Internet DRAFT - draft-trossen-sfc-name-based-sff
draft-trossen-sfc-name-based-sff
Network Working Group D. Trossen
Internet-Draft InterDigital Europe, Ltd
Intended status: Informational D. Purkayastha
Expires: November 27, 2019 A. Rahman
InterDigital Communications, LLC
May 26, 2019
Name-Based Service Function Forwarder (nSFF) component within SFC
framework
draft-trossen-sfc-name-based-sff-07
Abstract
Adoption of cloud and fog technology allows operators to deploy a
single "Service Function" to multiple "Execution locations". The
decision to steer traffic to a specific location may change
frequently based on load, proximity etc. Under the current SFC
framework, steering traffic dynamically to the different execution
end points require a specific 're-chaining', i.e., a change in the
service function path reflecting the different IP endpoints to be
used for the new execution points. This procedure may be complex and
take time. In order to simplify re-chaining and reduce the time to
complete the procedure, we discuss separating the logical Service
Function Path from the specific execution end points. This can be
done by identifying the Service Functions using a name rather than a
routable IP endpoint (or Layer 2 address). This document describes
the necessary extensions, additional functions and protocol details
in SFF (Service Function Forwarder) to handle name based
relationships.
This document presents InterDigital's approach to name-based service
function chaining. It does not represent IETF consensus and is
presented here so that the SFC community may benefit from considering
this mechanism and the possibility of its use in the edge data
centers.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Example use case: 5G control plane services . . . . . . . . . 4
4. Background . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. Relevant part of SFC architecture . . . . . . . . . . . . 6
4.2. Challenges with current framework . . . . . . . . . . . . 7
5. Name based operation in SFF . . . . . . . . . . . . . . . . . 8
5.1. General Idea . . . . . . . . . . . . . . . . . . . . . . 8
5.2. Name-Based Service Function Path (nSFP) . . . . . . . . . 8
5.3. Name Based Network Locator Map (nNLM) . . . . . . . . . . 10
5.4. Name-based Service Function Forwarder (nSFF) . . . . . . 12
5.5. High Level Architecture . . . . . . . . . . . . . . . . . 13
5.6. Operational Steps . . . . . . . . . . . . . . . . . . . . 14
6. nSFF Forwarding Operations . . . . . . . . . . . . . . . . . 16
6.1. nSFF Protocol Layers . . . . . . . . . . . . . . . . . . 16
6.2. nSFF Operations . . . . . . . . . . . . . . . . . . . . . 18
6.2.1. Forwarding between nSFFs and nSFF-NR . . . . . . . . 18
6.2.2. SF Registration . . . . . . . . . . . . . . . . . . . 21
6.2.3. Local SF Forwarding . . . . . . . . . . . . . . . . . 22
6.2.4. Handling of HTTP responses . . . . . . . . . . . . . 23
6.2.5. Remote SF Forwarding . . . . . . . . . . . . . . . . 23
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27
8. Security Considerations . . . . . . . . . . . . . . . . . . . 27
9. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 27
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10. References . . . . . . . . . . . . . . . . . . . . . . . . . 27
10.1. Normative References . . . . . . . . . . . . . . . . . . 27
10.2. Informative References . . . . . . . . . . . . . . . . . 28
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 29
1. Introduction
The requirements on today's networks are very diverse, enabling
multiple use cases such as IoT, Content Distribution, Gaming and
Network functions such as Cloud RAN and 5G control planes based on a
service-based architecture. These services are deployed, provisioned
and managed using Cloud based techniques as seen in the IT world.
Virtualization of compute and storage resources is at the heart of
providing (often web) services to end users with the ability to
quickly provisioning such virtualized service endpoints through,
e.g., container based techniques. This creates a dynamicity with the
capability to dynamically compose new services from available
services as well as move a service instance in response to user
mobility or resource availability where desirable. When moving from
a pure 'distant cloud' model to one of localized micro data centers
with regional, metro or even street level, often called 'edge' data
centers, such virtualized service instances can be instantiated in
topologically different locations with the overall 'distant' data
center now being transformed into a network of distributed ones. The
reaction of content providers, like Facebook, Google, NetFlix and
others, are not just relying on deploying content server at the
ingress of the customer network. Instead the trend is towards
deploying multiple POPs within the customer network, those POPs being
connected through proprietary mechanisms [Schlinker2017] to push
content.
The Service Function Chaining (SFC) framework [RFC7665] allows
network operators as well as service providers to compose new
services by chaining individual "Service Functions (SFs)". Such
chains are expressed through explicit relationships of functional
components (the service functions), realized through their direct
Layer 2 (e.g., MAC address) or Layer 3 (e.g., IP address)
relationship as defined through next hop information that is being
defined by the network operator, see Section 4 for more background on
SFC.
In a dynamic service environment of distributed data centers as the
one outlined above, with the ability to create and recreate service
endpoints frequently, the SFC framework requires to reconfigure the
existing chain through information based on the new relationships,
causing overhead in a number of components, specifically the
orchestrator that initiates the initial service function chain and
any possible reconfiguration.
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This document describes how such changes can be handled without
involving the initiation of new and reconfigured SFCs by lifting the
chaining relationship from Layer 2 and 3 information to that of
service function 'names', such as names for instance being expressed
as URIs. In order to transparently support such named relationships,
we propose to embed the necessary functionality directly into the
Service Function Forwarder (SFF), as described in [RFC7665]). With
that, the SFF described in this document allows for keeping an
existing SFC intact, as described by its service function path (SFP),
while enabling the selection of an appropriate service function
endpoint(s) during the traversal of packets through the SFC. This
document is an Independent Submission to the RFC Editor. It is not
an output of the IETF SFC WG.
2. Terminology
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. Example use case: 5G control plane services
We exemplify the need for chaining service functions at the level of
a service name through a use case stemming from the current 3GPP Rel
16 work on Service Based Architecture (SBA) [_3GPP_SBA],
[_3GPP_SBA_ENHANCEMENT]. In this work, mobile network control planes
are proposed to be realized by replacing the traditional network
function interfaces with a fully service-based one. HTTP was chosen
as the application layer protocol for exchanging suitable service
requests [_3GPP_SBA]. With this in mind, the exchange between, say
the 3GPP (Rel. 15) defined Session Management Function (SMF) and the
Access and Mobility management Function (AMF) in a 5G control plane
is being described as a set of web service like requests which are in
turn embedded into HTTP requests. Hence, interactions in a 5G
control plane can be modelled based on service function chains where
the relationship is between the specific (IP-based) service function
endpoints that implement the necessary service endpoints in the SMF
and AMF. The service functions are exposed through URIs with work
ongoing to define the used naming conventions for such URIs.
This move from a network function model (in pre-Rel 15 systems of
3GPP) to a service-based model is motivated through the proliferation
of data center operations for mobile network control plane services.
In other words, typical IT-based methods to service provisioning, in
particular that of virtualization of entire compute resources, are
envisioned to being used in future operations of mobile networks.
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Hence, operators of such future mobile networks desire to virtualize
service function endpoints and direct (control plane) traffic to the
most appropriate current service instance in the most appropriate
(local) data centre, such data centre envisioned as being
interconnected through a software-defined wide area network (SD-WAN).
'Appropriate' here can be defined by topological or geographical
proximity of the service initiator to the service function endpoint.
Alternatively, network or service instance compute load can be used
to direct a request to a more appropriate (in this case less loaded)
instance to reduce possible latency of the overall request. Such
data center centric operation is extended with the trend towards
regionalization of load through a 'regional office' approach, where
micro data centers provide virtualizable resources that can be used
in the service execution, creating a larger degree of freedom when
choosing the 'most appropriate' service endpoint for a particular
incoming service request.
While the move to a service-based model aligns well with the
framework of SFC, choosing the most appropriate service instance at
runtime requires so-called 're-chaining' of the SFC since the
relationships in said SFC are defined through Layer 2 or 3
identifiers, which in turn are likely to be different if the chosen
service instances reside in different parts of the network (e.g., in
a regional data center).
Hence, when a traffic flow is forwarded over a service chain
expressed as an SFC-compliant Service Function Path (SFP), packets in
the traffic flow are processed by the various service function
instances, with each service function instance applying a service
function prior to forwarding the packets to the next network node.
It is a Service layer concept and can possibly work over any Virtual
network layer and an Underlay network, possibly IP or any Layer 2
technology. At the service layer, Service Functions are identified
using a path identifier and an index. Eventually this index is
translated to an IP address (or MAC address) of the host where the
service function is running. Because of this, any change of service
function instance is likely to require a change of the path
information since either IP address (in the case of changing the
execution from one data centre to another) or MAC address will change
due to the newly selected service function instance.
Returning to our 5G Control plane example, a user's connection
request to access an application server in the internet may start
with signaling in the Control Plane to setup user plane bearers. The
connection request may flow through service functions over a service
chain in the Control plane, as deployed by network operator. Typical
SFs in a 5G control plane may include "RAN termination / processing",
"Slice Selection Function", "AMF" and "SMF". A Network Slice is a
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complete logical network including Radio Access Network (RAN) and
Core Network (CN). Distinct RAN and Core Network Slices may exist.
A device may access multiple Network Slices simultaneously through a
single RAN. The device may provide Network Slice Selection
Assistance Information (NSSAI) parameters to the network to help it
select a RAN and a Core network part of a slice instance. Part of
the control plane, the Common Control Network Function (CCNF), the
Network Slice Selection Function (NSSF) is in charge of selecting
core Network Slice instances. The Classifier, as described in SFC
architecture, may reside in the user terminal or at the eNB. These
service functions can be configured to be part of a Service Function
Chain. We can also say that some of the configurations of the
Service Function Path may change at the execution time. For example,
the SMF may be relocated as user moves and a new SMF may be included
in the Service Function Path based on user location. The following
diagram in Figure 1 shows the example Service Function Chain
described here.
+------+ +---------+ +-----+ +-----+
| User | | Slice | | | | |
| App |-->| Control |->| AMF |-->| SMF |-->
| Fn | | Function| | | | |
+------+ +---------+ +-----+ +-----+
Figure 1: Mapping SFC onto Service Function Execution Points along a
Service Function Path
4. Background
[RFC7665] describes an architecture for the specification, creation
and ongoing maintenance of Service Function Chains (SFCs). It
includes architectural concepts, principles, and components used in
the construction of composite services through deployment of SFCs.
In the following, we outline the parts of this SFC architecture
relevant for our proposed extension, followed by the challenges with
this current framework in the light of our example use case.
4.1. Relevant part of SFC architecture
SFC Architecture, as defined in [RFC7665], describes architectural
components such as Service Function (SF), Classifier, and Service
Function Forwarder (SFF). It describes the Service Function Path
(SFP) as the logical path of an SFC. Forwarding traffic along such
SFP is the responsibility of the SFF. For this, the SFFs in a
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network maintain the requisite SFP forwarding information. Such SFP
forwarding information is associated with a service path identifier
(SPI) that is used to uniquely identify an SFP. The service
forwarding state is represented by the Service Index (SI) and enables
an SFF to identify which SFs of a given SFP should be applied, and in
what order. The SFF also has information that allows it to forward
packets to the next SFF after applying local service functions.
The operational steps to forward traffic are then as follows: Traffic
arrives at an SFF from the network. The SFF determines the
appropriate SF the traffic should be forwarded to via information
contained in the SFC encapsulation. After SF processing, the traffic
is returned to the SFF, and, if needed, is forwarded to another SF
associated with that SFF. If there is another non-local hop (i.e.,
to an SF with a different SFF) in the SFP, the SFF further
encapsulates the traffic in the appropriate network transport
protocol and delivers it to the network for delivery to the next SFF
along the path. Related to this forwarding responsibility, an SFF
should be able to interact with metadata.
4.2. Challenges with current framework
As outlined in previous section, the Service Function Path defines an
ordered sequence of specific Service Functions instances being used
for the interaction between initiator and service functions along the
SFP. These service functions are addressed by IP (or any L2/MAC)
addresses and defined as next hop information in the network locator
maps of traversing SFF nodes.
As outlined in our use case, however, the service provider may want
to provision SFC nodes based on dynamically spun up service function
instances so that these (now virtualized) service functions can be
reached in the SFC domain using the SFC underlay layer.
Following the original model of SFC, any change in a specific
execution point for a specific Service Function along the SFP will
require a change of the SFP information (since the new service
function execution point likely carries different IP or L2 address
information) and possibly even the Next Hop information in SFFs along
the SFP. In case the availability of new service function instances
is rather dynamic (e.g., through the use of container-based
virtualization techniques), the current model and realization of SFC
could lead to reducing the flexibility of service providers and
increasing the management complexity incurred by the frequent changes
of (service) forwarding information in the respective SFF nodes.
This is because any change of the SFP (and possibly next hop info)
will need to go through suitable management cycles.
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To address these challenges through a suitable solution, we identify
the following requirements:
o Relations between Service Execution Points MUST be abstracted so
that, from an SFP point of view, the Logical Path never changes.
o Deriving the Service Execution Points from the abstract SFP SHOULD
be fast and incur minimum delay.
o Identification of the Service Execution Points SHOULD not use a
combination of Layer 2 or Layer 3 mechanisms.
The next section outlines a solution to address the issue, allowing
for keeping SFC information (represented in its SFP) intact while
addressing the desired flexibility of the service provider.
5. Name based operation in SFF
5.1. General Idea
The general idea is two-pronged. Firstly, we elevate the definition
of a Service Function Path onto the level of 'name-based
interactions' rather than limiting SFPs to Layer 3 or Layer 2
information only. Secondly, we extend the operations of the SFF to
allow for forwarding decisions that take into account such name-based
interaction while remaining backward compatible to the current SFC
architecture, as defined in [RFC7665]. In the following sections, we
outline these two components of our solution.
If the next hop information in the Network Locator Map (NLM) is
described using L2/L3 identifier, the name-based SFF (nSFF) may
operate as described for [traditional] SFF, as defined in [RFC7665].
On the other hand, if the next hop information in the NLM is
described as a name, then the nSFF operates as described in the
following sections.
In the following sections, we outline the two components of our
solution.
5.2. Name-Based Service Function Path (nSFP)
The existing SFC framework is defined in [RFC7665]. Section 4
outlines that the SFP information is representing path information
based on Layer 2 or 3 information, i.e., MAC or IP addresses, causing
the aforementioned frequent adaptations in cases of execution point
changes. Instead, we introduce the notion of a "name-based service
function path (nSFP)".
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In today's networking terms, any identifier can be treated as a name
but we will illustrate the realization of a "Name based SFP" through
extended SFF operations (see Section 6) based on URIs as names and
HTTP as the protocol of exchanging information. Here, URIs are being
used to name for a Service Function along the nSFP. It is to be
noted that the Name based SFP approach is not restricted to HTTP (as
the protocol) and URIs (as next hop identifier within the SFP).
Other identifiers such as an IP address itself can also be used and
are interpreted as a 'name' in the nSFP. IP addresses as well as
fully qualified domain names forming complex URIs (uniform resource
identifiers), such as www.example.com/service_name1, are all captured
by the notion of 'name' in this document.
Generally, nSFPs are defined as an ordered sequence of the "name" of
Service Functions (SF) and a typical name-based Service Function Path
may look like: 192.0.x.x -> www.example.com -> www.example2.com/
service1 -> www.example2.com/service2.
Our use case in Section 3 can then be represented as an ordered named
sequence. An example for a session initiation that involves an
authentication procedure, this could look like 192.0.x.x ->
smf.example.org/session_initiate -> amf.example.org/auth ->
smf.example.org/session_complete -> 192.0.x.x. [Note that this
example is only a conceptual one, since the exact nature of any
future SBA-based exchange of 5G control plane functions is yet to be
defined by standardization bodies such as 3GPP].
In accordance with our use case in Section 3, any of these named
services can potentially be realized through more than one replicated
SF instances. This leads to make dynamic decision on where to send
packets along the SAME service function path information, being
provided during the execution of the SFC. Through elevating the SFP
onto the notion of name-based interactions, the SFP will remain the
same even if those specific execution points change for a specific
service interaction.
The following diagram in Figure 2, describes this name-based SFP
concept and the resulting mapping of those named interactions onto
(possibly) replicated instances.
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+---------------------------------------------------------------+
|SERVICE LAYER |
| 192.0.x.x --> www.example.com --> www.example2.com --> |
| || || |
+----------------------||--------------||-----------------------+
|| ||
|| ||
+----------------------||--------------||-----------------------+
| Underlay network \/ \/ |
| +--+ +--+ +--+ +--+ +--+ +--+ |
| | | | | | | | | | | | | |
| +--+ +--+ +--+ +--+ +--+ +--+ |
| Compute and Compute and |
| storage nodes storage nodes |
+---------------------------------------------------------------+
Figure 2: Mapping SFC onto Service Function Execution Points along a
Service Function Path based on Virtualized Service Function Instance
5.3. Name Based Network Locator Map (nNLM)
In order to forward a packet within a name-based SFP, we need to
extend the network locator map as defined in [RFC8300] with the
ability to consider name relations based on URIs as well as high-
level transport protocols such as HTTP for means of SFC packet
forwarding. Another example for SFC packet forwarding could be that
of CoAP.
The extended Network Locator Map or name-based Network Locator Map
(nNLM) is shown in Figure 3 as an example for www.example.com being
part of the nSFP. Such extended nNLM is stored at each SFF
throughout the SFC domain with suitable information populated to the
nNLM during the configuration phase.
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+------+------+---------------------+-----------------------------+
| SPI | SI | Next Hop(s) | Transport Encapsulation (TE)|
+------+------+---------------------+-----------------------------+
| 10 | 255 | 192.0.2.1 | VXLAN-gpe |
| | | | |
| 10 | 254 | 198.51.100.10 | GRE |
| | | | |
| 10 | 253 | www.example.com | HTTP |
-----------------------------------------------------------------
| | | | |
| 40 | 251 | 198.51.100.15 | GRE |
| | | | |
| 50 | 200 | 01:23:45:67:89:ab | Ethernet |
| | | | |
| 15 | 212 | Null (end of path) | None |
+------+------+---------------------+-----------------------------+
Figure 3: Name-based Network Locator Map
Alternatively, the extended network locator map may be defined with
implicit name information rather than explicit URIs as in Figure 3.
In the example of Figure 4 below, the next hop is represented as a
generic HTTP service without a specific URI being identified in the
extended network locator map. In this scenario, the SFF forwards the
packet based on parsing the HTTP request in order to identify the
host name or URI. It retrieves the URI and may apply policy
information to determine the destination host/service.
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+------+------+---------------------+-----------------------------+
| SPI | SI | Next Hop(s) | Transport Encapsulation (TE)|
+------+------+---------------------+-----------------------------+
| 10 | 255 | 192.0.2.1 | VXLAN-gpe |
| | | | |
| 10 | 254 | 198.51.100.10 | GRE |
| | | | |
| 10 | 253 | HTTP Service | HTTP |
-----------------------------------------------------------------
| | | | |
| 40 | 251 | 198.51.100.15 | GRE |
| | | | |
| 50 | 200 | 01:23:45:67:89:ab | Ethernet |
| | | | |
| 15 | 212 | Null (end of path) | None |
+------+------+---------------------+-----------------------------+
Figure 4: Name-based Network Locator Map with Implicit Name
information
5.4. Name-based Service Function Forwarder (nSFF)
It is desirable to extend the SFF of the SFC underlay to handle nSFPs
transparently and without the need to insert any service function
into the nSFP. Such extended name-based SFF would then be
responsible for forwarding a packet in the SFC domain as per the
definition of the (extended) nSFP.
In our exemplary realization for an extended SFF, the solution
described in this document uses HTTP as the protocol of forwarding
SFC packets to the next (name-based) hop in the nSFP. The URI in the
HTTP transaction are the names in our nSFP information, which will be
used for name based forwarding.
Following our reasoning so far, HTTP requests (and more specifically
the plain text encoded requests above) are the equivalent of Packets
that enter the SFC domain. In the existing SFC framework, typically
an IP payload is assumed to be a packet entering the SFC domain.
This packet is forwarded to destination nodes using the L2
encapsulation. Any layer 2 network can be used as an underlay
network. This notion is now extended to packets being possibly part
of a entire higher layer application, such as HTTP requests. The
handling of any intermediate layers such as TCP, IP is left to the
realization of the (extended) SFF operations towards the next (named)
hop. For this, we will first outline the general lifecycle of an SFC
packet in the following subsection, followed by two examples for
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determining next hop information in Section 6.2.3, finalized by a
layered view on the realization of the nSFF in Section 6.2.4.
5.5. High Level Architecture
+----------+
| SF1 | +--------+ +------+
| instance |\ | NR | | SF2 |
+----------+ \ +--------+ +------+
\ || ||
+------------+ \ +-------+ +---------+ +---------+ +-------+
| Classifier |---| nSFF1 |---|Forwarder|---|Forwarder|---| nSFF2 |
+------------+ +-------+ +---------+ +---------+ +-------+
||
+----------+
| Boundary |
| node |
+----------+
Figure 5: High-level architecture
The high-level architecture for name based operation shown in
Figure 5 is very similar to the SFC architecture, as described in
[RFC7665]. Two new functions are introduced, as shown in the above
diagram, namely the name-based Service Function Forwarder (nSFF) and
the Name Resolver (NR).
nSFF (name-based Service Function Forwarder) is an extension of the
existing SFF and is capable of processing SFC packets based on name-
based network locator map (nNLM) information, determining the next
SF, where the packet should be forwarded and the required transport
encapsulation. Like standard SFF operation, it adds transport
encapsulation to the SFC packet and forwards it.
The Name Resolver is a new functional component, capable of
identifying the execution end points, where a "named SF" is running,
triggered by suitable resolution requests sent by the nSFF. Though
this is similar to DNS function, but it is not same. It does not use
DNS protocols or data records. A new procedure to determine the
suitable routing/forwarding information towards the Nsff (name-based
SFF) serving the next hop of the SFP (Service Function Path) is used.
The details is described later.
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The other functional components such as Classifier, SF are same as
described in SFC architecture, as defined in [RFC7665], while the
Forwarders shown in the above diagram are traditional Layer 2
switches.
5.6. Operational Steps
In the proposed solution, the operations are realized by the name-
based SFF, called nSFF. We utilize the high-level architecture in
Figure 5 to describe the traversal between two service function
instances of an nSFP-based transactions in an example chain of :
192.0.x.x -> SF1 (www.example.com) -> SF2 (www.example2.com) -> SF3
-> ... Service Function 3 (SF3)is assumed to be a classical Service
Function, hence existing SFC mechanisms can be used to reach it and
will not be considered in this example.
According to the SFC lifecycle, as defined in [RFC7665], based on our
example chain above, the traffic originates from a Classifier or
another SFF on the left. The traffic is processed by the incoming
nSFF1 (on the left side) through the following steps. The traffic
exits at nSFF2.
o Step 1: At nSFF1 the following nNLM is assumed
+------+------+---------------------+----------------------------+
| SPI | SI | Next Hop(s) | Transport Encapsulation(TE)|
+------+------+---------------------+----------------------------+
| 10 | 255 | 192.0.2.1 | VXLAN-gpe |
| | | | |
| 10 | 254 | 198.51.100.10 | GRE |
| | | | |
| 10 | 253 | www.example.com | HTTP |
| | | | |
| 10 | 252 | www.example2.com | HTTP |
| | | | |
| 40 | 251 | 198.51.100.15 | GRE |
| | | | |
| 50 | 200 | 01:23:45:67:89:ab | Ethernet |
| | | | |
| 15 | 212 | Null (end of path) | None |
+------+------+---------------------+----------------------------+
Figure 6: nNLM at nSFF1
o Step 2: nSFF1 removes the previous transport encapsulation (TE)
for any traffic originating from another SFF or classifier
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(traffic from an SF instance does not carry any TE and is
therefore directly processed at the nSFF).
o Step 3: nSFF1 then processes the Network Service Header (NSH)
information, as defined in [RFC8300], to identify the next SF at
the nSFP level by mapping the NSH information to the appropriate
entry in its nNLM (see Figure 6) based on the provided SPI/SI
information in the NSH (see Section 4) in order to determine the
name-based identifier of the next hop SF. With such nNLM in mind,
the nSFF searches the map for SPI = 10 and SI = 253. It
identifies the next hop as = www.example.com and HTTP as the
protocol to be used. Given the next hop resides locally, the SFC
packet is forwarded to the SF1 instance of www.example.com. Note
that the next hop could also be identified from the provided HTTP
request, if the next hop information was identified as a generic
HTTP service, as defined in Section 5.3.
o Step 4: The SF1 instance then processes the received SFC packet
according to its service semantics and modifies the NSH by setting
SPI = 10, SI = 252 for forwarding the packet along the SFP. It
then forwards the SFC packet to its local nSFF, i.e., nSFF1.
o Step 5: nSSF1 processes the NSH of the SFC packet again, now with
the NSH modified (SPI = 10, SI = 252) by the SF1 instance. It
retrieves the next hop information from its nNLM in Figure 6, to
be www.example2.com. Due to this SF not being locally available,
the nSFF consults any locally available information regarding
routing/forwarding towards a suitable nSFF that can serve this
next hop.
o Step 6: If such information exists, the Packet (plus the NSH
information) is marked to be sent towards the nSFF serving the
next hop based on such information in step 8.
o Step 7: If such information does not exist, nSFF1 consults the
Name Resolver (NR) to determine the suitable routing/forwarding
information towards the identified nSFF serving the next hop of
the SFP. For future SFC packets towards this next hop, such
resolved information may be locally cached, avoiding to contact
the Name Resolver for every SFC packet forwarding. The packet is
now marked to be sent via the network in step 8.
o Step 8: Utilizing the forwarding information determined in steps 6
or 7, nSFF1 adds the suitable transport encapsulation (TE) for the
SFC packet before forwarding via the forwarders in the network
towards the next nSFF22.
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o Step 9: When the Packet (+NSH+TE) arrives at the outgoing nSFF2,
i.e., the nSFF serving the identified next hop of the SFP, removes
the TE and processes the NSH to identify the next hop information.
At nSFF2 the nNLM in Figure 7 is assumed. Based on this nNLM and
NSH information where SPI = 10 and SI = 252, nSFF2 identifies the
next SF as www.example2.com.
+------+------+---------------------+-----------------------------+
| SPI | SI | Next Hop(s) | Transport Encapsulation (TE)|
+------+------+---------------------+-----------------------------+
| | | | |
| 10 | 252 | www.example2.com | HTTP |
| | | | |
| 40 | 251 | 198.51.100.15 | GRE |
| | | | |
| 50 | 200 | 01:23:45:67:89:ab | Ethernet |
| | | | |
| 15 | 212 | Null (end of path) | None |
+------+------+---------------------+-----------------------------+
Figure 7: nNLM at SFF2
o Step 10: If the next hop is locally registered at the nSFF, it
forwards the packet (+NSH) to the service function instance, using
suitable IP/MAC methods for doing so.
o Step 11: Otherwise, the outgoing nSFF adds a new TE information to
the packet and forwards the packet (+NSH+TE) to the next SFF or
boundary node, as shown in Figure 7.
6. nSFF Forwarding Operations
This section outlines the realization of various nSFF forwarding
operations in Section 5.6. Although the operations in Section 5
utilize the notion of name-based transactions in general, we
exemplify the operations here in Section 5 specifically for HTTP-
based transactions to ground our description into a specific protocol
for such name-based transaction. We will refer to the various steps
in each of the following sub-sections.
6.1. nSFF Protocol Layers
Figure 8 shows the protocol layers, based on the high-level
architecture in Figure 5.
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+-------+ +------+----+ +----+-----+
|App | | | | +--------+ | | |
|HTTP | |--------> | | NR | |nSFF----->|--
|TCP |->| TCP |nSFF| +---/\---+ | | TCP | |
|IP | | IP | | || | | IP | |
+-------+ +------+----+ +---------+ +---------+ +----------+ |
| L2 | | L2 |->|Forwarder|-->|Forwarder|-->| L2 | |
+-------+ +------+----+ +---------+ +---------+ +----------+ |
SF1 nSFF1 nSFF2 |
+-------+ |
| App |/ |
| HTTP | -----------+
| TCP |\
| IP |
| L2 |
+-------+
SF2
Figure 8: Protocol layers
The nSFF component here is shown as implementing a full incoming/
outgoing TCP/IP protocol stack towards the local service functions,
while implementing the nSFF-NR and nSFF-nSFF protocols based on the
descriptions in Section 6.2.3.
For the exchange of HTTP-based service function transactions, the
nSFF terminates incoming TCP connections from as well as outgoing TCP
connections to local SFs, e.g., the TCP connection from SF1
terminates at nSFF1, and nSFF1 may store the connection information,
such as socket information. It also maintains the mapping
information for the HTTP request such as originating SF, destination
SF and socket ID. nSFF1 may implement sending keep-alive messages
over the socket to maintain the connection to SF1. Upon arrival of
an HTTP request from SF1, nSFF1 extracts the HTTP Request and
forwards it towards the next node, as outlined in Section 6.2. Any
returning response is mapped onto the suitable open socket (for the
original request) and send towards SF1.
At the outgoing nSFF2, the destination SF2/Host is identified from
the HTTP request message. If no TCP connection exists to the SF2, a
new TCP connection is opened towards the destination SF2 and the HTTP
request is sent over said TCP connection. The nSFF2 may also save
the TCP connection information (such as socket information) and
maintain the mapping of the socket information to the destination
SF2. When an HTTP response is received from SF2 over the TCP
connection, nSFF2 extracts the HTTP response, which is forwarded to
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the next node. nSFF2 may maintain the TCP connection through keep-
alive messages.
6.2. nSFF Operations
In this section, we present three key aspects of operations for the
realization of the steps in Section 5.6, namely (i) the registration
of local SFs (for step 3 in Section 5.6), (ii) the forwarding of SFC
packets to and from local SFs (for step 3 and 4 as well as 10 in
Section 5.6), (iii) the forwarding to a remote SF (for steps 5, 6 and
7 in Section 5.6) and to the NR as well as (iv) for the lookup of a
suitable remote SF (for step 7 in Section 5.6). We also cover
aspects of maintaining local lookup information for reducing lookup
latency and others issues.
6.2.1. Forwarding between nSFFs and nSFF-NR
Forwarding between the distributed nSFFs as well as between nSFF and
NR is realized over the operator network via a path-based approach.
A path-based approach utilizes path information provided by the
source of the packet for forwarding said packet in the network. This
is similar to segment routing albeit differing in the type of
information provided for such source-based forwarding, as described
in this section. In this approach, the forwarding information to a
remote nSFF or the NR is defined as a 'path identifier' (pathID) of a
defined length where said "Length" field indicates the full pathID
length. The payload of the packet is defined by the various
operations outlined in the following sub-sections, resulting in an
overall packet being transmitted. With this, the generic forwarding
format (GFF) for transport over the operator network is defined in
Figure 9 with the length field defining the length of the pathID
provided.
+---------+-----------------+------------------------//------------+
| | | // |
| Length | Path ID | Payload // |
|(12 bit) | | // |
+---------+-----------------+--------------------//----------------+
Figure 9: Generic Forwarding Format(GFF)
o Length (12 bits): Defines the length of the pathID, i.e., up to
4096 bits
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o Path ID (): Variable length field, Bit field derived from IPv6
source and destination address
For the pathID information, solutions such as those in [Reed2016] can
be used. Here, the IPv6 source and destination addresses are used to
realize a so-called path-based forwarding from the incoming to the
outgoing nSFF or the NR. The forwarders in Figure 8 are realized via
SDN (software-defined networking) switches, implementing an AND/CMP
operation based on arbitrary wildcard matching over the IPv6 source
and destination addresses, as outlined in [Reed2016]. Note that in
the case of using IPv6 address information for path-based forwarding,
the step of removing the transport encapsulation at the outgoing nSFF
in Figure 8 is realized by utilizing the provided (existing) IP
header (which was used for the purpose of the path-based forwarding
in [Reed2016]) for the purpose of next hop forwarding, such as that
of IP-based routing. As described in step 8 of the extended nSFF
operations, this forwarding information is used as traffic
encapsulation. With the forwarding information utilizing existing
IPv6 information, IP headers are utilized as TE in this case. The
next hop nSFF (see Figure 8) will restore the IP header of the packet
with the relevant IP information used to forward the SFC packet to
SF2 or it will create a suitable TE (Transport Encapsulation)
information to forward the information to another nSFF or boundary
node. Forwarding operations at the intermediary forwarders, i.e.,
SDN switches, examine the pathID information through a flow matching
rule in which a specific switch-local output port is represented
through the specific assigned bit position in the pathID. Upon a
positive match in said rule, the packet is forwarded on said output
port.
Alternatively, the solution in
[I-D.ietf-bier-multicast-http-response] suggests using a so-called
BIER (Binary Indexed Explicit Replication) underlay. Here, the nSFF
would be realized at the ingress to the BIER underlay, injecting the
SFC packet (plus the NSH) header with BIER-based traffic
encapsulation into the BIER underlay with each of the forwarders in
Figure 8 being realized as a so-called Bit-Forwarding Router (BFR)
[RFC8279].
6.2.1.1. Transport Protocol Considerations
Given that the proposed solution operates at the 'named transaction'
level, particularly for HTTP transactions, forwarding between nSFFs
and/or NR SHOULD be implemented via a transport protocol between
nSFFs and/or NR in order to provide reliability, segmentation of
large GFF packets, and flow control, with the GFF in Figure 9 being
the basic forwarding format for this.
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Note that the nSFFs act as TCP proxies at ingress and egress, thus
terminating incoming and initiating outgoing HTTP sessions to SFs.
Figure 10 shows the packet format being used for the transmission of
data, being adapted from the TCP header. Segmentation of large
transactions into single transport protocol packets is realized
through maintaining a 'Sequence number'. A 'Checksum' is calculated
over a single data packet with the ones-complement TCP checksum
calculation being used. The 'Window Size' field indicates the
current maximum number of transport packets that are allowed in-
flight by the egress nSFF. A data packet is sent without 'Data'
field to indicate the end of (e.g., HTTP) transaction.
Note that in order to support future named transactions based on
other application protocols, such as CoAP, future versions of the
transport protocol MAY introduce a 'Type' field that indicates the
type of application protocol being used between SF and nSFF with
'Type' 0x01 proposed for HTTP. This is being left for future study.
| 16 bit | 16 bit |
+----------------------------------------------+
| Sequence number |
+----------------------------------------------+
| Checksum | Window Size |
+----------------------------------------------+
| ... |
| Data (Optional) |
+----------------------------------------------+
Figure 10: Transport protocol data packet format
Given the path-based forwarding being used between nSFFs, the
transport protocol between nSFFs utilizes negative acknowledgements
from the egress nSFF towards the ingress nSFF. The transport
protocol NACK packet carries the number of NACKs as well as the
specific sequence numbers being indicated as lost in the 'NACK
number' field(s), as shown in Figure 11.
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| 16 bit | 16 bit |
+----------------------------------------------+
| Number of NACKs | +
+----------------------------------------------+
| NACK number |
+----------------------------------------------+
+ ... NACK Number +
+----------------------------------------------+
Figure 11: Transport protocol NACK packet format
If the indicated number of NACKs in a received NACK packet in non-
zero, the ingress nSFF will retransmit all sequence numbers signalled
in the packet, while decreasing its congestion window size for future
transmissions.
If the indicated number of NACKs in a received NACK packet in zero,
it will indicate the current congestion window as being successfully
(and completely) being transmitted, increasing the congestion window
size if smaller than the advertised 'Window Size' in Figure 10.
The maintenance of the congestion window is subject to realization at
the ingress nSFF and left for further study in nSFF realizations.
6.2.2. SF Registration
As outlined in step 3 and 10 of Section 5.6, the nSFF needs to
determine if the SF derived from the nNLM is locally reachable or
whether the packet needs forwarding to a remote SFF. For this, a
registration mechanism is provided for such local SF with the local
nSFF. Two mechanisms can be used for this:
1. SF-initiated: We assume that the SF registers its FQDN to the
local nSFF. As local mechanisms, we foresee that either a REST-based
interface over the link-local link or configuration of the nSFF
(through configuration files or management consoles) can be utilized.
Such local registration event leads to the nSFF to register the given
FQDN with the NR in combination with a system-unique nSFF identifier
that is being used for path computation purposes in the NR. For the
registration, the packet format in Figure 12 is used (inserted as the
payload in the GFF of Figure 9 with the pathID towards the NR).
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+---------+-----------------+------------------+
| | | |
| R/D | hash(FQDN) | nSFF_ID |
| (1 bit) | (16 bit) | (8 bit) |
+---------+-----------------+------------------+
Figure 12: Registration packet format
o R/D: 1 bit length (0 for Register, 1 for De-register)
o Hash(FQDN): 16 bit length for a hash over the FQDN of the SF
o nSFF_ID: 8 bit for a system-unique identifier for the SFF related
to the SF.
We assume that the pathID towards the NR is known to the nSFF through
configuration means.
The NR maintains an internal table that associates the hash(FQDN),
the nSFF_id information as well as the pathID information being used
for communication between nSFF and NR. The nSFF locally maintains a
mapping of registered FQDNs to IP addresses, for the latter using
link-local private IP addresses.
2. Orchestration-based: in this mechanism, we assume that SFC to be
orchestrated and the chain being provided through an orchestration
template with FQDN information associated to a compute/storage
resource that is being deployed by the orchestrator. We also assume
knowledge at the orchestrator of the resource topology. Based on
this, the orchestrator can now use the same REST-based protocol
defined in option 1 to instruct the NR to register the given FQDN, as
provided in the template, at the nSFF it has identified as being the
locally servicing nSFF, provided as the system-unique nSFF
identifier.
6.2.3. Local SF Forwarding
There are two cases of local SF forwarding, namely the SF sending an
SFC packet to the local nSFF (incoming requests) or the nSFF sending
a packet to the SF (outgoing requests) as part of steps 3 and 10 in
Section 5.6. In the following, we outline the operation for HTTP as
an example named transaction.
As shown in Figure 8, incoming HTTP requests from SFs are extracted
by terminating the incoming TCP connection at their local nSFFs at
the TCP level. The nSFF MUST maintain a mapping of open TCP sockets
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to HTTP requests (utilizing the URI of the request) for HTTP response
association.
For outgoing HTTP requests, the nSFF utilizes the maintained mapping
of locally registered FQDNs to link-local IP addresses (see
Section 6.2.2 option 1). Hence, upon receiving an SFC packet from a
remote nSFF (in step 9 of Section 5.6), the nSFF determines the local
existence of the SF through the registration mechanisms in
Section 6.2.2. If said SF does exist locally, the HTTP (+NSH)
packet, after stripping the TE, is sent to the local SF as step 10 in
Section 5.6 via a TCP-level connection. Outgoing nSFF SHOULD keep
TCP connections open to local SFs for improving SFC packet delivery
in subsequent transactions.
6.2.4. Handling of HTTP responses
When executing step 3 and 10 in Section 5.6, the SFC packet will be
delivered to the locally registered next hop. As part of the HTTP
protocol, responses to the HTTP request will need to be delivered on
the return path to the originating nSFF (i.e., the previous hop).
For this, the nSFF maintains a list of link-local connection
information, e.g., sockets to the local SF and the pathID on which
the request was received. Once receiving the response, nSFF consults
the table to determine the pathID of the original request, forming a
suitable GFF-based packet to be returned to the previous nSFF.
When receiving the HTTP response at the previous nSFF, the nSFF
consults the table of (locally) open sockets to determine the
suitable local SF connection, mapping the received HTTP response URI
to the stored request URI. Utilizing the found socket, the HTTP
response is forwarded to the locally registered SF.
6.2.5. Remote SF Forwarding
In steps 5, 6, 7, and 8 of Section 5.6, an SFC packet is forwarded to
a remote nSFF based on the nNLM information for the next hop of the
nSFP. Section 6.2.5.1 handles the case of suitable forwarding
information to the remote nSFF not existing, therefore consulting the
NR to obtain suitable information, while Section 6.2.5.2 describes
the maintenance of forwarding information at the local nSFF, while
Section 6.2.5.3 describes the update of stale forwarding information.
Note that the forwarding described in Section 6.2.1 is used for the
actual forwarding to the various nSFF components. Ultimately,
Section 6.2.5.4 describes the forwarding to the remote nSFF via the
forwarder network.
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6.2.5.1. Remote SF Discovery
The nSFF communicates with the NR for two purposes, namely the
registration and discovery of FQDNs. The packet format for the
former was shown in Figure 10 in Section 6.2.2, while Figure 13
outlines the packet format for the discovery request.
+--------------+-------------+ +--------+-----------------//--------+
| | | | | // |
| hash(FQDN) | nSFF_ID | | Length | pathID // |
| (16 bit) | (8 bit) | | (4 bit)| // |
+--------------+-------------+ +--------+-------------//------------+
Path Request Path Response
Figure 13: Discovery packet format
For Path Request:
o Hash(FQDN): 16 bit length for a hash over the FQDN of the SF
o nSFF_ID: 8 bit for a system-unique identifier for the SFF related
to the SF
For Path Response:
o Length (4 bits): Defines the length of the pathID
o Path ID (): Variable length field, Bit field derived from IPv6
source and destination address
A path to a specific FQDN is requested by sending a hash of the FQDN
to the NR together with its nSFF_id, receiving as a response a pathID
with a length identifier. The NR SHOULD maintain a table of
discovery requests that map discovered (hash of) FQDN to the nSFF_id
that requested it and the pathID that is being calculated as a result
of the discovery request.
The discovery request for an FQDN that has not previously been served
at the nSFF (or for an FQDN whose pathID information has been flushed
as a result of the update operations in Section 6.2.5.3), results in
an initial latency incurred by this discovery through the NR, while
any SFC packet sent over the same SFP in a subsequent transaction
will utilize the nSFF local mapping table. Such initial latency can
be avoided by pre-populating the FQDN-pathID mapping proactively as
part of the overall orchestration procedure, e.g., alongside the
distribution of the nNLM information to the nSFF.
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6.2.5.2. Maintaining Forwarding Information at Local nSFF
Each nSFF MUST maintain an internal table that maps the (hash of the)
FQDN information to a suitable pathID information. As outlined in
step 7 of Section 5.6, if a suitable entry does not exist for a given
FQDN, the pathID information is requested with the operations in
Section 6.2.5.1 and the suitable entry is locally created upon
receiving a reply with the forwarding operation being executed as
described in Section 6.2.1.
If such entry does exist (i.e., step 6 of Section 5.6) the pathID is
locally retrieved and used for the forwarding operation in
Section 6.2.1.
6.2.5.3. Updating Forwarding Information at nSFF
The forwarding information maintained at each nSFF (see
Section 6.2.5.2) might need to be updated for three reasons:
o An existing SF is no longer reachable: In this case, the nSFF with
which the SF is locally registered, de-registers the SF explicitly
at the NR by sending the packet in Figure 10 with the hashed FQDN
and the R/D bit set to 1 (for de-register).
o Another SF instance has become reachable in the network (and
therefore might provide a better alternative to the existing SF):
in this case, the NR has received another packet with format
defined in Figure 11 but a different nSFF_id value.
o Links along paths might no longer be reachable: the NR might use
suitable southbound interface to transport networks to detect link
failures, which it associates to the appropriate pathID bit
position.
For this purpose, the packet format in Figure 14 is sent from the NR
to all affected nSFFs, using the generic format in Figure 9.
+---------+-----------------+--------------//----+
| | | // |
| Type | #IDs | IDs // |
| (1 bit) | (8 bit) | // |
+---------+-----------------+----------//--------+
Figure 14: Path update format
o Type: 1 bit length (0 for Nsff ID, 1 for Link ID)
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o #IDs: 8 bit length for number of IDs in the list
o IDs: List of IDs (Nsff ID or Link ID)
The pathID to the affected nSFFs is computed as the binary OR over
all pathIDs to those nSFF_ids affected where the pathID information
to the affected nSFF_id values is determined from the NR-local table
maintained in the registration/deregistration operation of
Section 6.2.2.
The pathID may include the type of information being updated (e.g.,
node identifiers of leaf nodes or link identifiers for removed
links). The node identifier itself may be a special identifier to
signal "ALL NODES" as being affected. The node identifier may signal
changes to the network that are substantial (e.g., parallel link
failures). The node identifier may trigger (e.g., recommend) purging
of the entire path table (e.g., rather than the selective removal of
a few nodes only).
It will include the information according to the type. The included
information may also be related to the type and length information
for the number of identifiers being provided.
In case 1 and 2, the Type bit is set to 1 (type nSFF_id) and the
affected nSFFs are determined by those nSFFs that have previously
sent SF discovery requests, utilizing the optional table mapping
previously registered FQDNs to nSFF_id values. If no table mapping
the (hash of) FQDN to nSFF_id is maintained, the update is sent to
all nSFFs. Upon receiving the path update at the affected nSFF, all
appropriate nSFF-local mapping entries to pathIDs for the hash(FQDN)
identifiers provided will be removed, leading to a new NR discovery
request at the next remote nSFF forwarding to the appropriate FQDN.
In case 3, the Type bit is set to 0 (type linkID) and the affected
nSFFs are determined by those nSFFs whose discovery requests have
previously resulted in pathIDs which include the affected link,
utilizing the optional table mapping previously registered FQDNs to
pathID values (see Section 6.2.5.1). Upon receiving the node
identifier information in the path update, the affected nSFF will
check its internal table that maps FQDNs to pathIDs to determine
those pathIDs affected by the link problems and remove path
information that includes the received node identifier(s). For this,
the pathID entries of said table are checked against the linkID
values provided in the ID entry of the path update through a binary
AND/CMP operation to check the inclusion of the link in the pathIDs
to the FQDNs. If any pathID is affected, the FQDN-pathID entry is
removed, leading to a new NR discovery request at the next remote
nSFF forwarding to the appropriate FQDN.
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6.2.5.4. Forwarding to remote nSFF
Once step 5, 6, and 7 in Section 5.6 are being executed, step 8
finally sends the SFC packet to the remote nSFF, utilizing the pathID
returned in the discovery request (Section 6.2.5.1) or retrieved from
the local pathID mapping table. The SFC packet is placed in the
payload of the generic forwarding format in Figure 9 together with
the pathID and the nSFF eventually executes the forwarding operations
in Section 6.2.1.
7. IANA Considerations
This document requests no IANA actions.
8. Security Considerations
The operations in Sections 5 and 6 describes the forwarding of SFC
packets between named SFs based on URIs exchanged in HTTP messages.
For security considerations, TLS is sufficient between originating
node and Nsff, Nsff to Nsff, Nsff to destination. TLS handshake
allows to determine the FQDN, which in turn is enough for the service
routing decision. Supporting TLS also allows the possibility of
HTTPS based transactions.
9. Acknowledgement
The authors would like to thank Dirk von Hugo and Andrew Malis for
their reviews and valuable comments. We would also like to thank
Joel Halpern, the chair of the SFC WG, and Adrian Farrel for guiding
us through the IETF Independent Submission Editor (ISE) path.
10. References
10.1. Normative References
[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>.
[RFC7665] Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
Chaining (SFC) Architecture", RFC 7665,
DOI 10.17487/RFC7665, October 2015,
<https://www.rfc-editor.org/info/rfc7665>.
[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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[RFC8279] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
Przygienda, T., and S. Aldrin, "Multicast Using Bit Index
Explicit Replication (BIER)", RFC 8279,
DOI 10.17487/RFC8279, November 2017,
<https://www.rfc-editor.org/info/rfc8279>.
[RFC8300] Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed.,
"Network Service Header (NSH)", RFC 8300,
DOI 10.17487/RFC8300, January 2018,
<https://www.rfc-editor.org/info/rfc8300>.
10.2. Informative References
[_3GPP_SBA]
3GPP, "Technical Realization of Service Based
Architecture", 3GPP TS 29.500 0.4.0, January 2018,
<http://www.3gpp.org/ftp/Specs/html-info/29500.htm>.
[_3GPP_SBA_ENHANCEMENT]
3GPP, "New SID for Enhancements to the Service-Based 5G
System Architecture", 3GPP S2-182904 , February 2018, <htt
p://www.3gpp.org/ftp/tsg_sa/WG2_Arch/TSGS2_126_Montreal/
Docs/S2-182904.zip>.
[I-D.ietf-bier-multicast-http-response]
Purkayastha, D., Rahman, A., Trossen, D., and T. Eckert,
"Applicability of BIER Multicast Overlay for Adaptive
Streaming Services", draft-ietf-bier-multicast-http-
response-00 (work in progress), February 2019.
[Reed2016]
Reed, M., Al-Naday, M., Thomas, N., Trossen, D., and S.
Spirou, "Stateless multicast switching in software defined
networks", ICC 2016, 2016,
<https://arxiv.org/pdf/1511.06069.pdf>.
[Schlinker2017]
Schlinker, B., Kim, H., Cui, T., Katz-Bassett, E.,
Madhyastha, Harsha., Cunha, I., Quinn, J., Hassan, S.,
Lapukhov, P., and H. Zeng, "Engineering Egress with Edge
Fabric, Steering Oceans of Content to the World", ACM
SIGCOMM 2017, 2017, <https://research.fb.com/wp-
content/uploads/2017/08/sigcomm17-final177-2billion.pdf>.
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Authors' Addresses
Dirk Trossen
InterDigital Europe, Ltd
64 Great Eastern Street, 1st Floor
London EC2A 3QR
United Kingdom
Email: Dirk.Trossen@InterDigital.com
Debashish Purkayastha
InterDigital Communications, LLC
1001 E Hector St
Conshohocken
USA
Email: Debashish.Purkayastha@InterDigital.com
Akbar Rahman
InterDigital Communications, LLC
1000 Sherbrooke Street West
Montreal
Canada
Email: Akbar.Rahman@InterDigital.com
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