Configuring IP Multicast Routing

The overview of multicast routing

The realization of multicast

Basic multicast routing configuration task list

Advanced multicast routing configuration task list

Start multicast routing

Enable multicast function on the interface

IGMP feature configuration task list

Configure the ttl threshold value

Cancel multicast quick forward

Configure PIM-DM task list

Configure static multicast routing

Configure IP multicast boundary

Configure IP flow control

Configure IP multicast Helper

Configure Stub multicast router

The supervision and maintenance of multicast router

Examples of multicast routing configuration

The overview of multicast routing

This chapter describes how to configure multicast routing protocol. For a detail description of multicast routing commands in this chapter, please refer to other chapters concerning “multicast routing command”.

Traditional IP transmission only permits one host to one host (unicast communication) or to all hosts (broadcast communication), multicast technique provides the third choice: permits one host to send messages to some hosts. These hosts are called the group members.

The target address of a message sent to the group member is a Class D address (224.0.0.0~239.255.255.255). The transmission of multicast message is similar to UDP, which is only a kind of service withbest-effort” reliability, yet does not provide reliable delivery and error control similar to TCP.

The application of multicast requires the sender and receiver. The sender can send multicast messages without joining a certain group, but the receiver must join a certain group to receive the messages from this group.

The relationship between the group members is dynamic, the host can join or leave a certain group at any moment, yet the position and the number of group members does not have any limitation. If required, a host can be members of many groups. So, the state of the group and the number of group members can change with time.

The router maintains the mroute routing table which forwards multicast messages by running multicast routing protocol (such as PIM-DM, PIM-SM, etc.), and gets to know the state of group members on the connected address by IGMP protocol. The host can join a certain IGMP group by sending IGMP Report information.

The above features of IP multicast technique is highly suitable for the “point to multi-point”multimedia application.

The realization of multicast

 The multicast routing includes the following protocols in Boda’s router software.

?          IGMP is functioning between the router and host in the LAN and tracking the relations between the group members.

?          OLNK is a kind of static mroute technique used in simple topology, it cannot only forward multicast, but also effectively reduce the waste of CPU and bandwidth for multicast routing protocol.

?          PIM-DM/PIM-SM/DVMRP is a dynamic multicast routing protocol running between the routers and makes multicast forward by establishing multicast routing table.

The following chart illustrates the multicast protocol applied in the IP multicast environment:

 

IGMP

IGMP is a kind of protocol aiming at the management of multicast group members; IGMP is the abbreviation of Internet Group Management Protocol. IGMP is an asymmetrical protocol, it includes content of two aspects (the host and the router): the host protocol defines how the host, as the member of multicast group member, reports its ID as part of different multicast group, and how the host corresponds to the Query messages from the router; the router protocol defines how the router, which supports IGMP, acquires the membership of multicast group of the host in LAN, how to change the members’ information of the multicast group saved by the router according to the report messages form the host.

The realization of IGMP router protocol in our router can provide the members’ existence situation in the current network to the multicast routing protocol of the router, so as to decide whether to forward multicast messages. As a conclusion, in order to let our router support the multicast procedure of IP messages, the realization of multicast protocol and IGMP router protocol is a must. Currently, our router has realized IGMP router protocol, it supports the newest version—IGMP V.3.

In practice, there is no separate start command for IGMP, the IGMP-Router function is started by the Multicast Routing Protocol.

OLNK

Strictly speaking, OLNKIGMP only-linkis not a multicast routing protocol, because it does not have an interaction of protocol. But, OLNK will have great effect under certain situations and simple topology environment. It is similar to the PIM-DM protocol without process of negotiation, can process the change of local IGMP group member, timely adjust RPF interface according to the topological change, namely, guarantee the forward of multicast and avoid the control messages of multicast routing protocol’s waste of bandwidth.

PIM-DM

PIM-DMProtocol Independent Multicast Dense Modeis a kind of dense mode multicast routing protocol, defaultly, when the multicast source begins to send multicast data, all the nodes in areas of the network need to receive these data. So, PIM-DM forward the multicast packets by the means of flooding and pruning. When multicast source begins to send data, routers along the way forward multicast data packets to all the PIM activation interfaces except the RPF interface toward the source. So, all the nodes in the PIM-DM net area will receive these multicast data packets. In order to enable multicast forward, routers along the way need to establish corresponding multicast routing entry (S.G) for group G and source S. (S.G) routing entry includes multicast source address, multicast group address, incoming interface, outgoing interface list, timers and tags, etc.

If one area in the network does not have any multicast group member, the mechanism of PIM-DM protocol will require to send prune packet, transform to pruned state upon upon the forward interface to this area,and set up a pruned state. The pruned state has a prune time-out timer. When the prune timer times out, pruned state changes into forwarding state, enables the multicast data flowing along these branches again. In addition, the prund state includes the information of the multicast source and multicast group. When multicast group member joined in the pruned field, the protocol need not wait for the time out for the upstream pruned state, but actively send graft packets to the upstream, so as to change prundstate to forwarding state.

If only source S still send messages to G group, the first hop router will periodically send (S.G) state refresh information to the intial downstream broadcast tree to refresh. The state refresh mechanism of PIM-DM can refresh the downstream’s state, so the pruning of the broadcast tress branch will not time out.

In the multi-access network, PIM-DM introduces the following mechanisms besides the election for DR: using assert mechanism to elect the only forwarder to prevent overlaped forwarding of multicast packet to the same address; using join/pune refrain mechanism to reduce the redundance of  join/prune information; Using pruned rejection mechanism to override unnecessary pruned activities.

In PIM-DM area, the router running PIM-DM protocol periodically sends Hello message, in order to find adjacent PIM router, adjudge leaf network, leaf router, and to be in charge of the electing on the designated router (DR) in the multi-access network.

In order to be used on IGMP v1, PIM-DM takes charge of the DR election. When all the PIM neighbors on the port support DR priority option, we selects the one with the highest DR priority as DR. For the ones with the same priority, select the router with highest IP address on the interface as DR; If any router does not announce its priority in the hello message or several routers have the same situation, select the router with highest IP address value on the interface as DR.

Boda router’s PIM-DM v2 supports neighbour filtering list, classless interdomain Router CIDR)、Variable length son-network maskVLSMand IGMP v1v2v3

Basic multicast routing configuration task list

Basic multicast configuration includes:  

Start multicast routing  (Optional)

Enable multicast function on the interface (Optional)

Enable OLNK

Enable PIM-DM

IGMP feature configuration task list  (Optional)

Configure the ttl threshold value  (Optional)

Cancel multicast quick forward  (Optional)

Advanced multicast routing configuration task list

Advanced multicast configuration includes:

Configure PIM-DM task list (Optional)

Configure static multicast routing (Optional)  

Configure IP multicast boundary (Optional)  

Configure IP multicast flow control (Optional)

Configure IP multicast Helper  (Optional)

Configure Stub multicast router (Optional)

The supervision and maintenance of multicast router (Optional)

Clear multicast cache, routing list

Show multicast routing table and system statistical information

Start multicast routing

Start multicast routing in order to allow Boda router software to forward multicast messages. Input the following command to enable multicast message forward under global configuration mode:

Command

Function

Router_config#ip multicast-routing

Enable multicast routing

Enable multicast function on the interface

Running multicast routing protocol on the interface will simultaneously activate the operation of IGMP on the interface. Multicast routing protocol includes OLNK, PIM-DM, PIM-SM or DVMRP. Maximum of one multicast routing protocol is allowed to run on the same interface. When Boda router connects several multicast fields, it can run different multicast protocol on different interfaces.

Although Boda router software can perfectly function as multicast boundary router (MBR), if possible, please guarantee that: do not simultaneously run several multicast routing protocols on the router, because this will produce unnecessary effect to some multicast routing protocols. For example, when PIM-DM (only supports (S,G) entry) abd BIDIR PIM-SM (only supports (*,G) item) runs, chaos emerges.

Enable OLNK

Run OLNK on the interface to enable multicast function. Input the following commands under interface configuration mode:

Command

Function

Router_config_f0/0#ip olnk

Start multicast routing

Enable PIM-DM

Run PIM-DM on the interface to activate dense mode multicast function, follow the steps below:

Command

Function

ip pim-dm

Enter the interface which needs to run PIM-DM, activate PIM-DM multicast routing process under interface configuration state

IGMP feature configuration task list

IGMP-Router feature configuration command mainly adjusts IGMP parameter, the following is the brief introduction of IGMP-Router basic configuration command. For full information about IGMP-Router realization, please refer to the command explanation document of IGMP.

Change the version of IGMP currently running

Configure IGMP query interval

Configure IGMP Querier interval

Configure the maximum response time of IGMP

Configure query interval of the last group member of IGMP

IGMP static configuration

Configure IGMP Immediate-level list

Change the version of IGMP currently running

After the introduction of IGMP, there are already 3 formal versions, the corresponding rfc is respectively: rfc1112, rfc2236 and rfc3376. Among these versions, IGMP v1 only realizes simplest multicast member recording function; v2 realizes the search function aims at certain multicast member and leave message of IGMP host to leave certain multicast group, reduces the latency time of group member change; v3 realizes the update and maintanence of multicast group member identity corresponding host source address, in addition, IGMP Router of v3 is fully compatible with IGMP host of v1 and v2, our router software system provides the full support to these 3 versions of IGMP Router protocol.

As IGMP is configured according to the interface of the router, i.e, IGMP-Router function can be configured on different interfaces respectively (respectively started with multicast routing protocol configured on different interfaces), and different versions of IGMP can be run on different interfaces.

The thing to be notified is that, for a certain multicast router, IGMP-router function can only be turned on on one interface of the various interfaces connect to the same network.

To change the version of IGMP-Router protocol run on one certain interface, use the following commands under interface configuration state:

Step

Command

Function

1

ip igmp version version_number

Change IGMP version running on current interface

The example of the change of IGMP version

Because the new version of IGMP-Router protocol can be fully compatible with the old version IGMP host, so when old version of IGMP host exists in the network, there is no need to change the IGMP-Router protocol version run by multicast router, but new version of IGMP-Router protocol is not compatible with the old version, so when old version of IGMP-Router protocol router runs in the network, the user need to change the the IGMP-Router protocol version on the related interface of IGMP router with newer version, the principle of change is: change the IGMP-Router protocol version to the oldest version on the same address.

Suppose the system administrator knows that there exists the router running IGMP-Router v1 and IGMP-Router v2 in the network connected with certain interface of the router, he/she should change the version number of IGMP-Router protocol of the corresponding interface of the router running newer version of IGMP-Router protocol to 1. The following example demonstrates the process of system administrator to change the IGMP version running on certain interface (in the folloing example, it is Ethernet 1/0 interface) to version 1:

interface ethernet 1/0

ip igmp version 1

Configure IGMP query interval

Whatever the currently running version of IGMP-Router protocol is, multicast router will send a IGMP General Query message every certain time through the interface with IGMP-Router interface function turned on, the address of sending is 224.0.0.1, with the aim to acquire the report message corresponds to IGMP host, thus acquires the information of IGMP host’s (the host on the current interface connected network) individual ascription to the certain multicast group. The interval of General Query message sending is called IGMP Query Interval, if too long the interval is set, the router cannot quickly acquire the ascription information of current IGMP host, but if the interval is set too short, it will increase the traffic of IGMP message of current network.

To change IGMP query interval on one certain interface, use the following commands under interface configuration state:

Step

Command

Function

1

ip igmp query-interval time

change the IGMP query interval of current interface, counted with the unit of second

The example of the configuration of IGMP query interval

The following example demonstrates the process of system administrator to change the IGMP query interval on certain interface (in the folloing example, it is Ethernet 1/0 interface) to 50 seconds:

interface ethernet 1/0

ip igmp query-interval 50

Configure IGMP Querier interval

Regarding IGMP-Router protocol version 2 and 3, if multiple routers running IGMP-Router protocol exists in the same network, the problem of querier selection emerges, the so called “querier”, indicates the router which is able to send query message (in fact an interface of router turned on IGMP-Router protocol), under normal operation, only one querier exists in the same network, which indicates that only one router sends IGMP Query message. For IGMP-Router protocol v1, there is no problem of querier selection, because in IGMP-Router v1, which router to send IGMP Query message is appointed by multicast routing protocol.

For IGMP-Router protocol v2 and v3, the same querier selection mechanism applies: the router with smallest IP address is set to be the querier of this network, for non-querier, a clock should be saved to record the time of querier existence, when this clock expires, non-querier changes into querier and start to transmit IGMP Query messages, this router once again changes into non-querier until it receives IGMP Query messages from a router with smaller IP address.

For IGMP-Router protocol version 2, the interval of other queriers can be configured through the following command:

Step

Command

Function

1

ip igmp querier-timeout time

Configure the interval of other querier, unit is set to second

For IGMP-Router protocol v1, the interval value of other queriers’ existence does not have actual effect; for IGMP-Router protocol v3, the interval is defined within the protocol and cannot be configured, so the above configuration commands only apply to IGMP-Router protocol v2.

The example of the configuration of IGMP Querier interval

The following example demonstrates the process of system administrator to change the IGMP querier interval on certain interface (in the folloing example, it is Ethernet 1/0 interface) to 100 seconds:

interface ethernet 1/0

ip igmp querier-timeout 100

Configure the maximum response time of IGMP

Regarding IGMP-Router protocol v2 and v3, when sending IGMP General Query messages, there is special data field in IGMP messages to notify the maximum response time of IGMP host, namely IGMP host must send the response messages to IGMP general query message within the maximum response time interval after receiving this General Query. If the maximum response time is set too long, the result will be delay of the change of IGMP host multicast group member identity, if it is set too short, the result will be an excess traffic of IGMP messages on the network.

Notice: the maximum response time of IGMP should be smaller than IGMP query interval, when using this command, if the maximum response time is longer than query interval, the system will automatically change the maximum response time to (query-interval - 1) second.

For IGMP-Router protocol v2 and v3, the maximum response time can be configured through the following command under interface configuration state:

Step

Command

Function

1

ip igmp query-max-response-time time

Configure maximum response time of IGMP, the unit is set as second

For IGMP-Router protocol v1, the maximum response interval value is defined within the protocol and can not be configured, so the above configuration command is not effective for IGMP-Router protocol v1 only.

The example of the configuration of IGMP maximum response time

The following example demonstrates the process of system administrator to change the maximum response time of IGMP on certain interface (in the following example, it is Ethernet 1/0

interface ethernet 1/0

ip igmp query-max-response-time 15

Configure query interval of the last group member of IGMP

For IGMP-Router protocol v2 and v3, when sending Group Specific Query messages aiming at certain multicast group, it will use last member query interval as the maximum response time of the host in the IGMP Query messages, which is, IGMP host should send the response message of group specific Query message within the last group member query interval after receiving this query message. If IGMP host finds out that there is no need to respond to this query message through query of its state, and after the interval, there is still no sending of response messages, then multicast router will make corresponding updating to the saved multicast group member information. If this interval is too long, the result is the delay of the change of IGMP host multicast group member identity, if the interval is too short, the traffic of IGMP messages on the network will be too heavy.

For IGMP-Router protocol v2 and v3, the user can configure the last member query interval time of IGMP through the following command under the interface configuration state:

Step

Command

Function

1

ip igmp last-member-query-interval time

Configure the last member query interval of IGMP, the unit is set as millisecond

For IGMP-Router protocol v1, the last group member’s query interval configured is not used, although when running IGMP v1 on the interface this command can be configured, but with no actual effect.

The example of the configuration of the last group member query interval

The following example demonstrates the process of system administrator’s change of IGMP’s last member group member query interval on certain interface (in the following example, it is Ethernet 1/0 interface) to 2000 milliseconds:

interface ethernet 1/0

ip igmp last-member-query-interval 2000

 

IGMP static configuration

During the realization of IGMP-Router protocol by our router, the router supports the static multicast group configuration on the interface besides the stated functions of the protocol. The so-called “static” is differentiated from the “dynamic” information of the IGMP host report, for IGMP host, its multicast member relation may be variable, suppose it only belongs to multicast group1 currently, and hopes to receive the multicast message to multicast group1; but after a period of time, it may also belong to multicast group2, and hopes to receive the multicast message to multicast group2; then after a period of time, this IGMP host may not belong to any multicast group, so the information of belonging to multicast group reported by the host is changed dynamically.

Different from the above mentioned “dynamic multicast group”, if a certain interface is statically configured to be part of a certain multicast group, then, except using “no” command to cancel this configuration, the multicast protocol will consider that this interface always need to receive the multicast messages to this multicast group. Additionally, in order to provide a better compatibility with IGMP-Router protocol v3, statically configured multicast group can specify the source addresses of multicast messages it wishes to receive, namely, increase the source-filter function of multicast message receiving.

The user can configure the static multicast group attributes of the interface under interface configuration state through the following command:

Step

Command

Function

1

ip igmp static-group { * | group-address} {include source-address | <cr> }

Configure the static multicast group on the interface

Examples of IGMP static configuration

Static multicast configuration command can define static multicast groups of various kinds with different parameters; the following example will introduce the result after using different command parameters respectively:

interface ethernet 1/0

ip igmp static-group *

The above mentioned configuration command has statically configured all the multicast groups on the Ethernet 1/0 interface, which means this interface belongs to all the multicast groups, multicast routing protocol will forward all the IP multicast messages to this interface.

interface ethernet 1/0

ip igmp static-group 224.1.1.7

The above mentioned configuration command has statically configured multicast group 224.1.1.7 on the Ethernet 1/0 interface, which means this interface belongs to multicast group 224.1.1.7, multicast routing protocol will forward all the IP multicast messages of this interface to multicast group 224.1.1.7.

interface ethernet1/0

ip igmp static-group 224.1.1.7 include 192.168.20.168

The above mentioned configuration command has statically configured multicast group 224.1.1.7 on the Ethernet 1/0 interface, but also defines the source-filter 192.168.20.168 of this multicast, which means this interface belongs to multicast group 224.1.1.7, but can only receive IP multicast messages from 192.168.20.168, multicast routing protocol will only forward the IP multicast messages of 192.168.20.168 to multicast group 224.1.1.7.

For the above example, if the router hopes to receive IP multicast messages from 192.168.20.169 to 224.1.1.7, then another command should be configured under interface configuration state:

ip igmp static-group 224.1.1.7 include 192.168.20.169

If other source-filter information of this multicast group needs to be added, the user can execute the above-mentioned command several times, and defines different source-address.

Notice: When using the above mentioned configuration command, the user can not both configure the multicast information of a certain source address and the multicast group information of all source addresses to the same multicast group; similarly, the user can not both configure the multicast information of all source addresses and the multicast group information of a certain source address to the same multicast group. The command configured after will be neglected. For example, if command “ip igmp static-group 224.1.1.7” is already configured, and then command “ip igmp static-group 224.1.1.7 include 192.168.20.168” is added, the later command will be neglected.

Configure IGMP Immediate-level list

If IGMP v2 is started on one interface of the router, and only one IGMP host exists on the network connected with this interface, the user can realize the “Immediate leave” function through the configuration of IGMP Immediate-leave list. According to the regulation of IGMP v2, when a certain host needs to leave the specific multicast group, this host will send “leave” message to all the multicast routers, and the multicast router will send “group specific” message to confirm. whether there is any host on the interface to receive the multicast message to this multicast group. But if “Immediate Leave” function is configured, the user can both avoid the message interaction between IGMP host and multicast router, and the delay of the change of multicast group member identity maintained by the multicast router.

Notice: because the user can both configure this command both under global configuration state and interface configuration state, but the priority of this command under global configuration state will be higher than the command under interface configuration state, so if the command is first configured under global configuration state, the command then configured under interface configuration state will be neglected; but if the command is first configured under interface configuration state, then the command configured under global configuration state will delete the original command configured under interface configuration state.

For IGMP-router protocol v2, the user can configure IGMP Immediate-leave list through the following commands under interface configuration state:

Step

Command

Function

1

ip igmp immediate-leave group-list list-name

Configure the IGMP host accessing list which can realize “Immediate leave multicast group” function

2

ip access-list standard list-name

Establish the IP standard accessing list named “list-name”

3

permit source-address

Configure the IP address of IGMP host we wish to realize “Immediate leave” function under the configuration mode of IP standard accessing list.

Because there are great differences in operating process of “leave” message by IGMPRouter protocol v1, v3 and v2, so the above mentioned configuration commands only not applies to IGMP-Router protocol v1 and v3.

The example of the configuration of IGMP Immediate-leave list

The following example demonstrates that the system administrator configures the accessing list name with the function to realize “Immediate leave” to be imme-leave on a certain interface ( Ethernet 1/0 interface in the following example) , and the complete process of adding a IGMP host address (192.168.20.168 in the following example) to this accessing list. Through these configuration processes, the user can guarantee the IGMP host with the IP address of 192.168.20.168 to realize “immediate leave” multicast group function.

interface ethernet 1/0

ip igmp immediate-leave imme-leave

exit

ip access-list standard imme-leave

permit 192.168.20.168

Configure the ttl threshold value

Using “ip multicast ttl-threshold” to configure the threshold value of multicast message TTL permitted to forward on the interface, using “no ip multicast ttl-threshold” to use default value. The default value is 1.

Step

Command

Function

1

ip multicast ttl-threshold ttl-value

Configure the ttl threshold value of interface

 

The demonstration of the configuration of TTL threshold value

The following example demonstrates that the system administrator configures the TTL threshold value on a certain interface

interface ethernet 1/0

ip multicast ttl-threshold 200

 

Cancel multicast quick forward

Use “ip multicast mroute-cache” configuration to enable the interface to use multicast’s quick forward function, use “no ip multicast mroute-cache” to diable that function

Step

Command

Function

1

ip multicast mroute-cache

Enable multicast’s quick forward function on the interface

 

The example of the cancellation of multicast’s quick forward function

The following example demonstrates that the system administrator configures to cancel the quick forward function on a certain interface

interface ethernet 1/0

no ip mroute-cache

Configure PIM-DM task list

Adjust the timer  

Specified version number

Refresh the configuration state

Configure filter list

Set DR priority

Clear (S.G) information

Adjust the timer

The routing protocol uses several timers to decide the frequency of sending “hello” message and state refresh control packet. The interval of “Hello”message sending has an influence on the correctness of neighbourship.

In order to adjust the timer, use the following commands under router interface configuration mode:

Command

Function

ip pim-dm hello-interval

Specify how much time interval(unit: second) does it take to send “hello” message from the interface to the neighbour

ip pim-dm state-refresh origination-interval

For the first hop router connected to the source, it is the interval of periodical sending of state refresh message, only applies to the configuration by upstream interface; for the later router, it is the time interval of the interface permits to receive and process state refresh message

Specified version number

D-Link router’s PIMDM only supports PIM v2.

As PIM v1 is stale, so whether we configure version or not, we support PIM v2 by default. The Function of this command is only for the compatibility of the style with the previous version:

Command

Function

ip pim-dm version [version]

Configure PIM-DM version on the interface of the router

Refresh the configuration state

Under configure mode, the router permits to run forward PIM dense mode state refresh control information. The configuration command under interface configuration state, for the first hop router connects to the source, is the interval of periodical sending for state refresh message, here only applies to the configuration of upstream interface; for later router, it is the time interval of the interface’s permittance between the receiving and processing of the state refresh messages.

Step

Command

Function

1

no ip pim-dm state-refresh disable

Allow to receive and send state refresh messages on the interface

2

ip pim-dm state-refresh origination-interval

The interval between the sending and receiving of state refresh message on the interface

 

Configure filter list

PIM-DM does not set the filter list by default condition, includes the neighbour filter list and multicast boundary filter list, are all configured under interface configuration mode.

If the user wants to prevent certain router or router with certain address from joining into PIM-DM negotiation, he/she should configure neighbor filter list. If the user wants to prevent or allow certain groups to join into current region, he/she need to configure boundary group filter list.

Command

Function

ip pim-dm neighor-filter

Configure neighbour filter list

ip multicast boundary

Configure group filter list

 

Set DR priority

Perform the selection of DR, so as to be adaptable to IGMP v1. By default, the priority of router DR is 1. When all the neighbours on the interface support DR Priority, select the one with highest priority as DR. If the priorities are the same, select the router with highest interface IP address value as DR; if there is any router that does not report its priority or several routers also have the same problem, select the router with highest interface IP value as DR.

Prerform the configuration of this command under interface configuration state

Command

Function

ip pim-dm dr-priority

Set the DR priority of local router on the specified interface

 

Clear (S.G) information

Under normal condition, the user may need to clear the (S.G) item in local MRT or the totaled number of multicast messages forwarded through (S.G) entry. Use the following commands under configure mode:

Command

Function

clear ip mroute pim-dm {* | group [source]}

Clear the (S.G) entry in the local MRT, this operation will delete all or part of the items in local multicast routing list, and may influence normal forward of multicast messages, this command can only delete (S.G) entry which upstream interface is created by PIM-DM multicast routing protocol

clear ip pim-dm interface

Reset the statistic of multicast message forwarded through (S.G) from PIM-DM interface, this command can only reset (S.G) entry which upstream interface  is created by PIM-DM multicast routing protocol

Configure static multicast routing

Multicast forward path is allowed to be different from unicast routing by static multicast routing. RPF check is always taken while forwarding multicast messages: the real interface receiving the messages is the expected one to receive the messages (the critical interface is the unicast next hop interface toward the transmitter). If the topology of unicast is the same as that of multicast, this check is reasonable. But, under certain circumstances, the path of multicast and unicast is still expected to be different.

The most familiar example is the using of tunnel technology. When the router on one path does not support multicast protocol, the solution is to configure GRE tunnel between the two routers. In the following chart, any of the unicast routers (UR) only supports unicast message; any of the multicast routers only supports multicast message. The source sends the multicast message to the destination through MR1 and MR2. For MR2, only until multicast message are received from the tunnel does it forward the message. If so, when sending unicast messages from destination to the source, it is also passing the tunnel. We know, sending a message through the tunnel is slower than sending directly.

Through the configuration of multicast static routing, the router is enabled to carry out RPF check with the configuration information, not the unicast routing table. So, multicast messages use tunnel, unicast messages do not. Multicast static routing only exsits locally, it will not announce or process routing forward.

Using the following commands to configure multicast static routing in global configuration mode:

Command

Function

Router_config#ip mroute source-address mask rpf-address type number[ distance]

Configure multicast static routing

 

Configure IP multicast boundary

Using “ip multicast boundary” to configure interface multicast boundary, using “no ip multicast boundary to cancel the defined boundary. The second configured command will override the first configured one.

Step

Command

Function

1

ip multicast boundary access-list

Configure IP multicast boundary on the interface

 

Configure IP multicast flow control

Use ip  multicast  rate-limit  Command to limit the packet receiving and sending flow on a source/group. Use no  ip multicast  rate-limit Command to cancel flow control.

    To configure input flow control as n kbps

Step

Command

Function

     1 ip  multicast rate-limit in group-list  access-list1 source-list  access-list2 nkbps   To configure the max input flow control on a port

 

    To configure input flow control as n kbps

Step

Command

Function

     1 ip  multicast rate-limit out group-list  access-list1 source-list  access-list2  kbps  Configure the max output flow control on a port

 

Configure IP multicast Helper

Using “ip multicast helper-map to configure so as to enable the using of multicast routing on the multicast network to connect two broadcasting networks. Using “no ip multicast helper-map” to cancel that command.

The first hop router connects to the original broadcasting network

Step

Command

Function

1

router_config#interface type number

Enter into interface configuration mode

2

route_config_if#ip multicast helper-map broadcast group-address access-list

Configure “ip multicast helper” command, convert the broadcast messages to multicast ones

3

route_config_if#ip directed-broadcast

Allow directed broadcast

4

router_config_if#ip forward-protocol [port]

Configure the message port number allowed to be forwarded

 The last router connects to the target broadcasting network

Step

Command

Function

1

router_config#interface type number

Enter into interface configuration mode

2

router_config_if#ip directed-broadcast

Allow directed broadcast

3

router_config_if#ip multicast helper-map group-address broadcast-address access-list

Configure “ip multicast helper”command, change the multicast messages to broadcast messages

4

router_config_if#ip forward-protocol [port]

Configure the message port number to forward

 

Configure Stub multicast router

Using “ip igmp helper-address” and “ip pim-dm neignbor-filter” to configure Stub multicast router .

Configure on the intrerface where stub router and host are connected

Step

Command

Function

1

router_config#interface type number

Enter into the interface configuration mode

2

route_config_if#ip igmp helper-address destination-address

Configure “ip igmp helper-address command, convert the multicast messages to the central router

   The interface where central router and stub router are connected

Step

Command

Function

1

router_config#interface type number

Enter into the interface configuration mode

2

router_config_if#ip pim neighbor-filter access-list

Filter all the pim messages sent to the stub router

The supervision and maintenance of multicast router

Clear multicast cache, routing list

If certain cache or routing table are suspected to be invalid, its content can be cleared.  Input the following commands under management status:  

Command  Function

Router#clear ip igmp group [type number] [group-address | <cr>]

Clear the list items in the IGMP cache

Router#clear ip mroute [* | group-address | source-address]

Clear entries in multicast routing table

Show multicast routing table and system statistical information

The user can estimate the resource usage information and solve the network problem through the showing of IP multicast routing table, related cache or database.

Using the following commands to observe the statistical information of multicast routing in management mode:

Command

Function

Router#show ip igmp groups [type number | group-address] [detail]

Show the multicast group information in IGMP cache

Router#show ip igmp interface [type number]

Show IGMP configuration information in the interface

Router#show ip mroute mfc

Show multicast forward cache

Router#show ip rpf [ucast | mstatic | pim-dm | pim-sm | dvmrp] source-address

Show RPF information

 

Examples of multicast routing configuration

The example of PIM-DM configuration

The example of PIM-DM state refresh configuration

The example of management boundary configuration

The example of multicast helper configuration

Examples of Stub multicast configuration

 

The example of PIM-DM configuration

This section includes the example of PIM-DM configuration:

The basic configuration of pim-dm

A 17 series router, a cisco 2620 configured as the following:

The 17 series router is configured as follows:

!

ip multicast-routing

!

interface Null0

!

interface Loopback1

 ip address 1.1.1.1 255.255.255.0

 no ip directed-broadcast

 ip pim-dm

 ip igmp static-group *

!

interface Ethernet1/1

 ip address 192.167.20.132 255.255.255.0

 no ip directed-broadcast

 duplex half

 ip pim-dm

 ip igmp static-group 239.1.1.1

!

!

interface Ethernet2/1

 ip address 192.168.20.132 255.255.255.0

 no ip directed-broadcast

 duplex half

 ip pim-dm

ip pim-dm neighbor-filter nbr_filter

!

!

ip access-list standard nbr_filter

 deny   192.167.20.132 255.255.255.255

 permit 192.168.20.0 255.255.255.0

!

routerB

interface ethernet 1/1

  ip address 192.168.20.82 255.255.255.0

interface loopback 0

  ip address 20.1.1.1 255.0.0.0

!

router PIM-DM

  network 192.168.20.0

  network 20.0.0.0

!

 

Configuration of cisco 2620 can be like that:

!

ip multicast-routing

!

interface Loopback1

 ip address 10.10.20.1 255.255.255.0

 ip igmp static-group 239.1.1.1

 ip pim dense-mode

!

interface FastEthernet0/0

ip address 192.168.20.204 255.255.255.0

 ip pim dr-priority 20

 ip pim query-interval 40

 ip pim dense-mode

!

interface FastEthernet0/1

ip address 192.168.20.204 255.255.255.0

 ip pim dr-priority 20

 ip pim query-interval 40

 ip pim dense-mode

!

The example of PIM-DM state refresh configuration

Please refer to "Refresh the configuration state "

The example of management boundary configuration

The following example demonstrates the system administrator’s configuration of management boundary of certain interface

interface ethernet 1/0

ip multicast boundary acl

 

ip access-list standard acl

  permit 192.168.20.97 255.255.255.0

 

The example of multicast helper configuration

The following example demonstrates the system administrator’s configuration of multicast helper command

The configuration of the router is demonstrated in the following chart, configure “ip directed-broadcast” on e0 interface of first hop router to allow the processing of directed broadcast messages, configure “ip multicast helper-map broadcast 230.0.0.1 testacl1” , allow to change the UDP broadcast message sent from source address of 192.168.20.97/24 on port number 4000 into sending the multicast message with the target address of 230.0.0.1.

Configure “ip directed-broadcast” to allow the processing of directed broadcast message on the e1 interface of the last router. Configure “ip multicast helper-map 230.0.0.1 172.10.255.255 testacl2”, allow to change the multicast message with the target address of 230.0.0.1 sent from source address 192.168.20.97/24, port number 4000 to broadcast message with target address of 172.10.255.255.

On the first hop router connects to the original broadcast network

interface ethernet 0

ip directed-broadcast

ip multicast helper-map broadcast 230.0.0.1 testacl

ip pim­-dm

!

ip access-list extended testacl  permit udp 192.168.20.97 255.255.255.0 any

ip forward-protocol udp 4000

  

  

On the last hop router connects to the target broadcast network

interface ethernet 1

ip directed-broadcast

ip multicast helper-map 230.0.0.1 172.10.255.255 testacl2

ip pim-dm

!

ip access-list extended testacl2  permit udp 192.168.20.97 255.255.255.0 any

ip forward-protocol udp 4000

Examples of Stub multicast configuration

The configuration of router A and B is demonstrated as the following chart

 

Stub Router A Configuration

ip multicast-routing

ip pim-dm

ip igmp helper-address 10.0.0.2

 

Central Router B Configuration

ip multicast-routing

ip pim-dm

ip pim-dm neighbor-filter stubfilter

 

ip access-list stubfilter

deny 10.0.0.1