http://blogs.technet.com/isablog/archive/2009/06/22/isa-integrated-nlb-multicast-with-igmp-isa-blocks-igmp-packets.aspxIntroduction After configuring ISA Integrated NLB to use multicast with IGMP, you may see blocked IGMP packets between your ISA array members. The ISA nodes don't need these packets to work properly, and it's ok when they are blocked by the Firewall Engine.en-USCommunityServer 2.1 SP1 (Build: 61025.2)http://blogs.technet.com/isablog/archive/2009/06/22/isa-integrated-nlb-multicast-with-igmp-isa-blocks-igmp-packets.aspx#3293129Wed, 11 Nov 2009 15:08:54 GMTd5e57398-b9ef-4490-9955-07cbb4e4a80d:3293129moebius<p>My Access rule only seems to block when the destination address is set to Localhost and not the newly created multicast address. Any ideas why? Is it a risk to leave it as Localhost?</p>