I-D ACTION:draft-ietf-ospf-2547-dnbit-03.txt

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A New Internet-Draft is available from the on-line Internet-Drafts directories.
This draft is a work item of the Open Shortest Path First IGP Working Group of the IETF.

	Title		: Using an LSA Options Bit to Prevent Looping in BGP/MPLS IP VPNs
	Author(s)	: E. Rosen
	Filename	: draft-ietf-ospf-2547-dnbit-03.txt
	Pages		: 8
	Date		: 2004-1-15
	
This document specifies a procedure that deals with a particular
issue that may arise when a Service Provider (SP) provides 'BGP/MPLS
IP VPN' service to a customer, and the customer uses OSPF to
advertise its routes to the SP.  In this situation, a Customer Edge
(CE) Router and a Provider Edge (PE) Router are OSPF peers, and
customer routes are sent via OSPF from the CE to the PE.  The
customer routes are converted into BGP routes, and BGP carries them
across the backbone to other PE routers.  The routes are then
converted back to OSPF routes sent via OSPF to other CE routers.  As
a result of converting the routes from OSPF to BGP and back to OSPF,
some of the information needed to prevent loops may be lost.  A
procedure is needed to ensure that once a route is sent from a PE to
a CE, the route will be ignored by any PE which receives it back from
a CE.  This document specifies the necessary procedure, using one of
the options bits in the LSA (Link State Advertisements) to indicate
that an LSA has already been forwarded by a PE, and should be ignored
by any other PEs that see it.

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