<?xml version='1.0'?>

<reference anchor='RFC2189'>

<front>
<title abbrev='CBTv2 Protocl Specification'>Core Based Trees (CBT version 2) Multicast Routing -- Protocol Specification --</title>
<author initials='T.' surname='Ballardie' fullname='Tony Ballardie'>
<organization>Research Consultant</organization>
<address>
<email>ABallardie@acm.org</email></address></author>
<date month='September' year='1997' />
<area>Routing</area>
<keyword>Core Based Tree</keyword>
<keyword>multicast</keyword>
<keyword>routing</keyword>
<abstract>
<t>
   This document describes the Core Based Tree (CBT version 2) network
   layer multicast routing protocol. CBT builds a shared multicast
   distribution tree per group, and is suited to inter- and intra-domain
   multicast routing.
</t>
<t>
   CBT may use a separate multicast routing table, or it may use that of
   underlying unicast routing, to establish paths between senders and
   receivers. The CBT architecture is described in .
</t>
<t>
   This document is progressing through the IDMR working group of the
   IETF.  CBT related documents include [1, 5, 6]. For all IDMR-related
   documents, see http://www.cs.ucl.ac.uk/ietf/idmr.
</t>
<t>
   This version of the CBT protocol specification differs significantly
   from the previous version. Consequently, this version represents
   version 2 of the CBT protocol.  CBT version 2 is not, and was not,
   intended to be backwards compatible with version 1; we do not expect
   this to cause extensive compatibility problems because we do not
   believe CBT is at all widely deployed at this stage. However, any
   future versions of CBT can be expected to be backwards compatible
   with this version.
   The most significant changes to version 2 compared to version 1
   include:

<list>
<t>
   o new LAN mechanisms, including the incorporation of an HELLO
     protocol.
</t>
<t>
   o new simplified packet formats, with the definition of a common CBT
     control packet header.
</t>
<t>
   o each group shared tree has only one active core router.
</t></list></t>
<t>
     This specification revision is a complete re-write of the previous
     revision.
</t></abstract></front>

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