Internet DRAFT - draft-dskc-bess-bgp-car-problem-statement
draft-dskc-bess-bgp-car-problem-statement
BESS WorkGroup D. Rao
Internet-Draft S. Agrawal
Intended status: Informational C. Filsfils
Expires: November 27, 2022 Cisco Systems
B. Decraene
Orange
D. Steinberg
Lapishills Consulting Limited
L. Jalil
Verizon
J. Guichard
Futurewei
K. Talaulikar
K. Patel
Arrcus, Inc
W. Henderickx
Nokia
May 26, 2022
BGP Color-Aware Routing Problem Statement
draft-dskc-bess-bgp-car-problem-statement-05
Abstract
This document explores the scope, use-cases and requirements for a
BGP based routing solution to establish end-to-end intent-aware paths
across a multi-domain service provider network environment.
Status of This Memo
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This Internet-Draft will expire on November 27, 2022.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Objective . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Color-Aware Routing . . . . . . . . . . . . . . . . . . . 3
1.2.1. Intent . . . . . . . . . . . . . . . . . . . . . . . 4
1.2.2. Color . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2.3. Colored Service Route . . . . . . . . . . . . . . . . 4
1.2.4. Color-Aware Route . . . . . . . . . . . . . . . . . . 4
1.2.5. Service Route Automated Steering on color-aware route 5
1.2.6. Inter-Domain color-aware routing with SR Policy . . . 5
1.2.7. Need for a BGP-based color-aware routing solution . . 5
1.2.8. BGP Color-Aware Routing . . . . . . . . . . . . . . . 5
1.2.9. Architectural consistency among color-aware routing
solutions . . . . . . . . . . . . . . . . . . . . . . 5
1.2.10. Color Domains . . . . . . . . . . . . . . . . . . . . 7
1.2.11. Per-Destination and Per-Flow Steering with BGP CAR . 7
2. Intent bound to a Color . . . . . . . . . . . . . . . . . . . 8
3. BGP CAR Use-cases . . . . . . . . . . . . . . . . . . . . . . 8
3.1. BGP Transport CAR . . . . . . . . . . . . . . . . . . . . 8
3.1.1. Use-case of minimization of a cost metric vs a
latency metric . . . . . . . . . . . . . . . . . . . 9
3.1.2. Use-case of exclusion/inclusion of link affinity . . 11
3.1.3. Use-case of exclusion/inclusion of domains . . . . . 11
3.1.4. Use-case of virtual network function chains in local
and core domains . . . . . . . . . . . . . . . . . . 12
3.2. BGP VPN CAR . . . . . . . . . . . . . . . . . . . . . . . 13
3.2.1. Use-case of minimization of a cost metric vs a
latency metric . . . . . . . . . . . . . . . . . . . 16
3.2.2. Use-case of exclusion/inclusion of link affinity . . 17
3.2.3. Use-case of virtual network function chains in local
and core domains . . . . . . . . . . . . . . . . . . 18
4. Deployment Requirements . . . . . . . . . . . . . . . . . . . 19
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5. Scalability . . . . . . . . . . . . . . . . . . . . . . . . . 20
5.1. Scale Requirements . . . . . . . . . . . . . . . . . . . 20
5.2. Scale Analysis . . . . . . . . . . . . . . . . . . . . . 22
6. Network Availability . . . . . . . . . . . . . . . . . . . . 24
7. BGP Protocol Requirements . . . . . . . . . . . . . . . . . . 25
8. Future Considerations . . . . . . . . . . . . . . . . . . . . 26
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 26
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 27
10.1. Normative References . . . . . . . . . . . . . . . . . . 27
10.2. Informative References . . . . . . . . . . . . . . . . . 30
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31
1. Introduction
1.1. Objective
This document explores the scope, use-cases and requirements for a
BGP based routing solution to establish end-to-end intent-aware paths
across a multi-domain service provider network environment.
The targeted design outcome is to define the technology and protocol
extensions that may be required in a manner that addresses the widest
application.
The problem that the document initially focuses on is the BGP-based
delivery of an intent across several transport domains. To do this,
it describes existing intent-aware routing solutions that are
deployed and then extends the solution scope and architecture to BGP.
The problem space is then widened to include any intent (including
NFV chains and their location), any dataplane and the application of
the intent-based routing to the Service/VPN routes. All of this is
detailed in the rest of the document.
1.2. Color-Aware Routing
Color-Aware Routing (CAR) establishes routed paths that satisfy
specific intent in a network. This section describes the basic
concepts that define CAR and the protocols that currently support it.
The figure below is used as reference.
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+-----------------------------------+
|----+ +----|
| E1 | | E2 |- V/v with C
|----+ +----|
+-----------------------------------+
Figure 1: Color-aware routing reference topology
1.2.1. Intent
Intent in routing may be any combination of the following behaviors:
o Topology path selection (e.g. minimize metric, avoid resource)
o NFV service insertion (e.g. service chain steering)
o Per-hop behavior (e.g. QoS for 5G slice)
An intent-aware routed path may be within a single network domain or
across multiple domains.
1.2.2. Color
Color is a 32-bit numerical value that is associated with an intent,
as defined in [I-D.ietf-spring-segment-routing-policy]
1.2.3. Colored Service Route
An Egress PE E2 colors a BGP service (e.g., VPN) route V/v to
indicate the particular intent that E2 requests for the traffic bound
to V/v. The color (C) is encoded as a BGP Color Extended community
[I-D.ietf-idr-tunnel-encaps].
1.2.4. Color-Aware Route
(E2, C) is a color-aware route to E2 which satisfies the intent
associated with color C.
Multiple technologies already provide color-aware paths in solutions
that are widely deployed.
o SR Policy [I-D.ietf-spring-segment-routing-policy]
o IGP Flex-Algo [I-D.ietf-lsr-flex-algo]
In the context of large-scale SR-MPLS networks, SR Policy is
applicable to both intra-domain and inter-domain deployments; whereas
IGP Flex-Algo is better suited to intra-domain scenarios.
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1.2.5. Service Route Automated Steering on color-aware route
An ingress PE E1 automatically steers V-destined packets onto a
Color-Aware path bound to (E2, C). If several such paths exist, a
preference scheme is used to select the best path: E.g. IGP Flex-
Algo first, then SR Policy.
1.2.6. Inter-Domain color-aware routing with SR Policy
If E1 and E2 are in different domains, E1 may request an SR-PCE in
its domain for a path to (E2, C). The SR-PCE (or a set of them)
computes the end-to-end path and installs it at E1 as an SR Policy.
The end-to-end color-aware path may seamlessly cross multiple
domains.
1.2.7. Need for a BGP-based color-aware routing solution
o An operator with an existing Seamless-MPLS/BGP-LU inter-domain
deployment [I-D.ietf-mpls-seamless-mpls] may prefer a BGP based
extension as a more incremental approach
o There may be an expectation that BGP would support a larger scale
o Trust boundaries in an inter-domain deployment leads to a
preference for a BGP peering based solution
1.2.8. BGP Color-Aware Routing
BGP Color-Aware Routing (CAR) is a new BGP solution which signals
intent-aware routes to reach a given destination (e.g., E2). (E2, C)
represents a BGP hop-by-hop distributed route that builds an inter-
domain color-aware path to E2 for color C.
1.2.9. Architectural consistency among color-aware routing solutions
As seen above, multiple technologies exist that provide color-aware
routing in a network. A BGP based solution must be compliant with
the existing principles that apply to them:
o Service routes MUST be colored using BGP Color Extended-Community
to request intent
* V/v via E, colored with C
o Colored service routes MUST be automatically steered on an
appropriate color-aware path
* V/v via E with C is steered via (E, C)
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* (E, C) provided by any color-aware technology or protocol
o Color-aware routes MAY resolve recursively via other color-aware
routes
* (E, C) via N recursively resolves via (N, C)
Here is a brief example that illustrates these principles.
+----------------+ +----------------+ +----------------+
| | | | | | V/v with C1
|----+ +----+ +----+ +----|/
| E1 | | N1 | | N2 | | E2 |\
|----+ +----+ +----+ +----| W/w with C2
| | | | | |
| Domain 1 | | Domain 2 | | Domain 3 |
+----------------+ +----------------+ +--- ------------+
Figure 2: Color-aware routing inter-domain reference topology
In the figure above, all the nodes are part of an inter-domain
network under a single authority and with a consistent color-to-
intent mapping:
o Color C1 is mapped to "low delay"
* Flex-Algo FA1 is mapped to "low delay" and hence to C1
o Color C2 is mapped to "low delay and avoid resource R"
* Flex-Algo FA2 is mapped to "low delay and avoid resource R" and
hence to C2
E1 receives two BGP colored service routes from E2:
o V/v with BGP Color Extended community C1
o W/w with BGP Color Extended community C2
E1 has the following inter-domain color-aware paths:
o (E2, C1) provided by BGP CAR which recursively resolves via intra-
domain color-aware paths:
* (N1, C1) provided by IGP FA1 in Domain1
* (N2, C1) provided by SR Policy bound to color C1 in Domain2
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o (E2, C2) provided by SR Policy
E1 automatically steers the received colored service routes as
follows:
o V/v via (E2, C1) provided by BGP CAR
o W/w via (E2, C2) provided by SR Policy
The example illustrates the benefits provided by leveraging the
architectural principles:
o Seamless co-existence of multiple color-aware technologies, e.g.,
BGP CAR and SR Policy
* V/v is steered on BGP CAR color-aware path
* W/w is steered on SR Policy color-aware path
o Seamless and complementary interworking between different color-
aware technologies
* V/v is steered on a BGP CAR color-aware path that is itself
resolved within domain 2 onto an SR Policy bound to the color
of V/v
1.2.10. Color Domains
o A color domain represents a collection of one or more network
(IGP/BGP) domains with a single, consistent color-to-intent
mapping
o Color re-mapping may happen at color domain boundaries
1.2.11. Per-Destination and Per-Flow Steering with BGP CAR
Ingress PE E1 steers packets destined for a service (VPN) route V/v
via BGP Color-Aware Route R/r to E2
o Per-Destination Steering: Incoming packets on E1 match BGP service
route V/v to be steered based on the destination IP address of the
packets.
o Per-Flow Steering: Incoming packets on E1 match BGP service route
V/v to be steered based on the combination of the destination IP
address and additional elements in the packet header (i.e., IP
flow). Such a packet lookup may recurse on a forwarding array
where some of the entries are BGP color-aware routes to E2. A
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given flow is mapped to a specific entry in this array i.e. via a
specific BGP color-aware route to E2.
2. Intent bound to a Color
The BGP CAR solution must support the following intents bound to a
color:
o Minimization of a cost metric vs a latency metric
* Minimization of different metric types, static and dynamic
o Exclusion/Inclusion of SRLG and/or Link Affinity and/or minimum
MTU/number of hops
o Bandwidth management
o In the inter-domain context, exclusion/inclusion of entire
domains, and border routers
o Inclusion of one or several virtual network function chains
* Located in a regional domain and/or core domain, in a DC
o Localization of the virtual network function chains
* Some functions may be desired in the regional DC or vice versa
o Per-Destination and Per-Flow steering
3. BGP CAR Use-cases
The BGP CAR route may be a transport route or a service route (in
this document, we use the term VPN instead of service for
simplicity).
3.1. BGP Transport CAR
o Transport Intent
* Intent-aware routing between PEs connected across multiple
transit domains
+ Set up BGP based end-to-end paths stitching intent-aware
intra-domain segments
o The network diagram below illustrates the reference network
topology used in this section for Transport CAR:
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+-----+ +-----+ +-----+
.....|S-RR1| <............. |S-RR2| <............... |S-RR3| <...
: +-----+ +-----+ +-----+ :
: :
: :
: :
+--:--------------+ +-----------------+ +--------------:--+
| : | | | | : |
| : | | | | : |
| : +---| D=20 |---+ +---| D=25 |---+ : |
| : |121|-------|211| |231|-------|321| : |
| : +---| \ / |---+ +---| \ / |---+ : |
|----+ | \ / | | \ / | +----|
|PE11| | V | | V | |PE31|
|----+ | / \ | | / \ | +----|
| +---| / \ |---+ +---| / \ |---+ |
| |122|-------|212| |232|-------|322| |
| +---| D=15 |---+ +---| D=10 |---+ |
| | | | | |
| Domain 1 | | Domain 2 | | Domain 3 |
+-----------------+ +-----------------+ +------------------+
Figure 3: Transport CAR Reference Topology
The following network design assumptions apply to the reference
topology above, as an example:
* Independent ISIS/OSPF SR instance in each domain.
* eBGP peering link between ASBRs (121-211, 121-212, 122-211,
122-212, 231-321, 231-322, 232-321 and 232-322).
* Peering links have equal cost metric.
* Peering links have delay configured or measured as shown by
"D". D=50 for cross peering links.
* VPN service is running from PE31 to PE11 via service RRs (S-RRn
in figure).
o The following sections illustrate a few examples of intent use-
cases applicable to transport routes.
3.1.1. Use-case of minimization of a cost metric vs a latency metric
o In the reference topology of Figure 3
Each domain has Algo 0 and Flex Algo 128
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Algo 0 is for minimum cost metric(cost optimized).
Flex Algo 128 definition is for minimum delay (low latency).
o Cost Optimized
* Color C1 - Minimum cost intent. (Here, a BGP CAR route with
Color C1 is being used, instead of BGP-LU.)
* On PE11, VPN routes colored with C1 are steered via (C1, PE31)
BGP CAR route
+ BGP CAR for C1 sets up path(s) between PEs for end-to-end
minimum cost.
+ (2) These paths traverse over intra-domain Algo 0 in each
domain and account for the peering link cost between ASBRs.
+ Example: PE11 learns (C1, PE31) CAR route via several equal
paths:
1. One such path is through FA0 to node 121, links 121-211,
FA0 to 231, link 231-321, FA0 to PE31
2. Another such path is through FA0 to node 122, link
122-212, FA0 to 232, link 232-322, FA0 to PE31.
o Minimize latency
* Color C2 - Minimum latency intent.
* On PE11, VPN routes colored with C2 are steered via (C2, PE31)
BGP CAR route.
+ BGP CAR for C2 advertises paths between PEs for minimum end-
to-end delay.
+ (2) These paths traverse over intra-domain Flex Algo 128 in
each domain and account for peering link delay between
ASBRs.
+ (3) Example: PE11 learns (C2, PE31) BGP CAR route and best
path is through FA128 to node 122, link 122-212, FA128 to
232, link 232-322, FA128 to PE31.
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3.1.2. Use-case of exclusion/inclusion of link affinity
o Color C3 - Intent to Minimize cost metric and avoid purple links
o In the reference topology of Figure 3
Each domain has Flex Algo 129 and some links have purple
affinity.
Flex Algo 129 definition is set to minimum cost metric and
avoid purple links (within domain).
Peering cross links are colored purple by policy.
o On PE11, VPN routes colored with C3 are steered via (C3, PE31) BGP
CAR route.
* BGP CAR for C3 sets up paths between PEs for minimum end-to-end
cost and avoiding purple link affinity.
* These paths traverse over intra domain Flex Algo 129 in each
domain and accounts for peering link cost between ASBR and
avoiding purple links.
* Example: PE11 learns (C3, PE31) BGP CAR route via 2 paths.
1. First path is through FA 129 to node 121, link 121-211,
FA129 to 231, link 231-321, FA129 to PE31.
2. Second path is through FA129 to node 122, link 122-212,
FA129 to 232, link 232-322, FA129 to PE31.
3.1.3. Use-case of exclusion/inclusion of domains
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+-----+ +-----+ +-----+
....|S-RR1| <............. |S-RR2| <.............. |S-RR3| <....
: +-----+ +-----+ +-----+ :
: :
: +----------------+ :
: | | :
+--:--------------+ |---+ +---| +--------------:--+
| : | |---|211| |241|---| | : |
| : | | |---+ +---| | | : |
| : +---| | | Domain 2 | | |---+ : |
| : |121|---| +----------------+ |---|421| : |
| : +---| |---+ : |
|----+ | | +----|
|PE11| | | |PE41|
|----+ | | +----|
| +---| |---+ |
| |131|---| +----------------+ |---|431| |
| +---| | | | | |---+ |
| | | |---+ +---| | | |
| Domain 1 | |---|311| |341|---| | Domain 4 |
+-----------------+ |---+ +---| +-----------------+
| Domain 3 |
+----------------+
Figure 4
Color C4 - Avoid sending selected traffic via Domain 3
o VPN routes advertised from PEs with Color C4
o BGP CAR for Color C4 should only set up paths between PE11 and
PE41 that exclude Domain 3
3.1.4. Use-case of virtual network function chains in local and core
domains
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____ ____
/ \ / \
| NFV1 | | NFV2 |
\ / \ /
+---------------------+ +--------------------+ +-------------------+
| |E11| | | |E21| | | |
| +---+ | | +---+ | | |
| | | | | |
| | | | | |
|----+ +------+ +------+ +----|
|PE11| | 121 | | 231 | |PE31|
|----+ +------+ +------+ +----|
| | | | | |
| | | | | |
| | | | | |
| | | | | |
| Domain 1 | | Domain 2 | | Domain 3 |
+---------------------+ +--------------------+ +-------------------+
Figure 5
o Color intent
* C5 - Routing via min-cost paths
* C6 - Routing via a local NFV service chain situated at E11
* C7 - Routing via a centrally located NFV service chain situated
at E21
o Forwarding of packets from PE11 towards PE31:
* (C5, PE31) mapped packets are sent via nodes 121, 231 to PE31
* (C6, PE31) mapped packets are sent to E11 and then post-service
chain, via 121, 231 to PE31
* (C7, PE31) mapped packets are sent via 121 to E21 and then
post-service chain, via 231 to PE31
3.2. BGP VPN CAR
o VPN (Service layer) intent
* Extend the signaling of intent awareness end-to-end: CE site to
CE site across provider networks
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+ Provide ability for a CE to select paths through specific
PEs for a given intent
- Example-1: Certain intent in transport not available via
specific PEs
- Example-2: Certain CE-PE connection does not support
specific intent
- Example-3: Site access via certain CE does not support
specific intent. For instance, link connecting a
specific CE to a DC hosting loss-sensitive service may
have better quality than a link from another CE
+ Provide ability for a CE to send traffic indicating a
specific intent (via suitable encapsulation) to the PE for
optimal steering.
* Intent aware routing support for multiple service (VPN)
interworking models
+ Beyond options such as iBGP or Inter-AS Option C that
inherently extend from PE to PE
1. Inter-AS Option A
2. Inter-AS Option B
3. GW based interworking(L3VPN, EVPN)
+ Interworking with existing L3VPN deployments, both PEs and
CEs
o The network diagram below illustrates the reference network
topology used in this section for VPN CAR.
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+-------------------+ +-------------------+
| ....|S-RR|.... | | ....|S-RR|..... |
| : +----+ : | | : +----+ : |
| : : : : | | : : : : |
|----+ : : +---| D=20 |---+ : : +----|
/|PE11| : : |121|-----------|211| : : |PE21|\
D=25/ |----+ : : +---| X X |---+ : : +----| \ D=25
/ | : : | X X | : : | \ V/24
CE1 | : : | X D=50| : : | CE2<---
X | : : | X X | : : | X
D=15 X |----+ : : +---| X X |---+ : : +----| X D=10
X|PE12|...: :...|212|-----------|232|...: :...|PE22|X
|----+ +---| D=10 |---+ +----|
| | | |
| AS 1 | | AS 2 |
+-------------------+ +-------------------+
Figure 6: VPN CAR reference topology
The following network design assumptions apply to the reference
topology above, as an example:
* Independent ISIS/OSPF SR instance in each AS.
* eBGP peering link between VPN ASBRs 121-211, 121-212, 122-211,
122-212.
* VPN service is running between PEs via service RRs in each AS
to local ASBRs. Between ASBRs, its Option-B i.e. next hop self
for VPN SAFI.
* CE1 is dual homed to PE11 and PE12. Similarly, CE2 is dual
homed to PE21 and PE22.
* Peering links have equal cost metric
* Peering links have delay configured or measured as shown by
"D".
* CE2 advertises prefix V/24 to CE1. It is advertised as RD:V/24
between PEs, including color-awareness
o The following sections illustrate a few examples of intent use-
cases applicable to VPN (service) routes.
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3.2.1. Use-case of minimization of a cost metric vs a latency metric
o In the reference topology of Figure 6
Each AS has Flex Algo 0 and 128.
Flex Algo 0 is for minimum cost metric(cost optimized).
Flex Algo 128 definition is for minimum delay (low latency).
o Cost Optimized
* Color C1 - Minimum cost intent.
* On CE1, flows requiring cost optimized paths to V/24 are
steered over (C1, V/24) route.
+ BGP CAR for C1 sets up paths between CEs for minimum end-to-
end cost.
+ This advertisement needs BGP CAR between PE-CE for V/24
prefix and color C1 awareness.
+ It also needs BGP VPN CAR between PEs and ASBRs for RD:V/24
prefix and color C1 awareness (C1, RD:V/24).
+ Paths traverse over PE-CE links, intra-domain Flex Algo 0 in
each AS and peering links between ASBRs, minimizing cost for
VPN.
+ Example: CE1 learns (C1, V/24) CAR route through several
equal cost paths:
1. One path is through link CE1-PE11, FA0 to 121, link
121-211, FA0 to PE21 and link PE21-CE2.
2. Another such path is through CE1-PE12, FA0 to node 122,
link 122-212, FA0 to PE22, link PE22-CE2.
o Minimize latency
* Color C2 - Minimum latency intent
* On CE1, flows requiring low latency paths to prefix V/24 are
steered over (C2, V/24) CAR route.
+ BGP CAR for C2 sets up paths between CEs for minimum end-to-
end delay.
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+ This advertisement needs BGP CAR between PE-CE for V/24
prefix and color C2 awareness.
+ It also needs BGP VPN CAR between PEs and ASBR for RD:V/24
prefix and color C2 awareness (C2, RD:V/24).
+ Paths traverse over intra-domain Flex Algo 128 in each AS
and accounts for inter ASBR link delays and PE-CE link
delays for the VPN.
+ Example: CE1 learns (C2, V/24) CAR best route through link
CE1-PE12, FA128 to 122, link 122-212, FA128 to PE22 and link
PE22-CE2.
3.2.2. Use-case of exclusion/inclusion of link affinity
o Color C3 - Intent to Minimize cost metric and avoid purple links
o In the reference topology of Figure 6
Each AS has Flex Algo 129 and some links have purple affinity.
Flex Algo 129 definition is set to minimum cost metric and
avoid purple links (within AS).
ASBR cross links are colored purple by policy. Bottom PE-CE
links are colored purple as well by policy
o On CE1, flows requiring minimum cost path avoiding purple links to
V/24 are steered over (C3, V/24) BGP CAR route.
* BGP CAR for C3 setup paths between CEs for minimum end-to-end
cost and avoiding purple link affinity.
* This advertisement needs BGP CAR between PE-CE for V/24 prefix
and color C3 awareness
* It also needs BGP VPN CAR between PEs and ASBRs for RD:V/24
prefix and color C3 awareness (C3, RD:V/24).
* The path avoids purple PE-CE links, traverses over intra-domain
Flex Algo 129 in each AS and avoids purple links between VPN
ASBRs.
* Example: CE1 learns (C3, V/24) CAR route through link CE1-PE11,
FA129 to 121, link 121-211, FA129 to PE21 and link PE21-CE2.
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3.2.3. Use-case of virtual network function chains in local and core
domains
+-----+
........................|S-RR | <.................
: +-----+ <........... :
: : :
: : :
: ___ ___ ___ : :
: / \ / \ / \ : :
:| S1 | | S2 | | S3 | : :
: \ / \ / \ / : :
+-:---------------+ +--------------+ +------:----:--+
| : |E11| |E12| | | |E21| | | : : |
| : +---+ +---+ | | +---+ | | : +----|<-(V1/24,C1)
| : | | | | : |PE31|--CE2
| V | | | | : +----|
|----+ +------+ +------+ : |
CE1--|PE11| | 121 | | 231 | : |
|----+ +------+ +------+ : +----|<-(V2/24/C2)
| | | | | :..|PE32|--CE3
| | | | | +----|
| | | | | |
| | | | | |
| Domain 1 | | Domain 2 | | Domain 3 |
+-----------------+ +--------------+ +--------------+
Figure 7
o Color intent
* C1 - Routing via NFV service chain comprising of [S1, S2]
attached to E11 and E12
* C2 - Routing via NFV service [S3] attached to E21
o CE1, CE2, CE3 are sites of VPN1.
o Prefix V1/24 colored with C1 from CE2, and advertised as RD:V1/24
with C1 by PE31 to PE11 via S-RR
o Prefix V2/24 colored with C2 from CE3, and advertised as RD:V2/24
with C2 by PE32 to PE11 via SS-RR
o From PE11:
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* [V1/24, C1] mapped packets are sent via S1, S2 and then routed
to PE31, CE2
* [V2/24, C2] mapped packets are sent via S3 and then routed to
PE32, CE3
4. Deployment Requirements
The figure below shows a reference large-scale multi-domain network
topology for targeted deployments. E1 and E2 are PEs; the other
nodes are border routers between domains in different tiers of the
network. A VPN route is advertised via service RRs (S-RR) between an
egress PE (E2) and an ingress PE (E1). BGP must provide reachability
from E1 to E2 based on various intent.
+-----+ +-----+ V/v via E2 +-----+
.......|S-RR1|<...............|S-RR2|<.................|S-RR3| <..
: +-----+ +-----+ Color C +-----+ :
: :
: :
+--:----------+-------------+--------------+-------------+----------:--+
| : | | | | : |
| : | | | | : |
| : +---+ +---+ +---+ +---+ : |
| : |121| |231| |341| |451| : |
| : +---+ +---+ +---+ +---+ : |
|----+ | | | | +----|
| E1 | | | | | | E2 |
|----+ | | | | +----|
| +---+ +---+ +---+ +---+ |
| |122| |232| |342| |452| |
| +---+ +---+ +---+ +---+ |
| Access | Metro | Core | Metro | Access |
| domain 1 | domain 2 | domain 3 | domain 4 | domain 5 |
+-------------+-------------+--------------+-------------+-------------+
iPE iBRM iBRC eBRC eBRM ePE
Figure 8: Reference large-scale multi-domain network topology
The solution must support the following :
o Co-existence, compatibility and interworking with currently
deployed SR-PCE based multi-domain color-aware solution
o Support different multi-domain deployment designs
* Multiple IGP domains within a single AS (Seamless MPLS)
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+ Inter-connect at node level (ABR)
* Multiple BGP AS domains
+ Inter-connect via peering links (ASBR)
o Support end-to-end path crossing transport domains with different
technologies and encapsulations
* LDP-MPLS
* RSVP-TE-MPLS
* SR-MPLS
* SRv6
* IPv4/IPv6
o Support interworking between domains with different encapsulations
(e.g, SR-MPLS and SRv6)
o Support multiple transport encapsulations within a domain for co-
existence and migration
o Provide a BGP-based control-plane solution for the use-case
illustrated in [RFC8604] together with deployment design
guidelines for the leverage of anycast and binding SIDs.
5. Scalability
5.1. Scale Requirements
o Support for massive scaled transport network
* Number of Remote PE's: >= 300k
* Number of Colors C: >= 5
o Scalable MPLS dataplane solution
* With one label per (C, Remote PE), the 1M MPLS dataplane does
not work.
* A notion of hierarchy or segment list is required.
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+ E.g. the SR-PCE builds the end-to-end path as a list of
segments such that no single node needs to support a data-
plane scaling in the order of (Remote PE * C)
+ The solution is thus not a direct extension of BGP-LU
* Additionally, PE and transit nodes (ABRs) may be devices with
limited forwarding table space
* Devices may have constraints on packet processing (e.g., label
operations, number of labels pushed) and performance
o Ability to abstract the topology from remote domains - for scale,
stability and faster convergence
* Abstracting PE and/or ABR related state and network events
o Support for an Emulated-PULL model for the BGP signaling
* The SR-PCE solution natively supports a PULL model: when PE1
installs a VPN route V/v via (C, PE2), PE1 requests its serving
SR-PCE to compute the SR Policy to (C, PE2). I.e. PE1 does
not learn unneeded SR policies.
* BGP Signaling is natively a PUSH model.
* Emulated-PULL refers to the ability for a BGP CAR node PE1 to
"subscribe" to (C, PE2) route such that only the related paths
are signaled to PE1.
* The subscription and related filtering solution must apply to
any BGP CAR node
+ Transport CAR routes
1. Ability for a node (PE/ABR/RR) to signal interest for
routes of specific colors.
2. PEs only learn routes that they need - remote VPN
endpoints (PEs/ASBRs) or transit nodes (ABRs, ASBRs).
3. ABRs also only learn and propagate routes they need
locally in domain
+ Service/VPN CAR routes
1. Ability for a node (PE) to signal interest for a
specific (Egress PE, Color) transport route
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2. CEs learn routes that they need - interested colors
3. PEs learn routes that they need - interested VPNs,
colors
+ Automation of the subscription/filter route
1. Similar to the SR-PCE solution, when an ingress PE1
installs VPN V/v via (C, PE2), PE1 originates its
subscription/filter route for (C, PE2).
+ Efficient propagation and processing of subscription/filter
routes.
+ Ability to perform aggregation and suppression of
subscription/filter routes at nodes in the route propagation
path to reduce explosion and churn in propagation of the
filter routes themselves.
+ The solution may be optional for networks that do not have
the large scaling requirements
5.2. Scale Analysis
It is useful to analyze the multiple scaling requirements and
specifically the data plane constraints in the context of a few
common reference designs and use-cases.
A couple of example scenarios are listed below for reference.
o Seamless-MPLS design, with IGP Flex-Algo in each domain
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+-----+
.............................. |S-RR | <........................
: +-----+ :
: :
: :
+--:-----------------+ +--------------------+ +-----------------:--+
| : | | | | : |
| : | | | | : |
| : +------+ +------+ : |
| : | 121 | | 231 | : |
| V +------+ +------+ : |
|----+ | | | | +----|
|PE11| | | | | |PE31|
|----+ | | | | +----|
| +------+ +------+ |
| | 122 | | 232 | |
| +------+ +------+ |
| | | | | |
| Domain 1 | | Domain 2 | | Domain 3 |
+--------------------+ +--------------------+ +--------------------+
Figure 9
o Inter-AS Option C VPN design, with IGP Flex-Algo in each domain,
and eBGP peering between domains
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+-----+ +-----+ +-----+
....|S-RR1| <............. |S-RR2| <............... |S-RR3| <...
: +-----+ +-----+ +-----+ :
: :
: :
: :
+--:---------------+ +------------------+ +--------------:--+
| : | | | | : |
| : | | | | : |
| : +---| |---+ +---| |---+ : |
| : |121|------|211| |231|------|321| : |
| : +---| |---+ +---| |---+ : |
|----+ | | | | +----|
|PE11| | | | | |PE31|
|----+ | | | | +----|
| +---| |---+ +---| |---+ |
| |122|------|212| |232|------|322| |
| +---| |---+ +---| |---+ |
| | | | | |
| Domain 1 | | Domain 2 | | Domain 3 |
+------------------+ +------------------+ +-----------------+
Figure 10
6. Network Availability
o The BGP CAR solution should provide high network availability for
typical deployment topologies, with minimum loss of connectivity
in different network failure scenarios.
o The network failure scenarios, applicable technologies and design
options described in [I-D.ietf-mpls-seamless-mpls] should be used
as a reference.
o In the Seamless-MPLS reference topology in previous section:
* Failure of intra-domain links should limit loss of connectivity
(LoC) to < 50ms. E.g., PE11 to a P node (not shown), 121 to a
P node in Domain1 or Domain2)
* Failure of an intra-domain node (P node in any domain) should
limit LoC to < 50ms
* Failure of an ABR node (e.g., 121, 231) should limit LoC to <
1sec
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* Failure of a remote PE node (e.g., PE3) should limit LoC to <
1sec
o In the Inter-AS Option C VPN reference topology in previous
section:
* Failure of intra-domain links should limit LoC to < 50ms.
E.g., PE11 to a P node (not shown), 121 to a P node in Domain1
or Domain2)
* Failure of an intra-domain node (P node in any domain) should
limit LoC to < 50ms
* Failure of an ASBR node (e.g., 121, 211) should limit LoC to <
1sec
* Failure of a remote PE node (e.g., PE3) should limit LoC to <
1sec
* Failure of an external link (e.g., 121-211) should limit LoC to
< 1sec
o The solution should explore and describe additional techniques and
design options that are applicable to further improve handling of
the failure cases listed above.
7. BGP Protocol Requirements
o Support signaling and distribution of different Color-Aware routes
to reach a participating node, e.g., a PE. Intent should be
indicated by the notion of a Color as defined in SR Policy
Architecture.
* Signal different instances of a prefix distinguished by color
* Signal intent associated with a given route
o Support for a flexible NLRI definition to accommodate both
efficiency of processing (e.g., packing) and future extensibility
* Avoid limitations associated with existing SAFI NLRI
definitions. For example, 24-bit label.
o Support for validation of paths
* Reachability of next-hop in control plane
* Availability and programming of encapsulation in data plane
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* Validation of intent
o Next-hop resolution for Color-Aware route
* Flexibility to use different intra-domain and inter-domain
mechanisms - IGP-FA, SR-TE, RSVP-TE, IGP, BGP-LU etc.
* Recursive resolution over BGP Color-Aware routes
* Ability to carry end-to-end cumulative metric for a given color
* Support setting up an end-to-end Color-Aware path using a
different/less preferred or best-effort paths in domains where
a particular intent is not available
o Separation of transport and VPN service semantics.
* Allow for different route distribution planes for service vs
transport routes.
o Support signaling of different transport encapsulations
o Support for signaling multiple encapsulations for co-existence and
migration
o Generation of BGP Color-Aware routes sourced from IGP-FA, SR-TE
policies and BGP-LU from a domain
o Support signaling across domains with different color mappings for
a given intent.
8. Future Considerations
Multicast service intent
9. Acknowledgements
Many people contributed to this document.
The authors would especially like to thank Jim Uttaro for his
guidance on the work and feedback on many aspects of the problem
statement. We would also like to thank Daniel Voyer, Luay Jalil and
Robert Raszuk for their review and valuable suggestions.
We also express our appreciation to Bruno Decreane, Keyur Patel, Jim
Guichard, Alex Bogdanov, Dirk Steinberg, Hannes Gredler and Xiaohu Hu
for discussions on several topics that have helped provide input to
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the document. We also thank Huaimo Chen for his valuable review
comments.
The authors would like to thank Stephane Litkowski for his detailed
review and for making valuable suggestions to improve the quality of
the document. We would also like to thank Kamran Raza and Kris
Michelson for their review and comments on the document and to Simon
Spraggs, Jose Liste and Jiri Chaloupka for their early inputs on the
problem statement.
10. References
10.1. Normative References
[I-D.agrawal-spring-srv6-mpls-interworking]
Agrawal, S., ALI, Z., Filsfils, C., Voyer, D., and Z. Li,
"SRv6 and MPLS interworking", draft-agrawal-spring-srv6-
mpls-interworking-08 (work in progress), March 2022.
[I-D.ietf-bess-srv6-services]
Dawra, G., Talaulikar, K., Raszuk, R., Decraene, B.,
Zhuang, S., and J. Rabadan, "SRv6 BGP based Overlay
Services", draft-ietf-bess-srv6-services-15 (work in
progress), March 2022.
[I-D.ietf-idr-bgp-ipv6-rt-constrain]
Patel, K., Raszuk, R., Djernaes, M., Dong, J., and M.
Chen, "IPv6 Extensions for Route Target Distribution",
draft-ietf-idr-bgp-ipv6-rt-constrain-12 (work in
progress), April 2018.
[I-D.ietf-idr-tunnel-encaps]
Patel, K., Velde, G. V. D., Sangli, S. R., and J. Scudder,
"The BGP Tunnel Encapsulation Attribute", draft-ietf-idr-
tunnel-encaps-22 (work in progress), January 2021.
[I-D.ietf-lsr-flex-algo]
Psenak, P., Hegde, S., Filsfils, C., Talaulikar, K., and
A. Gulko, "IGP Flexible Algorithm", draft-ietf-lsr-flex-
algo-20 (work in progress), May 2022.
[I-D.ietf-spring-segment-routing-policy]
Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and
P. Mattes, "Segment Routing Policy Architecture", draft-
ietf-spring-segment-routing-policy-22 (work in progress),
March 2022.
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[I-D.ietf-spring-sr-service-programming]
Clad, F., Xu, X., Filsfils, C., Bernier, D., Li, C.,
Decraene, B., Ma, S., Yadlapalli, C., Henderickx, W., and
S. Salsano, "Service Programming with Segment Routing",
draft-ietf-spring-sr-service-programming-05 (work in
progress), September 2021.
[I-D.ietf-spring-srv6-network-programming]
Filsfils, C., Garvia, P. C., Leddy, J., Voyer, D.,
Matsushima, S., and Z. Li, "Segment Routing over IPv6
(SRv6) Network Programming", draft-ietf-spring-srv6-
network-programming-28 (work in progress), December 2020.
[I-D.voyer-pim-sr-p2mp-policy]
Voyer, D., Filsfils, C., Parekh, R., Bidgoli, H., and Z.
Zhang, "Segment Routing Point-to-Multipoint Policy",
draft-voyer-pim-sr-p2mp-policy-02 (work in progress), July
2020.
[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>.
[RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
Communities Attribute", RFC 4360, DOI 10.17487/RFC4360,
February 2006, <https://www.rfc-editor.org/info/rfc4360>.
[RFC4684] Marques, P., Bonica, R., Fang, L., Martini, L., Raszuk,
R., Patel, K., and J. Guichard, "Constrained Route
Distribution for Border Gateway Protocol/MultiProtocol
Label Switching (BGP/MPLS) Internet Protocol (IP) Virtual
Private Networks (VPNs)", RFC 4684, DOI 10.17487/RFC4684,
November 2006, <https://www.rfc-editor.org/info/rfc4684>.
[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>.
[RFC5512] Mohapatra, P. and E. Rosen, "The BGP Encapsulation
Subsequent Address Family Identifier (SAFI) and the BGP
Tunnel Encapsulation Attribute", RFC 5512,
DOI 10.17487/RFC5512, April 2009,
<https://www.rfc-editor.org/info/rfc5512>.
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[RFC5701] Rekhter, Y., "IPv6 Address Specific BGP Extended Community
Attribute", RFC 5701, DOI 10.17487/RFC5701, November 2009,
<https://www.rfc-editor.org/info/rfc5701>.
[RFC7311] Mohapatra, P., Fernando, R., Rosen, E., and J. Uttaro,
"The Accumulated IGP Metric Attribute for BGP", RFC 7311,
DOI 10.17487/RFC7311, August 2014,
<https://www.rfc-editor.org/info/rfc7311>.
[RFC7606] Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K.
Patel, "Revised Error Handling for BGP UPDATE Messages",
RFC 7606, DOI 10.17487/RFC7606, August 2015,
<https://www.rfc-editor.org/info/rfc7606>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[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>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
[RFC8664] Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
and J. Hardwick, "Path Computation Element Communication
Protocol (PCEP) Extensions for Segment Routing", RFC 8664,
DOI 10.17487/RFC8664, December 2019,
<https://www.rfc-editor.org/info/rfc8664>.
[RFC8669] Previdi, S., Filsfils, C., Lindem, A., Ed., Sreekantiah,
A., and H. Gredler, "Segment Routing Prefix Segment
Identifier Extensions for BGP", RFC 8669,
DOI 10.17487/RFC8669, December 2019,
<https://www.rfc-editor.org/info/rfc8669>.
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10.2. Informative References
[I-D.filsfils-spring-sr-policy-considerations]
Filsfils, C., Talaulikar, K., Krol, P., Horneffer, M., and
P. Mattes, "SR Policy Implementation and Deployment
Considerations", draft-filsfils-spring-sr-policy-
considerations-09 (work in progress), April 2022.
[I-D.ietf-idr-performance-routing]
Xu, X., Hegde, S., Talaulikar, K., Boucadair, M., and C.
Jacquenet, "Performance-based BGP Routing Mechanism",
draft-ietf-idr-performance-routing-03 (work in progress),
December 2020.
[I-D.ietf-mpls-seamless-mpls]
Leymann, N., Decraene, B., Filsfils, C., Konstantynowicz,
M., and D. Steinberg, "Seamless MPLS Architecture", draft-
ietf-mpls-seamless-mpls-07 (work in progress), June 2014.
[RFC3906] Shen, N. and H. Smit, "Calculating Interior Gateway
Protocol (IGP) Routes Over Traffic Engineering Tunnels",
RFC 3906, DOI 10.17487/RFC3906, October 2004,
<https://www.rfc-editor.org/info/rfc3906>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<https://www.rfc-editor.org/info/rfc4271>.
[RFC4272] Murphy, S., "BGP Security Vulnerabilities Analysis",
RFC 4272, DOI 10.17487/RFC4272, January 2006,
<https://www.rfc-editor.org/info/rfc4272>.
[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>.
[RFC6952] Jethanandani, M., Patel, K., and L. Zheng, "Analysis of
BGP, LDP, PCEP, and MSDP Issues According to the Keying
and Authentication for Routing Protocols (KARP) Design
Guide", RFC 6952, DOI 10.17487/RFC6952, May 2013,
<https://www.rfc-editor.org/info/rfc6952>.
[RFC7911] Walton, D., Retana, A., Chen, E., and J. Scudder,
"Advertisement of Multiple Paths in BGP", RFC 7911,
DOI 10.17487/RFC7911, July 2016,
<https://www.rfc-editor.org/info/rfc7911>.
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Authors' Addresses
Dhananjaya Rao
Cisco Systems
USA
Email: dhrao@cisco.com
Swadesh Agrawal
Cisco Systems
USA
Email: swaagraw@cisco.com
Clarence Filsfils
Cisco Systems
Belgium
Email: cfilsfil@cisco.com
Bruno Decraene
Orange
France
Email: bruno.decraene@orange.com
Dirk Steinberg
Lapishills Consulting Limited
Germany
Email: dirk@lapishills.com
Luay Jalil
Verizon
USA
Email: luay.jalil@verizon.com
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Jim Guichard
Futurewei
USA
Email: james.n.guichard@futurewei.com
Ketan Talaulikar
Arrcus, Inc
India
Email: ketant.ietf@gmail.com
Keyur Patel
Arrcus, Inc
USA
Email: keyur@arrcus.com
Wim Henderickx
Nokia
Belgium
Email: wim.henderickx@nokia.com
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