9392 Nokia Network Voyager for IPSO 4.0 Reference Guide6. (Optional) Enter a value between 20 and 4000 in the Route expiration time text box to setthe interval, in seconds, after which a route that has not been refreshed is placed in the routehold-down queue.The default is 140 seconds.7. (Optional) Enter a value between 0 and 8000 in the Route hold-down period text box to setthe interval, in seconds, for which an expired route is kept in the hold-down queue before itis deleted from the route database. Set this interval to twice the value of the route reportinterval.The default is 120 seconds.8. (Optional) Enter a value between 60 and 86400 in the Cache lifetime text box to set theinterval, in seconds that a cached multicast forwarding entry is maintained in the kernelforwarding table before it is timed out because of inactivity.The default is 300 seconds.9. Click Apply, and then click Save to make your changes permanent.IGMPInternet Group Management Protocol (IGMP) allows hosts on multiaccess networks to informlocally attached routers of their group membership information. Hosts share their groupmembership information by multicasting IGMP host membership reports. Multicast routerslisten for these host membership reports, and then exchange this information with othermulticast routers.The group membership reporting protocol includes two types of messages: host membershipquery and host membership report. IGMP messages are encapsulated in IP datagrams, with an IPprotocol number of 2. Protocol operation requires that a designated querier router be elected oneach subnet and that it periodically multicast a host membership query to the all-hosts group.Hosts respond to a query by generating host membership reports for each multicast group towhich they belong. These reports are sent to the group being reported, which allows other activemembers on the subnet to cancel their reports. This behavior limits the number of reportsgenerated to one for each active group on the subnet. This exchange allows the multicast routersto maintain a database of all active host groups on each of their attached subnets. A group isdeclared inactive (expired) when no report is received for several query intervals.The IGMPv2 protocol adds a leave group message and uses an unused field in the IGMPv.1 hostmembership query message to specify a maximum response time. The leave group messageallows a host to report when its membership in a multicast group terminates. Then, the IGMPquerier router can send a group-directed query with a very small maximum response time toprobe for any remaining active group members. This accelerated leave extension can reduce thetime required to expire a group and prune the multicast distribution tree from minutes, down toseveral secondsThe unicast traceroute program allows the tracing of a path from one device to another, usingmechanisms that already exist in IP. Unfortunately, you cannot apply such mechanisms to IPmulticast packets. The key mechanism for unicast traceroute is the ICMP TTL exceededmessage that is specifically precluded as a response to multicast packets. The traceroute facility
