D-Link TM DES-6500, Руководство пользователя

Страница: 178 / 352

DES-6500 Chassis-based Layer 3 Ethernet Switch Manual
177
Version Enter the IGMP version (1, 2 or 3) that will be used to interpret IGMP queries on the
interface.
Query Interval Allows the entry of a value between 1 and 65535 seconds, with a default of 125
seconds. This specifies the length of time between sending IGMP queries.
Max Response Time Sets the maximum amount of time allowed before sending an IGMP response report.
A value between 1 and 25 seconds can be entered, with a default of 10 seconds.
Robustness Variable A tuning variable to allow for subnetworks that are expected to lose a large number of
packets. A value between 2 and 255 can be entered, with larger values being
specified for subnetworks that are expected to lose larger numbers of packets.
Last Member Query
Interval Specifies the maximum amount of time between group-specific query messages,
including those sent in response to leave group messages. A value between 1 and 25.
The default is
1 second.
State This field can be toggled between Enabled and Disabled and enables or disables
IGMP for the IP interface. The default is Disabled .
Click Apply to implement changes made.
DVMRP Interface Configuration
The Distance Vector Multicast Routing Protocol ( DVMRP ) is a hop-based method of building multicast delivery trees
from multicast sources to all nodes of a network. Because the delivery trees are ‘pruned’ and ‘shortest path’, DVMRP is
relatively efficient. Because multicast group membership information is forwarded by a distance-vector algorithm,
propagation is slow. DVMRP is optimized for high delay (high latency) relatively low bandwidth networks, and can be
considered as a ‘best-effort’ multicasting protocol.
DVMRP resembles the Routing Information Protocol (RIP), but is extended for multicast delivery. DVMRP builds a
routing table to calculate ‘shortest paths’ back to the source of a multicast message, but defines a ‘route cost’ (similar to the
hop count in RIP) as a relative number that represents the real cost of using this route in the construction of a multicast
delivery tree to be ‘pruned’ - once the delivery tree has been established.
When a sender initiates a multicast, DVMRP initially assumes that all users on the network will want to receive the
multicast message. When an adjacent router receives the message, it checks its unicast routing table to determine the
interface that gives the shortest path (lowest cost) back to the source. If the multicast was received over the shortest path,
then the adjacent router enters the information into its tables and forwards the message. If the message is not received on
the shortest path back to the source, the message is dropped.
Route cost is a relative number that is used by DVMRP to calculate which branches of a multicast delivery tree should be
‘pruned’. The ‘cost’ is relative to other costs assigned to other DVMRP routes throughout the network.
The higher the route cost, the lower the probability that the current route will be chosen to be an active branch of the
multicast delivery tree (not ‘pruned’) - if there is an alternative route.
DVMRP Configuration
To enable DVMRP globally on the Switch, click Configuration > Layer 3 IP Networking > IP Multicast Routing
Protocol > Configuration . This will give the user access to the following screen:
Figure 6- 143. DVMRP Global Settings window
Use the pull down menu, choose Enabled , and click Apply to implement the DVMRP function on the Switch.