HP ProCurve Routing Switch 9308M / 9304M Reviewer’s Guide

generate multicast path trees through the network so that a particular multicast stream is only sent on links that ultimately reach a receiver of that stream. This prevents multicast streams from being sent to parts of the network where it isn't needed. DVMRP builds and maintains a separate multicast tree for each of the offered multicast streams.

2.4.3.2 PIM (Dense)

Protocol-Independent Multicast (PIM) is very similar to DVMRP except that it uses the IP routing table of the switch rather than build its own table. Since it doesn't build a table directly, it doesn't need to send out routing protocol packets to the other routers in the network like DVMRP does, hence the protocol-independent name. The HP ProCurve routing switches support the dense form of PIM, the version useful in LAN applications where there may be a high concentration of receiving nodes.

PIM generates multicast path trees to transmit a multicast stream only on those links leaving the routing switch that have a receiver for that multicast stream somewhere downstream.

2.4.3.3 IGMP

Internet Group Multicast Protocol (IGMP) is another multicast control protocol that builds delivery trees, but does not keep or use any routing information in this process, making it useful for Layer 2 environments. IGMP, handling the Layer 2 environment, is used in conjunction with either DVMRP or PIM, which handle the Layer 3 environment. Both routing switches support Version 2 of IGMP and can act as an IGMP querier to determine who belongs to the multicast groups, as do all of HP's managed switches. The routing switch can then direct a specific multicast stream to only those segments that have nodes that have joined the multicast group associated with that stream.

The HP ProCurve routing switches support 256 IGMP groups at default, 1024 with a user configurator change.

2.4.3.4 IP Tunneling

Not all routers support DVMRP or PIM. If there are a series of non-supporting routers in-between the HP ProCurve routing switches, IP tunneling can be used for multicast traffic. This will prevent the multicast traffic from being treated as broadcast traffic on the non-supporting routers. (It will also prevent the any potential multicast clients connected to these intervening routers from seeing the multicast streams.) This will allow the DVMRP routing functions to work correctly, since logically the two routing switches will appear to be neighbors, even though physically they may be separated by a number of intervening routers.

2.4.4 Layer 4 Features

2.4.4.1 Priority Queues

As mentioned in section 2.2.5, each port on the 9300 routing switches has four priority queues. While these priority queues are automatically used for packets having an 802.1q priority field, the 9300 routing switches can also be configured by the user to specify the use of a particular priority queue based on the packet’s IP address or IP port number.

This capability provides QoS for a packet based on its Layer 4 information. Applications using particular port numbers can be given priority treatment through the switch without the end node clients having to be aware of QoS, particularly valuable since client operating systems and the applications themselves are generally not QoS aware at the moment.

Layer 4 control of priority is a very powerful feature for applications that use isochronous (time- sensitive) data streams, such as Voice-over-IP or conferencing. This feature can also be used to give high priority to multicast applications.

Other applications can be prioritized as appropriate. For example, http traffic could be prioritized lower through the switch, or data involved in backups prioritized higher.

©1999 Hewlett-Packard Company

Revision 4.0 – 4/1/1999

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