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Configuring IP Services

7-4

Upon initialization, the host may immediately send out a report for each of its

supported multicast groups. The router accepts and processes these asynchronous

reports the same way it accepts requested reports.

Once in a steady state, hosts and routers communicate in a way that minimizes the

exchange of the queries and reports.

A host that receives a query delays its reply by a random interval and listens for a

reply from any other host in the same host group. Consider a network that

includes two host members — Host A and Host B — of the same multicast group.

The router sends out a host membership query on the local network. Host A and

Host B both receive the query and listen on the network for a host membership

report. Host B’s delay time expires ﬁrst, so it responds to the query with a

membership report. Hearing the response, Host A does not send a report of its

own for the same group.

Each query from a router to a host includes a code ﬁeld. IGMP inserts a value — d

— into this ﬁeld specifying the maximum time in tenths of a second within which

the host must issue a reply. The host uses this value to calculate a random value

between 0 and d tenths of a second for the period that it waits before sending a

response.

Distance Vector Multicast Routing Protocol

The Distance Vector Multicast Routing Protocol (DVMRP) provides a mechanism

for routers to propagate multicast datagrams in a manner that minimizes the

number of excess copies sent to any particular network.

Each DVMRP router builds and maintains a routing table by exchanging routing

information with its DVMRP neighbors. In a DVMRP environment, neighbors are

multicasting routers that are connected directly or through a tunnel. Directly

connected neighbors are routers that have an interface to the same network.

Tunnel-connected neighbors are multicast routers that communicate through a

unicast network, exchanging DVRMP messages that are encapsulated in IP

datagrams.

IGMP has several conﬁgurable timers. For information on using Site Manager to set

these timers, see the Interface Query Rate parameter on page 7-32, the Designated

Router Timeout parameter on page 7-32, the Version Threshold Time parameter on

page 7-30, and the Max Host Response Time parameter on page 7-33.

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Avaya Configuring IP Services Manual do Utilizador Página 286