Multicast ip software

You might also want to disable fast switching, which places the router in process switching, if packets are not reaching their destinations. If fast switching is disabled and packets are reaching their destinations, then switching may be the cause. The following are properties of fast switching:.

The following is sample output from the mrinfo command:. The following is sample output from the mstat command in user EXEC mode:. The following is sample output from the mtrace command in user EXEC mode:.

The following is sample output from the show ip mroute command for a router operating in sparse mode:. The following is sample output from the show ip pim interface command when an interface is specified:. The following is sample output from the show ip mpacket command with the group-name argument:. The following is sample output from the show ip pim rp command:. The following is sample output from the show ip pim rp command when the mapping keyword is specified:. The following is sample output from the show ip pim rp command when the metric keyword is specified:.

The following is sample output from the show ip rpf command:. The following is sample output from the show ip rpf command when the metric keyword is specified:.

The following example shows how to monitor IP multicast packets forwarded through this router to group address The following example enables a router to listen to session directory announcements and changes the SAP cache timeout to 30 minutes. The following is sample output from the show ip sap command for a session using multicast group The following is sample output from the show ip mpacket command for the group named "smallgroup. The following sections provide references related to monitoring and maintaining IP multicast.

IP multicast commands: complete command syntax, command mode, defaults, usage guidelines, and examples. Technical Assistance Center TAC home page, containing 30, pages of searchable technical content, including links to products, technologies, solutions, technical tips, and tools. Registered Cisco. IP Multicast Heartbeat The IP Multicast Heartbeat feature enables you to monitor the delivery of IP multicast packets and to be alerted if the delivery fails to meet certain parameters.

Session Announcement Protocol SAP Session Announcement Protocol SAP listener support is needed to use session description and announcement protocols and applications to assist the advertisement of multicast multimedia conferences and other multicast sessions and to communicate the relevant session setup information to prospective participants.

Deploy operating systems over the network by using multicast in the following OS deployment scenarios:. Refresh an existing computer with a new version of Windows. Install a new version of Windows on a new computer bare metal. Complete the steps in one of these OS deployment scenarios. Then use the following sections to support multicast. To use multicast, configure at least one distribution point to support multicast. For more information, see Install and configure distribution points.

Bidirectional PIM routing devices must have the ability to accept traffic on many potential incoming interfaces.

Bidirectional PIM is recommended in deployments with many dispersed sources and many dispersed receivers. PIM dense mode —In this mode of PIM, the assumption is that almost all possible subnets have at least one receiver wanting to receive the multicast traffic from a source, so the network is flooded with traffic on all possible branches, then pruned back when branches do not express an interest in receiving the packets, explicitly by message or implicitly time-out silence.

This is the dense mode of multicast operation. LANs are appropriate networks for dense-mode operation. Some multicast routing protocols, especially older ones, support only dense-mode operation, which makes them inappropriate for use on the Internet.

PIM dense mode has an implicit join message, so routing devices use the flood-and-prune method to deliver traffic everywhere and then determine where the uninterested receivers are. PIM dense mode uses source-based distribution trees in the form S,G , as do all dense-mode protocols. PIM also supports sparse-dense mode, with mixed sparse and dense groups, but there is no special notation for that operational mode. If sparse-dense mode is supported, the multicast routing protocol allows some multicast groups to be sparse and other groups to be dense.

PIM sparse mode —In this mode of PIM, the assumption is that very few of the possible receivers want packets from each source, so the network establishes and sends packets only on branches that have at least one leaf indicating by message an interest in the traffic.

This multicast protocol allows a routing device to use any unicast routing protocol and performs reverse-path forwarding RPF checks using the unicast routing table. PIM sparse mode has an explicit join message, so routing devices determine where the interested receivers are and send join messages upstream to their neighbors, building trees from receivers to the rendezvous point RP.

PIM sparse mode migrates to an S,G source-based tree if that path is shorter than through the RP for a particular multicast group's traffic. WANs are appropriate networks for sparse-mode operation, and indeed a common multicast guideline is not to run dense mode on a WAN under any circumstances. CBT is rarely encountered outside academic discussions. There are no large-scale deployments of CBT, commercial or otherwise.

Used with IGMPv3 to create a shortest-path tree between receiver and source. IGMPv1 sends an explicit join message to the routing device, but uses a timeout to determine when hosts leave a group. Among other features, IGMPv2 adds an explicit leave message to the join message. RP addresses can also be statically configured.

Not appropriate if all receivers and sources are located in the same routing domain. SDP is a session directory protocol that advertises multimedia conference sessions and communicates setup information to participants who want to join the session. A client commonly uses SDP to announce a conference session by periodically multicasting an announcement packet to a well-known multicast address and port using SAP.

Pragmatic General Multicast PGM —Special protocol layer for multicast traffic that can be used between the IP layer and the multicast application to add reliability to multicast traffic. PGM allows a receiver to detect missing information in all cases and request replacement information if the receiver application requires it.

The differences among the multicast routing protocols are summarized in Table 1. It is important to realize that retransmissions due to a high bit-error rate on a link or overloaded routing device can make multicast as inefficient as repeated unicast. Therefore, there is a trade-off in many multicast applications regarding the session support provided by the Transmission Control Protocol TCP but TCP always resends missing segments , or the simple drop-and-continue strategy of the User Datagram Protocol UDP datagram service but reordering can become an issue.

Modern multicast uses UDP almost exclusively. The Juniper Networks T Series Core Routers handle extreme multicast packet replication requirements with a minimum of router load. Each memory component replicates a multicast packet twice at most. Even in the worst-case scenario involving maximum fan-out, when 1 input port and 63 output ports need a copy of the packet, the T Series routing platform copies a multicast packet only six times.

Most multicast distribution trees are much sparser, so in many cases only two or three replications are necessary. In no case does the T Series architecture have an impact on multicast performance, even with the largest multicast fan-out requirements.

Help us improve your experience. Let us know what you think. Do you have time for a two-minute survey? Maybe Later. Multicast Overview IP has three fundamental types of addresses: unicast, broadcast, and multicast. The differences among unicast, broadcast, and multicast can be summarized as follows: Unicast: One-to-one, from one source to one destination. Broadcast: One-to-all, from one source to all possible destinations. Note: This list does not include a special category for many-to-many applications, such as online gaming or videoconferencing, where there are many sources for the same receiver and where receivers often double as sources.

IP Multicast Uses Multicast allows an IP network to support more than just the unicast model of data delivery that prevailed in the early stages of the Internet. IP Multicast Terminology Multicast has its own particular set of terms and acronyms that apply to IP multicast routing devices and networks. Reverse-Path Forwarding for Loop Prevention The routing device's multicast forwarding state runs more logically based on the reverse path, from the receiver back to the root of the distribution tree.

Shortest-Path Tree for Loop Prevention The distribution tree used for multicast is rooted at the source and is the shortest-path tree SPT , but this path can be long if the source is at the periphery of the network. Administrative Scoping for Loop Prevention Scoping limits the routing devices and interfaces that can forward a multicast packet. Multicast Leaf and Branch Terminology Each subnetwork with hosts on the routing device that has at least one interested receiver is a leaf on the distribution tree.

Note: On Juniper Networks security devices, if the maximum number of leaves on a multicast distribution tree is exceeded, multicast sessions are created up to the maximum number of leaves, and any multicast sessions that exceed the maximum number of leaves are ignored.

Multicast Addresses Multicast host group addresses are defined to be the IP addresses whose high-order four bits are , giving an address range from Multicast Interface Lists To avoid multicast routing loops, every multicast routing device must always be aware of the interface that leads to the source of that multicast group content by the shortest path.

Multicast Routing Protocols Multicast routing protocols enable a collection of multicast routing devices to build join distribution trees when a host on a directly attached subnet, typically a LAN, wants to receive traffic from a certain multicast group, prune branches, locate sources and groups, and prevent routing loops.

Some of these addresses have been reserved by IANA for use by multicast applications. For example, the IP address This practice is called GLOP addressing. The AS number of the domain is embedded into the second and third octets of the For example, AS is written in hexadecimal format as F23A. Separating the two octets F2 and 3A results in and 58 in decimal format. These values result in a subnet of The range These addresses are constrained to a local group or organization.

Companies, universities, and other organizations can use limited scope addresses to have local multicast applications that will not be forwarded outside their domain. Routers typically are configured with filters to prevent multicast traffic in this address range from flowing outside an autonomous system AS or any user-defined domain. Within an AS or domain, the limited scope address range can be further subdivided so that local multicast boundaries can be defined. Network administrators may use multicast addresses in this range, inside a domain, without conflicting with others elsewhere in the Internet.

In IP multicast, several hosts need to be able to receive a single data stream with a common destination MAC address. Some means had to be devised so that multiple hosts could receive the same packet and still be able to differentiate between several multicast groups. With the unicast routes in the FIB, when a route is changed in the upper-layer routing table, only one route needs to be changed in the hardware routing state.

To forward unicast packets in hardware, the Integrated Switching Engine looks up source and destination routes in ternary content addressable memory TCAM , takes the adjacency index from the hardware FIB, and gets the Layer 2 rewrite information and next-hop address from the hardware adjacency table. The MFIB subsystem removes the protocol-specific information and leaves only the essential forwarding information. The device performs Layer 3 routing and Layer 2 bridging at the same time.

The following illustration shows a functional overview of how a Cisco device combines unicast routing, multicast routing, and Layer 2 bridging information to forward in hardware:. The following example shows an MFIB route:. With this information loaded in hardware, merging of the Layer 2 information can begin. The same process applies to VLAN 2. When the hardware routes a packet, in addition to sending it to all of the switch ports on all output interfaces, the hardware also sends the packet to all switch ports other than the one it arrived on in the input VLAN.

The packet should be forwarded only to switch ports where IGMP snooping has determined that there is either a group member or router. IP multicast delivery modes differ only for the receiver hosts, not for the source hosts. A source host sends IP multicast packets with its own IP address as the IP source address of the packet and a group address as the IP destination address of the packet.

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 network technology for the Cisco implementation of IP multicast targeted for audio and video broadcast application environments. By subscribing to this channel, the receiver host is indicating that it wants to receive IP multicast traffic sent by source host S to group G.

The network will deliver IP multicast packets from source host S to group G to all hosts in the network that have subscribed to the channel S, G. SSM does not require group address allocation within the network, only within each source host. Different applications running on the same source host must use different SSM groups. Different applications running on different source hosts can arbitrarily reuse SSM group addresses without causing any excess traffic on the network.

This interface is referred to as the reverse path forwarding interface. In some cases, when a packet arrives on an interface other than the expected RPF interface, the packet must be forwarded to the CPU subsystem software to allow PIM to perform special protocol processing on the packet.

However, processing in software is not necessary in many cases, because these non-RPF packets are often not needed by the multicast routing protocols. This flow-based congestion avoidance mechanism provides active queue management by tracking the queue length for each traffic flow. When the queue length of a flow exceeds its set limit, DBL drops packets. The packets are rate limited per flow to the CPU. Because installing fast-drop entries in the CAM is inaccessibly, the number of fast-drop flows that can be handled by the switch need not be limited.

Protocol events, such as a link going down or a change in the unicast routing table, can impact the set of packets that can safely be fast dropped. A packet that was correctly fast dropped before might, after a topology change, need to be forwarded to the CPU subsystem software so that PIM can process it.

The use of fast-drop entries in the hardware is critical in some common topologies because you may have persistent RPF failures. The MFIB translates the routing table information created by the multicast routing protocols into a simplified format that can be efficiently processed and used for forwarding by the Integrated Switching Engine hardware.

To display the information in the multicast routing table, use the show ip mroute command. To display the MFIB table information, use the show ip mfib command. Each route in the MFIB table can have one or more optional flags associated with it.

The route flags indicate how a packet that matches a route should be forwarded. The following flags can be associated with MFIB routes:. Internal Copy IC flag—Sets on a route when a process on the router needs to receive a copy of all packets matching the specified route. Signalling S flag—Sets on a route when a process needs to be notified when a packet matching the route is received; the expected behavior is that the protocol code updates the MFIB state in response to receiving a packet on a signalling interface.

Connected C flag—When set on an MFIB route, has the same meaning as the Signaling S flag, except that the C flag indicates that only packets sent by directly connected hosts to the route should be signaled to a protocol process.

A route can also have a set of optional flags associated with one or more interfaces. The per-interface flags supported in the MFIB include the following:. A packet that arrives on an interface that is marked as Accepting A is forwarded to all Forwarding F interfaces.

Forwarding F —Used in conjunction with the Accepting A flag as described above. Signaling S —Sets on an interface when some multicast routing protocol process in Cisco IOS needs to be notified of packets arriving on that interface.

It is a virtual interface that the MFIB subsystem creates to indicate that packets are being tunnelled to the specified destination address. A PimTunnel interface cannot be displayed with the normal show interface command.