Cabletron Systems SmartSwitch manual Dvmrp Overview

Chapter 12: Multicast Routing Configuration Guide

The SSR allows per-interface control of the host query interval and response time. Query interval defines the time between IGMP queries. Response time defines the time the SSR will wait for host responses to IGMP queries. The SSR can be configured to deny or accept group membership filters.

DVMRP Overview

DVMRP is an IP multicast routing protocol. On the SSR, DVMRP routing is implemented as specified in the draft-ietf-idmr-dvmrp-v3-06.txtfile, which is an Internet Engineering Task Force (IETF) document. The SSR’s implementation of DVMRP supports the following:

•The mtrace utility, which racks the multicast path from a source to a receiver.

•Generation identifiers, which are assigned to DVMRP whenever that protocol is started on a router.

•Pruning, which is an operation DVMRP routers perform to exclude interfaces not in the shortest path tree.

DVMRP uses the Reverse Path Multicasting (RPM) algorithm to perform pruning. In RPM, a source network rather than a host is paired with a multicast group. This is known as an (S,G) pair. RPM permits the SSR to maintain multiple (S,G) pairs.

On the SSR, DVMRP can be configured on a per-interface basis. An interface does not have to run both DVMRP and IGMP. You can start and stop DVMRP independently from other multicast routing protocols. IGMP starts and stops automatically with DVMRP. The SSR supports up to 64 multicast interfaces.

To support backward compatibility on DVMRP interfaces, you can configure the router expire time and prune time on each SSR DVMRP interface. This lets it work with older versions of DVMRP.

You can use threshold values and scopes to control internetwork traffic on each DVMRP interface. Threshold values determine whether traffic is either restricted or not restricted to a subnet, site, or region. Scopes define a set of multicast addresses of devices to which the SSR can send DVMRP data. Scopes can include only addresses of devices on a company's internal network and cannot include addresses that require the SSR to send DVMRP data on the Internet. The SSR also allows control of routing information exchange with peers through route filter rules.

You can also configure tunnels on SSR DVMRP interfaces. A tunnel is used to send packets between routers separated by gateways that do not support multicast routing. A tunnel acts as a virtual network between two routers running DVMRP. A tunnel does not run IGMP. The SSR supports a maximum of eight tunnels.

Note: Tunnel traffic is not optimized on a per-port basis, and it goes to all ports on an interface, even though IGMP keeps per-port membership information. This is done to minimize CPU overload for tunneled traffic.

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