DJ, Bookmark this link. ftp://ftpeng.cisco.com/ipmulticast/index.html
Typically you have IGMP running, PIM DR's elected, and PIM forwarding routers. Elections are based on this: - Lowest IP = IGMP2 querier - Highest IP = PIM DR - PIM forwarding router = if distance is not equal, lowest distance wins. if distance is equal, highest IP wins. IGMPv1 routers do not have group-specific queries, nor a querier election process like IGMPv2. These types of routers require the routing protocol to determine the DR for the network. In most cases the protocol will be PIM. So the PIM DR is elected and manages IGMP queries. There also exists the forwarder. In a multi-access network, there might be more than one path from a source. There must be a way to determine which router is going to be responsible for forwarding the traffic from the source so you aren't flooding the group with unnecessary traffic. This is where the forwarder comes in. Via the little test on distance or IP addresses I mentioned earlier, PIM can determine which router in a multi-access segment should be the designated forwarder. I hope this explanation helps. I can understand your confusion, its a common question. Ultimately, the best advice I've ever received is: "If in doubt, read the RFC." -Mark -----Original Message----- From: maine dude [mailto:[EMAIL PROTECTED]] Sent: Wednesday, August 21, 2002 4:44 AM To: [EMAIL PROTECTED] Subject: Multicast...please help [7:51822] Hi I have a question regarding the election of the LAN router which is supposed to send the queries for multicast accesses. In chapter 8, page 302, IGMPv2 querier election, it is mentioned that the router with the lowest IP address is elected as multicast querier. In Chapter 9, page 336, it is mentioned that the DR (designated Router) elected is the one with the highest IP address. "The DR is responsible for sending IGMP host-query messages to all host on the LAN". Could you please help me understand the differences between the two above cases, because for me, routers seem to have the exactly same role but are elected an opposite way... thanks DJ --------------------------------- Get a bigger mailbox -- choose a size that fits your needs. http://uk.docs.yahoo.com/mail_storage.html "The information transmitted is intended only for the person or entity to which it is addressed and may contain confidential and/or privileged material. Any review, retransmission, dissemination or other use of, or taking of any action in reliance upon, this information by persons or entities other than the intended recipient is prohibited. If you received this in error, please contact the sender and delete the material from all computers." Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=51836&t=51822 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
