Cabletron Systems SSIM-R8-02 Specifikace stáhnout pdf (Strana 238)

IP Multicast Overview

218 Enterasys Xpedition User Reference Manual

will wait for host responses to IGMP queries. The XP can be configured to deny or accept

group membership filters.

DVMRP Overview

DVMRP is an IP multicast routing protocol. On the XP, DVMRP routing is implemented

as specified in the draft-ietf-idmr-dvmrp-v3-06.txt file, which is an Internet Engineering

Task Force (IETF) document. The XP’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 XP to maintain multiple (S,G) pairs.

On the XP, 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 XP

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 XP 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 XP can send DVMRP data. Scopes can include only addresses of devices on a

company's internal network and cannot include addresses that require the XP to send

DVMRP data on the Internet. The XP also allows control of routing information exchange

with peers through route filter rules.

You can also configure tunnels on XP 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 XP 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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Cabletron Systems SSIM-R8-02 Specifikace Strana 238