The NEXT-C-SID mechanism described in [1] offers the possibility of
encoding several SRv6 segments within a single 128 bit SID address. Such
a SID address is called a Compressed SID (C-SID) container. In this way,
the length of the SID List can be drastically reduced.
A SID instantiated with the NEXT-C-SID flavor considers an IPv6 address
logically structured in three main blocks: i) Locator-Block; ii)
Locator-Node Function; iii) Argument.
C-SID container
+------------------------------------------------------------------+
| Locator-Block |Loc-Node| Argument |
| |Function| |
+------------------------------------------------------------------+
<--------- B -----------> <- NF -> <------------- A --------------->
(i) The Locator-Block can be any IPv6 prefix available to the provider;
(ii) The Locator-Node Function represents the node and the function to
be triggered when a packet is received on the node;
(iii) The Argument carries the remaining C-SIDs in the current C-SID
container.
The NEXT-C-SID mechanism relies on the "flavors" framework defined in
[2]. The flavors represent additional operations that can modify or
extend a subset of the existing behaviors.
This patch introduces the support for flavors in SRv6 End behavior
implementing the NEXT-C-SID one. An SRv6 End behavior with NEXT-C-SID
flavor works as an End behavior but it is capable of processing the
compressed SID List encoded in C-SID containers.
An SRv6 End behavior with NEXT-C-SID flavor can be configured to support
user-provided Locator-Block and Locator-Node Function lengths. In this
implementation, such lengths must be evenly divisible by 8 (i.e. must be
byte-aligned), otherwise the kernel informs the user about invalid
values with a meaningful error code and message through netlink_ext_ack.
If Locator-Block and/or Locator-Node Function lengths are not provided
by the user during configuration of an SRv6 End behavior instance with
NEXT-C-SID flavor, the kernel will choose their default values i.e.,
32-bit Locator-Block and 16-bit Locator-Node Function.
[1] - https://datatracker.ietf.org/doc/html/draft-ietf-spring-srv6-srh-compression
[2] - https://datatracker.ietf.org/doc/html/rfc8986
Signed-off-by: Andrea Mayer <andrea.mayer@uniroma2.it>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
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