Network Working Group L. Dunbar
Internet Draft H. Chen
Intended status: Standard Futurewei
Expires: January 12, 2022 Aijun Wang
China Telecom
July 12, 2021
IS-IS & OSPF extension for 5G Edge Computing Service
draft-dunbar-lsr-5g-edge-compute-00
Abstract
This draft describes an IS-IS and OSPF extension for
routers to advertise the running status and environment
(Site-Cost) for the directly attached 5G Edge Computing
servers. Routers in the 5G Local Data Network can use the
Site-Cost and the network condition to optimize forwarding
flows from UEs. The goal is to improve latency and
performance for 5G Edge Computing services.
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 provisions of BCP 78 and BCP 79. This document may not
be 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
Engineering Task Force (IETF), its areas, and its working
groups. Note that other groups may also distribute working
documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of
six months and may be updated, replaced, or obsoleted by
other documents at any time. It is inappropriate to use
Internet-Drafts as reference material or to cite them other
than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
xxx, et al. Expires January 12, 2022 [Page 1]
Internet-Draft OSPF Extension for 5G EC Service
The list of Internet-Draft Shadow Directories can be
accessed at http://www.ietf.org/shadow.html
This Internet-Draft will expire on April 7, 2021.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as
the document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's
Legal Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the
date of publication of this document. Please review these
documents carefully, as they describe your rights and
restrictions with respect to this document. Code Components
extracted from this document must include Simplified BSD
License text as described in Section 4.e of the Trust Legal
Provisions and are provided without warranty as described
in the Simplified BSD License.
Table of Contents
1. Introduction........................................... 3
1.1. 5G Edge Computing Background...................... 3
1.2. Problem#1: ANYCAST in 5G EC Environment........... 5
1.3. Problem #2: Unbalanced Anycast Distribution due to
UE Mobility............................................ 6
1.4. Problem 3: Application Server Relocation.......... 6
2. Conventions used in this document...................... 6
3. Solution Overview...................................... 8
3.1. Flow Affinity to an ANYCAST server................ 8
3.2. IP Layer Metrics to Gauge App Server Running Status
....................................................... 9
3.3. To Equalize traffic among Multiple ANYCAST
Locations............................................. 10
3.4. Reason for using IGP Based Solution.............. 11
4. IS-IS Extension....................................... 11
4.1. IS-IS extension for the Aggregated cost.......... 12
4.2. IS-IS extension for IP Layer App-Metrics
Advertisements........................................ 13
4.3. IS-IS App-Metrics SubTLVs for IPv6 attachment.... 13
4.4. IS-IS IP Layer App-Metrics for IPv4.............. 14
Dunbar, et al. Expires January 12, 2022 [Page 2]
Internet-Draft OSPF Extension for 5G EC Service
5. Aggregated Cost Advertisement in OSPF................. 14
5.1. OSPFv3 LSA to carry the Aggregated Cost.......... 15
5.2. OSPFv2 LSA to carry the Aggregated Cost.......... 15
6. IP Layer App-Metrics Advertisements by OSPF........... 15
6.1. OSPFv3 Extension to carry the App-Metrics........ 16
6.2. OSPFv2 Extension to advertise the IP Layer App-
Metrics............................................... 17
6.3. IP Layer App-Metrics Sub-TLVs.................... 18
7. Manageability Considerations.......................... 20
8. Security Considerations............................... 20
9. IANA Considerations................................... 20
10. References........................................... 20
10.1. Normative References............................ 21
10.2. Informative References.......................... 21
11. Acknowledgments...................................... 22
1. Introduction
This document describes an IS-IS and OSPF extension to
advertise the indexes of the running environment, a.k.a.
Site-Cost, for the directly attached 5G Edge Computing
servers. The goal is for other routers in the 5G Local Data
Network (LDN) to optimize the forwarding of flows from UEs
and to improve latency and performance for 5G Edge
Computing services.
In a nutshell, one application can be instantiated on
multiple servers close in proximity. Those multiple server
instances can share one IP address (ANYCAST) so that
traffic can be forwarded in consideration of transient
network and load conditions.
1.1. 5G Edge Computing Background
As described in [3GPP-EdgeComputing], it is desirable for a
mission-critical application to be hosted on multiple
servers attached to different edge routers to minimize
latency and optimize the user experience. Those App Servers
are usually hosted very close to or co-located with 5G base
stations.
When a UE (User Equipment) initiates application packets
using the destination address from a DNS reply or its
Dunbar, et al. Expires January 12, 2022 [Page 3]
Internet-Draft OSPF Extension for 5G EC Service
cache, the packets from the UE are carried in a PDU session
through 5G 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 the
Ingress router of the Edge Computing (EC) Local Data
Network (LDN), which 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), the handover procedure is
initiated, which includes the 5G SMF (Session Management
Function) selecting a new UPF-PSA [3GPP TS 23.501 and TS
23.502]. When the handover process is complete, the UE has
a new IP address, and the IP point of attachment is to the
new UPF-PSA. 5GC may maintain a path from the old UPF to
the new UPF for a short time for SSC [Session and Service
Continuity] mode 3 to make the handover process more
seamless.
Dunbar, et al. Expires January 12, 2022 [Page 4]
Internet-Draft OSPF Extension for 5G EC Service
+--+
|UE|---\+---------+ +------------------+
+--+ | 5G | +---------+ | S1: aa08::4450 |
+--+ | Site +--++---+ +----+ |
|UE|----| A |PSA| 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 |PSA| Rb | | R2 | S2: aa08::4460 |
+--+ | +--++----+ +----+ |
+--+ | | +-----------+ | S3: aa08::4470 |
|UE|---/+---------+ +------------------+
+--+ L-DN2
Figure 1: App Servers in different edge DCs
1.2. Problem#1: ANYCAST in 5G EC Environment
ANYCAST makes it possible to load balance across server
locations based on network conditions dynamically. With
multiple servers having the same ANYCAST address, it
eliminates the single point of failure and bottleneck at
the application layer load balancers. Another benefit of
using ANYCAST address is removing the dependency on how UEs
get the IP addresses for their Applications. Some UEs (or
clients) might use stale cached IP addresses for an
extended period.
But, having multiple locations of the same ANYCAST address
in the 5G Edge Computing environment can be problematic
Dunbar, et al. Expires January 12, 2022 [Page 5]
Internet-Draft OSPF Extension for 5G EC Service
because all those edge computing Data Centers can be close
in proximity. There might be very little difference in the
routing distance to reach the Application Servers attached
to a different edge router, which can cause packets from
one flow to be forwarded to different locations, resulting
in service glitches.
1.3. 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 the App Servers should be
hosted. When one App server is heavily utilized, other App
servers of the same address close by can be under-utilized.
The difference in the routing distance to reach multiple
Application Servers might be relatively small. The network
cost, the traffic load at the router where the App Server
is attached, and the site capacity, when combined, are more
significant from the latency and performance perspective.
Since the condition can be short-lived, it is difficult for
the application controller to anticipate the moving and
adjusting.
1.4. Problem 3: Application Server Relocation
When an Application Server is added to, moved, or deleted
from a 5G Edge Computing server site (mini-DC), not only
the reachability changes but also the utilization and
capacity for the site might change.
Note: for the ease of description, the Edge Computing
server, Application server, App server are used
interchangeably throughout this document.
2. Conventions used in this document
A-ER: Egress Edge Router to an Application Server,
[A-ER] is used to describe the last router that
the Application Server is attached. For 5G EC
environment, the A-ER can be the gateway router
to a (mini) Edge Computing Data Center.
Dunbar, et al. Expires January 12, 2022 [Page 6]
Internet-Draft OSPF Extension for 5G EC Service
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 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. It might be co-
located with 5G Base Station and not only host
5G core functions, but also host frequently
used Edge server instances.
gNB next generation Node B
LDN: Local Data Network
PSA: PDU Session Anchor (UPF)
SSC: Session and Service Continuity
UE: User Equipment
Dunbar, et al. Expires January 12, 2022 [Page 7]
Internet-Draft OSPF Extension for 5G EC Service
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. Solution Overview
From IP Layer, the Application Servers are identified by
their IP (ANYCAST) addresses. To a router, having multiple
servers with the same (ANYCAST) address attached to
different egress edge routers (A-ER) is the same as having
multiple paths to reach the (ANYCAST) address.
The proposed solution is for the egress edge router (A-ER)
to which the Application Servers are attached to advertise
the "Site-Cost" [Section 3.2] to other routers in 5G EC
LDN. The routers in LDN can consider the "Site-Cost" in
computing the optimal path to the App Server directly
attached to the A-ER.
The solution assumes that the 5G Edge Computing controller
or management system is aware of the ANYCAST addresses that
need optimized forwarding. To minimize the processing, only
the applications that match with the ACLs configured by the
5G Edge Computing controller will have their Site-Cost
collected and advertised.
3.1. Flow Affinity to an ANYCAST server
In an environment where multiple servers with the same
(ANYCAST) address are attached to different A-ERs, Flow
Affinity means routers sending the packets of the same flow
to the same A-ER even if the cost towards the A-ER is no
longer optimal.
Today, many commercial routers support some forms of flow
affinity to ensure packets belonging to one flow be
forwarded along the same path.
Dunbar, et al. Expires January 12, 2022 [Page 8]
Internet-Draft OSPF Extension for 5G EC Service
Editor's note: for IPv6 traffic, Flow Affinity can be
supported by the routers forwarding the packets with the
same Flow Label in the packets' IPv6 Header along the same
path towards the same egress edge router.
3.2. IP Layer Metrics to Gauge App Server Running Status
Most applications do not expose their internal logic to the
network. Their communications are generally encrypted. Most
of them do not even respond to PING or ICMP messages
initiated by routers or network gears.
[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 are collected by the A-ER that has the
direct connection to the App Server.
The A-ER is configured with an ACL that can filter out
the packets for the Application Server.
- Capacity Index:
Capacity Index is used to differentiate the running
environment of the attached application server. Some
data centers can have hundreds, or thousands, of
servers behind an application server's App Layer Load
Balancer. Other data centers can have a very small
number of servers for the application. "Capacity
Index", which is a numeric number, is used to
represent the capacity of the application server
attached to an A-ER.
- Site preference index:
[IPv6-StickyService] describes a scenario that some
sites are more preferred for handling an application
than others for flows from a specific UE.
For ease of description, those metrics with more to be
added later are called IP Layer Site-Cost throughout the
document.
Dunbar, et al. Expires January 12, 2022 [Page 9]
Internet-Draft OSPF Extension for 5G EC Service
3.3. To Equalize traffic among Multiple ANYCAST Locations
The main benefit of using ANYCAST is to leverage the
network layer information to balance the traffic among
multiple Application Server locations.
For the 5G Edge Computing environment, the routers in the
LDN need to be notified of various measurements of the App
Servers attached to each A-ER to make the intelligent
decision on where to forward the traffic for the
application from UEs.
[5G-EC-Metrics] describes the algorithms that the routers
in LDN can use to compare the cost to reach the App Servers
between the Site-i or Site-j:
Load-i * CP-j Pref-j * Network-Delay-i
Cost-i=min(w *(----------------) + (1-w) *(-------------------------))
Load-j * CP-i Pref-i * Network-Delay-j
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.
Network Delay-i: Network latency measurement (RTT) to
the A-ER that has the Application Server attached at the
site-i.
Noted: Ingress nodes can easily measure RTT to all the
egress edge nodes by existing IPPM metrics. But it is
not so easy for ingress nodes to measure RTT to all the
App Servers. Therefore, "Network-Delay-i", a.k.a.
Network latency measurement (RTT), is between the
Ingress and egress edge nodes. The link cost between the
egress edge nodes to their attached servers is embedded
in the "capacity index".
Pref-i: Preference index for 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;
Dunbar, et al. Expires January 12, 2022 [Page 10]
Internet-Draft OSPF Extension for 5G EC Service
otherwise, Server load and its capacity have more
influence.
3.4. Reason for using IGP Based Solution
Here are some benefits of using IGP to propagate the IP
Layer App-Metrics:
- Intermediate routers can derive the aggregated cost to
reach the Application Servers attached to different
egress edge nodes, especially:
- The path to the optimal egress edge node can be
more accurate or shorter.
- Convergence is shorter when there is any failure
along the way towards the optimal ANYCAST server.
- When there is any failure at the intended ANYCAST
server, all the packets in transit can be optimally
forwarded to another App Server attached to a
different egress edge router.
- Doesn't need the ingress nodes to establish tunnels with
egress edge nodes.
There are limitations of using IGP too, such as:
- The IGP approach might not suit well to 5G EC LDN
operated by multiple ISPs.
For LDN operated by multiple IPSs, BGP should be used.
AppMetaData NLRI Path Attribute [5G-AppMetaData]
describes the BGP UPDATE message to propagate IP Layer
App-Metrics crossing multiple ISPs.
4. IS-IS Extension
The Application-Specific Link Attribute sub-TLV described
in [RFC8919] can be used to carry the "Site-Cost" for the
App server directly attached to the router.
When carrying the "Site-Cost" sub-sub TLVs, the App
specific Link Attribute sub-TLV can be included in TLV 22
(extended IS reachability), 23 (IS Neighbor Attribute), or
25(L2 bundle Member Attribute).
The Site-Cost bit is added to the Standard Applications Bit
Mask (SABM).
0 1 2 3 4 5 6 7 ...
+-+-+-+-+-+-+-+-+...
Dunbar, et al. Expires January 12, 2022 [Page 11]
Internet-Draft OSPF Extension for 5G EC Service
|R|S|F|C| ...
+-+-+-+-+-+-+-+-+...
Figure 2: Extended Application Identifier Bit Mask
C-bit: set to specify the Site Cost related sub-sub TLVs,
described in the Section 3.2, are included in the App-
Specific Sub-TLV.
The R-bit, S-bit, F-bit are specified by the RFC8919.
The Extended App Specific Link Attributes Sub-TLV is as
following:
Type: 16
Length: (1 octet)
Value:
Extended Application Identifier Bit Mask [Figure 2]
Site-Cost sub-sub-TLVs - described in the following
sections.
4.1. IS-IS extension for the Aggregated cost
If egress edge routers to which the App Servers are
directly attached can get the aggregated cost, the
Aggregated cost sub-sub-TLV can be directly appended to the
App Specific Bit Mask.
The aggregated cost can be from App controller or from a
consistent algorithm that considers the Load Measurement,
Capacity value, and Preference value across all A-ERs.
Dunbar, et al. Expires January 12, 2022 [Page 12]
Internet-Draft OSPF Extension for 5G EC Service
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|AggCostSubTLV | Length | AggCost to the App Server |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PrefixLength | PrefixOptions | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address Prefix |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Aggregated Cost to App Server
4.2. IS-IS extension for IP Layer App-Metrics Advertisements
This section describes the sub-sub TLVs that carry the
detailed IP Layer Metrics when the A-ERs in the domain do
not have a consistent algorithm to compute the aggregated
cost or the detailed IP Layer metrics for the App Servers
are needed for other purposes.
It worth noting that not all hosts (prefix) attached to an
A-ER are ANYCAST servers that need network optimization.
An A-ER only needs to advertise the site-Cost Metrics for
the ANYCAST addresses requested by the Controller.
Draft [draft-wang-lsr-passive-interface-attribute]
introduces the Stub-Link TLV for OSPFv2/v3 and ISIS
protocol respectively. Considering the interfaces on an
edge router that connects to the App servers are normally
configured as passive interfaces, these IP-layer App-
metrics can also be advertised as the attributes of the
passive/stub link. The associated prefixes can then be
advertised in the "Stub-Link Prefix Sub-TLV" that is
defined in [draft-wang-lsr-passive-interface-attribute].
All the associated prefixes share the same characteristic
of the link. Other link related sub-TLVs defined in
[RFC8920] can also be attached and applied to the
calculation of path to the associated prefixes.
4.3. IS-IS App-Metrics SubTLVs for IPv6 attachment
For App Servers using IPv6, the App-Metrics subTLV is
encoded as below:
Dunbar, et al. Expires January 12, 2022 [Page 13]
Internet-Draft OSPF Extension for 5G EC Service
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| App-Metrics IPv6 subTLV Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 AppServer (ANYCAST) address |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Load measurement sub-TLV |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Capability sub-TLV |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Preference sub-TLV |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: IPv6 App Server App-Metrics Encoding
4.4. IS-IS IP Layer App-Metrics for IPv4
Here is the proposed encoding for App Servers using IPv4
addresses:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| App-Metrics IPv4 subTLV Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address Prefix (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Load Measurement Sub-TLV |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| capacity Index Sub-TLV |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Site Preference Sub-TLV |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: App-Metrix Sub-TLVs for IPv4
5. Aggregated Cost Advertisement in OSPF
If all egress edge routers that have a direct connection to
the App Servers can get a periodic update of the aggregated
Dunbar, et al. Expires January 12, 2022 [Page 14]
Internet-Draft OSPF Extension for 5G EC Service
cost to the App Servers or can be configured with a
consistent algorithm to compute an aggregated cost that
takes into consideration the Load Measurement, Capacity
value, and Preference value, this aggregated cost can be
considered as the Metric of the link to the App Server.
In this scenario, there is no protocol extension needed.
5.1. OSPFv3 LSA to carry the Aggregated Cost
If the App Servers use IPv6 ANYCAST address, the aggregated
cost computed by the egress edge routers can be encoded in
the Metric field [the interface cost] of Intra-Area-Prefix-
LSA specified by Section 3.7 of the [ RFC5340].
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 6 (Intra-Area Prefix) | TLV Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 | Aggregated Cost to the App Server |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PrefixLength | PrefixOptions | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address Prefix |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Aggregated Cost to App Server
5.2. OSPFv2 LSA to carry the Aggregated Cost
For App Servers in IPv4 address, the Aggregated Cost can be
encoded in the "Metric" field of the Stub Link LSA [Link
type =3] specified by Section 12.4 of the [RFC2328].
6. IP Layer App-Metrics Advertisements by OSPF
This section describes the OSPF extension that can carry
the detailed IP Layer Metrics when it is not possible for
all the egress edge routers to have a consistent algorithm
to compute the aggregated cost or some routers need all the
detailed IP Layer metrics for the App Servers for other
purposes.
Since only a subset of routers within an IGP domain need to
know those detailed metrics, it makes sense to use the
OSPFv2 Extended Prefix Opaque LSA for IPv4 and OSPFv3
Dunbar, et al. Expires January 12, 2022 [Page 15]
Internet-Draft OSPF Extension for 5G EC Service
Extended LSA with Intra-Area-Prefix TLV to carry the
detailed sub-TLVs. For routers that don't care about those
metrics, they can ignore them very easily.
It worth noting that not all hosts (prefix) attached to an
A-ER are ANYCAST servers that need network optimization.
An A-ER only needs to advertise the App-Metrics for the
ANYCAST addresses that match with the configured ACLs.
Draft [draft-wang-lsr-passive-interface-attribute]
introduces the Stub-Link TLV for OSPFv2/v3 and ISIS
protocol respectively. Considering the interfaces on an
edge router that connects to the App servers are normally
configured as passive interfaces, these IP-layer App-
metrics can also be advertised as the attributes of the
passive/stub link. The associated prefixes can then be
advertised in the "Stub-Link Prefix Sub-TLV" that is
defined in [draft-wang-lsr-passive-interface-attribute].
All the associated prefixes share the same characteristic
of the link. Other link related sub-TLVs defined in
[RFC8920] can also be attached and applied to the
calculation of path to the associated prefixes.
6.1. OSPFv3 Extension to carry the App-Metrics
For App Servers using IPv6, the OSPFv3 Extended LSA with
the Intra-Area-Prefix Address TLV specified by the Section
3.7 of RFC8362 can be used to carry the App-Metrics for the
attached App Servers.
Dunbar, et al. Expires January 12, 2022 [Page 16]
Internet-Draft OSPF Extension for 5G EC Service
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|7 (IPv6 Local-Local Address) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 AppServer (ANYCAST) address |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Load measurement sub-TLV |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Capability sub-TLV |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Preference sub-TLV |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: IPv6 App Server App-Metrics Encoding
6.2. OSPFv2 Extension to advertise the IP Layer App-Metrics
For App Servers using IPv4 addresses, the OSPFv2 Extended
Prefix Opaque LSA with the extended Prefix TLV can be used
to carry the App Metrics sub-TLVs, as specified by the
Section 2.1 [RFC7684].
Dunbar, et al. Expires January 12, 2022 [Page 17]
Internet-Draft OSPF Extension for 5G EC Service
Here is the proposed encoding:
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 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Route Type | Prefix Length | AF | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address Prefix (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Load Measurement Sub-TLV |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| capacity Index Sub-TLV |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Site Preference Sub-TLV |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: App-Metrix Sub-TLVs in OSPFv2 Extended Prefix TLV
6.3. IP Layer App-Metrics Sub-TLVs
Two types of Load Measurement Sub-TLVs are specified:
a) The Aggregated Load Index based on a weighted
combination of the collected measurements;
b) The raw measurements of packets/bytes to/from the App
Server address. The raw measurement is useful when the
egress edge routers cannot be configured with a
consistent algorithm to compute the aggregated load
index or the raw measurements are needed by a central
analytic system.
The Aggregated Load 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 (TBD2) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Measurement Period |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Aggregated Load Index to reach the App Server |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: Aggregated Load Index Sub-TLV
Dunbar, et al. Expires January 12, 2022 [Page 18]
Internet-Draft OSPF Extension for 5G EC Service
Type=TBD2 (to be assigned by IANA) indicates that the
sub-TLV carries the 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.
The 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 (TBD3) | 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 9: Raw Load Measurement Sub-TLV
Type= TBD3 (to be assigned by IANA) indicates that the
sub-TLV carries the Raw measurements of packets/bytes
to/from the App Server ANYCAST address.
Measurement Period: A user-specified period in seconds,
default is 3600 seconds.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: Capacity Index Sub-TLV
Dunbar, et al. Expires January 12, 2022 [Page 19]
Internet-Draft OSPF Extension for 5G EC Service
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 11: Preference Index Sub-TLV
Note: "Capacity Index" and "Site preference" can be more
stable for each site. If those values are configured to
nodes, they might not need to be included in every OSPF
LSA.
7. Manageability Considerations
To be added.
8. Security Considerations
To be added.
9. IANA Considerations
The following Sub-TLV types need to be added by IANA
to OSPFv4 Extended-LSA Sub-TLVs and OSPFv2 Extended
Link Opaque LSA TLVs Registry.
- Aggregated Load Index Sub-TLV type
- Raw Load Measurement Sub-TLV type
- Capacity Index Sub-TLV type
- Preference Index Sub-TLV type
10. References
Dunbar, et al. Expires January 12, 2022 [Page 20]
Internet-Draft OSPF Extension for 5G EC Service
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to
Indicate Requirement Levels", BCP 14, RFC 2119,
March 1997.
[RFC2328] J. Moy, "OSPF Version 2", RFC 2328, April 1998.
[RFC7684] P. Psenak, et al, "OSPFv2 Prefix/Link Attribute
Advertisement", RFC 7684, Nov. 2015.
[RFC8200] S. Deering R. Hinden, "Internet Protocol, Version
6 (IPv6) Specification", July 2017.
[RFC8326] A. Lindem, et al, "OSPFv3 Link State
advertisement (LSA0 Extensibility", RFC 8362,
April 2018.
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-AppMetaData] L. Dunbar, K. Majumdar, H. Wang, "BGP NLRI
App Meta Data for 5G Edge Computing Service",
draft-dunbar-idr-5g-edge-compute-app-meta-data-
01, work-in-progress, Nov 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-01, work-in-progress, Nov 2020.
[5G-StickyService] 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.
Dunbar, et al. Expires January 12, 2022 [Page 21]
Internet-Draft OSPF Extension for 5G EC Service
[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.
11. Acknowledgments
Acknowledgements to Acee Lindem, Gyan Mishra, Jeff
Tantsura, and Donald Eastlake for their review and
suggestions.
This document was prepared using 2-Word-v2.0.template.dot.
Dunbar, et al. Expires January 12, 2022 [Page 22]
Internet-Draft OSPF Extension for 5G EC Service
Authors' Addresses
Linda Dunbar
Futurewei
Email: ldunbar@futurewei.com
Huaimo Chen
Futurewei
Email: huaimo.chen@futurewei.com
Aijun Wang
China Telecom
Email: wangaj3@chinatelecom.cn
Dunbar, et al. Expires January 12, 2022 [Page 23]