Name: draft-ietf-ospf-2547-dnbit-04
Title: Using an LSA Options Bit to Prevent Looping in BGP/MPLS IP VPNs
State: Pending
Authors: Eric Rosen
Group: Open Shortest Path First IGP (ospf)
Date: 2004-03-10
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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