Network Working Group L. Dunbar
Internet Draft Futurewei
Intended status: Standard K. Majumdar
Expires: February 24, 2023 Microsoft
H. Wang
Huawei
G. Mishra
Verizon
August 24, 2022
BGP Extension for 5G Edge Service Metadata
draft-dunbar-idr-5g-edge-compute-app-meta-data-14
Abstract
This draft describes three new sub-TLVs for egress routers to
advertise the Edge Service Metadata of the directly attached
edge services (ES). The Edge Service Metadata can be used by
the ingress routers in the 5G Local Data Network to make path
selection not only based on the routing cost but also the
running environment of the edge services. The goal is to
improve latency and performance for 5G edge services.
The extension enables an edge service at one specific location
to be more preferred than the others with the same IP address
(ANYCAST) to receive data flows from a specific source, like
specific User Equipment (UE).
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
This Internet-Draft is submitted in full conformance with the
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modified, and derivative works of it may not be created,
except to publish it as an RFC and to translate it into
languages other than English.
Internet-Drafts are working documents of the Internet
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groups. Note that other groups may also distribute working
documents as Internet-Drafts.
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Table of Contents
1. Introduction.............................................. 3
2. Conventions used in this document......................... 4
3. BGP Protocol Extension for Edge Service Metadata.......... 5
3.1. Ingress Node BGP Path Selection Behavior............. 5
3.1.1. Edge Service Metadata Influenced BGP Path
Selection.............................................. 5
3.1.2. Ingress Router Forwarding Behavior.............. 6
3.1.3. Forwarding Behavior when UEs moving to new 5G
Sites.................................................. 6
4. Edge Service Metadata Encoding............................ 6
4.1. Metadata Path Attribute.............................. 6
4.2. The Site Preference Index sub-TLV format............. 7
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4.3. Capacity Index Metadata.............................. 8
4.3.1. Capacity Site Index attached to services........ 9
4.3.2. BGP UPDATE with standalone Capacity Site Index.. 9
4.4. Load Measurement sub-TLV format..................... 10
5. Consideration for Optimal Paths Selection................ 11
6. Edge Service Metadata Propagation Scope.................. 11
7. Minimum Interval for Metrics Change Advertisement........ 12
8. Manageability Considerations............................. 12
9. Security Considerations.................................. 12
10. IANA Considerations..................................... 12
11. References.............................................. 13
11.1. Normative References............................... 13
11.2. Informative References............................. 13
12. Appendix A.............................................. 14
12.1. Example of Flow Affinity........................... 14
13. Acknowledgments......................................... 15
1. Introduction
[5g-edge-Compute] describes the 5G Edge Computing background
and how BGP can be used to advertise the running status and
environment of the directly attached 5G edge services. Besides
the Radio Access, 5G is characterized by having edge services
closer to the Cell Towers reachable by Local Data Networks
(LDN) [3GPP TS 23.501]. From IP network perspective, the 5G
LDN is a limited domain with edge services a few hops away
from the ingress nodes. Only selective services by UEs are
considered as 5G Edge Services.
This document describes a new Metadata Path Attribute and
three new sub-TLVs for egress routers to advertise the Edge
Service Metadata of the directly attached edge services. The
Edge Service Metadata in this document refers to edge
services' site capacity, the site preference, and the load
index, which are further explained in Section 3. Note: the
proposed Edge Service Metadata are not intended for the
services reachable via the networks outside the 5G LDN. The
Edge Service Metadata can be used by the ingress routers in
the 5G Local Data Network to make path selection not only
based on the routing distance but also the running environment
of the edge cloud sites. The goal is to improve latency and
performance for 5G edge services.
The extension is targeted for a single domain with RR
controlling the propagation of the BGP UPDATE. The Edge
Service Metadata is only attached to the services (routes)
hosted in the 5G edge cloud sites, which are only a small
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subset of services initiated from UEs. E.g., not for UEs
accessing many internet sites.
2. Conventions used in this document
Application Server: An application server is a physical or
virtual server that hosts the software system for
the application.
Application Server Location: Represent a cluster of servers at
one location serving the same Application. One
application may have a Layer 7 Load balancer,
whose address(es) are reachable from an external
IP network, in front of a set of application
servers. From an IP network perspective, this
whole group of servers is considered as the
Application server at the location.
Edge Application Server: used interchangeably with Application
Server throughout this document.
Edge Hosting Environment: An environment providing the support
required for Edge Application Server's execution.
NOTE: The above terminologies are the same as
those used in 3GPP TR 23.758
Edge DC: Edge Data Center, which provides the Hosting
Environment for the edge services. An Edge DC
might host 5G core functions in addition to the
frequently used application servers.
gNB next generation Node B
PSA: PDU Session Anchor (UPF)
SSC: Session and Service Continuity
UE: User Equipment
UPF: User Plane Function
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The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be
interpreted as described in BCP 14 [RFC2119] [RFC8174] when,
and only when, they appear in all capitals, as shown here.
3. BGP Protocol Extension for Edge Service Metadata
The goal of the BGP extension is for egress routers to
propagate the metrics about their running environment to
ingress routers, which are call the Edge Service Metadata
throughout the document. Here are some examples of the
metrics propagated by the egress routers:
- The site Capacity Index,
- The Site Preference Index,
- The Load Measurement Index for the attached edge services.
This section specifies how those Metadata impact the ingress
nodes' path selections.
3.1. Ingress Node BGP Path Selection Behavior
3.1.1. Edge Service Metadata Influenced BGP Path Selection
When an ingress router receives BGP updates for the same IP
address from multiple egress routers, all those egress routers
are considered as the next hops for the IP address. For the
selected edge services, the ingress router's BGP engine would
call a Plugin function that can select paths based on the Edge
Service Metadata received. [5G-EC-Metrics] has an example
algorithm to compute the weighted path cost based on the Edge
Service Metadata carried by the sub-TLVs specified in this
document. The Plugin function is called Cost Compute Engine
throughout this document.
Suppose a destination address for a service (aa08::4450) can
be reached by three next hops (R1, R2, R3). Further, suppose
the local BGP's Compute Engine Identifies the R1 as the
optimal next hop for flows to be sent to this destination
(aa08::4450). The Cost Compute Engine can insert a higher
weight for the path towards R1 for the prefix. Suppose BGP Add
Path is supported [RFC7911], all three paths can be added to
the FIB who can choose the optimal paths for the received data
packets.
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3.1.2. Ingress Router Forwarding Behavior
When the ingress router receives a packet and lookup the route
in the FIB, it gets the destination prefix's whole path. It
encapsulates the packet destined towards the optimal egress
node.
For subsequent packets belonging to the same flow, the ingress
router needs to forward them to the same egress router unless
the selected egress router is no longer reachable. Keeping
packets from one flow to the same egress router, a.k.a. Flow
Affinity, is supported by many commercial routers. Most
registered EC services have relatively short flows.
How Flow Affinity is implemented is out of the scope for this
document. Appendix A has one example illustrating achieving
flow affinity.
3.1.3. Forwarding Behavior when UEs moving to new 5G Sites
When a UE moves to a new 5G gNB which is anchored to the same
UPF, the packets from the UE traverse to the same ingress
router. Path selection and forwarding behavior are same as
before.
If the UE maintains the same IP address when anchored to a new
UPF, the directly connected ingress router might use the
information passed from a neighboring router to derive the
optimal Next Hop for this route. [5G-Edge-Sticky] describes
some methods for the ingress router connected to the UPF in
the new site to consider the information passed from other
ingress routers in selecting the optimal paths. The detailed
algorithm is out of the scope of this document.
4. Edge Service Metadata Encoding
4.1. Metadata Path Attribute
The Metadata Path Attribute is an optional transitive BGP Path
attribute to carry the Edge Service Metadata described in this
document. Will need IANA to assign a value as the Type code
of the Path Attribute. The Metadata Path Attribute,
illustrated below, consists of a set of sub-TLVs, with each
sub-TLV containing the information corresponding to a specific
metrics of the Edge Service Metadata.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Service-Metadata Type | Length (2 Octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Value (multiple Metadata sub-TLVs) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Edge Service Metadata Path Attribute
Service-Metadata Path Attribute Type (2 octets): identify the
Metadata Path Attribute, to be assigned by IANA.
o Length (2 octets): the total number of octets of the
value field.
o Value (variable): comprised of multiple sub-TLVs.
There are three types of Edge Service Metadata sub-TLVs
specified by this document for the Capacity Index Value, the
Site Preference Index Value, and the Load Measurement.
All values in the Sub-TLVs are unsigned 32 bits integers.
4.2. The Site Preference Index sub-TLV format
The Site Preference Index is one of the factors integrated
into the total cost for path selection. One Edge Cloud site
can have fewer computing servers, less power, or lower
internal network bandwidth than another. E.g., one micro edge
computing center located at a remote cell site has less
preference index value than an edge site in a metro area that
hosts management systems, analytics functions, and security
functions.
The Preference Index sub-TLV has the following format:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Site-Preference Sub-Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Preference Index value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Preference Index Sub-TLV
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Preference Index value: 1-100, with 1 being the least
preferred, and 100 being the most preferred.
4.3. Capacity Index Metadata
Capacity Index indicates the capacity value for a site or a
pod where the edge services are hosted. One Edge Site can be
in full capacity, reduced capacity, or completely out of
service.
Cloud Site/Pod failures and degradation include, but not
limited to, a site capacity degradation or entire site going
down caused by a variety of reasons, such as fiber cut
connecting to the site or among pods within one site, cooling
failures, insufficient backup power, cyber threats attacks,
too many changes outside of the maintenance window, etc.
Fiber-cut is not uncommon within a Cloud site or between
sites.
When those failure events happen, the Edge (egress) router
visible to the ingress routers can be running fine. Therefore,
the ingress routers can't use BFD to detect the failures.
When there is a failure occurring at an edge site (or pod),
many instances can be impacted. In addition, the routes (i.e.,
the IP addresses) in an Edge Cloud Site might not be
aggregated nicely. Instead of many BGP UPDATE messages for
each instance to the impacted ingress routers, the egress
router can send one single BGP UPDATE indicating the capacity
of the site. The ingress routers can switch all or a portion
of the instances that are associated with the site depending
on how much the site is degraded.
The Capacity Index sub-TLV:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Capacity-SubType | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Site-ID (2 octets) | Site Capacity |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- Capacity subtype: (TBD by IANA)
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- Site ID: identifier for a group of routes whose capacity is
indicated by the capacity value carried in the UPDATE. There
could be more than one sites (or Pods) connected to the egress
router (a.k.a. Edge DC GW)
- Site Capacity: represent the percentage of the site
availability, e.g., 100%, 50%, or 0%. When a site goes dark,
the Index is set to 0. 50 means 50% capacity functioning.
4.3.1. Capacity Site Index attached to services
The purpose of the Capacity Site index is to advertise the
service instance's site reference identifier and the capacity
value of the site.
However, it is not necessary to include the Capacity Site
Index for every BGP Update message if there is no change to
the site-reference identifier or the Capacity value for the
service instances.
The ingress routers associate the Site reference Identifier to
the routes in the Routing table.
4.3.2. BGP UPDATE with standalone Capacity Site Index
When there are failures or degradation to a site, the
corresponding egress router can send a BGP UPDATE with the
Capacity Site Index without attaching any routes.
When an ingress router receives a BGP Update message from
Router-X with the Site-Capacity Sub-TLV without routes
attached, the new Site-Capacity value is applied to all routes
that have the Router-X as their next hops and are associated
with the Site-ID in the Sub-TLV.
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4.4. Load Measurement sub-TLV format
Two types of Load Measurement Sub-TLVs are specified. One is
to carry the aggregated cost Index based on a weighted
combination of the collected measurements; another one is to
carry the raw measurements of packets/bytes to/from the Edge
Service address. The raw measurement is useful when ingress
routers have embedded analytics relying on the raw
measurements.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| subType=Aggregated-Cost | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Measurement Period |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Aggregated Load Index to reach the Edge Service |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Aggregated Load Index Sub-TLV
Aggregated-Cost Sub-Type(TBD1): Aggregated Load Measurement
Index to reach the Edge Service, which is configured or
calculated by the egress nodes.
Raw Load Measurement sub-TLV has the following format:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| subType= Raw-Measurements | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Measurement Period |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| total number of packets to the Edge Service |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| total number of packets from the Edge Service |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| total number of bytes to the Edge Service |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| total number of bytes from the Edge Service |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Raw Load Measurement Sub-TLV
Raw-Measurement Sub-Type (TBD2): Raw measurements of
packets/bytes to/from the Edge Service address.
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The receiver nodes can calculate the cost to reach the Edge
Service by a weighted combination of raw measurements sent
from the Edge Service, e.g.
Index=w1*ToPackets+w2*FromPackes+w3*ToBytes+w4*FromBytes
Where wi, which are configured by operators, is a value
between 0 and 1; w1+ w2+ w3+ w4 = 1.
Measure Period: BGP Update period in Seconds or user-
specified period.
5. Consideration for Optimal Paths Selection
When an ingress router receives BGP updates for the same IP
address from multiple routers, all those egress routers are
considered as the potential paths (or next hops) for the IP
address (i.e., if the BGP Add Path is supported). For the
selected services, the ingress router's BGP engine would call
a Plugin function that can select paths based on the cost
associated with the client route received, such as Site-
Capacity-Index, Site Preference, load index, and network cost.
The Plugin function is called Cost Compute Engine throughout
this document. When any of those factors goes to 0, the effect
is the same as the egress router not reachable, which triggers
the ingress nodes to switch to another egress router. But when
any of those factors just degrade, the effect could be a path
to another egress router becoming more optimal.
Suppose a destination address for aa08::4450 can be reached by
three next hops (R1, R2, R3). Further, suppose the local BGP's
Compute Engine Identifies the R1 as the optimal next hop for
flows to be sent to this destination (aa08::4450). The Cost
Compute Engine can insert a higher weight for the path towards
R1 for the prefix.
Note: The Edge Service Metadata Path Attribute are applicable
to different NLRIs.
6. Edge Service Metadata Propagation Scope
Edge Service Metadata is only to be distributed to the
relevant ingress nodes of the 5G EC local data networks. Only
the ingress routers that are configured with the 5G EC
services need to receive the Edge Service Metadata for
specific Service IDs.
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For each registered Edge Service, a corresponding filter group
can be formed on RR to represent the interested ingress
routers that are interested in receiving the corresponding
Edge Service Metadata information.
7. Minimum Interval for Metrics Change Advertisement
As the metrics change can impact the path selection, the
Minimum Interval for Metrics Change Advertisement is
configured to control the update frequency to avoid route
oscillations. Default is 30s.
Significant load changes at EC data centers can be triggered
by short-term gatherings of UEs, like conventions, lasting a
few hours or days, which are too short to justify adjusting EC
server capacities among DCs. Therefore, the load metrics
change rate can be in the magnitude of hours or days.
8. Manageability Considerations
The Edge Service Metadata described in this document are only
intended for propagating between Ingress and egress routers of
one single BGP domain, i.e., the 5G Local Data Networks, which
is a limited domain with edge services a few hops away from
the ingress nodes. Only the selective services by UEs are
considered as 5G Edge Services. The 5G LDN is usually managed
by one operator, even though the routers can be by different
vendors.
9. Security Considerations
The proposed Edge Service Metadata are advertised within the
trusted domain of 5G LDN's ingress and egress routers. There
are no extra security threats compared with iBGP.
10. IANA Considerations
Need IANA to assign the Metadata Path Attribute Type.
Metadata Path Attribute Type = TBD1.
Need IANA to assign three new Sub-TLV types under the
Metadata Path Attribute:
Type = TBD2: Site preference value sub-TLV
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Type = TBD3: Site Capacity Index sub-TLV
Type = TBD4: Aggregated Load Measurement Index derived from
the Weighted combination of bytes/packets sent to/received
from the Edge Service address.
Type = TBD5: Raw measurements of packets/bytes to/from the
Edge Service address.
11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4364] E. rosen, Y. Rekhter, "BGP/MPLS IP Virtual Private
networks (VPNs)", Feb 2006.
[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>.
[RFC7911] D. Walton, et al, "Advertisement of Multiple Paths
in BGP", RFC7911, July 2016.
11.2. Informative References
[3GPP TS 23.501] 3rd Generation Partnership Project;
Technical Specification Group Services and System
Aspects; System architecture for the 5G System (5GS)
[3GPP-EdgeComputing] 3GPP TR 23.748, "3rd Generation
Partnership Project; Technical Specification Group
Services and System Aspects; Study on enhancement of
support for Edge Computing in 5G Core network
(5GC)", Release 17 work in progress, Aug 2020.
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[5G-EC-Metrics] L. Dunbar, H. Song, J. Kaippallimalil, "IP
Layer Metrics for 5G Edge Computing Service", draft-
dunbar-ippm-5g-edge-compute-ip-layer-metrics-00,
work-in-progress, Oct 2020.
[5g-edge-Compute] L. Dunbar, K. Majumdar, H. Wang, and G.
Mishra, "BGP Usage for 5G Edge Computing service
Metadata", draft-dunbar-idr-5g-edge-compute-bgp-
usage-00, work-in-progress, July 2022.
[5G-Edge-Sticky] L. Dunbar, J. Kaippallimalil, "IPv6 Solution
for 5G Edge Computing Sticky Service", draft-dunbar-
6man-5g-ec-sticky-service-00, work-in-progress, Oct
2020.
[SDWAN-EDGE-Discovery] L. Dunbar, S. Hares, R. Raszuk, K.
Majumdar, "BGP UPDATE for SDWAN Edge Discovery",
draft-ietf-idr-sdwan-edge-discovery-03, July 2022.
12. Appendix A
12.1. Example of Flow Affinity
Here is one example to illustrate how Flow Affinity can be
achieved. This illustration is an informational example.
For the registered EC services, the ingress node keeps a table
of
- Service ID (i.e., IP address)
- Flow-ID
- Sticky Egress ID (egress router loopback address)
- A timer
The Flow-ID in this table is to identify a flow, initialized
to NULL. How Flow-ID is constructed is out of the scope for
this document. Here is one example of constructing the Flow-
ID:
- For IPv6, the Flow-ID can be the Flow-ID extracted from the
IPv6 packet header with or without the source address.
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- For IPv4, the Flow-ID can be the combination of the Source
Address with or without the TCP/UDP Port number.
The Sticky Egress ID is the egress node address for the same
flow. [5G-Edge-Sticky] describes several methods to derive the
Sticky Egress ID.
The Timer is always refreshed when a packet with the matching
EC Service ID (IP address) is received by the node.
If there is no Stick Egress ID present in the table for the EC
Service ID, the forwarding plane can select a NextHop
influenced by the Cost Compute Engine. The forwarding plane
encapsulates the packet with a path to the chosen NextHop. The
chosen NextHop and the Flow ID are recorded in the EC Service
table entry.
When the selected optimal NextHop (egress router) is no longer
reachable, ingress router needs to select another path.
13. Acknowledgments
Acknowledgements to Adrian Farrel, Robert Raszuk, Sue Hares,
Donald Eastlake, Dhruv Dhody, and Cheng Li for their review
and contributions.
This document was prepared using 2-Word-v2.0.template.dot.
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Authors' Addresses
Linda Dunbar
Futurewei
Email: ldunbar@futurewei.com
Kausik Majumdar
Microsoft
Email: kmajumdar@microsoft.com
Haibo Wang
Huawei
Email: rainsword.wang@huawei.com
Gyan Mishra
Verizon
Email: gyan.s.mishra@verizon.com
Contributors' Addresses
Cheng Li
Huawei
Email: c.l@huawei.com
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