The following timer(1-3) are configurable in the Cisco router under the interface.
1. Query interval: (ip igmp query-interval)
A time period between General Queries sent by a router. Cisco default is 60 sec. (RFC is 125 sec)
2. Query Response Interval: (ip igmp max-response-time)
The maximum response time (MRT) for hosts to respond to the periodic general Queries. Default is 10 sec. MRT timer to suppress many of the unnecessary IGMP reports. Report suppression is when a host receives a report sent by another host for the same mcast group for which it is planning to send a report, host does not send. 3 second MRT is expressed as 30.
3. Other Querier Present Interval (RFC) or Querier Timeout (Cisco)
To configure the timeout period before the router triggers Internet Group Management Protocol (IGMP) querier reelection for the interface, use the ip igmp querier-timeout command in interface configuration mode. To restore the default value, use the no form of this command.
4. Last Member Query Interval and Last Member Query Count
These values determine how long it takes a router to believe that all hosts on a LAN have left a particular group. By default, routers use an MRT of 10 (1 second) for Group-Specific Queries; because a router should receive a response to a Group-Specific Query in that amount of time, the router uses the MRT value as the value of the Last Member Query Interval. So, the router uses the following process:
1). Send a Group-Specific Query in response to an IGMP Leave.
2). If no Report is received within the Last Member Query Interval, repeat Step 1.
3). Repeat Step 1 the number of times defined by the value of the Last Member Query Count.
The Last Member Query Count is the number of consecutive Group-Specific Queries sent for the same group before the router concludes that there are no active members of the group on a subnet.
The default value for the Last Member Query Count is 2. So, the leave latency is typically less than 3 seconds, compared to up to 3 minutes with IGMPv1.
ip igmp last-member-query-count
ip igmp last-member-query-interval
The following ones are not configurable.
1. Group Membership Interval
The Group Membership Interval is the amount of time that must pass before a multicast router decides there are no more members of a group on a network. This value MUST be ((the Robustness Variable) times (the Query Interval)) plus (one Query Response Interval).
Thursday, March 19, 2009
Friday, March 06, 2009
Using IP Multicast Over Frame Relay Networks
A few concern.
A multipoint interface won't, by default, send multicast received from one spoke out to another spoke.
Either of the following recommended solutions—which are described in this document—can be used to configure IP multicast over Frame Relay:
•NBMA mode
•Point-to-point subinterfaces
Cisco suggests to use P2P. But in the lab, you have no choise to choose.
NBMA interface:
In reality, however, broadcast or multicast traffic sent by a remote site router will be received only by the central site router, not by the other remote site routers, because each remote site router is connected point-to-point to the central site router.
The following example illustrates a specific issue regarding IP multicast deployment within the partial mesh design of Frame Relay networks. If a remote site router sends a Protocol Independent Multicast (PIM) prune message, only the central site router will receive the prune message. Consequently, other remote site routers cannot override this prune message. This situation could prevent members of multicast groups from receiving multicast traffic that they want.
NBMA mode solution:
In a Frame Relay network that uses IP multicast, NBMA mode improves router performance for the following reasons:
•Traffic is fast-switched rather than process-switched.
•Routers receive traffic only for the multicast groups to which they are joined.
When using the ip pim nbma-mode command, note the following usage guidelines:
•This command applies to only PIM sparse mode configurations because its functionality is dependent on the PIM sparse mode join message.
•As the number of PIM neighbors increases, the outgoing interface list increases. Each interface entry requires additional resources from the NBMA mode-enabled router, therefore increasing data replication time and memory utilization.
Auto-RP Issues with NBMA Mode
The NBMA mode feature does not support PIM dense mode. Auto-RP, a method for disseminating rendezvous point (RP) information in an IP multicast network, relies on dense mode flooding of data from two well-known multicast group addresses, 224.0.1.39 and 224.0.1.40. These groups are candidate RP and RP mapping information groups. Without dense mode flooding capability, multicast routers in a Frame Relay network using Auto-RP may have problems receiving RP mapping information unless the Mapping Agent (MA) is placed in the appropriate location within the network or a more costly full mesh architecture is created.
Use the following guidelines when placing the MA in your network:
•All candidate RPs must be connected to the MA.
•All MAs must be connected to all PIM routers.
A multipoint interface won't, by default, send multicast received from one spoke out to another spoke.
Either of the following recommended solutions—which are described in this document—can be used to configure IP multicast over Frame Relay:
•NBMA mode
•Point-to-point subinterfaces
Cisco suggests to use P2P. But in the lab, you have no choise to choose.
NBMA interface:
In reality, however, broadcast or multicast traffic sent by a remote site router will be received only by the central site router, not by the other remote site routers, because each remote site router is connected point-to-point to the central site router.
The following example illustrates a specific issue regarding IP multicast deployment within the partial mesh design of Frame Relay networks. If a remote site router sends a Protocol Independent Multicast (PIM) prune message, only the central site router will receive the prune message. Consequently, other remote site routers cannot override this prune message. This situation could prevent members of multicast groups from receiving multicast traffic that they want.
NBMA mode solution:
In a Frame Relay network that uses IP multicast, NBMA mode improves router performance for the following reasons:
•Traffic is fast-switched rather than process-switched.
•Routers receive traffic only for the multicast groups to which they are joined.
When using the ip pim nbma-mode command, note the following usage guidelines:
•This command applies to only PIM sparse mode configurations because its functionality is dependent on the PIM sparse mode join message.
•As the number of PIM neighbors increases, the outgoing interface list increases. Each interface entry requires additional resources from the NBMA mode-enabled router, therefore increasing data replication time and memory utilization.
Auto-RP Issues with NBMA Mode
The NBMA mode feature does not support PIM dense mode. Auto-RP, a method for disseminating rendezvous point (RP) information in an IP multicast network, relies on dense mode flooding of data from two well-known multicast group addresses, 224.0.1.39 and 224.0.1.40. These groups are candidate RP and RP mapping information groups. Without dense mode flooding capability, multicast routers in a Frame Relay network using Auto-RP may have problems receiving RP mapping information unless the Mapping Agent (MA) is placed in the appropriate location within the network or a more costly full mesh architecture is created.
Use the following guidelines when placing the MA in your network:
•All candidate RPs must be connected to the MA.
•All MAs must be connected to all PIM routers.
Subscribe to:
Posts (Atom)