Network Working Group M. Beckman
Internet Draft: 00 U.S. Department of Defense
Category: Standards Track 14 September 2006
IPv6 Dynamic Flow Label Switching (FLS)
draft-martinbeckman-ietf-ipv6-fls-ipv6flowswitching-00.txt
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Copyright (C) The Internet Society (2006).
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By submitting this Internet-Draft, each author represents that any applicable patent
or other IPR claims of which he or she is aware have been or will be disclosed,
and any of which he or she becomes aware will be disclosed, in accordance with
Section 6 of BCP 79.
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."
Abstract
This document seeks to establish a standard for the utilization of the Class of Service Field
and the us of the Flow Label Field within the IPv6 Header and establish a methodology of
switching packets through routers using the first 32-bits of the IPv6 header using Flow Label
Switching on packets rather than full routing of packets.Within the first 32-bits of an IPv6
header exists the requisite information to allow for the immediate switching on an ingress
packet of a router, allowing for Label Switching of a native IPv6 packet. This allows the
establishment of VPN circuits in a dynamic manner across transit networks.The establishment of
Flows based upon the 20-bit Flow Label value can be done dynamically with minimal effort
and configuration of the end-point routers of the flow. The flows can be managed or open,
encrypted or in the clear, and will allow for greater scalability, security, and agility in
the management and operation of networks.
Comments are solicited and should be addressed to martin.beckman@disa.mil
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. The Flow Label Switching Class of Service . . . . . . . . . . 3
4. Flow Label Switching Setup and Management . . . . . . . . . . 4
5. Managed Flow Label Switching . . . . . . . . . . . . . . . . . 5
6. Encrypted Flow Label Switching . . . . . . . . . . . . . . . . 7
7. Flow Sets and Queuing . . . . . . . . . . . . . . . . . . . . 9
8. Contextual Uses of Flow Label Switching . . . . . . . . . . . 9
9. Intellectual Property Statement . . . . . . . . . . .. . . . . 10
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 10
12. Author's Address . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction and Abstract
To traverse the Internet or any large enterprise network, each router hop represents
a decision point about the life cycle of each datagram. A major latency inducing function
is the look-up of the destination of the packet in the routing table of each router along
the way. This is for simplistic routing. If there are additional considerations, such as
queuing or filtering, the process can become more laborious. Additionally, two or more
networks requiring secure communications require the establishment of a VPN tunnel to assure
security of the traffic as it traverses the backbone or in most cases, a carriers
internetworking autonomous system. In all cases, the entire IPv6 header of 320 bits must be
read, cached, and processed at each router along the path between the networks. What is
proposed is a methodology of determining the destination port for a packet at is enters
a router within the first 32-bits of information. This can be done using a hierarchical
methodology of applying values to the Class of Service Field (8-bits) and switching the
packet based upon the value of the Flow Label Field (20-bits) based upon a flow label
switching table within the router. The only requirement is that all routers along the
paths available can read the Class of Service Field and are capable of Flow Label Switching.
Additionally, the Flow Switch Path are dynamically established by the two end-point routers
with simple recognition of the flow by the intervening Next-Hop-Routers along the paths
between the two End Point Routers.
The flows are capable of being controlled either manually or through a Flow Label Server
within an autonomous system. This is essential for the secure functioning of a network or
conflicting Flow Labels will result. Fin ally, the Flow establishment and operation is
encryptable, allowing for secure establishment and operation between the two end point
routers of the flow.
Succinctly put, packets can be switched based upon Flow Label Value allowing for a myriad
of possibilities in both topologies and secure network operations across carriers across
the globe. The end result is a limiting of the need for VPN servers, IPv6 tunnels, and
greater mobility of entire networks within an enterprise if proper planning and
considerations are understood.
2. Definitions
Flow Initiating Router (FIR) The FIR is the router that initiates a flow label switch path.
The FIR sets the Class of Service Field and Flow Label Values to the required value to set
the flow up across the routing fabric between the two end points.
Flow Destination Router (FDR) The FDR is the router the FIR seeks to establish a flow with.
The FDR resets the Class of Service Field and Flow Label Values to the required value to send
the packet to its final destination based upon the path determined by the local routing table.
Next-Hop-Router (NHR) The NHR established and maintains the Flow Switch Path using a Flow
Switch Table that is maintained based upon instructions from the FIR and its own local
routing table.
Switched Flow Path (SFP) is the switched path taken by packet across a routed fabric based upon
the value of the Flow Label and, if used, flow set.
Flow Set (FS) a group of flows through a router identified by the FS value in the Class of Service.
Flow Path Server (FPS) is a physical or virtual host on the network the FIR, FDR, and NHRs
use to validate Flow Path setup requests.
3. The Flow Label Switching Class of Service.
The first requirement is to establish a flow path across a routed fabric based upon a flow label.
The second requirement is to identify a packet as being flow switched versus routed.
To accomplish this, the Class of Service Field is used. In any event the packet is either routed
of flow switched. Therefore, the differentiation is set in the first bit of the Class of Service
Field, which is set to 1 for flow switched. This leaves the lower half values of the Class of
Service (0-127) available of use in routing. The remaining values of the Class of Service Field of
a Flow Switched packet are as follows:
|version| Class of Service| Flow Label |
|1 2 3 4| 1 2 3 4 5 6 7 8 | 20 bits |
|0 1 1 0| 1 a b c d e f g | 1 - 1,048,574 |
Value a 0 = Open / 1 = Managed
Value b 0 = Clear / 1 = Encrypted
Value c 0 = Data Traffic / 1 = Flow Management Message
Values d through f are dependant upon the value of c.
When c = 0, the packet is user traffic moving across the flow. The balance of 4 bits is used
for priority, differentiating between inter-AS or intra AS Flows, or a combination of both. This
allows for 16 priorities, sixteen different set of flows, or a combination of differing flow sets
with internal priority queues. When it is a combination of both, priority is set first, and the
flow set is set second. As an example, two flow sets (blue and red) are set in field g with
blue or red being a value of 0 and the other a value of 1. Each flow set then has 3 bits for
setting priority using d f.
When c = 1, the packet is a Flow Management Packet between the two end point routers
(the FIR and FDR) as well as for the intervening NHRs along the flow path. The follow are
the Values of d though g in this circumstance and are covered in the mechanics of setting
of a Flow Switch Path:
| d e f g | Decimal | Purpose
| 0 0 0 0 | 0 |Set up an Asymmetric Flow
| 0 0 0 1 | 1 |Set up a Symmetric Flow
| 0 0 1 0 | 2 |NHR Acknowledgment
| 0 0 1 1 | 3 |NHR Failed
| 0 1 0 0 | 4 |Restart Flow
| 0 1 0 1 | 5 |Keep Alive from FIR
| 0 1 1 0 | 6 |Keep Alive from FDR
| 0 1 1 1 | 7 |Flow Tear Down
| 1 n n 0 | 8-14 |FPS Management
| 1 1 1 1 | 15 |Reserved
4. Flow Label Switching Setup and Management
Across a routed fabric, a switched flow is initiated by a Flow Initiation Router (FIR).
To accomplish this, the router has a virtual interface established with a routable
128-bit Unicast address. The Flow Destination Router has the same setup with a different
routable 128-bit Unicast address. The initiating packet from the FIR to the FDR is
as follows:
|version| Class of Service| Flow Label |
|1 2 3 4| 1 2 3 4 5 6 7 8 | 20 bits |
|0 1 1 0| 1 0 0 1 0 0 0 0 | 0-FE |
____________________________________________
|Payload Length | Next Hdr 59| Hop Limit |
____________________________________________
| |
| FIR 128-bit Address |
| |
| |
____________________________________________
| |
| FDR 128-bit Address |
| |
| |
____________________________________________
| Next Header 59 and Padding |
This establishes a simple, asymmetric Flow Path. The FIR send the packet via
the destination port of the FDR based upon the route listed in the routing table.
The FIR then sets the flow label value with the end-points into a flow switch
table and marks the label as the router being an end-point for the flow.
The Next Hop Router (NHR) receives the packet and established an entry in the
flow switch table based upon the routing table as port to the FIR and FDR
associated with the flow label. Since this flow in asymmetric, the ports used by
the flow path could be dissimilar is the best paths per the routing table have
an asymmetric pattern. This is possible for Flows over ASNs where BGP parameters
may make ingress and egress to another AS asymmetric.
For Symmetric flows, bit 5 is set to one, and the NHR simply duplicates the
Flow Switch Table Entry reversing the ingress/egress ports for the flow label
association.
Once the flow switch table is updated by the NHR, the packet is sent to the
next NHR on the routed path, each updating its own Flow Switch Table. The NHR
then sends an acknowledgement to the sending router with a COS field of:
1 n n 1 0 0 1 0, where n is the value of the COS filed received.
This is of importance later when flows are setup as managed, with or without encryption.
The receiving this acknowledgement then marks the Flow Switch Table entries as active.
This process through the NHRs continues until the packet is received by the FDR.
Since the destination address is local to the router, the FDR then sets the flow label
value with the end-points into a flow switch table and marks the label as the router
being an end-point for the flow. The FDR then sends a keep-alive to the FIR with a
COS value of 1 n n 1 0 1 1 0 via the flow path established. The FIR will send a
keep-alive with a COS value of 1 n n 1 0 1 0 1. Both the FIR and FDR will send their
respective keep-alive packets over the flow path on a varying interval of 1-180 seconds.
If the end point routers do not receive a keep-alive from their respective end-point,
the FIR and/or FDR will send a restart message using a COS Value of 1 n n 1 0 1 0 0.
This initiates the Flow over the NHR path. The purpose of the restart message is to force
the NHRs on the path to revalidate the Flow Switch table entry for that particular flow.
During the startup phase of the flow. If there is a duplicate flow label entry
in an NHR along the path (Example: The Network Administrator attempts to use the
same flow label values for two different sets of end points, that NHR sends back
a NHR Fail message with a COS value of 1 n n 1 0 0 1 1. Any Reviving NHR then
drops that entry from the flow switch table and forwards the messages back to
the FIR. The FIR then logs to console and drops the flow setup.
The Flow Switch Table entries for Next Hop Routers (NHRs) remains valid
for 1 to 30 minutes if there are no packets matching the entry. The purpose
for this control is to purge unused flow paths from the routed path automatically;
however, care should be taken to ensure the FIR/FDR Keep-Alive messages transpire
within the purge time set.
5. Managed Flow Label Switching
In the proceeding section, the flows are openly established from one FIR to and FDR
with automatic processing by the intervening NHRs along the routed path. While
convenient and possibly applicable within a large enterprise network, the management
of possibly over 1 million flows will become problematic. Further, while Flow Label
Switching is generally for routers, flows could conceivably be established between
host on the network for a variety of purposes such as server-to-server updating and
archiving, true peer-to-peer networking where latency of service is problematic;
however, the openness of open flow label switching allows for greater risks to the
routed infrastructure. To mitigate these risks and allow for more centralized
management, the second bit of the COS filed can be set to one making the establishment
of Flow Switch Paths centrally controlled.
As a methodology, Managed Flow Switching is simple. The second bit of the COS field
is set to 1. Caching the packet, the receiving router then and requests a validation
of the Flow Path from a flow path server (FPS) on the network. Multiple Flow Path Servers
(FPS) are required for redundancy. The recommended methodology would to imbed the server
as an internal service on a set of routers within the infrastructure with a common
128-bit Anycast address for the server.
The transaction for setup should be simplistic and allow for secure means of
authentication between the routers and the FPS devices on the network. The
conceptual transaction methodology is as follows:
- A Flow Path Server is established on the network with a predetermined
Anycast Address available to only the routers or specified devices on the network.
- Each router in the fabric has the Anycast address loaded in the configuration
to request a Flow Path Lookup. Additionally, each router should be configurable
to globally deny non-managed Flow Path Switching request, yet have the option
of permitting individual
- A Flow Path is loaded into the server with the Flow Label,
Flow Set, Priority, FIR Unicast Address, and the FDR Unicast Address.
- The Flow Label with Flow Set, Priority, and FDR Address are setup in the FIR.
- The FIR requests validation of the Flow Path from the FPS.
- Once the FPS validates the Flow requested by the FIR and responds with
an acknowledgement, the NHR sends the set packet to the next NHR on the Flow
Path per the routing table.
- Caching the packet, the first NHR then and requests a validation of the Flow
Path from a flow path server (FPS) on the network. When the Flow is validated,
the request is forwarded to the next NHR on the path per the local route table.
Each NHR responds with an acknowledgement to the requesting router as in the
unmanaged flow operation.
- The process repeats through the chain of NHRs until the request is received
by the FDR. Caching the packet, the FDR then and requests a validation of the
Flow Path from a flow path server (FPS) on the network. Once acknowledged,
the FDR has acknowledgement, it sends a Keep-Alive to the FIR as in the
unmanaged flow.
Once the Flow Switching Path is established, the FPS is no longer used. The
validity on the Flow Switch Path continues to be maintained via keep-alive
packets between the endpoint routers and timers on the NHRs along the path.
Inter-FPS updating for multiple FPS on a routed fabric is essential when using
Anycasting. Each FPS will belong to a hierarchy of servers, with one being
designated as the root server in a fashion similar to DNS; however ,the exchange
need to take place via TCP in a point-to-point fashion. If a flow is configured
into a secondary server, the root server is notified. In the event of a root
server failure, the next server will assume the role as root server. The
recommended approach is to prioritize based upon lowest MAC address or unicast
end-station address or the servers.
Since updates are not immediate, A Flow Path Validation request will query the
closest FPS per Anycasting methodologies. If the Flow is not found, the FPS queries
the root server for an update. If not found the validation fails, yet if the root FPS
has the entry, is sends a validation to the secondary server. The secondary server
then updates its Flow Path Database.
The root FPS will send an initial full database update to the secondary FPS
and will only send adds and drop on a periodic basis after that.
If a new secondary FPS is placed into the service, the root server must be
manually configured with the address on the secondary servers unicast address.
The root FPS will then send the full database to the secondary FPS. A secondary
FPS will not request and update. This precludes a rouge FPS from hijacking the
FPS database.
The FPS database will identify the following:
Current Root FPS by Unicast Address
All Secondary FPS by Unicast Address
All Flow Path Entries including FIR by Unicast Address, FDR by Unicast Address,
Flow Label Value, Flow Set Value (If used), Flow Priority (If Used), Encryption COS bit
setting, Flow Symmetry Value, Time Last Keep-Alive received from FIR, keep alive interval.
The root FPS sends a Keep-Alive Query to the FIR and FDR for each flow. The FIR and
FDR each respond to their respective Anycast FPS. If an FPS has not received an
Acknowledgement from the End-Points within three attempts, the FPS updates is local
database and sends a Flow Failure message to the root FPS. The root server takes
three actions: Updates the local database by suspending the Flow Path Information,
Sends an FPS Database Update to each secondary FPS, Sends a Flow Halt Message to
the End-points, The FIR in turn issues a Flow Tear Down Packet to the NHRs to clear
the entry from the FIR, FDR, and NHR local Flow Switch Table. The following is a
summary of the second half of the COS field binary settings used with
the 11n1 set first half of the COS.
| d e f g | Decimal | Purpose
| 1 0 0 0 | 8 |End Point Keep-Alive Query to FIR/FDR
| 1 0 0 1 | 9 |End Point Keep-Alive Acknowledgement from FIR/FDR
| 1 0 1 0 | 10 |Flow Halt, Issue Flow Teardown Message
| 1 0 1 1 | 11 |FPS Full Database Update (from root FPS to secondary FPS)
| 1 1 0 0 | 12 |FPS Full Database Ack (from secondary FPS to root FPS)
| 1 1 0 1 | 13 |FPS Database Update (from root FPS to secondary FPS)
| 1 1 1 0 | 14 |FPS Database Ack (from secondary FPS to root FPS)
| 1 1 1 1 | 15 |Flow Failure from secondary FPS to root FPS
6. Encrypted Flow Label Switching
The envisioned use of Flow Label Switching is to allow communities of interest
connected to a common infrastructure to connect internally to each other without
the overhead associated with tunneling or VPN arrangements; however, the Flows
need to be secure from monitoring in some cases, as the packets traverse a
common backbone or carrier level Autonomous System. This section deals with
purpose and use of the third (3rd) bit of the COS Field for encrypting the
Flows between Endpoints via either locally agreeable encryption between the
endpoint routers (or hosts of the Flows are between Servers, or via a PPKI
infrastructure setup.
To encrypt a Flow Path, the FIR sets the third bit of the COS field to a value
of one (1). There are two possible methodologies: In the Clear Setup and
Management with Encrypted Traffic or Complete Encryption. There are also two
levels of Encryption: First 32-bit in the clear and the Entire IPv6 Header in
the Clear. In all cases, this is not to be confused with IPv6 security and
authentication headers! That is a separate function performed by the end station
hosts traversing the network and is functionally performed after the actual IPv6
header is read. In this context, only the first 32-bits of the header are being
read to determine a switching decision.
6.a. Encryption Methodologies
In the Clear Setup and Management with Traffic Encryption, while less secure,
has logically less overhead for the intervening NHRs along the Flow Switch Path.
In this case, all Flow Setup and management is (fourth bit of the COS filed is
set to one) done as previously described, except that the third bit of the COS
field is set to one. Once the Flow Switch path is established between the two
endpoints, the FIR and FDR exchange keys or perform another authentication and
encryption algorithm. The FIR and FDR then encrypt all Traffic traversing the
Flow Switch Path at either a high level or a low level. Simplistically, the
transmitter encrypts and the receiver decrypts.
Complete Encryption is far more extensive in that all participating routers
and, in the case of Managed Flow Label Switching, the Flow Path Servers (FPS)
Encrypt all traffic, after the first 32-bits of the header. In this case the
unicast addresses of the end-points of the Flow Switch Path are hidden from view
by traffic monitoring. Problematic to this is having all of the routers (as well
as possibly hosts) and participating FPS devices encrypting and decrypting all
Flow Label Management Packets. This will increase processor overhead as well as
add to the complexity of what is meant to be a simplistic, yet dynamic switching
protocol; however, the actual traffic traversing the flow switch path only encrypted
and decrypted by the end-point routers of the Flow Switch Path.
6.b. Encryption Levels
In this context, the level of encryption corresponds depth within the packet that
the encryption takes place and the type of encryption (IE: Strong or Weak). The
Encryption Algorithm determines the strength, the level determines how much of the
header and packet is encrypted. The level is determined as part of the exchange between
the end-point routers on the Flow Switch Path. The difference between High level and
Low level is that High level encryption scrambles all information after the Flow Label
in the IPv6 packet, making the destination and source addresses as well as the type and
content of the datagram unreadable as it passes through the NHR fabric.
Low level Encryption scrambles all data after the source and destination address.
This allows the destination and source addresses as well as the next header field
to be monitored as the packet traverses the NHRs on the Flow Switch path.
7. Flow Sets and Queuing
Once a Flow Switching path is established, the end-points of the flow will have
a COS value of: 1 m n 0 a b c d, where m = managed/open, n = encrypted/clear, and
the fourth bit is set to 1. The remaining four bits (0-F) can be parsed for two uses:
Flow Set Identification or Flow Priority. This feature is to allow equal flow values
to be shared on a set of NHRs by differentiating them through a Flow Set value
similar to concept of an ATM Virtual Path Identifier differentiating equal value
for Virtual Circuit Identifiers (VCIs).
Alternatively, the 16-bits can be used to prioritize which flow has priority on
the routers switching based upon Flow Value. Conceivably, a Next Hop Router in a
large Transit Network with multiple flows may receive Flow Switched packets on several
ports over a brief interval of time. This allows the switching function of the router
to queue the traffic based upon the value set in the 16 bits as the priority level.
In this case, each flow has 16 priority levels of traffic, allowing a differentiation
of latency sensitive traffic versus generic best effort traffic.
Finally, the combination of the two methodologies. Flow Sets can be determine in
the first one to three bits leaving the remainder for Priority queuing of traffic.
Alternatively, the first 1 to 3 bits can determine priority allowing for equal
priority flow sets to be established.
8. Contextual Uses of Flow Label Switching
The exist two functional uses for Flow Label Switching. First, it affords an alternative
to MPLS be establishing VPN circuits between to remote routers. Second, it allows for
faster determination of a packets destiny as it ingresses into a router. Rather than read
the entire 320-bit packet header and executing a closest match route lookup, only the first
32 bits are read and the packet is switched to an egress port, sending the packet on its way
with 90% less effort in what to read to determine what to do. Both these facets allow for
some interesting capabilities for aggregation of geographically separate locations behind a
single DMZ structure.
Since each end-point sends and receives their packets based upon Flow Label Value, forming
an adjacency, allowing the flow to act similar to a tunnel across a Wide Area Network.
Router A sees Router B directly through their respective Flow Interfaces, allowing either
A or B to act as the overall gateway for the other network. This can extremely effective
for large organizations such as the Government or Corporations who have internal organizations
that each operate on differing security policies. In this context, each internal organization
can be wrapped into a single security domain with a simplifying restructuring of the DMZ.
This mitigates the need for VPN servers in numerous cases, and due to the dynamic setup nature
of both Clear and Managed Flow Switching Paths, the mobility of entire networks can
be readily achieved.
9. Intellectual Property Statement
Copyright (C) The Internet Society (2006).
This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set
forth therein, the authors retain all their rights.
This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR,
THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY
THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
10. References
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
11. Acknowledgments
12. Author's Address
Martin Beckman
Defense Information Systems Agency
5275 Leesburg Pike, 7 Skyline Place
Falls Church, VA 22041
United States of America
Phone: 703-861-6865 // 703-882-0225
EMail: martin.beckman@disa.mil