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+.. _srv6_mobile_plugin_doc:
+
+SRv6 Mobile User Plane
+======================
+
+Introduction
+------------
+
+This plugin module can provide the stateless mobile user plane protocols
+translation between GTP-U and SRv6. The plugin also provides FIB table
+lookup for an IPv4/IPv6 packet encapsulated in GTP-U. These plugin
+functions take advantage of SRv6 network programmability.
+
+`SRv6 Mobile User
+Plane <https://tools.ietf.org/html/draft-ietf-dmm-srv6-mobile-uplane>`__
+defines the user plane protocol using SRv6 including following stateless
+translation functions:
+
+-  **T.M.GTP4.D:** GTP-U over UDP/IPv4 -> SRv6
+-  **End.M.GTP4.E:** SRv6 -> GTP-U over UDP/IPv4
+-  **End.M.GTP6.D:** GTP-U over UDP/IPv6 -> SRv6
+-  **End.M.GTP6.E:** SRv6 -> GTP-U over UDP/IPv6
+
+These functions benefit user plane(overlay) to be able to utilize data
+plane(underlay) networks properly. And also it benefits data plane to be
+able to handle user plane in routing paradigm.
+
+In addition to the above functions, the plugin supports following
+functions:
+
+-  **T.M.GTP4.DT{4|6|46}:** FIB table lookup for IPv4/IP6 encapsulated
+   in GTP-U over UDP/IPv4
+-  **End.M.GTP6.DT{4|6|46}:** FIB table lookup for IPv4/IP6 encapsulated
+   in GTP-U over UDP/IPv6
+
+Noted that the prefix of function names follow naming convention of SRv6
+network programming. “T” means transit function, “End” means end
+function, “M” means Mobility specific function. The suffix “D” and “E”
+mean that “decapsulation” and “encapsulation” respectively.
+
+Implementation
+--------------
+
+All SRv6 mobile functions are implemented as VPP plugin modules. The
+plugin modules leverage the sr_policy and sr_localsid mechanisms.
+
+Configurations
+--------------
+
+GTP-U to SRv6
+~~~~~~~~~~~~~
+
+The GTP-U tunnel and flow identifiers of a receiving packet are mapped
+to a Segment Identifier(SID) of sending SRv6 packets.
+
+IPv4 infrastructure case
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+In case that **IPv4** networks are the infrastructure of GTP-U,
+T.M.GTP4.D function translates the receiving GTP-U packets to SRv6
+packets.
+
+A T.M.GTP4.D function is associated with the following mandatory
+parameters:
+
+-  SID: A SRv6 SID to represents the function
+-  DST-PREFIX: Prefix of remote SRv6 segment. The destination address or
+   last SID of out packets consists of the prefix followed by dst IPv4
+   address, QFI and TEID of the receiving packets.
+-  SRC-PREFIX: Prefix for src address of sending packets. The src IPv6
+   address consists of the prefix followed by the src IPv4 address of
+   the receiving packets.
+
+The following command instantiates a new T.M.GTP4.D function.
+
+::
+
+   sr policy add bsid SID behavior t.m.gtp4.d DST-PREFIX v6src_prefix SRC-PREFIX [nhtype {ipv4|ipv6|non-ip}]
+
+For example, the below command configures the SID 2001:db8::1 with
+``t.m.gtp4.d`` behavior for translating receiving GTP-U over IPv4
+packets to SRv6 packets with next-header type is IPv4.
+
+::
+
+   sr policy add bsid 2001:db8::1 behavior t.m.gtp4.d D1::/32 v6src_prefix A1::/64 nhtype ipv4
+
+It should be interesting how a SRv6 BSID works to decapsulate the
+receiving GTP-U packets over IPv4 header. To utilize ``t.m.gtp4.d``
+function, you need to configure some SR steering policy like:
+
+::
+
+   sr steer l3 172.20.0.1/32 via bsid 2001:db8::1
+
+The above steering policy with the BSID of ``t.m.gtp4.d`` would work
+properly for the GTP-U packets destined to 172.20.0.1.
+
+If you have a SID(s) list of SR policy which the configured gtp4.d
+function to be applied, the SR Policy can be configured as following:
+
+::
+
+   sr policy add bsid D1:: next A1:: next B1:: next C1::
+
+IPv6 infrastructure case
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+In case that GTP-U is deployed over **IPv6** infrastructure, you don’t
+need to configure T.M.GTP4.D function and associated SR steering policy.
+Instead of that, you just need to configure a localsid of End.M.GTP6.D
+segment.
+
+An End.M.GTP6.D segment is associated with the following mandatory
+parameters:
+
+-  SID-PREFIX: SRv6 SID prefix to represent the function. In this
+   function, it should be the dst address of receiving GTP-U packets.
+-  DST-PREFIX: Prefix of remote SRv6 Segment. The destination address or
+   last SID of output packets consists of the prefix followed by QFI and
+   TEID of the receiving packets.
+
+The following command instantiates a new End.M.GTP6.D function.
+
+::
+
+   sr localsid prefix SID-PREFIX behavior end.m.gtp6.d DST-PREFIX [nhtype {ipv4|ipv6|non-ip}]
+
+For example, the below command configures the SID prefix 2001:db8::/64
+with ``end.m.gtp6.d`` behavior for translating receiving GTP-U over IPv6
+packets which have IPv6 destination addresses within 2001:db8::/64 to
+SRv6 packets. The dst IPv6 address of the outgoing packets consists of
+D4::/64 followed by QFI and TEID.
+
+::
+
+   sr localsid prefix 2001:db8::/64 behavior end.m.gtp6.d D4::/64
+
+In another case, the translated packets from GTP-U over IPv6 to SRv6
+will be re-translated back to GTP-U, which is so called ‘Drop-In’ mode.
+
+In Drop-In mode, an additional IPv6 specific end segment is required,
+named End.M.GTP6.D.Di. It is because that unlike ``end.m.gtp6.d``, it
+needs to preserve original IPv6 dst address as the last SID in the SRH.
+
+Regardless of that difference exists, the required configuration
+parameters are same as ``end.m.gtp6.d``.
+
+The following command instantiates a new End.M.GTP6.D.Di function.
+
+::
+
+   sr localsid prefix 2001:db8::/64 behavior end.m.gtp6.d.di D4::/64
+
+SRv6 to GTP-U
+~~~~~~~~~~~~~
+
+The SRv6 Mobile functions on SRv6 to GTP-U direction are End.M.GTP4.E
+and End.M.GTP6.D.
+
+In this direction with GTP-U over IPv4 infrastructure, an End.M.GTP4.E
+segment is associated with the following mandatory parameters:
+
+-  SID-PREFIX: SRv6 SID prefix to represent the function.
+-  V4SRC-ADDR-POSITION: Integer number indicates bit position where IPv4
+   src address embedded.
+
+The following command instantiates a new End.M.GTP4.E function.
+
+::
+
+   sr localsid prefix SID-PREFIX behavior end.m.gtp4.e v4src_position V4SRC-ADDR-POSITION
+
+For example, the below command configures the SID prefix 2001:db8::/32
+with ``end.m.gtp4.e`` behavior for translating the receiving SRv6
+packets to GTP-U packets encapsulated with UDP/IPv4 header. All the
+GTP-U tunnel and flow identifiers are extracted from the active SID in
+the receiving packets. The src IPv4 address of sending GTP-U packets is
+extracted from the configured bit position in the src IPv6 address.
+
+::
+
+   sr localsid prefix 2001:db8::/32 behavior end.m.gtp4.e v4src_position 64
+
+In IPv6 infrastructure case, an End.M.GTP6.E segment is associated with
+the following mandatory parameters:
+
+-  SID-PREFIX: SRv6 SID prefix to represent the function.
+
+The following command instantiates a new End.M.GTP6.E function.
+
+::
+
+   sr localsid prefix SID-PREFIX behavior end.m.gtp6.e
+
+For example, the below command configures the SID prefix 2001:db8::/64
+with ``end.m.gtp6.e`` behavior for translating the receiving SRv6
+packets to GTP-U packets encapsulated with UDP/IPv6 header. While the
+last SID indicates GTP-U dst IPv6 address, 32-bits GTP-U TEID and 6-bits
+QFI are extracted from the active SID in the receiving packets.
+
+::
+
+   sr localsid prefix 2001:db8::/64 behavior end.m.gtp6.e
+
+FIB Table Lookup for Inner IPv4/IPv6 packet
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+SRv6 Mobile functions of ``t.m.gtp4.dt*`` and ``end.m.gtp6.dt*`` support
+decapsulating outer IP/UDP/GTP-U headers and forwarding inner IP packet
+based on specific fib table.
+
+In case of the both outer and inner IP address families are IPv4,
+``t.m.gtp4.dt4`` function supports GTP-U decapsulation and fib lookup
+for inner IPv4 with an associated steering policy and the following
+parameters:
+
+-  SID: A SRv6 SID to represents the function
+-  FIB: fib-table number for inner IPv4 packet lookup and forwarding
+
+The following command instantiates a new T.M.GTP4.DT4 function.
+
+::
+
+   sr policy add bsid SID behavior t.m.gtp4.dt4 fib-table FIB
+
+For example, the below commands configure D5:: as the SID instantiates
+``t.m.gtp4.dt4`` function. A steering policy for packets destine to
+172.20.0.1 binds to the SID.
+
+::
+
+   sr steer l3 172.20.0.1/32 via bsid D5::
+   sr policy add bsid D5:: behavior t.m.gtp4.dt4 fib-table 0
+
+In addition, inner IPv6, or mix of IPv4 and IPv6 inner packet cases
+require the function to be configured with local-fib table.
+
+-  LOCAL-FIB: fib-table number for lookup and forward GTP-U packet based
+   on outer IP destination address
+
+This is inner IPv6 case specific. The reason is that GTP-U encapsulates
+link local IPv6 packet for NDP (Neighbor Discovery Protocol). Outer
+GTP-U header should be kept until the packets reach to the node
+responsible for NDP handling. It is typically UPF(User Plane Function)
+node.
+
+The following command instantiate a new T.M.GTP4.DT6 function.
+
+::
+
+   sr policy add bsid D5:: behavior t.m.gtp4.dt6 fib-table 0 local-fib-table LOCAL-FIB
+
+Following example configures fib 0 for inner packet and fib 1 for outer
+GTP-U packet forwarding:
+
+::
+
+   sr policy add bsid D5:: behavior t.m.gtp4.dt6 fib-table 0 local-fib-table 1
+
+If you need to support both IPv4 and IPv6 inner packet lookup with just
+one SID, you can configure ``t.m.gtp4.dt46`` function:
+
+::
+
+   sr policy add bsid D5:: behavior t.m.gtp4.dt46 fib-table 0 local-fib-table 1
+
+In case of GTP-U over IPv6 case, ``end.m.gtp6.dt4``, ``end.m.gtp6.dt6``
+and ``end.m.gtp6.dt46`` functions support inner IPv4, IPv6 and IPv4/IPv6
+lookup and forwarding respectively. Specifying fib table for inner IP
+packet forwarding is required as same as GTP-U over IPv4 case, and
+local-fib table for inner IPv6 and IPv4/IPv6 cases as well.
+
+::
+
+   sr localsid prefix D::/64 behavior end.m.gtp6.dt46 fib-table 0 local-fib-table 0
+
+To run some demo setup please refer to: :ref:`srv6_mobile_runner_doc`