Hello Messages - Cisco Nexus 7000 Series Configuration Manual

Hello Messages

Note Cisco NX-OS does not support PIM dense mode.
In Cisco NX-OS, multicast is enabled only after you enable the PIM or PIM6 feature on each router and then
enable PIM or PIM6 sparse mode on each interface that you want to participate in multicast. You can configure
PIM for an IPv4 network and PIM6 for an IPv6 network. In an IPv4 network, if you have not already enabled
IGMP on the router, PIM enables it automatically. In an IPv6 network, MLD is enabled by default. For
information about configuring IGMP and MLD, see Configuring IGMP and Configuring MLD.
Note
Beginning with Cisco NX-OS Release 5.2(1) for the Nexus 7000 Series devices, you can configure PIMv4
to run over generic routing encapsulation (GRE) tunnels including outgoing interfaces (OIFs).
You use the PIM and PIM6 global configuration parameters to configure the range of multicast group addresses
to be handled by each of the three distribution modes:
• Any Source Multicast (ASM) provides discovery of multicast sources. It builds a shared tree between
• Single Source Multicast (SSM) builds a source tree originating at the designated router on the LAN
• Bidirectional shared trees (Bidir) build a shared tree between sources and receivers of a multicast group
You can combine the three modes to cover different ranges of group addresses. For more information, see
Configuring PIM and PIM6.
For more information about PIM sparse mode and shared distribution trees used by ASM and Bidir modes,
see RFC 4601.
For more information about PIM SSM mode, see RFC 3569.
For more information about PIM Bidir mode, see draft-ietf-pim-bidir-09.txt.
Hello Messages
The PIM process begins when the router establishes PIM neighbor adjacencies by sending PIM hello messages
to the multicast address 224.0.0.13. Hello messages are sent periodically at the interval of 30 seconds. When
all neighbors have replied, the PIM software chooses the router with the highest priority in each LAN segment
as the designated router (DR). The DR priority is based on a DR priority value in the PIM hello message. If
the DR priority value is not supplied by all routers, or the priorities match, the highest IP address is used to
elect the DR.
The hello message also contains a hold-time value, which is typically 3.5 times the hello interval. If this hold
time expires without a subsequent hello message from its neighbor, the device detects a PIM failure on that
link.
Cisco Nexus 7000 Series NX-OS Multicast Routing Configuration Guide
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sources and receivers of a multicast group and supports switching over to a source tree when a new
receiver is added to a group. ASM mode requires that you configure an RP.
segment that receives a request to join a multicast source. SSM mode does not require you to configure
RPs. Source discovery must be accomplished through other means.
but do not support switching over to a source tree when a new receiver is added to a group. Bidir mode
requires that you configure an RP. Bidir forwarding does not require source discovery because only the
shared tree is used.
Configuring PIM and PIM6