I-D ACTION:draft-ietf-ospf-2547-dnbit-02.txt

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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-02.txt
	Pages		: 6
	Date		: 2003-12-4
	
[VPN] describes a method by which a Service Provider (SP) may
provide an 'IP VPN' service to its customers.  In VPNs of that sort,
a Customer Edge (CE) Router and a Provider Edge Router become routing
peers, and the customer routes are sent to the SP.  BGP is then used
to carry the customer routes across the SP's backbone to other PE
routers, and the routes are then sent to other CE routers.  Since CE
routers and PE routers are routing peers, it is customary to run a
routing protocol between them.  [VPN] allows a number of different
PE-CE protocols.  If OSPF is used as the PE-CE routing protocol, the
PE must execute additional procedures not specified in [VPN]; these
procedures are specified in [OSPF-VPN].  These additional procedures
translate customer OSPF routes from a CE router into BGP routes.  The
BGP routes are sent to the other PE routers, which translate them
back into OSPF routes, and then distribute them to CE routers.
During this translation, some of the information needed to prevent
loops may be lost.  The procedures specified in this document remedy
this situation by specifying that one of the OSPF options bits be
used to ensure that when a VPN route is sent from a PE to a CE, the
route will be ignored by any PE which receives it back from a CE.

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