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Detecting Multicast Routers
Local Management Supplement A-3
There are many multicast routing protocols that the switch supports.
These include the following:
• PIM version 1 and 2
• CBT (core based trees)
• MOSPF
• DVMRP
The routing protocols are detected as follows:
• All the multicast routing protocols have a destination address of
01-00-5E.
• DVMRP and PIM version 1 run over IGMP. If the IGMP frame type is
not a REPORT, QUERY, OR LEAVE, then the frame is assumed to be
one of these.
• PIM version 2 is IP protocol type 0x67.
• OSPF is IP protocol type 0x59. To detect that the frame is a multicast
OSPF (MOSPF), the OSPF data must be looked at. The data starts
after the IP header. Byte 31 (options) needs to be checked. If bit 2 is
set (0x02 the MC bit), the frame is a MOSPF frame.
• CBT is IP protocol type 0x07.
• IGMP frames are detected by checking the IP protocol type. If the type
is -x02, it is IGMP. The first byte following the IP header is the IGMP
frame type and version. (Note that the lower 4 bits of the first byte in
the IP header is the length of the IP header in 32 bit words.) The
version is always 1, so the entire byte (version +type) may be used to
check the IGMP type as follows:
• 0x11 = query
• 0x12 = report version 1
• 0x16 = report version 2
• 0x17 = leave