: D - Dense, S - Sparse, C - Connected, L - Local, P - PrunedR - RP-bit set, F - Register flag, T - SPT-bit set, J - Join SPTTimers: Uptime/ExpiresInterface state: Interface, Next-Hop, State/Mode(*, 224.255.255.255), 2d16h/00:02:30, RP 171.69.10.13, flags: SJPC(*, 224.2.127.253), 00:58:18/00:02:00, RP 171.69.10.13, flags: SJC(*, 224.1.127.255), 00:58:21/00:02:03, RP 171.69.10.13, flags: SJC(*, 224.2.127.254), 2d16h/00:00:00, RP 171.69.10.13, flags: SJCL(128.9.160.67/32, 224.2.127.254), 00:02:46/00:00:12, flags: CLJT(129.48.244.217/32, 224.2.127.254), 00:02:15/00:00:40, flags: CLJT(130.207.8.33/32, 224.2.127.254), 00:00:25/00:02:32, flags: CLJT(131.243.2.62/32, 224.2.127.254), 00:00:51/00:02:03, flags: CLJT(140.173.8.3/32, 224.2.127.254), 00:00:26/00:02:33, flags: CLJT(171.69.60.189/32, 224.2.127.254), 00:03:47/00:00:46, flags: CLJTThe following is sample output from the show ip mroute command with the active keyword:
Router# show ip mroute activeActive IP Multicast Sources - sending >= 4 kbpsGroup: 224.2.127.254, (sdr.cisco.com)Source: 146.137.28.69 (mbone.ipd.anl.gov)Rate: 1 pps/4 kbps(1sec), 4 kbps(last 1 secs), 4 kbps(life avg)Group: 224.2.201.241, ACM 97Source: 130.129.52.160 (webcast3-e1.acm97.interop.net)Rate: 9 pps/93 kbps(1sec), 145 kbps(last 20 secs), 85 kbps(life avg)Group: 224.2.207.215, ACM 97Source: 130.129.52.160 (webcast3-e1.acm97.interop.net)Rate: 3 pps/31 kbps(1sec), 63 kbps(last 19 secs), 65 kbps(life avg)The following is sample output from the show ip mroute command with the count keyword:
Router# show ip mroute countIP Multicast Statistics - Group count: 8, Average sources per group: 9.87Counts: Pkt Count/Pkts per second/Avg Pkt Size/Kilobits per secondGroup: 224.255.255.255, Source count: 0, Group pkt count: 0RP-tree: 0/0/0/0Group: 224.2.127.253, Source count: 0, Group pkt count: 0RP-tree: 0/0/0/0Group: 224.1.127.255, Source count: 0, Group pkt count: 0RP-tree: 0/0/0/0Group: 224.2.127.254, Source count: 9, Group pkt count: 14RP-tree: 0/0/0/0Source: 128.2.6.9/32, 2/0/796/0Source: 128.32.131.87/32, 1/0/616/0Source: 128.125.51.58/32, 1/0/412/0Source: 130.207.8.33/32, 1/0/936/0Source: 131.243.2.62/32, 1/0/750/0Source: 140.173.8.3/32, 1/0/660/0Source: 146.137.28.69/32, 1/0/584/0Source: 171.69.60.189/32, 4/0/447/0Source: 204.162.119.8/32, 2/0/834/0Group: 224.0.1.40, Source count: 1, Group pkt count: 3606RP-tree: 0/0/0/0Source: 171.69.214.50/32, 3606/0/48/0, RPF Failed: 1203Group: 224.2.201.241, Source count: 36, Group pkt count: 54152RP-tree: 7/0/108/0Source: 13.242.36.83/32, 99/0/123/0Source: 36.29.1.3/32, 71/0/110/0Source: 128.9.160.96/32, 505/1/106/0Source: 128.32.163.170/32, 661/1/88/0Source: 128.115.31.26/32, 192/0/118/0Source: 128.146.111.45/32, 500/0/87/0Source: 128.183.33.134/32, 248/0/119/0Source: 128.195.7.62/32, 527/0/118/0Source: 128.223.32.25/32, 554/0/105/0Source: 128.223.32.151/32, 551/1/125/0Source: 128.223.156.117/32, 535/1/114/0Source: 128.223.225.21/32, 582/0/114/0Source: 129.89.142.50/32, 78/0/127/0Source: 129.99.50.14/32, 526/0/118/0Source: 130.129.0.13/32, 522/0/95/0Source: 130.129.52.160/32, 40839/16/920/161Source: 130.129.52.161/32, 476/0/97/0Source: 130.221.224.10/32, 456/0/113/0Source: 132.146.32.108/32, 9/1/112/0The following is sample output from the show ip mroute command for a router supporting SSM services:Router# show ip mroute 232.6.6.6IP Multicast Routing TableFlags:D - Dense, S - Sparse, B - Bidir Group, s - SSM Group, C -Connected, L - Local, P - Pruned, R - RP-bit set, F - Register flag, T - SPT-bit set, J - Join SPT, M - MSDP created entry, X - Proxy Join Timer Running, A - Advertised via MSDP, U - URD, I - Received Source Specific Host ReportOutgoing interface flags:H - Hardware switchedTimers:Uptime/ExpiresInterface state:Interface, Next-Hop or VCD, State/Mode(*, 232.6.6.6), 00:01:20/00:02:59, RP 0.0.0.0, flags:sSJPIncoming interface:Null, RPF nbr 0.0.0.0Outgoing interface list:Null(2.2.2.2, 232.6.6.6), 00:01:20/00:02:59, flags:CTIIncoming interface:Ethernet3/3, RPF nbr 0.0.0.0Outgoing interface list:Ethernet3/1, Forward/Sparse-Dense, 00:00:36/00:02:35Table 2 describes the significant fields shown in the output.
Related Commands
ip multicast-routing
Enables IP multicast routing or multicast distributed switching.
ip pim
Enables PIM on an interface.
Defines the SSM range of IP multicast addresses.
Debug Commands
This section documents the following new and modified debug commands. All other commands used with this feature are documented in the Cisco IOS Release 12.1 command reference publications.
debug ip igmp
To display Internet Group Management Protocol (IGMP) packets received and sent, and IGMP-host related events, use the debug ip igmp privileged EXEC command. To disable debugging output, use the no form of this command.
debug ip igmp
no debug ip igmp
Syntax Description
This command has no arguments or keywords.
Defaults
None
Command History
10.2
This command was introduced.
12.1(3)T
Additional fields were added to the output of this command to support the Source Specific Multicast (SSM) feature.
Usage Guidelines
This command helps discover whether the IGMP processes are functioning. In general, if IGMP is not working, the router process never discovers that another host is on the network that is configured to receive multicast packets. In dense mode, this situation will result in packets being delivered intermittently (a few every 3 minutes). In sparse mode, packets will never be delivered.
Use this command in conjunction with the debug ip pim and debug ip mrouting commands to observe additional multicast activity and to learn what is happening to the multicast routing process, or why packets are forwarded out of particular interfaces.
Examples
The following is sample output from the debug ip igmp command:
Router# debug ip igmpIGMP: Received Host-Query from 172.24.37.33 (Ethernet1)IGMP: Received Host-Report from 172.24.37.192 (Ethernet1) for 224.0.255.1IGMP: Received Host-Report from 172.24.37.57 (Ethernet1) for 224.2.127.255IGMP: Received Host-Report from 172.24.37.33 (Ethernet1) for 225.2.2.2The messages displayed by the debug ip igmp command show query and report activity received from other routers and multicast group addresses.
The following is sample output from the debug ip igmp command when SSM is enabled. Because IGMP Version 3 lite (IGMP v3lite) requires the host to send IGMP Version 2 (IGMPv2) packets, IGMPv2 host reports also will be displayed in response to the router IGMPv2 queries. If SSM is disabled, the word "ignored" will be displayed in the debug ip igmp command output.
IGMP:Received v3-lite Report from 10.0.119.142 (Ethernet3/3), group count 1IGMP:Received v3 Group Record from 10.0.119.142 (Ethernet3/3) for 232.10.10.10IGMP:Update source 1.1.1.1IGMP:Send v2 Query on Ethernet3/3 to 224.0.0.1IGMP:Received v2 Report from 10.0.119.142 (Ethernet3/3) for 232.10.10.10IGMP:Update source 1.1.1.1Related Commands
debug ip mrm
Displays MRM control packet activity.
debug ip pim
Displays PIM packets received and sent, and PIM-related events.
debug ip urd
To display debug messages for URL Rendezvous Directory (URD) channel subscription report processing, use the debug ip urd EXEC command. To disable debugging of URD reports, use the no form of this command.
debug ip urd [hostname | ip-address]
no debug ip urd
Syntax Description
Defaults
If no host name or IP address is specified, all URD reports are debugged.
Command History
Examples
The following is sample output from the debug ip urd command:
Router# debug ip urd13:36:25 pdt:URD:Data intercepted from 171.71.225.10313:36:25 pdt:URD:Enqueued string:'/cgi-bin/error.pl?group=232.16.16.16&port=32620&source=171.69.214.1&li'13:36:25 pdt:URD:Matched token:group13:36:25 pdt:URD:Parsed value:232.16.16.1613:36:25 pdt:URD:Creating IGMP source state for group 232.16.16.16Glossary
first hop router—A router that is directly connected to a host that is sending traffic (for example, a router on the same Ethernet as the host). To illustrate, if the host is sending multicast traffic to a group in PIM-SM, then one of the first hop routers (specifically, the one that is elected as designated router) must send PIM-SM register messages for this host toward the RP.
last hop router—A router that is directly connected to a host that is receiving traffic (for example, a router on the same Ethernet as the host). To illustrate, if the host wants to receive multicast traffic, then the last hop router must listen to the IGMP membership reports sent by the host.
Guest
