Source Packet Routing in Networking
Source Packet Routing in Networking WG
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The Source Packet Routing in NetworkinG (SPRING) Working Group is the
home of Segment Routing (SR) using MPLS (SR-MPLS) and IPv6 (SRv6).
SPRING WG serves as a forum to discuss SPRING networks operations,
define new applications of, and specify extensions of Segment Routing
SPRING WG should avoid modification to existing data planes that would
make them incompatible with existing deployments. Where possible,
existing control and management plane protocols must be used within
existing architectures to implement the SPRING function. Any
modification of -or extension to- existing architectures, data planes,
or control or management plane protocols should be carried out in the
WGs responsible for the architecture, data plane, or control or
management plane protocol being modified and in coordination with the
SPRING WG, but may be done in SPRING WG after agreement with all the
relevant WG chairs and responsible Area Directors.
The SPRING WG defines procedures that allow a node to steer a packet
through an SR Policy instantiated as an ordered list of instructions
called segments and without the need for per-path state information to
be held at transit nodes. Full explicit control (through loose or strict
path specification) can be achieved in a network comprising only SPRING
nodes, however SPRING nodes must inter-operate through loose routing in
existing networks and may find it advantageous to use loose routing for
other network applications.
The scope of the SPRING WG work includes both single Autonomous System
(AS) and multi-AS environments. Segment Routing typically operates within
a single trust domain which requires the enforcement of a strict boundary
and preventing Segment Routing packets from entering the trusted domain
from the untrusted exterior. Certain deployments may however involve
multiple trust domains which in turn may imply the use of cross/inter
domain segments. Risk models associated with these various scenarios may
necessitate the use of a cryptographic integrity checks to validate that
the segment list is provided by an authorised entity.
As is customary in the Routing Area, the SPRING WG will also identify and
address any other security considerations introduced by the technologies
it defines; addressing such considerations may require the introduction of
new functionality in protocols leveraged for Source Routing, in which case
the SPRING WG will formulate requirements to be considered by the
appropriate WG for that work. The SPRING WG is however not expected to
wait on the development of a solution to these requirements before
progressing its own documents. SPRING technologies may be deployed in
environments spanning a range of risk and threat models, which may impact
both the security considerations and the requirements placed on other
protocols in order to support Source Routing protocols.
The technologies SPRING WG defines may be applicable to both centralised
and distributed path computation.
The SPRING WG will manage its specific work items by milestones agreed
with the responsible Area Director.
The work-items of the SPRING WG include functional specifications for:
o Segment Routing policies and the associated steering, signalling and
traffic engineering mechanisms.
o Source-routed stateless service chaining using SR-MPLS and SRv6
o SRv6 network programming for the underlay networks and overlay
services, and including data plane behavior and functions associated
o Operation, Administration and Management (OAM), and traffic accounting
in networks with SR-MPLS and SRv6 data planes in the case where SR
introduces specificities compared to MPLS or IPv6 technologies.
o Performance Management (PM) and monitoring in networks with SR-MPLS
and SRv6 data planes in the case where SR introduces specificities
compared to MPLS or IPv6 technologies.
o Inter-working between SRv6 and SR-MPLS and between SR and existing
routing solutions to allow for seamless deployment and co-existence.
o New types of segments mapping to forwarding behaviour (e.g., local
ingress replication, local forwarding resources, a pre-existing
replication structure) if needed for new usages.
Any of the above may require architectural extensions.
The work-items of SPRING WG also include:
o Specification of management models (YANG) for Segment Routing
applications, services and networks with SR-MPLS and SRv6 dataplanes.
The SPRING WG will coordinate and collaborate with other WGs as needed.
Specific expected interactions include (but may not be limited to):
* mpls on the MPLS dataplane and OAM extensions,
* 6man on the IPv6 dataplane for SR and associated OAM extensions
* lsr on OSPF and IS-IS extensions to flood SPRING-related information
* idr for BGP extensions
* bess for VPN control plane
* pce on extensions to communicate with an external entity to compute
and program SPRING paths
* teas on generic traffic engineering architecture
* sfc on service chaining applications
* rtgwg on fast-reroute technologies