Internet DRAFT - draft-foglar-ipv6-ull-routing
draft-foglar-ipv6-ull-routing
Routing Area Working Group A. Foglar, InnoRoute
INTERNET-DRAFT M. Parker, Uni Essex
Intended status: EXPERIMENTAL T. Rokkas, Incites
M. Khokhlov, IP Tek
M. Godzina, ISC
Expires: May 11, 2024 November 12, 2023
IPv6 Source Routing for ultralow Latency
draft-foglar-ipv6-ull-routing-14
Abstract
This Internet-Draft describes a hierarchical addressing scheme
for IPv6, intentionally very much simplified to allow for ultralow
latency source routing experimentation using simple forwarding
nodes. Research groups evaluate achievable latency reduction for
special applications such as radio access networks, industrial net-
works or other networks requiring very low latency.
Status of This Memo
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Revision Note for Version 02
Reference to experimental verification of the concept is added in the
section "Acknowledgements".
Revision Note for Version 03
Section 6 about Security Considerations has been inserted.
Revision Note for Version 04
Section 7 about Redundancy has been inserted.
Revision Note for Version 05
Section 8 about IANA Considerations added.
Revision Note for Version 06
Section 8 about IANA Considerations updated.
Revision Note for Version 07
Section 6 about Security Considerations improved.
Revision Note for Version 08
Soome typos corrected
Revision Note for Version 09
Improved address generation and ITU-T section added at the end of the
document. An additional author is added.
Revision Note for Version 10
Section 10 has been added describing a simple introduction scenario.
Revision Note for Version 11
Section 11 has been added introducing administrative domains.
Revision Note for Version 12
Section 12 has been added introducing Information Centric Networking
over hierarchical routing network.
Revision Note for Version 13
Section 10 is updated to describe the commercial service deployed in
Germany.
Revision Note for Version 14
Section 13 is added describing the local sub-addressing of end devices
by the node of lowest hierarchy.
1. Introduction
To achieve minimum latency the forwarding nodes must support
cut-through technology as opposed to the commonly used store-
and-forward technology. Cut-through means, that the packet
header already leaves a node at the egress port while the tail
of the packet is still received at the ingress port. This
short time does not allow complex routing decisions.
Therefore, a very simple routing address field structure is
specified below. It should limit the complexity of the
forwarding node used in the experiments. Therefore, in this
text the term "forwarding node" is used instead of "router",
although the device is operating in OSI Layer 3 and accordingly
executes router functions such as decrementing the hop limit field.
2. IPv6 address prefix structure
The following proposal uses the 64-bit IPv6 address prefix.
Each forwarding node has up to 16 ports and hence needs 4 bits
of the address field to decide to which port a packet should
be forwarded. The 64-bit prefix is divided into 16 sub-fields
of 4 bit, defining up to 16 hierarchy levels. A forwarding
node is configured manually to which of the sub-fields it should
evaluate for the forwarding decision.
A number n of leading 4-bit fields cannot be used for forwarding
decisions, but must have a special value to indicate the
'escape prefix' of the experimental forwarding mode.
The 64-bit prefix of the IPv6 address has this structure:
| n x 4-bit escape prefix |(16-n) x 4-bit address fields |
The first 4-bit field following the escape prefix has the
highest hierarchy level, the last 4-bit field has the lowest
hierarchy level.
3. Forwarding node behavior
The forwarding node has up to 16 downlink ports and at least
one uplink port. Typically, the forwarding nodes are arranged
in a regular tree structure with one top node, up to 16 nodes
in the second hierarchy, up to 256 nodes in the third hierarchy
and so on for up to 16-n hierarchies.
A forwarding node must be configured to operate at a certain
position in the hierarchical network. For example, at third
hierarchy level, branch 4 of the first hierarchy and branch 12
of the second hierarchy.
The behavior of each forwarding node is depending on the
position of a node in a hierarchical network. For all
positions, the first step is to check the escape prefix. Only
packets with matching escape prefix are forwarded.
The top forwarding node with the highest hierarchy level
evaluates the first 4-bit field following the n x 4-bit escape
prefix. The value of the evaluation field determines the
output port of the packet. The remaining fields are don't
care:
| escape prefix | 4-bit | (16-n-1) x 4-bit |
< mandatory > <eval.> < don't care >
A forwarding node in a lower hierarchy first checks if the 4-
bit fields preceding the evaluation field match the configured
value. In case of match the value of the configured evaluation
field of the packet is used as downlink port number where the
packet is forwarded. The remaining 4-bit fields are ignored.
In case of mismatch the packet is forwarded to the uplink
port(s).
| escape prefix | m x 4-bit | 4-bit | (16-n-m-1) x 4-bit |
< mandatory > < match > <eval.> < don't care >
The parameter m indicates the hierarchy level with m=0
denoting the highest hierarchy.
Hence, when a packet enters a hierarchical network at the
lowest layer node it is forwarded in uplink direction until it
reaches a node where the m x 4-bit prefix matches the
configured value of the node. At latest, the highest-level
node will always match and forward the packet in the desired
downlink direction.
4. Numerical values
As mentioned, one pre-requisite of the simple forwarding
concept is to keep the complexity of the forwarding nodes low.
Also, the configuration of the nodes should be kept simple. In
particular, industrial networks are operated by persons who are
not experts in communication. Configurations should be
intuitively understandable by all without long explication.
Therefore, for the first experimental forwarding node the
number of downlink ports is limited to 10 with numbers 0...9. 16
digits at the front panel of the forwarding device show the
configuration. Use of classical 7-segment digits make the
limits of the configuration obvious.
As escape code, the first two digits are fixed to the value
"AF" (binary '10101111'). These two characters contrast with
the following numerical digits, so that the escape code can be
clearly differentiated from the following configuration. The
display uses the 'H' character instead of the 'X' the usual
term for a variable. It can be interpreted as 'hierarchy'.
The H specifies the digit of the packet prefix which is
evaluated for forwarding. When the H is selected all lower
digits are automatically set to '-' to indicate the don't care
nature.
To make the configuration still more obvious it is recommended
to configure the local telephone number. With that measure,
every local experimentation has unique numbers and can
potentially be interconnected via tunnels (IP, MPLS, VPN etc.)
with other experimental setups.
The length of 14 digits allows sufficient in-house
hierarchies, even for industrial applications where forwarding
nodes interconnect large numbers of sensor controllers.
Inhouse installations would be structured for example in
building, floor, fabrication unit, machine - with one sensor
controller per machine. For the sake of simplicity numbers are
deliberately wasted, for example if the building has only 3
stories the digits 4...9 are unused.
5. Example configuration
A company office in Munich with the telephone number +49-89-
45241990 configures its local top-level forwarding node to:
AF49.8945.2419.90H-
Note that for the sake of simplicity this simplified notation
is introduced here as alternative to the usual notation
AF49:8945:2419:90:0/56. With the new notation, the cabling
staff people can immediately check the hierarchy location of
the forwarding node and connect the cables to the floors at
ports 0...3.
The next hierarchy level is related to the floor. In case of a
3-story building only three next level forwarding nodes are
used with these configured values:
AF49.8945.2419.900H at the ground level
AF49.8945.2419.901H at the first floor
AF49.8945.2419.902H at the second floor
AF49.8945.2419.903H at the third floor.
In each floor, up to 10 sensor nodes can be connected.
Each of the sensor nodes can address several sensors/
actuators addressed via the interface identifier contained in
the second part of the 128-bit IPv6 address.
In the following a connection between sensors in this office to
other IoT equipment located in Essex University is described. The
connection is realized with one additional forwarding node
installed at Essex University premises with the second level address
AF4H.----.----.----.
This high level forwarding node can be used although the phone number
of the researcher is +44 1206 872413, as long as there is no further
node in UK.
At downlink port 9 the 13th level forwarding node in Munich is con-
nected via a Layer 2 link such as VLAN or SDH pipe or MPLS tunnel.
The levels in between must not be populated by forwarding nodes as
long as no other branch is needed at one of the two sides. If for
example another site in Munich center must be connected one additio-
nal forwarding node must be installed with the 5th level address
AF49.89H-.----.----.
The small office mentioned above would be connected to downlink port
4 while the new site would be connected at downlink port 1, the
prefix for Munich center. The configuration is visualized in the
Figure below.
Essex (UK) Munich (DE)
|---------U-----------|
| AF4H.----.----.---- |
|-0-1-2-3-4-5-6-7-8-9-|
| \
| ------ L2 Link ------
|----------| \
| IoT node | |----------U----------|
|----------| | AF49.89H-.----.---- |
|-0-1-2-3-4-5-6-7-8-9-|
/ \
--- -----------
/ \
|----------U----------| |----------U----------|
| AF49.891H.----.---- | | AF49.8945.2419.90H- |
|-0-1-2-3-4-5-6-7-8-9-| |-0-1-2-3-4-5-6-7-8-9-|
|
|----------U----------|
| AF49.8945.5419.901H |
|-0-1-2-3-4-5-6-7-8-9-|
U = Uplink |
|----------|
| IoT node |
|----------|
Figure: Example Configuration with Node Addresses
6. Security Considerations
In a hierarchical network as described above every forwarding node
can easily check a part of the source address of the packets. Packets
received from lower hierarchy must have a source address from that
hierarchy branch. A node checks this by comparing the prefix of the
source address with its own node address and in addition checks if
the lower hierarchy digit matches the number of the receiving port. In
case of mismatch of any comparison a packet is discarded silently.
The term 'silently' means that no further action is taken. In other
cases, for example when a packet is sent to a non-existing destination
the packet could be discarded with a notification of the sender. This
issue is for further study.
For example, the node AF49.89H-.----.---- in the Figure above expects
that packets received from dowlink 1 have source addresses
AF49.891x.xxxx.xxxx with x is don't care. To that aim the node checks
if the leading digits of the packet source address match with AF49.89
and if the digit at the 'H' position matches with the receiving down-
link port number.
The lower the hierarchy level of a node the more digits are checked.
In particular, the lowest hierarchy node checkes the complete prefix.
For example, the Munich IoT node in the Figure above must send packets
with the source address AF49.8945.5419.9014 to the higher level node.
It will discard packets with any other source address.
Hence in upstream direction every higher level node will check a
shorter part of the prefix. At the highest level the node
AFH-.----.----.---- will check if the source address digit at the 'H'
position matches with the receiving downlink port number.
As packets with non-matching source address are discarded a receiver
can rely on the correctness of the source adress. This feature pro-
vides an orthogonal level of security to existing security measures
such as password authentication and encryption. Anonymous hackers are
not possible in such hierarchical networks. Receivers may use white-
listing for address filtering.
To circumvent the source address check a hacker must break into the
network and insert packets in downstream direction. At the highest
level node the network is most vulnerable, as any address can be rea-
ched from there. However, the higher a network node level the more
sophisticated are the security means to avoid intrusion.
At lower level nodes an additional source address check in downstream
direction may be implemented: at the uplink ports packets with source
address from the own hierarchy branch are not expected. These packets
should have been forwarded within the hierarchy branch. At the uplink
ports these packets are discarded silently.
For example the node AF49.89H-.----.---- in the Figure above would not
expect a packet with the source address AF49.8945.5419.9014 at an
uplink port. Hence this packet will be discarded.
7. Redundancy
The hierarchical structure implied by the addressing leads to the fact
that node failures have more implications the higher the hierarchy of
a node. Therefore, a node should be equipped with at least two redun-
dant uplink ports. Each of them is connected to a next higher hierar-
chy node, each of them having again at least two redundant uplinks.
In the case of nodes with ten downlinks and two uplinks the number of
nodes grows with the power of two and the number of terminals grows
with the power of ten. A three-dimensional network is constructed
with up to n hierarchies and up to 2^n redundancy planes. With 14
hierarchies the number of redundancy planes becomes 16384. This number
of top hierarchy nodes sounds very high, but distributed around the
world would lead to well-balanced redundancy.
With two or more uplinks a routing feature emerges in the network. In
other words, each node has to take a routing decision in upstream di-
rection, when forwarding packets to one the uplinks. This decision
should be based on node-local information (autarkic) to avoid routing
protocols. One option is learning prefixes from packets received in
downstream direction.
8. IANA Considerations
In Q2/2021 a local field trial with ultra-low latency routing starts
in Germany. A temporary /16 prefix "AF49" will be requested from the
national registry or RIR. Later, extension of the field trial to other
countries is planned. The other countries will apply for "AF33" for
France, "AF44" for UK, "AF43" for Austria and so on.
9. Numbering Considerations
The international telephone number format and the country prefixes are
standardized by Study Group 2 of ITU-T in the Recommendation E.164.
This numbering, however, specifies several exceptions such as 800 or
900 special calling codes. The numbering used for ultra-low according
to this document shall have no exception at all. Hence, in future the
Study Group 2 could open a new Recommendation.
When mapping a telephone number to IPv6 prefix one problem is the dif-
ferent length of numbers. At the one side, telephone numbers according
to E.164 can have up to 15 digits and would not fit into the remaining
14 digits in case of a 2-digit escape prefix. A future ITU-T numbering
recommendation could deal with that problem. At the other side, some
private phone numbers are very short. For example, the city of Munich
has numbers as short as +49-89-886757. Still, the private subscriber
would get a /64 prefix. To solve this problem the solution is to fill
the remaining part of the IPv6 prefix with 'F' digits:
AF49:8988:6757:FFFF::/64
This rule has the advantage that the reverse process of converting an
IPv6 prefix back to a telephone number always works.
10. Introduction Scenario
An introduction scenario is in operation since end 2021 in Germany. It
does not use dedicted hardware forwarding nodes, so that ultra-low
latency feature is not supported. Instead, software forwarding nodes
are used: initially, a root server with a 2.5Gb/s Internet uplink in a
data center in Nuremberg.
WireGuard tunnels assure secure access to the initial forwarding node.
The tunnel encryption includes the source prefix of the subscriber, so
that false prefixes are automatically discarded. The service can be
booked at https://innoroute.com/save in Germany only i.e. for prefixes
starting with AF49.
The registration procedure includes a phone call of the subscriber to
a SIP server to verify the the subscribers phone number - which is
used to generate the subscribers IPv6 prefix. Using a toll-number for
the phone call to avoids denial-of-service attacks and at the same
time provides income to finance the routing service. In Germany phone
calls to national numbers starting with 01806 cost a fixed amount of
20Cent. One call gives access for one week.
The calls are received by a SIP server which uses the infrastructure
number with in the SIP message, not the displayed number. The infra-
structure number is generated by the network operator and cannot be
falsified by the caller. Hence, the call provides a verified phone
number. The solution has been accepted by the German authorities for
network operation:
https://www.bundesnetzagentur.de/DE/Vportal/TK/start.html
The per-call payment via telephone bill can be considered as prepaid
service for the subscriber. For the operator it has the advantage,
that no individual invoices must be issued; the payments are collected
by a service company which makes one single bank transfer per month,
regardless of the number of calls. This fact allows almost unlimited
scalability without administrative burden.
With growing number of subscribers the central forwarding node can be
completed by regional forwarding nodes. A smooth, on-demand growth of
the network is possible without large investment steps. In a later
stage dedicated hardware forwarding nodes will be deployed, starting
with regional nodes in industrial areas for initial transition to
ultralow latency service.
11. Administrative Domains
Forwarding nodes may be located in differet administrative domains.
In such case a contract is needed, where the domain holders grant each
other the fulfillment of address checking.
In upstream direction the domain holder of the lower hierarchy node
grants the correctness of all sub-addresses in its domain. For example
an access network provider grants that all subscribers have correct
source address.
In case of breach of obligation, i.e. when source addresses are false,
a possible measure could be the temporary disconnect of the respective
administrative domain from the network.
12. ICN Consideration
The forwarding nodes mentioned in this text match almost perfectly to
the Forwarding (capital F) node defined in RFC8793, Information-Cen-
tric Networking (ICN): CCN and NDN Terminology. In ICN, forwarding
nodes forward interest packets towards data sources/ replica nodes and
data packets towards the requestor node. With hierarchical network
structure the direction towards data source or replica node is up-
stream, the direction towards the requestor is downstream. Hence, the
forwarding decision of the forwarding (lower case) nodes described in
this text is easy:
- Interest packets are forwarded to uplink ports
- Data packets are forwarded to downlink ports
By adding data cache to a forwarding node it becomes a replica node.
13. Routing and DHCPv6 Considerations
As mentioned in Section 5 a lowest layer node (with /64 address) can
asssign addresses to devices in the local network with different
interface identifiers. Such lowest layer node is usually called Gate-
way. To address devices in the local network the Gateway must provide
not only DHCPv6, but also Router Advertisement.
At the IETF-118 Hackathon an exemplary implementation was achieved by
a Raspberry Pi as Gateway running the Router Advertisment Daemon
https://github.com/radvd-project/radvd configured with these
parameters:
interface eth0 {
AdvSendAdvert on;
AdvLinkMTU 1280;
MaxRtrAdvInterval 120;
AdvSourceLLAddress on;
AdvManagedFlag on;
AdvDefaultLifetime 0;
route af49::/16 {};
};
For the DHCPv6 Master the open source project https://dhcpy6d.de/ was
selected, as it explicitly allows a device to be configured as DHCPv4
Slave and DHCPv6 Master.
14. Acknowledgements
The authors would like to thank the consortium of the European
research project CHARISMA for the possibility to experiment. The
description of the final demonstration is available for download:
http://www.charisma5g.eu/wp-content/uploads/2015/08/D4.3-Demonst
rators-Evaluation-and-Validation-vFinal.pdf
The authors thank Henri Wahl for advice about hdcpy6d.
The authors are thankful to IETF-118 Hackathon in Prague, where the
local sub-addressing could be elaborated.
15. Authors' Addresses
Andreas Foglar
InnoRoute GmbH
Marsstr. 14a
80335 Munich
Germany
Email: foglar@innoroute.de
Mike Parker
Wivenhoe Park, Colchester
Essex, CO3 4HG
United Kingdom
Email: mcpark@essex.ac.uk
Theodoros Rokkas
Incites S.A.R.L.
130, Route d' Arlon
Strassen L-8008
Luxembourg
Email: trokkas@incites.eu
Mikhail Khokhlov
IP Tek UG
Dircksenstr. 50
10178 Berlin
Germany
Email: info@ip-tek.net
Marcin Godzina
Internet Systems Consortium
PO Box 360
Newmarket, NH 03857 USA
Email: mgodzina@isc.org
Foglar, Parker, Rokkas, Khokhlov Expires May 11, 2024
