interesting, do you have the link to the original article? thanks, Charles
""Greg Owens Jr"" wrote in message news:200211081900.TAA20943@;groupstudy.com... > Some LAN Switches with IGMP Snooping Enabled Stop Forwarding Multicast > Packets on RRAS Startup > > The information in this article applies to: > > * Microsoft Windows 2000 Advanced Server > > SUMMARY > > Routers connected to LAN switches configured with IGMP snooping may have > problems when a Windows 2000 RRAS-capable server comes online or when > OSPF or RIP version 2 is enabled. > > MORE INFORMATION > > Switches with IGMP snooping enabled have a feature that attempts to > determine which ports connect to devices that belong to a particular > multicast group. If the port does not connect to a device in the > multicast group, the switch does not forward packets destined to the > multicast group out that port. Some switches attempt to do this smart > multicast forwarding for all multicast destinations, while others do > this only for non-permanent groups (groups outside the range > 224.0.0.1-224.0.0.255). Switches doing this for permanent groups, such > as the all-routers group 224.0.0.2, the OSPF multicast groups 224.0.0.5 > and 224.0.0.6, and the RIP 2 multicast group 224.0.0.9, could cause > problems on the switched network. > > This behavior occurs if the switch has Cisco routers connected to it, > running Hot Standby Routing Protocol, OSPF, or RIP 2, and a Windows 2000 > server is connected to the switch and initialized. Other routers may be > affected as well. > > Before the server is brought online, the routers are communicating > through the switch using one or more of the above multicast addresses. > The routers never send IGMP join packets for these groups so the switch > never tries to parse which ports will receive the multicast packets. > When the server with RRAS comes online, it sends an IGMP join packet for > the all-routers multicast group (224.0.0.2), and for the OSPF and RIP 2 > groups if the protocols are running. The switch sees the join message > and sends a membership query out all its ports to determine which ports > have devices that also belong to this group. The routers do not respond > to membership queries for these multicast groups. The switch then stops > sending packets destined to these multicast groups to the router's > ports, and effectively disables the routing protocol communication > between routers. > > Hewlett-Packard (HP) and Nortel Networks (formerly Bay) switches operate > in this manner when IGMP snooping is enabled. Both switches have an > option for defining filters that enable them to always forward multicast > packets to all ports for specific groups. These filters must be enabled > to assure that the routers will continue functioning. Other switches > always forward all multicast packets for these groups to all ports > without requiring filters be enabled. > > The IGMP join packets sent from the Windows 2000 server with RRAS can be > observed by monitoring the data sent by the server when it first > initializes. Without any RRAS configuration, the server sends the IGMP > join for the all-routers group (224.0.0.2). When RRAS is started and > OSPF is configured the server sends the join for the OSPF groups > 224.0.0.5 and 224.0.0.6. When RIP 2 is configured, the server sends the > join for the RIP 2 group 224.0.0.9. Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=57167&t=57126 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
