Internet DRAFT - draft-kaliraj-bess-bgp-sig-private-mpls-labels
draft-kaliraj-bess-bgp-sig-private-mpls-labels
Network Working Group K. Vairavakkalai, Ed.
Internet-Draft M. Jeyananth
Intended status: Standards Track Juniper Networks, Inc.
Expires: 22 April 2024 P.R. Ramadenu
AT&T Services, Inc.
I. Means
AT&T
20 October 2023
BGP Signaled MPLS Namespaces
draft-kaliraj-bess-bgp-sig-private-mpls-labels-07
Abstract
The MPLS forwarding layer in a core network is a shared resource.
The MPLS FIB at nodes in this layer contains labels that are
dynamically allocated and locally significant at that node. These
labels are scoped in context of the global loopback address. Let us
call this the global MPLS namespace.
For some usecases like upstream label allocation, it is useful to
create private MPLS namespaces (virtual MPLS FIB) over this shared
MPLS forwarding layer. This allows installing deterministic label
values in the private FIBs created at nodes participating in the
private MPLS namespace, while preserving the "locally significant"
nature of the underlying shared global MPLS FIB.
This document defines new address families (AFI: 16399, SAFI: 128, or
1) and associated signaling mechanisms to create and use MPLS
forwarding contexts in a network. Some example use cases are also
described.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
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Internet-Drafts are draft documents valid for a maximum of six months
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 22 April 2024.
Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 5
3. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Constructs and Building Blocks . . . . . . . . . . . . . . . 7
4.1. Context Protocol Nexthop Address . . . . . . . . . . . . 7
4.2. MPLS Context FIB . . . . . . . . . . . . . . . . . . . . 7
4.3. Context Label . . . . . . . . . . . . . . . . . . . . . . 7
4.4. Roles of Nodes in a MPLS Plane . . . . . . . . . . . . . 8
4.4.1. Edge Nodes (PLER) . . . . . . . . . . . . . . . . . . 8
4.4.2. Transit Nodes (PLSR) . . . . . . . . . . . . . . . . 8
4.5. Sending Traffic into a MPLS Plane . . . . . . . . . . . . 8
5. BGP Families, Routes and Encoding . . . . . . . . . . . . . . 9
5.1. New Address Families for "MPLS Namespace Signaling" . . . 9
5.1.1. AFI: 16399, SAFI: 128 . . . . . . . . . . . . . . . . 9
5.1.2. AFI: 16399, SAFI: 1 . . . . . . . . . . . . . . . . . 10
5.2. Routes and Operational Procedures . . . . . . . . . . . . 10
5.2.1. "Context-Nexthop" Discovery Route . . . . . . . . . . 10
5.2.2. MPLS Namespace "Private Label" Routes . . . . . . . . 11
6. Example of Usecases . . . . . . . . . . . . . . . . . . . . . 14
6.1. Label Spoof Protection in Inter-AS Option C Network . . . 14
6.1.1. Reference Topology . . . . . . . . . . . . . . . . . 15
6.1.2. Spoof protection for Transport Labels . . . . . . . . 16
6.1.3. Spoof protection for Service Labels . . . . . . . . . 16
6.1.4. Applicability to Inter-AS Option B . . . . . . . . . 18
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6.2. Improve Scaling and Convergence of a Seamless MPLS
Network . . . . . . . . . . . . . . . . . . . . . . . . . 18
6.2.1. Illustration . . . . . . . . . . . . . . . . . . . . 20
6.2.2. Topology . . . . . . . . . . . . . . . . . . . . . . 20
6.2.3. Context Protocol Nexthop Address (CPNH) . . . . . . . 21
6.2.4. Service Forwarding Helper, and Changes to Transport
Layer . . . . . . . . . . . . . . . . . . . . . . . . 21
6.2.5. BGP MPLS Namespace Address family (AFI:16399,
SAFI:128) . . . . . . . . . . . . . . . . . . . . . . 22
6.2.6. Changes to Service Layer Route Exchange . . . . . . . 22
6.2.7. Analysis of Forwarding Behavior . . . . . . . . . . . 23
6.3. VNF Service Forwarding Helper usecase . . . . . . . . . . 23
6.4. BGP Based Standard API to Network's MPLS Forwarding
Plane . . . . . . . . . . . . . . . . . . . . . . . . . . 23
6.5. Traffic Engineering and Service Chaining . . . . . . . . 24
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
8. Security Considerations . . . . . . . . . . . . . . . . . . . 24
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 24
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 24
10.1. Normative References . . . . . . . . . . . . . . . . . . 24
10.2. Informative References . . . . . . . . . . . . . . . . . 25
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 26
1. Introduction
The MPLS forwarding layer in a core network is a shared resource.
The MPLS FIB at nodes in this layer contains labels that are
dynamically allocated and locally significant at that node. These
labels are scoped in context of the global loopback address. Let us
call this the global MPLS namespace.
For some usecases like upstream label allocation, it is useful to
create private MPLS namespaces (virtual MPLS FIB) over this shared
MPLS forwarding layer. This allows installing deterministic label
values in the private FIBs created at nodes participating in the
private MPLS namespace, while preserving the "locally significant"
nature of the underlying shared global MPLS FIB.
This document defines new address families (AFI: 16399, SAFI: 128, or
1) and associated signaling mechanisms to create and use MPLS
forwarding contexts in a network.
The mechanism described in this document reuse [RFC4364] and
[RFC8277] procedures to implement Upstream label allocation. The
MPLS Namespace family uses BGP VPN style NLRI where the FEC is a MPLS
Label, instead of IP prefix. The concepts of MPLS Context tables and
upstream allocation are described in [RFC5331].
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A BGP speakers participating in a private MPLS namespace creates
instance of "MPLS forwarding context" FIB, which is identified using
a "Context Protocol Nexthop (CPNH)". A Context label MAY be
advertised for the Context Protocol Nexthop (CPNH) using a transport
layer protocol or BGP family to other nodes.
2. Terminology
LSR : Label Switch Router
PE : Provider Edge
SFH : Service Forwarding Helper
UHP : Ultimate Hop Pop
MPLS FIB : MPLS Forwarding table
NLRI: Network Layer Reachability Information
AFI: Address Family Identifier
SAFI: Subsequent Address Family Identifier
BN : Border Node
TN : Transport Node, P-router
PE : Provider Edge
BGP VPN : VPNs built using RFC4364 mechanisms
BGP LU: BGP Labeled Unicast family (AFI/SAFIs 1/4, 2/4)
BGP CT: BGP Classful Transport family (AFI/SAFIs, 1/76, 2/76)
RT : Route-Target extended community
RD : Route-Distinguisher
VRF: Virtual Router Forwarding Table
PNH : Protocol Next hop address carried in a BGP Update message
CPNH: Context Protocol Nexthop
MNH : BGP MultiNexthop attribute
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FEC : Forwarding Equivalence Class
RSVP-TE : Resource Reservation Protocol - Traffic Engineering
SEP : Service Endpoint, the PNH of a Service route
MPLS: Multi Protocol Label Switching
VNF : Virtual Network Function
vCP : VNF Control Plane
vFP : VNF Forwarding Plane
2.1. Definitions
PLSR: a BGP CT or BGP LU transit node in a private MPLS plane, that
does label-swap forwarding for Context label.
PLER: an edge node in a private MPLS plane. It has a forwarding
context for private labels.
Global MPLS FIB : Global MPLS Forwarding table, to which shared-
interfaces are connected
Private MPLS FIB : Private MPLS Forwarding table, to which private
interfaces are connected
Private MPLS FIB Layer (Private MPLS plane): The group of Private
MPLS FIBs in the network, connected together via Context labels
Context label : Locally-significant Non-reserved label pointing to a
private MPLS FIB
Context nexthop IP-address (CPNH) : An IP-address that identifies the
"Private MPLS FIB Layer". RD:CPNH identifies a Private MPLS FIB at a
specific BGP node.
Global nexthop IP-address (GPNH) : Global Protocol Nexthop address.
E.g. a loopback address used as transport tunnel end-point.
Detour-router : A BGP border node that is used as a loose-hop in a
traffic-engineered path
Service Family : BGP address family used for advertising routes for
"data traffic" as opposed to tunnels (e.g. AFI/SAFIs 1/1 or 1/128).
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Transport Family : BGP address family used for advertising tunnels,
which are in turn used by service routes for resolution (e.g. AFI/
SAFIs 1/4 or 1/76).
3. Motivation
A provider's core network consists of a global-domain (default
forwarding-tables in P and PE nodes) that is shared by all tenants in
the network and may also contain multiple private user-domains (e.g.
VRF route tables).
The global MPLS forwarding-layer can be viewed as the collection of
all default MPLS forwarding-tables. This global MPLS Fib layer
contains labels locally significant to each node. The "local-
significance of labels" gives the nodes freedom to participate in
MPLS-forwarding with whatever label-ranges they can support in
forwarding hardware.
In emerging usecases some applications using the MPLS-network may
benefit from a "static labels" view of the MPLS-network. In some
other usecases, a standard mechanism to do Upstream label-allocation
is beneficial.
It is desirable to leave the global MPLS FIB layer intact, and build
private MPLS FIB-layers on top of it to achieve these requirements.
The private MPLS FIBs can then be used by the applications as
desired. The private MPLS FIBs need to be created only at the nodes
in the network where predictable label-values (external label
allocation) is desired. E.g. BNs that need to act as a "Detour-
nodes" or "Service-Forwarding-Helpers" that need to mirror service-
labels.
In other words, provisioning of these private MPLS FIBs can be
gradual and can co-exist with nodes not supporting the feature
described in this document. These private MPLS FIBs can be stitched
together using either the Context labels over the existing shared
MPLS-network tunnels, or 'private' context-interfaces - to form the
"private MPLS FIB layer".
An application can then install the routes with desired label-values
in the private forwarding contexts with desired forwarding-semantics.
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4. Constructs and Building Blocks
The building-blocks that construct a private MPLS plane are described
in this section.
4.1. Context Protocol Nexthop Address
A private MPLS plane (just "MPLS plane" here-after) is identified by
an IP-address called Context Protocol Nexthop (CPNH). This address
is unique in the core-network, like any other loopback address.
A loopback-address uniquely identifies a specific node in the
network, and we call it Global Protocol Nexthop (GPNH) in this
document. The CPNH address uniquely identifies a MPLS plane, aka
"MPLS Namespace".
Each node that has forwarding context for a MPLS plane MUST be
configured with the same CPNH but a different RD, such that the
RD:CPNH will uniquely identify that node in the MPLS plane.
4.2. MPLS Context FIB
An instance of a MPLS forwarding-table at a node in the private MPLS
plane. This Private MPLS FIB contains the private label routes.
A node can have context FIB for multiple MPLS planes. The same
label-value can have a different forwarding-semantic in each MPLS
plane. Thus the applications using that MPLS plane get a
deterministic label-value independent of other applications using
other MPLS planes.
The terms "MPLS Namespace", "MPLS FIB-layer" and "MPLS plane" are
used interchangeably in this document.
4.3. Context Label
A Context label is a non-reserved dynamically allocated label, that
is installed in the global MPLS FIB, and points to a MPLS-context
FIB. The Context Label have forwarding semantics as follows in the
global MPLS FIB:
Context Label -> Pop and Lookup in MPLS-context FIB
Advertising the "context label in conjunction with the GPNH" tells
the network how to reach a "RD:CPNH".
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4.4. Roles of Nodes in a MPLS Plane
The node roles in a MPLS plane can be classified into "edge nodes"
(call them PLER) or "transit-nodes" (call them PLSR).
4.4.1. Edge Nodes (PLER)
Private Label Edge-routers (PLER) have MPLS context FIB that belong
to the MPLS plane. They advertise the presence of this context FIB
using transport layer address families like BGP CT (SAFI 76) or BGP
LU (SAFI 4), and private label routes from this FIB are advertused
using new BGP AFI/SAFI described in this document.
4.4.2. Transit Nodes (PLSR)
These are just Border-nodes that do label-swap forwarding for the
context labels they see in the Context-Protocol-Nexthop advertisement
routes (BGP CT or BGP LU) going thru them. They basically stitch/
extend the label switched path to a PLER's CPNH when they re-
advertise the CPNH routes with next hop as self.
PLSRs dont have MPLS context FIBs. PLSRs dont have Context Protocol-
Nexthop. Because they dont have Private label routes to originate.
However a node in the network can play both roles, of PLER and PLSR.
4.5. Sending Traffic into a MPLS Plane
At a PLER, MPLS-traffic arriving with private label hits the correct
private MPLS FIB by virtue of either arriving on a "private network-
interface" that is attached to the MPLS context FIB, or arriving with
a "Context label" on a network-interface attached to the global MPLS
FIB.
To send data traffic into this private MPLS plane, the sender MUST
use as handle either a "Context label" advertised by a node or a
"Private interface" owned by the MPLS context FIB at the node. The
MPLS context FIB is created for an application that needs a private
MPLS plane.
The Context label is the only dynamic label-value the application
needs to learn from the network (PLER node it is connected to), to be
able to use the private MPLS plane. The application can chose
predictable value for the labels to be programmed in the private MPLS
FIBs.
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Once the packet enters the private MPLS plane at an edge-node (PLER),
the node will forward the packet to the next node (PLSR or PLER), by
pushing the Context label advertised by that next-node, and the
transport-label to reach that node's GPNH. This will repeat until
the packet reaches the PLER's private MPLS FIB that originated that
private MPLS-label.
At each PLER in the MPLS plane, the private label value remains the
same, and points towards the same resource attached to the MPLS
plane. This allows the applications using the MPLS-network a static-
labels view of the resourses attached to the private MPLS plane.
At each PLSR in the MPLS plane, the Context label value will change
(be swapped in forwarding), but is transparent to the application.
5. BGP Families, Routes and Encoding
This section describes the new constructs defined by this document.
5.1. New Address Families for "MPLS Namespace Signaling"
This document defines a new AFI: "MPLS Namespaces" (IANA code 16399).
And two new address-families, using SAFIs 128 and 1. These address
families are used to signal MPLS namespaces in BGP. To send or
receive routes of these address families, these AFI, SAFI pair of
values MUST be negotiated in Multiprotocol Extensions capability
described in RFC4760 [RFC4760]
5.1.1. AFI: 16399, SAFI: 128
This address-family is used to exchange private label-routes in
private MPLS FIBs at routers that are connected using a common
network interface. The private label route has NLRI prefix format
"RD:PrivateLabel" and contains Route-Target extended-community
identifying the private FIB Layer (VPN) the route belongs to. The
nexthop of these routes is set to either the GPNH or the CPNH of the
BGP-speaker advertising the RFC-8277 label.
Any transport layer protocol is used to advertise the Context label
that the receiving router uses to send traffic into the private MPLS
FIB. The Context label installed in the global MPLS FIB points to
the private MPLS FIB. The Context label is required when the
connecting-interface is a shared common interface that terminates
into the global MPLS FIB.
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Routes of this address-family can be sent with either IPv4 or IPv6
nexthop. The type of nexthop is inferred from the length of the
nexthop.
When the length of Next Hop Address field is 24 (or 48) the nexthop
address is of type VPN-IPv6 with 8-octet RD set to zero (potentially
followed by the link-local VPN-IPv6 address of the next hop with an
8-octet RD).
When the length of Next Hop Address field is 12 the nexthop address
is of type VPN-IPv4 with 8-octet RD.
5.1.2. AFI: 16399, SAFI: 1
This address-family is used to exchange private label-routes in
private MPLS FIBs to routers that are connected using a private
network-interface.
Because the interface is private, and terminates directly into the
private MPLS FIB, a Context label is not required to access the
private MPLS FIB and NLRI prefix format is just "PrivateLabel/24",
without the RD.
Routes of this address-family can be sent with either IPv4 or IPv6
nexthop. The type of nexthop is inferred from the length of the
nexthop.
When the length of Next Hop Address field is 16 (or 32) the nexthop
address is of type IPv6 (potentially followed by the link-local IPv6
address of the next hop).
When the length of Next Hop Address field is 4 the nexthop address is
a 4 octet IPv4 address.
5.2. Routes and Operational Procedures
5.2.1. "Context-Nexthop" Discovery Route
The Context-NH discovery route may be a BGP LU or [BGP-CT] family
route that carries CPNH in the "Prefix" portion of the NLRI. And the
Context label is carried in the "Label" field in the [RFC8277] format
NLRI.
This route is advertised with the following path-attributes:
* BGP Nexthop attribute (code 14, MP_REACH) carrying GPNH address.
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* Route-Target extended community, identifying the Transport class,
if applicable.
The "Context-Nexthop discovery route" is originated by each speaker
who acts as a PLER. The "RD:Context-nexthop" uniquely identifies the
private MPLS FIB at the speaker. The "Context-nexthop address"
uniquely identifies the private MPLS plane in the network. The
Context label advertised in this route has a local forwarding
semantic of "Pop, Lookup in Private MPLS FIB".
A BGP speaker readvertising a BGP CT Context-Nexthop for RD:CPNH
discovery-route MUST follow the mechanisms described in [BGP-CT].
Specifically when re-advertising with "next-hop self" MUST allocate a
new Label with a forwarding semantic of "Swap Received-Context-Label,
Forward to Received-GPNH". This extends reachability to the CPNH
across tunnel domains.
5.2.2. MPLS Namespace "Private Label" Routes
The Private Label routes are carried in the new address-family "MPLS
VpnUnicast" (AFI:16399, SAFI:128) aka "MPLS namespace signaling",
defined in this document.
The NLRI format follows the specifications in [RFC8277], with the
"Prefix" portion of the NLRI comprising of the RD and "Private MPLS
Label" encoded as shown below.
In a MP_REACH_NLRI attribute whose AFI/SAFI is MPLS/128, the "Length"
field will be 112 bits or less, comprising of the Label, RD and
"Private MPLS Label".
In a MP_REACH_NLRI attribute whose AFI/SAFI is MPLS/1, the "Length"
field will be 48 bits or less, comprising of the Label, and "Private
MPLS Label".
NLRI Prefix (Private Label route, AFI:16399, SAFI:128)
This picture shows NLRI format when the RFC-8277 Multiple Labels
Capability is not used:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length | Label |Rsrv |S|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Route Distinguisher (RD) (8 octets) |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Route Distinguisher (RD cont.) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Private MPLS Label |Rsrv |S|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Fig 1: RFC-8277 NLRI with one Label.
- Length:
The Length field consists of a single octet. It specifies the
length in bits of the remainder of the NLRI field.
In a MP_REACH_NLRI attribute whose AFI/SAFI is MPLS/128, the
"Length" field will be 112 bits or less, comprising of the
Label, RD and "Private MPLS Label".
As specified in [RFC4760], the actual length of the NLRI field
will be the number of bits specified in the Length field,
rounded up to the nearest integral number of octets.
- Label:
The Label field is a 20-bit field containing an MPLS label value
(see [RFC3032]). This label is locally significant, downstream
allocated at the speaker identified in the BGP Nexthop field
in MP_REACH_NLRI (code 14). This label is pushed in nexthop of
the route installed in MPLS context FIB at receiving router.
- Route Distinguisher (RD):
The 8 byte Route Distinguisher as specified in [RFC4760].
- Private MPLS Label:
The "Private MPLS Label" field is a 20-bit field containing an
MPLS label value (see [RFC3032]). This is an upstream assigned
MPLS label, used as destination of route installed in MPLS
context FIB at the receiving router.
- Rsrv:
This 3-bit field SHOULD be set to zero on transmission and
MUST be ignored on reception.
- S:
This 1-bit field MUST be set to one on transmission and MUST
be ignored on reception.
Attributes on this route:
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* BGP Nexthop attribute (code 14, MP_REACH) carrying a GPNH address.
(OR)
* The MultiNextHop attribute [MNH] with forwarding-semantic:
- "Forward to RD:CPNH"
* Route-Target extended-community, identifying the private FIB-layer
MultiNexthop BGP-attribute (Private Label route)
+--------------------------------------------+
| MultiNH.Num-Nexthops = 1 |
+--------------------------------------------+
| FwdSemanticsTLV.FwdAction = Forward |
+--------------------------------------------+
| NHDescrTLV.NhopDescrType = RD:CPNH or GPNH|
+--------------------------------------------+
Fig 2: MultiNexthop attr of Private Label route
A speaker MAY readvertise a private label route without changing the
Nexthop (RD:CPNH) carried in it, if the speaker is a pure PLSR.
If it does alter the nexthop to SelfRD:CPNH, it SHOULD act as a PLER,
and for e.g. originate a "Context-Nexthop discovery route" for prefix
"SelfRD:CPNH".
Even if the speaker sets nexthop-address to Self because of regular
BGP readvertisement-rules, Label Prefix MUST NOT be altered, and the
received NLRI "RD:Private-Label1" MUST be re-advertised as-is. Such
that value of label "Private-Label1" doesn't change while the packet
traverses multiple nodes in the private MPLS FIB layer.
The Route target attached to the route is the one identifying the
private MPLS FIB layer (VPN). The Private label routes resolve over
the Context-nexthop route that belong to the same VPN.
A node receiving a "Private Label route" RD:L1 MUST install the label
L1 in the private MPLS Forwarding-context idenfied by the Route-
Target attached to the route.
The label route MUST be installed with forwarding-semantic as
specified in the received MultiNextHop attribute. As an example, a
Detour node MAY receive the private label route with a forwarding-
semantic of "Forward to RD:CPNH" operation. And an Egress node MAY
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receive a private label route with a forwarding-semantic pointing to
a resource it houses. Note that such a Private label BGP route MAY
be received from external-application also.
5.2.2.1. Resolving Received Private Label Routes
A node receiving a "Context-nexthop discovery route" MUST be capable
of using either the CPNH or the RD:CPNH carried in the NLRI, to
resolve other routes received with this CPNH address or RD:CPNH in
the "Nexthop-attributes".
The receiver of a private label route MUST recursively resolve the
received nexthop (RD:CPNH) over the Context-Nexthop discovery-route
for prefix "RD:CPNH" to determine the label stack "Context Label,
Transport Label" to push, so that the MPLS packet with private label
reaches the private MPLS FIB originating the route.
If a node receives multiple "Context-nexthop discovery route" for a
CPNH, it SHOULD run path-selection after stripping the RD, to find
the closest ingress to the private MPLS plane identified by the CPNH.
This best path SHOULD be used to resolve a received private label
route.
6. Example of Usecases
6.1. Label Spoof Protection in Inter-AS Option C Network
In certain deployments, some domains of an Inter AS Option C network
may be located in an untrusted geography. Even though such domains
are administered by the same operator, employing security mechanisms
may be desirable on interfaces connecting such domains.
This section describes how an Inter domain Option C MPLS network can
be protected against Label spoofing, using MPLS Namespaces
technology.
The inter-AS labeled traffic will be protected against spoofing, such
that the transport ASBRs will accept labeled traffic on inter-AS
links only if the MPLS label stack matches the transport and service
MPLS labels that have been advertised in BGP (LU and L3VPN) families
to the peers in untrusted zone.
In order to achieve this security, new functionality is required on
only the BNs, PEs or RRs in the trusted zone.
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This section illustrates the mechanisms using BGP LU as transport
family and L3VPN as service family. But the mechanisms described
will work in similar manner for other labeled transport families
(e.g., BGP CT) and service families (e.g., L3VPNv6, EVPN, VPLS) as-
well.
6.1.1. Reference Topology
[RR13] [RR23]
| |
| |
[PE11]\ | /[ASBR14]------[ASBR24]\ | /[PE21]
\ | / \ | /
[P11] [P21]
/ \ / \
.. / \[ASBR15]------[ASBR25]/ \
[PE12] [PE22]
|
..AS1.. | ..AS2..
(trusted zone) | (untrusted zone)
<---- Traffic Direction ----
Figure 1: Inter-AS Option C Network with a domain in untrusted zone
Figure 1 shows an Inter-AS Option C network with two domains. AS1 is
in a trusted geography, and AS2 is in an untrusted geography.
BGP LU (AFI/SAFI: 1/4) is negotiated on EBGP sessions between ASBR14
- ASBR24 and ASBR15 - ASBR25. BGP LU is also negotiated on IBGP
sessions in AS1 between RR13 and the nodes PE11, PE12, ASBR13, and
ASBR14; also in AS2 between RR23 and the nodes PE21, PE22, ASBR24,
and ASBR25. The ASBRs readvertise the BGP LU routes rewriting next
hop to self. The RRs readvertise the BGP LU routes with the next hop
unchanged.
L3VPN Service routes are present only at PEs and RRs in the two ASes.
L3VPN family (AFI/SAFI: 1/128) is negotiated between PE11, PE12 and
RR13. RR13 has multihop EBGP peering with RR23 and negotiates AFI/
SAFI: 1/128. RR23 further peers with PE21, PE22 in AS2. The RRs
readvertise the L3VPN service routes with next hop unchanged.
In this example loopback addresses of all PEs in one AS are reachable
via BGP LU to the other AS.
Following sections describe the control plane and forwarding plane
mechanics to deploy label spoofing protection using MPLS Namespaces
in this network.
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Traffic direction being described is AS2 to AS1, since focus is on
traffic entering a trusted zone from an untrusted zone.
6.1.2. Spoof protection for Transport Labels
6.1.2.1. MPLS Namespace to Confine Untrusted Interfaces
At ASBR14 and ASBR15, the interfaces connecting to the BGP peers in
untrusted zone are provisioned to terminate in a separate MPLS
Namespace, lets call it "From-AS2" namespace. It identifies traffic
that is allowed from AS2. This namespace contains a distinct MPLS
FIB, which is different from the global MPLS FIB. MPLS packets
received on these interfaces are forwarded based on lookup in this
MPLS FIB.
ASBR14 and ASBR15 advertise BGP LU routes for PE11, PE12 loopbacks to
peers in AS2 with next hop self. Routes for the labels advertised in
these routes are installed in the "From-AS2" MPLS namespace. Thus,
MPLS packets received on these interfaces will be accepted only if
the outermost label is installed in this MPLS namespace FIB. Packets
with unknown labels will be discarded.
This provides spoof protection for the transport labels advertised in
BGP LU.
6.1.2.2. UHP Labels for PE Loopbacks
The border nodes ASBR14 and ASBR15 use UHP labels in BGP LU routes
when advertising a AS1 PE loopback to neighbors in AS2. This label
serves as Context Label that identifies traffic sent by AS2 towards
that PE in AS1.
The route for Context Label advertised to AS2 neighbors is installed
in the "From-AS2" MPLS namespace FIB. This route is installed with a
nexthop which has the forwarding semantic as "Pop, Lookup in MPLS-
namespace for the PE".
In this manner, the incoming MPLS traffic is validated against the
outermost label to match an advertised PE label, and then sent for
futher processing in context of the corresponding PE MPLS namespace.
6.1.3. Spoof protection for Service Labels
6.1.3.1. MPLS Namespace for Traffic Destined to a PE
At ASBR14 and ASBR15, a separate MPLS Namespace is created for PE11
and PE12. Lets call them "To-PE1" and "To-PE2" namespaces.
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The namespace "To-PE11" identifies traffic direction towards PE11.
MPLS packets destined towards PE11 are forwarded based on lookup in
this MPLS namespace FIB.
The namespace "To-PE12" identifies traffic direction towards PE12.
MPLS packets destined towards PE12 are forwarded based on lookup in
this MPLS namespace FIB.
Packets are directed to these namespaces after being processed in the
"From-AS2" MPLS namespace FIB.
6.1.3.2. BGP MPLS Namespaces Family Routes
Correspondingly, MPLS Namespaces "To-PE11" and "To-PE12" are created
at RR13 which acts as an external label allocator for these
namespaces at these ASBRs. The namespace To-PE11 has an associated
Route Target RT-PE11. The namespace To-PE12 has an associated Route
Target RT-PE12. These Route Targets are exported by the RR and
imported by the ASBRs.
In AS1, the route reflector RR13 negotiates MPLS Namespace Signaling
family (AFI/SAFI: 16399/128) with the border nodes ASBR14 and ASBR15.
Using the MPLS namespace signaling family, the RR13 insalls the VPN
service labels advertised by PE11 and PE12 into their corresponding
namespaces at the ASBRs.
Consider PE11 advertising to RR13 a VPN prefix RD:Pfx1 with VPN label
VL1, next hop as PE11. RR13 advertises this route with next hop and
label unchanged to RR23. When doing so, RR13 originates a MPLS
namespace signaling family (AFI/SAFI: 16399/128) route with NLRI
RDx:VL1, next hop as PE11, label field containing VL1, and the Route
Target RT-PE11.
ASBR14 receives this route and installs in the "To-PE11" MPLS
namespace FIB, based on matching import route target RT-PE11. The
received next hop PE11 is resolved to map to available tunnel from
ASBR14 to PE11. The MPLS route for label VL1 is installed to the
"To-PE11" MPLS namespace FIB. This ensures that packets sent by AS2
with VPN label as VL1 will be forwarded properly to PE11. But if an
unknown inner label was sent by AS2, such a packet will be dropped
after lookup in "To-PE11" MPLS FIB.
Similar mechanism works for labels advertised by PE12, using "To-
PE12" MPLS namespace RIB and FIB at RR and ASBRs.
In this manner, protection is provided against nodes in AS2 spoofing
service label also.
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6.1.4. Applicability to Inter-AS Option B
These mechanisms can be used in Inter-AS Option B scenarios as-well.
In such cases, the procedures specified in Section 6.1.2.1 are
applied to L3VPN family routes instead of BGP LU routes. MPLS
namespace signaling family (AFI/SAFI: 16399/128) is not used in this
case.
In Inter-AS Option B scenarios, ASBR14 and ASBR15 re-advertise BGP
L3VPN (AFI/SAFI: 1/128) routes from PE11, PE12 to peers in AS2 with
next hop self. Routes for the labels advertised in these routes are
installed in the "From-AS2" MPLS namespace. Thus, MPLS packets
received on these interfaces will be accepted only if the outermost
label is installed in this MPLS namespace FIB. Packets with unknown
labels will be discarded.
This provides spoof protection for the L3VPN service labels
advertised in BGP L3VPN (AFI/SAFI: 1/128) family.
6.2. Improve Scaling and Convergence of a Seamless MPLS Network
MPLS Namespaces can be used to improve scaling and convergence
properties of a scaled BGP MPLS network. It acts like a Mezanine
transport layer that decouples the service layer from the actual
transport layer.
Typically service routes in a MPLS network bind to the following
entities that identify point-of-presence of a service:
* Protocol Nexthop - PE loopback address (GPNH)
* Service Label - PE advertised locally signifcant label that
identifies the service
In such a model, whenever a PE is taken out of service the GPNH
changes, and Service-Label changes - which makes maintenance a heavy
convergence event. Because the service routes with massive-scale
need to be readvertised with new service-label or PE-address.
An alternate model could be: to advertise the service routes with a
protocol-nexthop of CPNH identifying a namespace, with a forwarding-
semantic of:
* "Push <Private-Label>, and Forward to CPNH"
This model fully decouples the service-layer from the transport-layer
identifiers, by making the Service routes refer to the CPNH and
Private Labels. Thus the underlying transport layer can change
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(nodes representing a Private label can be added or removed) without
any changes to the service routes. This presents good convergence
scaling properties for the network.
This model also allows anycast traffic forwarding to any resource in
the network. Multiple PEs can advertise the same Private label to
identify a specific service (e.g. peering with an AS) they are
offering.
Once the service route traffic enters the private FIB layer, at the
closest entry-point determined by path-selection of CPNH auto-
discovery routes; then the Private Labels (with pre determined
values) pushed will determine the loose hop path taken by the traffic
and also the destination-resource.
This section describes how scaling is achieved in an inter-domain
MPLS network, where a domain is an AS or IGP area. Domain boundary
is demarcated by a BN performing BGP next hop self action on the
transport route.
It considers the scenario suggested in Section 6.3.2.1 of
[Intent-Routing-Color] where 300K nodes exist in the network with 5
transport classes.
This may result in 1.5M transport layer routes and MPLS transit
routes in all Border Nodes in the network, which may overwhelm the
nodes' MPLS forwarding resources.
This section explains how "MPLS Namespaces" is used to scale such a
network. This approach reduces the number of PNHs that are globally
visible in the network, thus reducing forwarding resource usage
network wide. Service route state is kept confined closer to network
edge, and any churn is confined within the region containing the
point of failure, which improves convergence.
In order to achieve these scaling benefits, new functionality is
required only at a Region's Border Nodes and the Regional RRs. All
other nodes can remain legacy nodes, and still get the scaling and
convergence benefits of this mechanism. This is mainly advantageous
to ingress and egress PE devices which may be low end devices not
capable of pushing deep label stacks or supporting large number of
ECMP next hops. They can enjoy the scaling benefits without needing
software upgrades.
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6.2.1. Illustration
Let us consider the decomposition of this example network with 300K
nodes to be such that there are 300 domains containing 1000 nodes
each. The mechanism described here will reduce the forwarding
resource usage in all Border Nodes to become a function of number of
domains (300) instead of number of nodes (300K). Thus, drastically
reducing MPLS transit routes from 1.5M to 1500. The Border Nodes and
Regional RRs in a Region do the job of abstracting the 1000 PE
loopbacks from the rest of the network. The rest of the network sees
this region as 1 BGP next hop, and not as 1000 BGP next hops.
6.2.2. Topology
[RR11] [RR31]
| |
| |
[PE11]\ | /[BN11]--+ +--[BN31]\ | /[PE31]
\ | / \ / \ | /
[CE41]--[PE12]--[P11] [BN21] [P31]--[PE32]--[CE31]
.. / \ / \ / \ ..
.. / \[BN12]--+ +--[BN32]/ \ ..
[PE11000] [PE31000]
| | | |
AS4 | ..Domain1.. | ..Domain2.. | ..Domain3.. | AS3
| | (backbone) | |
<---- Traffic Direction ----
Figure 2: BGP MPLS Namespaces.
This topology in Figure 2 shows a cross section of the network with
focus on two domains Domain1 and Domain3 connected via a backbone
domain Domain2. Rest of the domains are not shown for brevity. The
border nodes have forwarding state pertaining to all domains in the
network. The control plane and forwarding plane state in node BN21
can be examined to determine the MPLS scaling characteristics of the
network.
L3VPN Service routes are present only at ingress and egress PEs.
L3VPN family (AFI/SAFI 1/128) is negotiated between PE11..PE11000 and
regional route reflector RR11. RR11 has multihop EBGP peering with
RR31 and negotiates AFI/SAFI 1/128. RR31 further peers with all PEs
PE31..PE31000 in Domain3.
At the Transport layer - in Domain1, PE11..PE11000 negotiate BGP
families (AFI/SAFI 1/4, AFI/SAFI 1/76) with BN11, BN12. In Domain2,
BN11 and BN12 similarly negotiate the transport families with BN21,
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which in turn peers with BN31 and BN32. In Domain3, BN31 and BN32
peer with PEs PE31..PE31000. Each of these BNs change BGP next hop
to self, when re advertising the AFI/SAFI 1/4, AFI/SAFI 1/76
transport routes.
When all nodes loopback addresses are visible throughout the network,
it will result in 1.5M transport layer routes and MPLS transit routes
in BN21.
Following sections describe the control plane and forwarding plane
mechanics to reduce this to 1500 routes, when MPLS Namespaces is
deployed in this network.
Traffic direction being described is CE41 to CE31. Reverse direction
would work in similar way.
Traffic direction being described is CE41 to CE31. Reverse direction
would work in similar way.
6.2.3. Context Protocol Nexthop Address (CPNH)
A MPLS Namespace is identified by a Context PNH address. In MPLS
forwarding, labels are locally significant to the node advertising
it. E.g. labels in default/global MPLS Namespace are scoped by the
node's loopback address. The labels belonging to a MPLS Namespace
are locally significant in scope of the Context PNH address.
A UHP label called as "Context Label" is advertised for the CPNH in a
transport protocol, which points to the MPLS Namespace forwarding
context. When Context label is received as outer label in a MPLS
packet, it is Popped, and lookup is performed for the MPLS label that
appears in the MPLS Namespace identified by the CPNH.
In this example, CPNH is an anycast IP address that represents set of
PEs in a domain. E.g. CPNH1 represent all PEs in Domain1. And
CPNH3 represents all PEs in Domain3.
6.2.4. Service Forwarding Helper, and Changes to Transport Layer
The border nodes BN11, BN12 maintain the forwarding context for MPLS
Namespace identified by CPNH1. They advertise CPNH1 in transport
layer routes like AFI/SAFI 1/4 or AFI/SAFI 1/76 with a UHP Context
Label CL1. Any transport layer protocol may be used to advertise the
UHP Context Label for the CPNH.
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In this way, BN11 and BN12 serve as Service Forwarding Helpers for
CPNH1 MPLS Namespace. They attract traffic that remote devices send
towards the BGP next hop CPNH1, and forward the MPLS packets received
with the MPLS labels belonging to the MPLS Namespace identified by
CPNH1.
The individual loopback addresses of the PEs need not be advertised
outside the local region. E.g. PE11..PE11000 are not advertised
beyond BN11, BN12. Only CPNH1 and RR11 addresses are advertised out.
RR1 is used for the control plane peering and CPNH1 is used as a
forwarding anchor point.
Similarly, Domain3 advertises only RR31 and CPNH3 to Domain2. This
significantly reduces the transport route scale and MPLS forwarding
resource usage at the border nodes throughout the network.
6.2.5. BGP MPLS Namespace Address family (AFI:16399, SAFI:128)
In Domain1, the regional route reflector RR11 negotiates MPLS
Namespace Signaling address family with the border nodes BN11, BN12.
RR11 is an external label allocator for the MPLS Namespace identified
by CPNH1. RR1 advertises in the MPLS Namespace address family, the
labels it allocated in scope of CPNH1. These routes are advertised
with a route target that identifies CPNH1. BN11 and BN12 use this
route target to import the label route into the forwarding context
associated with CPNH1.
Similarly, in Domain3, RR31 negotiates MPLS Namespace Signaling
address family with the border nodes BN31, BN32.
6.2.6. Changes to Service Layer Route Exchange
When RR11 re-advertises to RR31 a VPN route RD:Pfx1 received with
label VL1 from egress PE11 in Domain1, it sets BGP next hop to CPNH1,
and advertises a new label PL1. This label PL1 is allocated within
the scope of CPNH1 namespace.
The label PL1 is advertised to BN1, BN2 in MPLS Namespace address
family with a route target identifying CPNH1, and BGP next hop PE11
and label VL1 that were received from the egress PE. BN1 and BN2
resolve the path to that BGP next hop PE11 and use as next hop for
the PL1 route installed in CPNH1 forwarding context.
The remote PEs in Domain3 consume the BGP updates from Domain1
following regular procedures for AFI/SAFI 1/128. When resolving the
BGP next hop CPNH1, they will push the context label that lands the
traffic into the correct forwarding context in one of the border
nodes.
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6.2.7. Analysis of Forwarding Behavior
The forwarding behavior thus achieved is similar to Inter-AS Option
B, without carrying any service routes at the border nodes.
Furthermore, the MPLS namespace labels are installed in all the
border nodes, which allows for quicker traffic convergence in case of
border node failure. The number of border nodes can be increased in
a scale out manner, which gives a cookie cutter template to scale a
network region.
In conclusion, this mechanism provides both scaling and convergence
benefits for the MPLS network, and allows to support huge scale
networks.
6.3. VNF Service Forwarding Helper usecase
In a virtualized environment a Service PE node (that comprises of a
vCP and multiple vFPs) can mirror MPLS labels (GL1) in its global
MPLS FIB to a private forwarding context at an upstream node (SFH)
with information on which vFPs are optimal exit-points for that
label. Such that the SFH can optimally forward traffic to GL1 to the
right vFPs, thus avoiding intra fabric traffic hops.
To do this, the service PE advertises a private label route with
RD:GL1 to the SFH node. The route is advertised with a MultiNextHop
attribute with one or more legs that have a "Forward to SEPx"
semantics. Where SEPx is one of many exit-points at the Service-PE
node.
6.4. BGP Based Standard API to Network's MPLS Forwarding Plane
This mechanism facilitates predictable (external allocator) label
values, using a standard BGP family as the API. This gives the
external applications a separate MPLS FIB to play with, totally
separate from other applications.
This also avoids vendor specific API dependencies between external
label allocators (e.g., Controller software), and network routers.
This mechanism also increases the overal MPLS label space available
in the network. Because it creates per application label forwarding
contexts (namespaces), instead of reserving ranges and splitting the
global MPLS FIB among various applications.
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6.5. Traffic Engineering and Service Chaining
MPLS namespaces provide an ingress PE the ability to steer MPLS
traffic thru specific detour loose hop nodes using predictable label
stack.
Labels in a MPLS namespace may be used to identify service chain
hops, thus allowing to create a Service Chain consisting of multiple
service functions.
Allows private MPLS label usage to spread across multiple
domains(e.g., ASes) and works seamlessly with existing technologies
like Inter-AS VPN option C.
7. IANA Considerations
This document makes following requests of IANA.
New BGP AFI code ("Address Family Numbers" registry):
* 16399 for "MPLS Namespaces"
Note to RFC Editor: this section may be removed on publication as an
RFC.
8. Security Considerations
Using separate mpls forwarding contexts for separate applications and
stitching them into separate MPLS planes increases the security
attributes of the MPLS network.
9. Acknowledgements
The authors thank Jeffrey (Zhaohui) Zhang, Ron Bonica, Jeff Haas,
John Scudder, Jim Uttaro, Israel Means, Torunn Narvestad, Christian
Graf, Natarajan Venkataraman, Reshma Das and Aravind Srinivas
Srinivasa Prabhakar for the valuable discussions and feedback.
10. References
10.1. Normative References
[BGP-CT] Vairavakkalai, K. and N. Venkataraman, "BGP Classful
Transport Planes", 10 July 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-bgp-
ct-12>.
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[MNH] Vairavakkalai, Ed., "BGP MultiNexthop Attribute", 23 July
2023, <https://datatracker.ietf.org/doc/html/draft-
kaliraj-idr-multinexthop-attribute-09>.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
2006, <https://www.rfc-editor.org/info/rfc4364>.
[RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
"Multiprotocol Extensions for BGP-4", RFC 4760,
DOI 10.17487/RFC4760, January 2007,
<https://www.rfc-editor.org/info/rfc4760>.
[RFC5331] Aggarwal, R., Rekhter, Y., and E. Rosen, "MPLS Upstream
Label Assignment and Context-Specific Label Space",
RFC 5331, DOI 10.17487/RFC5331, August 2008,
<https://www.rfc-editor.org/info/rfc5331>.
[RFC8277] Rosen, E., "Using BGP to Bind MPLS Labels to Address
Prefixes", RFC 8277, DOI 10.17487/RFC8277, October 2017,
<https://www.rfc-editor.org/info/rfc8277>.
10.2. Informative References
[Intent-Routing-Color]
Hegde, Ed., "Intent-aware Routing using Color", 13 March
2022, <https://datatracker.ietf.org/doc/html/draft-hr-
spring-intentaware-routing-using-color-01#section-6.3.2>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001,
<https://www.rfc-editor.org/info/rfc3032>.
Contributors
Moshiko Nayman
Juniper Networks, Inc.
18 Buckingham Dr
Manalapan, New Jersey 07726
United States of America
Email: mnayman@juniper.net
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Authors' Addresses
Kaliraj Vairavakkalai (editor)
Juniper Networks, Inc.
1133 Innovation Way,
Sunnyvale, CA 94089
United States of America
Email: kaliraj@juniper.net
Minto Jeyananth
Juniper Networks, Inc.
1133 Innovation Way,
Sunnyvale, CA 94089
United States of America
Email: minto@juniper.net
Praveen Ramadenu
AT&T Services, Inc.
3538 Torrance Blvd, Unit 124
Torrance, CA 90503
United States of America
Email: pr9637@att.com
Israel Means
AT&T
2212 Avenida Mara,
Chula Vista, California 91914
United States of America
Email: israel.means@att.com
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