Network Working Group L. Dunbar
Internet Draft Futurewei
Intended status: Standard K. Majumdar
Expires: March 23, 2022 CommScope
H. Wang
Huawei
September 23, 2021
BGP App Metadata for 5G Edge Computing Service
draft-dunbar-idr-5g-edge-compute-app-meta-data-03
Abstract
This draft describes a new AppMetaData subTLV carried by
Tunnel Encap[RFC9012] Path Attribute for egress router to
advertise the running status and environment of the directly
attached 5G Edge Computing servers. The AppMetaData can be
used by the ingress routers in the 5G Local Data Network to
make intelligent path selection for flows from UEs. The goal
is to improve latency and performance for 5G Edge Computing
services.
The extension enables a feature, called soft anchoring, which
makes one Edge Computing Server at one specific location to be
more preferred than others for the same application to receive
packets from a specific source (UE).
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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except to publish it as an RFC and to translate it into
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Table of Contents
1. Introduction.............................................. 3
1.1. 5G Edge Computing Background......................... 3
1.2. 5G Edge Computing Network Properties................. 4
1.3. Problem#1: ANYCAST in 5G EC Environment.............. 6
1.4. Problem #2: Unbalanced Anycast Distribution due to UE
Mobility.................................................. 7
1.5. Problem 3: Application Server Relocation............. 7
2. Conventions used in this document......................... 7
3. Usage of App-Meta-Data for 5G Edge Computing.............. 9
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3.1. Assumptions.......................................... 9
3.2. IP Layer Metrics to Gauge Application Behavior....... 9
3.3. AppMetaData Constrained Optimal Path Selection...... 10
3.4. BGP Protocol Extension to advertise Load & Capacity. 11
3.5. Ingress Node BGP Path Selection Behavior............ 12
3.5.1. AppMetaData Influenced BGP Path Selection...... 12
3.5.2. Forwarding Behavior............................ 12
3.5.3. Forwarding Behavior after a UE moving to a new 5G
Site.................................................. 13
4. The Sub-TLVs for App-Meta-Data........................... 14
4.1. Load Measurement sub-TLV format..................... 14
4.2. Capacity Index sub-TLV format....................... 15
4.3. The Site Preference Index sub-TLV format............ 15
5. AppMetaData Propagation Scope............................ 16
6. Soft Anchoring of an ANYCAST Flow........................ 16
7. Manageability Considerations............................. 18
8. Security Considerations.................................. 18
9. IANA Considerations...................................... 18
10. References.............................................. 18
10.1. Normative References............................... 18
10.2. Informative References............................. 19
11. Acknowledgments......................................... 20
1. Introduction
This document describes a new subTLV, AppMetaData, for egress
routers to advertise the running status and environment of the
directly attached Edge Computing servers. The AppMetaData can
be used by the ingress routers in the 5G Local Data Network to
make intelligent path selection for flows from UEs. The goal
is to improve latency and performance for 5G Edge Computing
services.
1.1. 5G Edge Computing Background
In 5G Edge Computing (EC), one Application can be hosted on
multiple Application Servers in different EC data centers that
are close in proximity. The network connecting the EC data
centers with the 5G Base stations consists of small number of
routers dedicated for the 5G Local Data Network (LDN), to
minimize latency and optimize the user experience.
When a User Equipment (UE) initiates application packets using
the destination address from a DNS reply or its cache, the
packets from the UE are carried in a PDU session through 5G
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Core [5GC] to the 5G UPF-PSA (User Plan Function - PDU Session
Anchor). The UPF-PSA decapsulates the 5G GTP outer header and
forwards the packets from the UEs to its directly connected
Ingress router of the 5G LDN. The LDN for 5G EC, which is the
IP Networks from the 5GC perspective, is responsible for
forwarding the packets to the intended destinations.
When the UE moves out of coverage of its current gNB (next-
generation Node B) (gNB1), handover procedures are initiated,
and the 5G SMF (Session Management Function) selects a new
UPF-PSA. The standard handover procedures described in 3GPP TS
23.501 and TS 23.502 are followed. When the handover process
is complete, the UE is anchored to the new UPF-PSA, meaning
the packets to/from the UE is carried by the GTP tunnel to the
new UPF-PSA. The UE usually maintains its IP address when
anchored to the new UPF-PSA unless the new UFP-PSA belongs to
different mobile operators. 5GC may maintain a path from the
old UPF to new the UPF for a short time for the SSC [Session
and Service Continuity] mode 3 to make the handover process
more seamless.
1.2. 5G Edge Computing Network Properties
In this document, 5G Edge Computing Network refers to multiple
Local IP Data Networks (LDN) in one region that interconnect
the Edge Computing data centers. Those IP LDN networks are the
N6 interfaces from 3GPP 5G perspective.
The ingress routers to the 5G Edge Computing Network are the
routers directly connected to 5G UPFs. The egress routers to
the 5G Edge Computing Network are the routers that have a
direct link to the Edge Computing servers. The servers and the
egress routers are co-located. Some of those Edge Computing
Data centers may have Virtual switches or Top of Rack switches
between the egress routers and the servers. But transmission
delay between the egress routers and the Edge Computing
servers is too small to be considered in this document.
When one EC data center has multiple EC Servers attached to
one App Layer Load Balancer, only the App Layer Load Balancer
is visible to the 5G Edge Computing Network. How the App Layer
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Load balancer manages the individual servers is out of the
scope of the network layer.
The 5G EC Services are specially managed services optimized by
utilizing the network topology and multiple servers with the
same IP address (ANYCAST) in multiple EC Data Centers. Many
services by the UEs are not part of the registered 5G EC
Services.
+--+
|UE|---\+---------+ +------------------+
+--+ | 5G | +--------+ | S1: aa08::4450 |
+--+ | Site +--+-+---+ +----+ |
|UE|----| A |PSA1| Ra| | R1 | S2: aa08::4460 |
+--+ | +----+---+ +----+ |
+---+ | | | | | S3: aa08::4470 |
|UE1|---/+---------+ | | +------------------+
+---+ |IP Network | L-DN1
|(3GPP N6) |
| | | +------------------+
| UE1 | | | S1: aa08::4450 |
| moves to | +----+ |
| Site B | | R3 | S2: aa08::4460 |
v | +----+ |
| | | S3: aa08::4470 |
| | +------------------+
| | L-DN3
+--+ | |
|UE|---\+---------+ | | +------------------+
+--+ | 5G | | | | S1: aa08::4450 |
+--+ | Site +--+--+---+ +----+ |
|UE|----| B |PSA2| Rb | | R2 | S2: aa08::4460 |
+--+ | +--+-+----+ +----+ |
+--+ | | +-----------+ | S3: aa08::4470 |
|UE|---/+---------+ +------------------+
+--+ L-DN2
Figure 1: App Servers in different edge DCs
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1.3. Problem#1: ANYCAST in 5G EC Environment
Increasingly, Anycast is used extensively by various
application providers and CDNs because ANYCAST makes it
possible to dynamically load balance across server locations
based on network conditions.
Using Anycast address leverages the proximity information
present in the network (routing) layer. It eliminates the
single point of failure and bottleneck at the DNS resolvers
and application layer load balancers. Another benefit of using
the ANYCAST address is removing the dependency on UEs. Some
UEs (or clients) might use their cached IP addresses, instead
of querying DNS, for an extended period.
But, having multiple locations of the same ANYCAST address in
the 5G EC environment can be problematic because all those EC
Data Centers can be close in proximity. There might be a very
small difference in the routing cost to reach the Application
Servers in different EC DCs. This list elaborates the issues
in detail:
a) Path Selection: When a new flow comes to an ingress node
(Ra), how to select the optimal egress router to reach an
ANYCAST server.
The mechanism described in this draft is for solving this
Path Selection problem.
b) How Ingress node keeps the packets from one flow to the
same ANYCAST server.
a.k.a. Flow Affinity, or Flow-based load balancing, which
is supported by many commercial routers.
The ingress node, (Ra/Rb) uses Flow ID (in IPv6 header)
or UDP/TCP port number combined with the source address
to enforce packets in one flow being placed in one tunnel
to one Egress router. No new features are needed.
c) When a UE moves to a new Cell Tower, a method is needed
to stick the flow to the same ANYCAST server, which is
required by 5G Edge Computing: 3GPP TR 23.748.
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This problem is Out of scope for this draft. [5g-edge-
compute-sticky-service] describes several approaches to
solve this problem.
From BGP perspective, the multiple servers with the same IP
address (ANYCAST)attached to different egress routers is the
same as multiple next hops for the IP address.
This draft describes the BGP UPDATE to enable ingress routers
to take the App Server load, the capacity index, and the
location preference into consideration when computing the
optimal path to egress routers.
1.4. Problem #2: Unbalanced Anycast Distribution due to UE
Mobility
UEs frequent moving from one 5G site to another can make it
difficult to plan where and how many to deploy the App
servers. When one App server is heavily utilized, other
servers of the same App close-by can be very underutilized.
Since the condition can be short-lived, it is difficult for
the application controller to anticipate the move and adjust.
1.5. Problem 3: Application Server Relocation
When an Application Server is added to, moved, or deleted from
a 5G EC Data Center, the routing protocol needs to propagate
the changes to 5G PSA or the PSA adjacent routers. After the
change, the cost associated with the site might change as
well.
Note: for ease of description, the Edge Application Server and
Application Server are used interchangeably throughout this
document.
2. Conventions used in this document
A-ER: Egress Router to an Application Server, [A-ER] is
used to describe the last router that the
Application Server is attached. For a 5G EC
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environment, the A-ER can be the gateway router to
a (mini) Edge Computing Data Center.
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.
EC: Edge Computing
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 Edge
Computing Hosting Environment. An Edge DC might
host 5G core functions in addition to the
frequently used application servers.
gNB next generation Node B
L-DN: Local Data Network
PSA: PDU Session Anchor (UPF)
SSC: Session and Service Continuity
UE: User Equipment
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UPF: User Plane Function
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. Usage of App-Meta-Data for 5G Edge Computing
3.1. Assumptions
From IP Layer, the Application servers are identified by their
IP (ANYCAST) addresses. Here are some assumptions about the 5G
EC services:
- Only the registered EC services, which are only a small
portion of the services, need to include the AppMetadata
in path selection.
- The 5G EC controller or management system push down the
policies (e.g., ACLs) on the relevant routers to filter
out those registered EC services.
- The ingress routers' local BGP path compute algorithm
includes a special plugin that can compute the path to
the optimal Next Hop (egress router) based on the BGP
AppMetaData TLV received for the registered EC services.
The proposed solution is for the egress routers, i.e. A-ER,
that have direct links to the Application Servers to collect
various measurements about the Servers' running status [5G-EC-
Metrics] and advertise the metrics to other routers in 5G EC
LDN (Local Data Network).
3.2. IP Layer Metrics to Gauge Application Behavior
[5G-EC-Metrics] describes the IP Layer Metrics that can gauge
the application servers running status and environment:
- IP-Layer Metric for App Server Load Measurement:
The Load Measurement to an App Server is a weighted
combination of the number of packets/bytes to the App Server
and the number of packets/bytes from the App Server which
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are collected by the A-ER to which the App Server is
directly attached.
The A-ER is configured with an ACL that can filter out the
packets for the Application Server.
- Capacity Index
a numeric number, configured on all A-ERs in the domain
consistently, is used to represent the capacity of the
application server attached to an A-ER. At some sites, the
IP address exposed to the A-ER is the App Layer Load
balancer that have many instances attached. At other sites,
the IP address exposed is the server instance itself.
- Site preference index:
is used to describe some sites are more preferred than
others. For example, a site with higher bandwidth has a
higher preference number than other.
In this document, the term "Application Server Egress Router"
[A-ER] is used to describe the last router that an Application
Server is attached. For the 5G EC environment, the A-ER can be
the gateway router to the EC DC where multiple Application
servers are hosted.
From IP Layer, an Application Server is identified by its IP
(ANYCAST) Address. Those IP addresses are called the
Application Server IDs throughout this document.
3.3. AppMetaData Constrained Optimal Path Selection
The main benefit of using ANYCAST is to leverage the network
layer information to select an optimal path among multiple
application Server locations of the same application
identified by its ANYCAST addresses.
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For the 5G EC environment, the ingress routers to the LDN need
to be notified of the Load Index and Capacity Index of the App
Servers at different EC data centers to make the intelligent
decision on where to forward the traffic for the application
from UEs.
Here is an algorithm that computes the cost to reach the App
Servers attached to Site-i relative to another site, say Site-
b. When the reference site, Site-b, is plugged in the formula,
the cost is 1. So, if the formula returns a value less than 1,
the cost to reach Site-i is less than reaching Site-b.
CP-b * Load-i Pref-b * Network-Delay-i
Cost-i= (w *(----------------) + (1-w) *(-------------------------))
CP-i * Load-b Pref-i * Network-Delay-b
Load-i: Load Index at Site-i, it is the weighted
combination of the total packets or/and bytes sent to and
received from the Application Server at Site-i during a
fixed time period.
CP-i: capacity index at Site-i, a higher value means higher
capacity.
Delay-i: Network latency measurement (RTT) to the A-ER that
has the Application Server attached at the site-i.
Pref-i: Preference index for the Site-i, a higher value
means higher preference.
w: Weight for load and site information, which is a value
between 0 and 1. If smaller than 0.5, Network latency and
the site Preference have more influence; otherwise, Server
load and its capacity have more influence.
3.4. BGP Protocol Extension to advertise Load & Capacity
The goal of the protocol extension:
- Propagate the Load Measurement Index for the attached App
Servers to other routers in the LDN.
- Propagate the Capacity Index &
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- Propagate Site Preference Index.
The BGP extension is to include the Load Index Sub-TLV,
Capacity Sub-TLV, and the Site Preference Sub-TLV in the
Tunnel Encap Path Attribute associated with the routes.
3.5. Ingress Node BGP Path Selection Behavior
3.5.1. AppMetaData Influenced BGP Path Selection
In this scenario, an ingress router will receive one ANYCAST
address's multiple routes from different egress routers that
have the direct links to the ANYCAST servers. The ingress
router's BGP engine will do path selection, select the best
route, and download to FIB. And BGP engine will also download
the other paths to FIB that with the AppMetaData taken into
the consideration.
Assume that both Ra and Rb in Figure-1 have BGP Multipath
enabled. As a result, Dst Address: S1:aa08::4450 is resolved
via multiple NextHop: R1, R2, R3.
Suppose the local BGP special Plugin for AppMetaData finds R1
is the best for the flow towards S1:aa08::4450. Then this
special Plugin can insert a higher weight for the path R1 so
that BGP Best Path is locally influenced by the weight
parameter based on the local decision.
3.5.2. Forwarding Behavior
When the ingress router receives a packet and lookup the FIB,
it gets the destination prefix's whole path and AppMetaData.
The Forwarding Plane will do computing for the packet and
choose the suitable path as the result of the computing. Then
the Forwarding Plane 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.
How Flow Affinity is implemented is out of the scope for this
document. Here is one example to illustrate how Flow Affinity
can be achieved. This illustration is not to be standardized.
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For the registered EC services, the ingress node keeps a
table of
- Service ID (i.e., ANYCAST 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.
- 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-Sticky-Service] describes several methods to
derive the Sticky Egress ID.
The Timer is always refreshed when a packet with the
matching EC Service ID (ANYCAST 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 computes the optimal
path to an egress (NextHop) with the AppMetaData taken into
consideration. The forwarding plane encapsulates the packet
with a tunnel to the chosen egress (NextHop). The chosen
NextHop and the Flow ID are recorded in the table entry of
the EC Service ID.
When the selected optimal egress router is no longer
reachable, refer to Section 6 Soft Anchoring on how another
path is selected.
3.5.3. Forwarding Behavior after a UE moving to a new 5G Site
When a UE moves to a new 5G Site, the new ingress router might
use the pre-computed Egress Router which is passed from the
neighboring router. [5G-Edge-Sticky] describes the method for
the ingress router connected to the UPF in the new site to
take into consideration the information passed from other
ingress routers in selecting the optimal paths. The detailed
algorithm is out of the scope of this document.
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4. The Sub-TLVs for App-Meta-Data
The App-Meta-Data attribute is encoded in an optional subTLV
within the Tunnel Encap [RFC9012] Path Attribute.
4.1. 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 App
Server address. The raw measurement is useful when the egress
routers cannot be configured with a consistent algorithm to
compute the aggregated load index and the raw measurements are
needed by a central analytic system.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type (TBD1) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Measurement Period |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Aggregated Load Index to reach the App Server |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Aggregated Load Index Sub-TLV
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type (TBD2) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Measurement Period |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| total number of packets to the AppServer |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| total number of packets from the AppServer |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| total number of bytes to the AppServer |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| total number of bytes from the AppServer |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Raw Load Measurement Sub-TLV
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Type =TBD1: Aggregated Load Measurement Index derived from
the Weighted combination of bytes/packets sent to/received
from the App server:
Index=w1*ToPackets+w2*FromPackes+w3*ToBytes+w4*FromBytes
Where wi is a value between 0 and 1; w1+ w2+ w3+ w4 = 1;
Type= TBD2: Raw measurements of packets/bytes to/from the
App Server address;
Measure Period: BGP Update period or user-specified period.
4.2. Capacity Index sub-TLV format
The Capacity 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type (TBD3) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Capacity Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Note: "Capacity Index" can be more stable for each site. If
those values are configured to nodes, they might not need to
be included in every BGP UPDATE.
4.3. The Site Preference Index sub-TLV format
The site Preference Index is used to achieve Soft Anchoring
[Section 5] an application flow from a UE to a specific
location when the UE moves from one 5G site to another.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type (TBD4) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Preference Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Note: "Site Preference Index" can be more stable for each
site. If those values are configured to nodes, they might not
need to be included in every BGP UPDATE.
5. AppMetaData Propagation Scope
AppMetaData 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 ACLs need
to receive the AppMetaData for specific services.
For each registered EC service, a corresponding filter group
can be formed on RR to represent the interested ingress
routers that are interested in receiving the corresponding
AppMetaData information.
6. Soft Anchoring of an ANYCAST Flow
"Sticky Service" in the 3GPP Edge Computing specification
(3GPP TR 23.748) requires a UE to a specific ANYCAST location
when the UE moves from one 5G Site to another.
"Soft Anchoring" is referring to forwarding the Application
flow from a UE to a preferred location of the ANYCAST servers
when the preferred location is in good condition. But if
there is any failure reaching the preferred location, the
Application flow from the UE will be forwarded to another
location of the ANYCAST servers.
This section describes a solution that can softly anchor an
application flow from a UE to a preferred location.
Lets assume one application "App.net" is instantiated on four
servers that are attached to four different routers R1, R2,
R3, and R4 respectively. It is desired for packets to the
"App.net" from UE-1 to stick with one server, say the App
Server attached to R1, even when the UE moves from one 5G
site to another. When there is a failure reaching R1 or the
Application Server attached to R1, the packets of the flow
"App.net" from UE-1 need to be forwarded to the Application
Server attached to R2, R3, or R4.
We call this kind of sticky service "Soft Anchoring", meaning
that anchoring to the site of R1 is preferred, but other
sites can be chosen when the preferred site encounters a
failure.
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Here are the details of this solution:
- Assign a group of ANYCAST addresses to one application.
For example, "App.net" is assigned with 4 ANYCAST
addresses, L1, L2, L3, and L4. L1/L2/L3/L4 represents
the location preferred ANYCAST addresses.
- For the App.net Server attached to a router, the router
has four Stub links to the same Server, L1, L2, L3, and
L4 respectively. The cost to L1, L2, L3, and L4 is
assigned differently for different routers. For example,
o When attached to R1, the L1 has the lowest cost,
say 10, when attached to R2, R3, and R4, the L1 can
have a higher cost, say 30.
o ANYCAST L2 has the lowest cost when attached to R2,
higher cost when attached to R1, R3, R4
respectively.
o ANYCAST L3 has the lowest cost when attached to R3,
higher cost when attached to R1, R2, R4
respectively, and
o ANYCAST L4 has the lowest cost when attached to R4,
higher cost when attached to R1, R2, R3
respectively
- When a UE queries for the "App.net" for the first time,
the DNS reply has the location preferred ANYCAST
address, say L1, based on where the query is initiated.
- When the UE moves from one 5G site-A to Site-B, UE
continues sending packets of the "App.net" to ANYCAST
address L1. The routers will continue sending packets to
R1 because the total cost for the App.net instance for
ANYCAST L1 is lowest at R1. If any failure occurs making
R1 not reachable, the packets of the "App.net" from UE-1
will be sent to R2, R3, or R4 (depending on the total
cost to reach each of them).
If the Application Server supports the HTTP redirect, more
optimal forwarding can be achieved.
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- When a UE queries for the "App.net" for the first time,
the global DNS reply has the ANYCAST address G1, which
has the same cost regardless of where the Application
servers are attached.
- When the UE initiates the communication to G1, the
packets from the UE will be sent to the Application
Server that has the lowest cost, say the Server attached
to R1. The Application server is instructed with HTTPs
Redirect to reply with a location-specific URL, say
App.net-Loc1. The client on the UE will query the DNS
for App.net-Loc1 and get the response of ANYCAST L1. The
subsequent packets from the UE-1 for App.net are sent to
L1.
7. Manageability Considerations
To be added.
8. Security Considerations
To be added.
9. IANA Considerations
To be added.
10. References
10.1. 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>.
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[RFC8200] s. Deering R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", July 2017
10.2. Informative References
[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.
[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-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.
[RFC5521] P. Mohapatra, E. Rosen, "The BGP Encapsulation
Subsequent Address Family Identifier (SAFI) and the
BGP Tunnel Encapsulation Attribute", April 2009.
[BGP-SDWAN-Port] L. Dunbar, H. Wang, W. Hao, "BGP Extension
for SDWAN Overlay Networks", draft-dunbar-idr-bgp-
sdwan-overlay-ext-03, work-in-progress, Nov 2018.
[SDWAN-EDGE-Discovery] L. Dunbar, S. Hares, R. Raszuk, K.
Majumdar, "BGP UPDATE for SDWAN Edge Discovery",
draft-dunbar-idr-sdwan-edge-discovery-00, work-in-
progress, July 2020.
[Tunnel-Encap] E. Rosen, et al "The BGP Tunnel Encapsulation
Attribute", draft-ietf-idr-tunnel-encaps-10, Aug
2018.
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11. Acknowledgments
Acknowledgements to Donald Eastlake for their review and
contributions.
This document was prepared using 2-Word-v2.0.template.dot.
Authors' Addresses
Linda Dunbar
Futurewei
Email: ldunbar@futurewei.com
Kausik Majumdar
CommScope
350 W Java Drive, Sunnyvale, CA 94089
Email: kausik.majumdar@commscope.com
Haibo Wang
Huawei
Email: rainsword.wang@huawei.com
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