% % $XORP: xorp/docs/user_manual/igmp.tex,v 1.21 2006/07/05 03:38:51 pavlin Exp $ % \chapter{IGMP and MLD} \label{igmp} \section{Terminology and Concepts} When a receiver joins a multicast group, the multicast routers serving that receiver's subnet need to know that the receiver has joined so that they can arrange for multicast traffic destined for that group to reach this subnet. The Internet Group Management Protocol (IGMP) is a link-local protocol for IPv4 that communicates this information between receivers and routers. The same role for IPv6 is performed by the Multicast Listener Discovery protocol (MLD). The basic IGMP mechanism works as follows. When a multicast receiver joins a multicast group it multicasts an IGMP Join message onto the subnet on which it is joining. The local routers receive this join, and cause multicast traffic destined for the group to reach this subnet. Periodically one of the local routers sends a IGMP Query message onto the subnet. If there are multiple multicast routers on the subnet, then one of them is elected as the sole querier for that subnet. In response to an IGMP query, receivers respond by refreshing their IGMP Join. If the join is not refreshed in response to queries, then the state is removed, and multicast traffic for this group ceases to reach this subnet. There are three different versions of IGMP: \begin{itemize} \item IGMP version 1 functions as described above. \item IGMP version 2 adds support for IGMP Leave messages to allow fast leave from a multicast group. \item IGMP version 3 adds support for source include and exclude lists, to allow a receiver in indicate that it only wants to hear traffic from certain sources, or not receive traffic from certain sources. \end{itemize} XORP supports IGMPv1, IGMPv2, and IGMPv3. MLD for IPv6 functions in basically the same way as IGMP. The functionality of MLDv1 corresponds with that of IGMPv2, and the functionality of MLDv2 corresponds with that of IGMPv3. XORP supports MLDv1 and MLDv2. \vfill\eject \section{Standards} XORP complies with the following standards for multicast group membership: \begin{description} \item{\bf RFC 2236}: Internet Group Management Protocol, Version 2 \item{\bf RFC 3376}: Internet Group Management Protocol, Version 3 \item{\bf RFC 2710}: Multicast Listener Discovery (MLD) for IPv6 \item{\bf RFC 3810}: Multicast Listener Discovery Version 2 (MLDv2) for IPv6 \end{description} \section{Configuring IGMP and MLD} IGMP and MLD only require the interfaces/vifs to be configured that are intended to have multicast listeners. \subsection{Configuration Syntax} \vspace{0.1in} \noindent\framebox[\textwidth][l]{\scriptsize \begin{minipage}{6in} \begin{alltt} \begin{tabbing} xx\=xx\=xx\=xx\=xx\=\kill protocols \{\\ \>igmp \{\\ \>\>targetname: {\it text}\\ \>\>disable: {\it bool}\\ \>\>interface {\it text} \{\\ \>\>\>vif {\it text} \{\\ \>\>\>\>disable: {\it bool}\\ \>\>\>\>version: {\it uint(1..3)}\\ \>\>\>\>enable-ip-router-alert-option-check: {\it bool}\\ \>\>\>\>query-interval: {\it uint(1..1024)}\\ \>\>\>\>query-last-member-interval: {\it uint(1..1024)}\\ \>\>\>\>query-response-interval: {\it uint(1..1024)}\\ \>\>\>\>robust-count: {\it uint(2..10)}\\ \>\>\>\}\\ \>\>\}\\ \>\>traceoptions \{\\ \>\>\>flag all \{\\ \>\>\>\>disable: {\it bool}\\ \>\>\>\}\\ \>\>\}\\ \>\}\\ \}\\ \\ \\ {\rm continued overleaf....} \end{tabbing} \end{alltt} \end{minipage} } \newpage \vspace{0.1in} \noindent\framebox[\textwidth][l]{\scriptsize \begin{minipage}{6in} \begin{alltt} \begin{tabbing} xx\=xx\=xx\=xx\=xx\=\kill protocols \{\\ \>mld \{\\ \>\>targetname: {\it text}\\ \>\>disable: {\it bool}\\ \>\>interface {\it text} \{\\ \>\>\>vif {\it text} \{\\ \>\>\>\>disable: {\it bool}\\ \>\>\>\>version: {\it uint(1..2)}\\ \>\>\>\>enable-ip-router-alert-option-check: {\it bool}\\ \>\>\>\>query-interval: {\it uint(1..1024)}\\ \>\>\>\>query-last-member-interval: {\it uint(1..1024)}\\ \>\>\>\>query-response-interval: {\it uint(1..1024)}\\ \>\>\>\>robust-count: {\it uint(2..10)}\\ \>\>\>\}\\ \>\>\}\\ \>\>traceoptions \{\\ \>\>\>flag all \{\\ \>\>\>\>disable: {\it bool}\\ \>\>\>\}\\ \>\>\}\\ \>\}\\ \} \end{tabbing} \end{alltt} \end{minipage} } \vspace{0.1in} \begin{description} \item{\tt protocols}: this delimits the configuration for all routing protocols in the XORP router configuration. It is mandatory that IGMP configuration is under the {\stt protocols} node in the configuration. \item{\tt igmp}: this delimits the IGMP configuration part of the XORP router configuration. \item{\tt targetname}: this is the name for this instance of IGMP. It defaults to ``{\stt IGMP}'', and it is not recommended that this default is overridden under normal usage scenarios. \item{\stt disable}: this takes the value {\stt true} or {\stt false}, and determines whether IGMP as a whole is enabled on this router~\footnote{Note that prior to XORP Release-1.1, the {\tt enable} flag was used instead of {\tt disable}.}. The default value is {\stt false}. \item{\stt interface}: this specifies an interface to be monitored by IGMP for the presence of multicast receivers. Each interface to be monitored by IGMP needs to be explicitly listed. The value is the name of an interface that has been configured in the {\stt interfaces} section of the router configuration (see Chapter \ref{interfaces}). For each interface, one or more VIFs must be specified: \begin{description} \item{\stt vif}: this specifies a vif to be monitored by IGMP for the presence of multicast receivers. Each vif to be monitored by IGMP needs to be explicitly listed. The value is the name of a vif that has been configured in the {\stt interfaces} section of the router configuration (see Chapter \ref{interfaces}). Each vif takes the following optional parameter: \begin{description} \item{\stt disable}: this takes the value {\stt true} or {\stt false}, and determines whether IGMP is disabled on this vif~\footnote{Note that prior to XORP Release-1.1, the {\tt enable} flag was used instead of {\tt disable}.}. The default value is {\stt false}. \item{\tt version}: this directive specifies the protocol version for this interface/vif~\footnote{Note that the {\tt version} statement appeared after XORP Release-1.1.}. In case of IGMP it takes a non-negative integer in the interval [1..3] with default value of {\stt 2}. In case of MLD the value must be in the interval [1..2] with default value of {\stt 1}. \item{\tt enable-ip-router-alert-option-check}: this directive specifies whether the router should check that the link-local protocol packets received on this interface/vif have the IP Router Alert option (see RFC-2213) in them~\footnote{Note that the {\tt enable-ip-router-alert-option-check} statement appeared after XORP Release-1.1.}. If it is enabled, all link-local protocol packets that do not contain the IP Router Alert option will be dropped. \item{\tt query-interval}: this directive specifies the interval (in seconds) between general queries sent by the querier on this interface/vif~\footnote{Note that the {\tt query-interval} statement appeared after XORP Release-1.1.}. The default value is {\stt 125} seconds. \item {\tt query-last-member-interval}: this directive specifies the maximum response time (in seconds) inserted into group-specific queries sent in response to leave group messages on this interface/vif. It is also the interval between group-specific query messages~\footnote{Note that the {\tt query-last-member-interval} statement appeared after XORP Release-1.1.}. The default value is {\stt 1} second. \item {\tt query-response-interval}: this directive specifies the maximum response time (in seconds) inserted into the periodic general queries on this interface/vif~\footnote{Note that the {\tt query-response-interval} statement appeared after XORP Release-1.1.}. It must be less than the {\tt query-interval}. The default value is {\stt 10} seconds. \item {\tt robust-count}: this directive specifies the robustness variable count that allows tuning for the expected packet loss on a subnet for this interface/vif~\footnote{Note that the {\tt robust-count} statement appeared after XORP Release-1.1.}. The {\tt robust-count} specifies the startup query count, and the last member query count. It is also used in the computation of the group membership interval and the other querier present interval. The IGMP/MLD protocol is robust to {\tt robust-count} packet losses. The default value is {\stt 2}. \end{description} \end{description} \item{\stt traceoptions}: this directive delimits the configuration of debugging and tracing options for IGMP. \begin{description} \item{\stt flag}: this directive is used to specify which tracing options are enabled. Possible parameters are: \begin{description} \item{\stt all}: this directive specifies that all tracing options should be enabled. Possible parameters are: \begin{description} \item{\stt disable}: this takes the value {\stt true} or {\stt false}, and disables or enables tracing~\footnote{Note that prior to XORP Release-1.1, the {\tt enable} flag was used instead of {\tt disable}.}. The default is {\stt false}. \end{description} \end{description} \end{description} \end{description} Note that in case of IGMP each enabled interface must have a valid IPv4 address. The configuration for MLD is identical to IGMP, except for the following: \begin{itemize} \item The {\stt mld} directive is used in place of the {\stt igmp} directive. \item The default value of {\stt targetname} is {\stt ``MLD''} instead of {\stt ``IGMP''}. \item Each enabled interface must have a valid link-local IPv6 address. \end{itemize} \vfill\eject \subsection{Example Configurations} \vspace{0.1in} \noindent\framebox[\textwidth][l]{\scriptsize \begin{minipage}{6in} \begin{alltt} \begin{tabbing} xx\=xx\=xx\=xx\=xx\=\kill protocols \{\\ \>igmp \{\\ \>\>interface dc0 \{\\ \>\>\>vif dc0 \{\\ \>\>\>\>/* version: 2 */\\ \>\>\>\>/* enable-ip-router-alert-option-check: false */\\ \>\>\>\>/* query-interval: 125 */\\ \>\>\>\>/* query-last-member-interval: 1 */\\ \>\>\>\>/* query-response-interval: 10 */\\ \>\>\>\>/* robust-count: 2 */\\ \>\>\}\\ \>\}\\ \}\\ \\ protocols \{\\ \>mld \{\\ \>\>disable: false\\ \>\>interface dc0 \{\\ \>\>\>vif dc0 \{\\ \>\>\>\>disable: false\\ \>\>\>\>/* version: 1 */\\ \>\>\>\>/* enable-ip-router-alert-option-check: false */\\ \>\>\>\>/* query-interval: 125 */\\ \>\>\>\>/* query-last-member-interval: 1 */\\ \>\>\>\>/* query-response-interval: 10 */\\ \>\>\>\>/* robust-count: 2 */\\ \>\>\>\}\\ \>\>\}\\ \>\>traceoptions \{\\ \>\>\>flag all \{\\ \>\>\>\>disable: false\\ \>\>\>\}\\ \>\>\}\\ \>\}\\ \} \end{tabbing} \end{alltt} \end{minipage} } \vspace{0.1in} In the example configuration above, IGMP is enabled on two vifs on two different interfaces ({\stt dc0/dc0} and {\stt dc1/dc1}). In addition, MLD is enabled on interface/vif {\stt dc0/dc0}, and all MLD tracing functionality is enabled for diagnostic purposes. \newpage \section{Monitoring IGMP} The {\stt show igmp group} command can be used to display information about IGMP group membership: \vspace{0.1in} \noindent\framebox[\textwidth][l]{\scriptsize \begin{minipage}{6in} \begin{alltt} \begin{tabbing} xxxxxxxxxxxxx\=xxxxxxxxxxxxxxxx\=xxxxxxxxxxxxxxxx\=xxxxxxxxxxxxx\=xxxx\=xx\=xx\=xx\=xxxx\=xxxx\=\kill user@hostname> \textbf{show igmp group}\\ Interface \>Group \>Source \>LastReported \>Timeout\>\>\>V \>State\\ dc0 \>224.0.0.2 \>0.0.0.0 \>10.4.0.1 \> \>161 \>\>3 \> \>E\\ dc0 \>224.0.0.13 \>0.0.0.0 \>10.4.0.1 \> \>159 \>\>3 \> \>E\\ dc0 \>224.0.0.22 \>0.0.0.0 \>10.4.0.1 \> \>159 \>\>3 \> \>E\\ dc0 \>224.0.1.15 \>0.0.0.0 \>10.4.0.3 \> \>160 \>\>2 \> \>E\\ dc0 \>224.0.1.20 \>0.0.0.0 \>10.4.0.2 \> \>\>0 \>3 \> \>I\\ dc0 \>224.0.1.20 \>1.2.3.4 \>10.4.0.2 \> \>\>0 \>3 \> \>F\\ dc2 \>224.0.0.2 \>0.0.0.0 \>10.3.0.2 \> \>155 \>\>3 \> \>E\\ dc2 \>224.0.0.13 \>0.0.0.0 \>10.3.0.1 \> \>157 \>\>3 \> \>E\\ dc2 \>224.0.0.22 \>0.0.0.0 \>10.3.0.1 \> \>156 \>\>3 \> \>E \end{tabbing} \end{alltt} \end{minipage} } \vspace{0.1in} In the above example, {\stt Source} refers to the multicast source address in the case of source-specific IGMP join entries, or it is set to {\stt 0.0.0.0} in case of any-source IGMP join entries. The {\stt LastReported} field contains the address of the most recent receiver that responded to an IGMP Join message. The {\stt Timeout} field shows the number of seconds until it is next time to query for host members (\ie to send an IGMP Query message for this particular entry). The {\stt V} field shows the IGMP protocol version. The {\stt State} field shows the state of the entry: \begin{itemize} \item {\bf I} = INCLUDE (for group entry) \item {\bf E} = EXCLUDE (for group entry) \item {\bf F} = Forward (for source entry) \item {\bf D} = Don't forward (for source entry) \end{itemize} \vspace{0.1in} The {\stt show igmp interface} command can be used to display information about IGMP interfaces: \vspace{0.1in} \noindent\framebox[\textwidth][l]{\scriptsize \begin{minipage}{6in} \begin{alltt} \begin{tabbing} xxxxxxxxxxxxx\=xxxxxxxxx\=xxxxxxxxxxxxxxxx\=xxx\=x\=xxxx\=xxxxxx\=xx\=xxxxx\=x\=\kill user@hostname> \textbf{show igmp interface}\\ Interface \>State \>Querier \>Timeout\>\>\>Version\>\>Groups\\ dc0 \>UP \>10.4.0.1 \>\>None \>\>\>3 \>\>5\\ dc2 \>UP \>10.3.0.1 \>\>\>136 \>\>3 \>\>3\\ register\_vif\>DISABLED\>0.0.0.0 \>\>None \>\>\>3 \>\>0 \end{tabbing} \end{alltt} \end{minipage} } \vspace{0.1in} The information indicates whether IGMP is enabled on the interface and the IP address of the IGMP querier. If this router is the querier, then the time until the next query message is shown. Finally the number of multicast groups with receivers on this subnet is shown. Note that in the above example it is normal for the interface named {\stt register\_vif} to be {\stt DISABLED}. This interface has special purpose and is used only by PIM-SM. \vspace{0.1in} The {\stt show igmp interface address} command can be used to display information about addresses of IGMP interfaces: \vspace{0.1in} \noindent\framebox[\textwidth][l]{\scriptsize \begin{minipage}{6in} \begin{alltt} \begin{tabbing} xxxxxxxxxxxxx\=xxxxxxxxxxxxxxxx\=xxxxxxxxxxxxx\=\kill user@hostname> \textbf{show igmp interface address}\\ Interface \>PrimaryAddr \>SecondaryAddr\\ dc0 \>10.4.0.1\\ dc2 \>10.3.0.2\\ register\_vif\>10.4.0.1 \end{tabbing} \end{alltt} \end{minipage} } \vspace{0.1in} As shown above, the {\stt PrimaryAddr} per interface is the address used to originate IGMP messages, and all other alias addresses on that interface are listed as {\stt SecondaryAddr}, with one address per line. The equivalent commands for MLD are: \begin{itemize} \item {\stt show mld group} \item {\stt show mld interface} \item {\stt show mld interface address} \end{itemize}