%% $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 servingthat receiver's subnet need to know that the receiver has joined sothat they can arrange for multicast traffic destined for that group toreach this subnet.  The Internet Group Management Protocol (IGMP) isa link-local protocol for IPv4 that communicates this informationbetween receivers and routers.  The same role for IPv6 is performed bythe Multicast Listener Discovery protocol (MLD).The basic IGMP mechanism works as follows.  When a multicast receiverjoins a multicast group it multicasts an IGMP Join message onto thesubnet on which it is joining.  The local routers receive this join,and cause multicast traffic destined for the group to reach thissubnet.  Periodically one of the local routers sends a IGMP Querymessage onto the subnet.  If there are multiple multicast routers onthe subnet, then one of them is elected as the sole querier for thatsubnet.  In response to an IGMP query, receivers respond by refreshingtheir IGMP Join.  If the join is not refreshed in response to queries,then the state is removed, and multicast traffic for this group ceasesto 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.  Thefunctionality of MLDv1 corresponds with that of IGMPv2, and thefunctionality 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 thatare 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\=\killprotocols \{\\\>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\=\killprotocols \{\\\>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 IPv4address.The configuration for MLD is identical to IGMP, except for thefollowing:\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\=\killprotocols \{\\\>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 ontwo vifs on two different interfaces ({\stt dc0/dc0} and {\sttdc1/dc1}).  In addition, MLD is enabled on interface/vif {\sttdc0/dc0}, and all MLD tracing functionality is enabled for diagnosticpurposes.\newpage\section{Monitoring IGMP}The {\stt show igmp group} command can be used to displayinformation 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\=\killuser@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 sourceaddress in the case of source-specific IGMP join entries, or it is setto {\stt 0.0.0.0} in case of any-source IGMP join entries.  The {\sttLastReported} field contains the address of the most recent receiverthat responded to an IGMP Join message.  The {\stt Timeout} fieldshows the number of seconds until it is next time to query for hostmembers (\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 displayinformation 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\=\killuser@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 theinterface and the IP address of the IGMP querier.  If this router isthe querier, then the time until the next query message is shown.Finally the number of multicast groups with receivers on this subnetis shown.Note that in the above example it is normal for the interface named{\stt register\_vif} to be {\stt DISABLED}. This interface has specialpurpose and is used only by PIM-SM.\vspace{0.1in}The {\stt show igmp interface address} command can be used to displayinformation about addresses of IGMP interfaces:\vspace{0.1in}\noindent\framebox[\textwidth][l]{\scriptsize\begin{minipage}{6in}\begin{alltt}\begin{tabbing}xxxxxxxxxxxxx\=xxxxxxxxxxxxxxxx\=xxxxxxxxxxxxx\=\killuser@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 addressused to originate IGMP messages, and all other alias addresses on thatinterface are listed as {\stt SecondaryAddr}, with one address perline.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}