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backbone
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... method by which a Service Provider may use
an IP backbone to provide IP Virtual Private Networks (VPNs) for its
...
... customer data packet travels across the Service Provider's
backbone, it is encapsulated with the MPLS label that corresponds, in
...
... header [MPLS-in-IP-GRE]) so that
it gets tunneled across the backbone to the proper PE router. Thus,
the backbone ...
... backbone to the proper PE router. Thus,
the backbone core routers do not need to know the VPN routes.
...
... method is to support the case in which a
client obtains IP backbone services from a Service Provider or
...
... method makes it very
simple for the client to use the backbone services. It is also very
scalable and flexible for the Service Provider ...
... Consider a set of "sites" that are attached to a common network that
we call "the backbone". Now apply some policy to create a number of
subsets of that set, and impose the following rule: two sites may
...
... subsets of that set, and impose the following rule: two sites may
have IP interconnectivity over that backbone only if at least one of
these subsets contains them both.
...
... VPNs). Two sites have IP
connectivity over the common backbone only if there is some VPN that
contains them both. Two sites that have no VPN ...
... contains them both. Two sites that have no VPN in common have no
connectivity over that backbone.
If all the sites in a VPN ...
... We refer to the owners of the sites as the "customers". We refer to
the owners/operators of the backbone as the "Service Providers"
(SPs ...
...
We also restrict our discussion to the case in which the backbone
provides an IP service to the customer ...
... Point-to-Point
Protocol (PPP). The customer may attach to the backbone via one of
these (or other) layer 2 services, but the layer 2 service ...
... layer 2 service is
terminated at the "edge" of the backbone, where the customer's IP
datagrams are removed ...
... to know of each other at all. As a consequence, the customer has no
backbone or "virtual backbone" to manage, and does not have to deal
with any inter-site ...
... customer has no
backbone or "virtual backbone" to manage, and does not have to deal
with any inter-site routing ...
... SP Backbone Routers ...
...
If every router in an SP's backbone had to maintain routing
information for all the VPNs supported by the SP ...
...
So just as the VPN owners do not have a backbone or "virtual
backbone" to administer, the SPs ...
... VPN owners do not have a backbone or "virtual
backbone" to administer, the SPs themselves do not have a separate
backbone ...
... backbone" to administer, the SPs themselves do not have a separate
backbone or "virtual backbone" to administer for each VPN. Site-to-
...
... SPs themselves do not have a separate
backbone or "virtual backbone" to administer for each VPN. Site-to-
site routing ...
... VPN. Site-to-
site routing in the backbone is optimal (within the constraints of
the policies used to form the VPNs ...
...
Section 10 discusses some of the special issues that arise when the
backbone spans several Service Providers.
...
... security equivalent to that obtainable when a layer 2 backbone (e.g.,
Frame Relay) is used. That is, in the absence of misconfiguration or
...
...
From the perspective of a particular backbone network, a set of IP
systems may be regarded as a "site" if those systems have mutual IP ...
... systems may be regarded as a "site" if those systems have mutual IP
interconnectivity that doesn't require use of the backbone. In
general, a site will consist of a set of systems that are in
geographic proximity. However, this is not universally true. If two
...
... route, but the two geographic
locations can continue to communicate by using the VPN backbone, then
one site has become two.)
...
... might require that the site have two attachment circuits to the
backbone, one for the intranet and one for the extranet; it might
...
... RDs are given this structure in order to ensure that an SP that
provides VPN backbone service can always create a unique RD when it
...
... VRF, the PE will know that packets from the
backbone that arrive with this label must have their destination
addresses looked up in a VRF. When the PE ...
... the VPN-IPv4 routes for all the VPNs supported by the backbone.
We outline below two different ways to partition ...
... Just as there is no one PE router that needs to know all the VPN-IPv4
routes supported over the backbone, these distribution rules ensure
that there is no one Route Reflector (RR ...
... RR) that needs to know all the
VPN-IPv4 routes supported over the backbone. As a result, the total
number of such routes that can be supported over the backbone is not
...
... VPN-IPv4 routes supported over the backbone. As a result, the total
number of such routes that can be supported over the backbone is not
bounded by the capacity of any single device, and therefore can
increase virtually without bound.
...
...
If the intermediate routers in the backbone do not have any
information about the routes to the VPNs, how are packets forwarded
...
... next hop is NOT reached through a VRF attachment
circuit, then the packet must travel at least one hop through the
backbone. The packet thus has a "BGP Next Hop", and the BGP Next Hop
...
... backbone. This enables MPLS, at each node in the backbone
network, to assign a label corresponding to the route to each PE
router. To ensure interoperability ...
... setting up the
label switched paths across the backbone. However, other methods
of setting up ...
...
- MPLS will then carry the packet across the backbone to the BGP
Next Hop, where the VPN label will be examined.
...
... VPN label will be examined.
If the backbone does not support MPLS, the MPLS packet carrying only
...
... The fact that packets with VPN route labels are tunneled through the
backbone is what makes it possible to keep all the VPN routes out of
the P routers ...
... scalability of the
scheme. The backbone does not even need to have routes to the CEs,
only to the PEs ...
... VPN from another, it is important
that no router in the backbone accept a tunneled packet from outside
the backbone, unless it is sure that both endpoints ...
... router in the backbone accept a tunneled packet from outside
the backbone, unless it is sure that both endpoints of that tunnel
...
... tunneling technology, this means that a
router in the backbone MUST NOT accept a labeled packet from any
adjacent non-backbone device unless the following two conditions
...
... router in the backbone MUST NOT accept a labeled packet from any
adjacent non-backbone device unless the following two conditions
hold:
...
...
1. the label at the top of the label stack was actually
distributed by that backbone router to that non-backbone
...
... device, and
2. the backbone router can determine that use of that label will
cause the packet to leave the backbone ...
... backbone router can determine that use of that label will
cause the packet to leave the backbone before any labels lower
in the stack will be inspected, and before the IP header will
...
...
The first condition ensure that any labeled packets received from
non-backbone routers have a legitimate and properly assigned label at
...
...
the top of the label stack. The second condition ensures that the
backbone routers will never look below that top label. Of course,
the simplest way to meet these two conditions is just to have the
...
... routers will never look below that top label. Of course,
the simplest way to meet these two conditions is just to have the
backbone devices refuse to accept labeled packets from non-backbone
devices.
...
... the simplest way to meet these two conditions is just to have the
backbone devices refuse to accept labeled packets from non-backbone
devices.
...
... MPLS-in-IP or MPLS-in-GRE packet can
be accepted into the backbone only if the packet's IP destination
address will cause it to be sent outside the backbone ...
... backbone only if the packet's IP destination
address will cause it to be sent outside the backbone.
...
... BGP backbone are not
sent back into the backbone.
Specification of the complete set of procedures for the use of
...
... Multi-AS Backbones ...
... PE's default forwarding table. If a match is made there, the
packet can be forwarded natively through the backbone to the
Internet, instead of being forwarded by MPLS ...
... Under the following conditions:
1. a backbone router does not accept labeled packets over a
particular data ...
... data link
attaches only to trusted systems, or unless it is known that
such packets will leave the backbone before the IP header or
any labels lower in the stack will be inspected, and
...
... VPNs by Frame Relay or ATM backbones.
If the devices under the control of the SP are properly configured,
...
... MPLS-ENCAPS], or, where ATM
is used as the backbone, through the use of ATM QoS capabilities.
...
... Luyuan Fang
AT&T
IP Backbone Architecture
200 Laurel Ave.
...