[Dshield] Stumped by 238.7.6.6

Johannes Ullrich jullrich at sans.org
Mon Jun 17 16:48:13 GMT 2002


 224.0.0.0 - 239.255.255.255 is reserved for 'multicast' 
purposes. Multicast packets can be used to address multiple
computers at the same time (similar to a 'broadcast' which
will address all computers)

 While not all routers across the Internet route multicast
packets, it is theoretically possible to route multicast 
traffic (broadcast traffic can be routed, but should not be
routed by default).

 There are a number of predefined multicast addresses:

224.0.0.1 - all machines on this subnet (like a x.y.z.255 
            broadcast)
224.0.0.2 - all routers on this subnet.
224.0.1.1 - reserved for network time protocol. 
224.0.0.9 - RIP-2 (routing protocol)

 There is a protocol called 'IGMP', which can be used to
join a multicast group (Internet Group Management Protocol).

 Multicasting is 'neat' if you need to stream data to multiple
hosts across a couple of "friendly" networks (networks where
you can convince the admin to route multicast traffic). It is
more efficient than sending the same packet several times 
to the individual hosts. There is a somewhat experimental
global multicast network called 'MBONE'.

Quick whois tip: Always start with ARIN (whois.arin.net).
RIPE or APNIC only respond to queries for the parts of IP space
that they are responsible for. ARIN will tell you to query
RIPE or APNIC, but RIPE will not tell you to query ARIN if it
does not know the answer.


-- 
---------------------------------------------------------------
jullrich at sans.org             Collaborative Intrusion Detection         
                                     join http://www.dshield.org
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