Pim (Dense); Igmp; Ip Tunneling; Layer 4 Features - HP ProCurve 9304M Reviewer's Manual

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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