Internet DRAFT - draft-foglar-ipv6-ull-routing
Routing Area Working Group A. Foglar, InnoRoute
INTERNET-DRAFT M. Parker, Uni Essex
Intended status: EXPERIMENTAL T. Rokkas, Incites
Expires: January 13, 2021 July 24, 2020
IPv6 Source Routing for ultralow Latency
This Internet-Draft describes a hierarchical addressing scheme
for IPv6, intentionally very much simplified to allow for very
fast source routing experimentation using simple forwarding
nodes. Research groups evaluate achievable latency reduction
for special applications such as radio access networks,
industrial networks or other networks requiring very low
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Revision Note for Version 02
Reference to experimental verification of the concept is added in the
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.
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.
Redundancy issues are not considered.
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
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
| 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
| 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
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 the variable.
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
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 small office in Munich with the telephone number +49-89-
45241990 configures its local top-level forwarding node to:
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
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
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
additional forwarding node must be installed with the 5th level
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
Essex (UK) Munich (DE)
| AF4H.----.----.---- |
| ------ L2 Link ------
| IoT node | |----------U----------|
|----------| | AF49.89H-.----.---- |
| AF49.891H.----.---- | | AF49.8945.2419.90H- |
| AF49.8945.5419.901H |
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 in the range 0...9. 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 dowlink 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
provides 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.
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 two redundant uplink
ports. Each of them is connected to a next higher hierarchy node, each
of them having again two redundant uplinks.
Hence, with each hierarchy the number of uplinks doubles - and also
the number of nodes. In the case of 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-
With the two uplinks (could also be more) a routing feature emerges in
the network. In other words, each node has to take a routing decision
in upstream direction, when forwarding packets to one the uplinks.
This decision could be based on node-local information (autarkic) or
based on routing protocols. This topic is for further study.
8. IANA Considerations
In Q1/2020 a local field trial with ultra-low latency routing is plan-
ned in Germany. A temporary /16 prefix "AF49" will be requested from
IANA for that. In Q3/2020 a field trial with several European
countries is planned. The other countries will apply for "AF33",
"AF44" etc. for France, UK etc., respectively.
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:
10. Authors' Addresses
Wivenhoe Park, Colchester
Essex, CO3 4HG
130, Route d' Arlon
Foglar, Parker, Rokkas Expires January 13, 2021