IP Multicast Stub Routing in AOS
Frequently Asked Questions (FAQs)
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Copyright © 2005 ADTRAN, Inc.
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Frequently Asked Questions (FAQs)
Q1: What multicast applications does AOS support?
A1: AOS 7.x (and later) supports local IP multicast (source and receivers attached to local router
interfaces) and IP multicast in stub networks using IGMP forwarding.
Q2: What is a stub network and why is it important in this application?
A2: A stub network is one that has a single connection to the remainder of the network. A router with two
PVCs is not a stub network. Since AOS 7.x does not support a multicast routing protocol, it cannot prevent
multicast loops; nor can it converse with other multicast routers to resolve proper paths. While IGMP
forwarding can be used in non-stub networks, it requires very precise design and provides no dynamic
safeguards.
Q3: My network has two PVCs connecting to the WAN backbone. Does AOS support multicast in this applica-
tion?
A3: See answer A2.
Q4: Will AOS 7.x support multicast in a dial backup scenario?
A4: Using IGMP forwarding (ip mcast-stub helper-address), AOS 7.2 can forward IGMP over a primary
link, then re-resolve the forwarding via the unicast route table over a dial backup link when the primary
fails.
Q5: What versions of IGMP does AOS 7.x support?
A5: AOS 7.x supports IGMP Versions 1 and 2.
Q6: Can a multicast source be connected to an AOS 7.x router?
A6: In AOS 7.x, a locally connected multicast source can be connected, but only locally connected
receivers can join the group. AOS will not forward local sources upstream toward the multicast-enabled
network. In other words, a source connected to a downstream interface may be received by devices
connected to other downstream interfaces on the same router, but the stream will not be sent to the
upstream interface.
Q7: Does AOS 7.x multicast interoperate with other router vendors located in the multicast network?
A7: Any router that runs IGMP in router mode on its adjacent interface will work with AOS 7.x.
Q8: I’m familiar with multicast using other vendors’ products, but I don’t recognize the AOS multicast com-
mands. Why the differences?
A8: Since the multicast stub architecture is significantly different in AOS, a new set of commands is used
to illustrate the differences and better align the command with the capability. In some other operating
systems, PIM, IGMP, and multicast forwarding are tightly intertwined. Even in a multicast stub application
using IGMP forwarding, PIM commands are used to enable the feature. Since AOS performs the function
without enabling PIM, a unique set of commands was implemented.
