Network Programming extension: SRv6 uSID instruction

SRv6 Network Programming defines a mechanism to build a network program with topological and service segments. It leverages the SRH to encode a network program together with optional metadata shared among the different SIDs. This draft extends SRv6 Network Programming with a new type of SRv6 SID behaviors: SRv6 uN, uA, uDT, uDX. This extension fully leverages the SRv6 network programming solution: The SRv6 Control Plane is leveraged without any change The SRH dataplane encapsulation is leveraged without any change Any SID in the SID list can carry micro segments Based on the Compressed SRv6 Segment List Encoding in SRH framework This enables: ultra-scale (e.g. multi-domain 5G deployments) minimum MTU overhead installed-base reuse

The SRv6 Network Programming, SRH and Compressed SRv6 Segment List Encoding in SRH terminology is leveraged and extended with the following terms: Term Definition uSID block A block of uSID's. It can be any IPv6 prefix available to the provider. uSID A Compressed-SID. In this document a 16-bit ID. A different uSID length may be used. Active uSID First uSID after the uSID block. Next uSID Next uSID after the Active uSID. Last uSID From left to right, the last uSID before the first End-of-Container uSID. End-of-Container Reserved uSID used to mark the end of a uSID container. The value 0000 is selected as End-of-Container. All of the empty uSID container positions must be filled with the End-of-Container ID. Hence, the End-of-Container can be present more than once in a uSID container. uSID container A CSID container. A 128bit SRv6 SID of format <uSID-Block><Active-uSID><Next-uSID>...<Last-uSID><End-of-Container>...<End-of-Container>. A uSID container can be encoded in the Destination Address of an IPv6 header or at any position in the Segment List of an SRH.

GIB: The set of IDs available for global uSID allocation. LIB: The set of IDs available for local uSID allocation.

A uSID from the GIB. A Global uSID typically identifies a shortest-path to a node in the SR domain. An IP route (e.g., /64) is advertised by the parent node to each of its global uSID's, under the associated uSID block. The parent node executes a variant of the END behavior. A node can have multiple global uSID's under the same uSID blocks (e.g. one per IGP flex-algorithm). Multiple nodes may share the same global uSID (anycast).

A uSID from the LIB. A local uSID may identify a cross-connect to a direct neighbor over a specific interface or a VPN context. No IP route is advertised by a parent node for its local uSID'. If N1 and N2 are two different physical nodes of the uSID domain and I is a local uSID value, then N1 and N2 may bind two different behaviors to I.

For illustration simplicity, we will use: uSID block length: 48 bits uSID block: 2001:db8:0::/48 uSID length: 16 bits uSID: 2001:db8:0:XYZW::/64 GIB: nibble X from hexa(0) to hexa(D) LIB: nibble X hexa(E) or hexa(F) Leveraging our reference illustration, A uSID 2001:db8:0:XYZW::/64 is said to be allocated from its block (2001:db8:0::/48). More specifically, a uSID is allocated from the GIB or LIB of block 2001:db8:0::/48 depending on the value of the "X" nibble: 0-D for GIB, and E-F for LIB. With the above allocation scheme, the uSID Block 2001:db8:0::/48 supports up to 57k global uSID's (e.g. routers) while each router would support up to 8k local uSID's. Another illustration could assume a 32-bit uSID length and a LIB restricted to the uSIDs with the first byte set to FF. In this context, the network as a whole would support 2^32-2^24 global uSID's (e.g. routers) while each router would support up to 2^24 local uSID's.

The SRv6 SRH encapsulation and its network programming model are extended with the following functions:

The uN is a short notation for the End behavior with NEXT-CSID, PSP and USD flavors as defined in . As a reminder the pseudo-code of the End behavior with NEXT-CSID flavor, when applied to a 48b uSID block and a 16b uSID length is as follows:

Ref 1: DA[X..Y] refers to the bits from position X to Y (included) in the IPv6 Destination Address of the received packet. The bit 0 is the MSB, while the bit 127 is the LSB.

In ISIS, a uN is advertised with the following information: Value = 2001:db8:0:0N00:: Behavior = uN Structure = LBL = 48 LNL = 16 FL = 0 AL = 64 Algorithm = 0 (or other)

The uA local behavior is a short notation for the End.X behavior with NEXT-CSID, PSP and USD flavors . An instance of the uA SRv6 uSID behavior is associated with a set, J, of one or more Layer-3 adjacencies. As a reminder the pseudo-code of the End.X behavior with NEXT-CSID flavor, when applied to a 48b uSID block and a 16b uSID length is as follows:

Ref 1: DA[X..Y] refers to the bits from position X to Y (included) in the IPv6 Destination Address of the received packet. The bit 0 is the MSB, while the bit 127 is the LSB.

In ISIS, a uA is advertised with the following information: Value = 2001:db8:0:0N00:FNAJ:: Behavior = uA Structure = LBL = 48 LNL = 16 FL = 16 AL = 48 Algorithm = 0 (or other) Note: From a formal viewpoint, a uA SID of node N is defined by the local FIB entry B:uA/64 of N (i.e. this definition is independent from any uN SID of node N). In order to signal in ISIS a container SID with the same routable semantics as End.X, the ISIS advertisement of a uA SID is done as uN+uA. uN provides the global route to the node like the End behavior. uA provides the cross-connect function like the "X" of the End.X.

A local uDT behavior of Node D 2001:db8:0:FNVT:: is defined by the following single FIB entry and pseudo-code: 2001:db8:0:FNVT::/80 bound to the same pseudocode as End.DT4/End.DT6/End.DT2*

In BGP, a uDT is advertised with the following information: Value = 2001:db8:0:0N00:FNVT:: Behavior = uDT Structure = LBL = 48 LNL = 16 FL = 16 AL = 0 TL = 16 TO = 64 Algorithm = 0 (or other) Note: the advertised SID value includes the uN SRv6 uSID of the parent.

A local uDX behavior of Node D 2001:db8:0:FNXJ:: is defined by the following single FIB entry and pseudo-code: 2001:db8:0:FNXJ::/80 bound to the same pseudocode as End.DX4/End.DX6/End.DX2

In BGP, a uDX is advertised with the following information: Value = 2001:db8:0:0N00:FNXJ:: Behavior = uDX Structure = LBL = 48 LNL = 16 FL = 16 AL = 0 TL = 16 TO = 64 Algorithm = 0 (or other) Note: the advertised SID value includes the uN SRv6 uSID of the parent.

If Node 1 is configured with a uN SID 2001:db8:0:0100::/64 then the operator must ensure that Node 1 advertises 2001:db8:0:0100::/64 in the routing protocol.

Leverages SRv6 Network Programming with NO change SRv6 uSID is a flavor of the SRv6 network programming model Leverages SRv6 dataplane (SRH) with NO change Any SID in DA or SRH can be an SRv6 uSID container Leverages SRv6 Control-Plane with NO change Ultra-Scale 6 uSID's per uSID container 18 source routing waypoints in only 40bytes of overhead H.Encaps.Red with an SRH of 40 bytes (8 fixed + 2 * 16 bytes) 6 uSID's in DA and 12 in SRH Lowest MTU overhead In apple to apple comparison, the SRv6 solution outperforms any alternative (VxLAN with SR-MPLS, CRH). Scalable number of globally unique nodes in the domain 16-bit uSID: 65k uSIDs per domain block 32-bit uSID: 4.3M uSIDs per domain block Proven Hardware-friendliness Leverages mature hardware capabilities (Inline DA edit, DA longest match) Avoids any extra lookup in indexed mapping table Demonstrated by the number of linerate interoperable hardware implementations at the first Interop report in February 2020, less than 9 months after the first public version of this document. Public operator report of leverage of installed base A micro-program which requires less than 6 uSID's only requires legacy IPinIP encapsulation behavior Scalable Control-Plane No indexed mapping table is required Summarization at area/domain boundary provides massive scaling advantage No routing extension is required: a simple prefix advertisement suffices Seamless Deployment A uSID may be used as a SID: i.e. the container holds a single uSID The inner structure of an SR Policy can stay opaque to the source: i.e. a container with uSID's is just seen as a SID by the policy headend Security Leverages SRv6's native SR domain security Large-Scale DC SID's may be used to address applications on hosts (scale in 2^128) Hardware friendliness of uSID's may be used to specify billions of waypoints in cost/power-optimized DC fabric

The hardware and software platforms listed below have demonstrated support for the uN instruction defined in this document. Further on, all these implementations have participated in a joint interoperability testing . Hardware implementations (in alphabetical order): Arrcus ArcOS (based on Broadcom Jericho2) Barefoot Tofino P4-programmable Ethernet switch ASIC Cisco 8000 Series Routers (based on Cisco Silicon One Q100) Cisco ASR9000 platform (with 3rd gen Tomahawk and 4th gen Lightspeed line-cards) Cisco NCS5500 platform (based on Broadcom Jericho/Jericho+) Marvell Prestera Packet Processor Software open-source implementations (in alphabetical order): FD.io VPP Linux Kernel

The security rules defined in Section 7 of , protect intra-domain deployments that includes SRv6 uSID.

This document requests IANA to allocate the following codepoints within the "SRv6 Endpoint Behaviors" sub-registry under the top-level "Segment Routing Parameters" registry. Value Hex Endpoint behavior Reference 42 0x002A uN [This.ID] 43 0x002B uN (S&L+End) [This.ID] 44 0x002C uN (S&L+End PSP) [This.ID] 45 0x002D uN (S&L+End USP) [This.ID] 46 0x002E uN (S&L+End PSP/USP) [This.ID] 47 0x002F uN (S&L+End USD) [This.ID] 48 0x0030 uN (S&L+End PSP/USD) [This.ID] 49 0x0031 uN (S&L+End USP/USD) [This.ID] 50 0x0032 uN (S&L+End PSP/USP/USD) [This.ID] 51 0x0033 uA [This.ID] 52 0x0034 uA (S&X+End.X) [This.ID] 53 0x0035 uA (S&X+End.X PSP) [This.ID] 54 0x0036 uA (S&X+End.X USP) [This.ID] 55 0x0037 uA (S&X+End.X PSP/USP) [This.ID] 56 0x0038 uA (S&X+End.X USD) [This.ID] 57 0x0039 uA (S&X+End.X PSP/USD) [This.ID] 58 0x003A uA (S&X+End.X USP/USD) [This.ID] 59 0x003B uA (S&X+End.X PSP/USP/USD) [This.ID] 60 0x003C uDX6 [This.ID] 61 0x003D uDX4 [This.ID] 62 0x003E uDT6 [This.ID] 63 0x003F uDT4 [This.ID] 64 0x0040 uDT46 [This.ID] 65 0x0041 uDX2 [This.ID]

The authors would like to acknowledge Francois Clad, Peter Psenak, Ketan Talaulikar, Jakub Horn, Swadesh Agrawal, Zafar Ali, Darren Dukes, Kiran Sasidharan, Junaid Israr, Lakshmanan Srikanth, Asif Islam, Saleem Hafeez, Michael MacKenzie, Sushek Shekar, YuanChao Su, Alexander Preusche, Alberto Donzelli, Miya Kohno, David Smith, Ianik Semco, Bertrand Duvivier, Frederic Trate, Kris Michielsen, Eyal Dagan, Eli Stein, Ofer Iny, Elad Naor, Guy Caspari, Mel Tsai, Anand Sridharan, Aviad Behar, Joseph Chin.

Jisu Bhattacharyaa Cisco Systems, Inc. United States of America Email: jisu@cisco.com Kamran Raza Cisco Systems, Inc. Canada Email: skraza@cisco.com John Bettink Cisco Systems, Inc. United States of America Email: jbettink@cisco.com Tomonobu Niwa KDDI Japan Email: to-niwa@kddi.com Luay Jalil Verizon United States of America Email: luay.jalil@one.verizon.com Zhichun Jiang Tencent China Email: zcjiang@tencent.com Ahmed Shawky Saudi Telecom Company Saudi Arabia Email: ashawky@stc.com.sa Nic Leymann Deutsche Telekom Germany Email: N.Leymann@telekom.de Dirk Steinberg Lapishills Consulting Limited Cyprus Email: dirk@lapishills.com Shawn Zandi LinkedIn United States of America Email: szandi@linkedin.com Gaurav Dawra LinkedIn United States of America Email: gdawra@linkedin.com Jim Uttaro AT&T United States of America Email: ju1738@att.com Ning So Reliance United States of America Email: Ning.So@ril.com Michael Fiumano Sprint United States of America Email: michael.f.fiumano@sprint.com Mazen Khaddam Cox United States of America Email: Mazen.Khaddam@cox.com Jichun Ma China Unicom China Email: majc16@chinaunicom.cn Satoru Matsushima Softbank Japan Email: satoru.matsushima@g.softbank.co.jp Francis Ferguson CenturyLink United States of America Email: Francis.Ferguson@centurylink.com Takuya Miyasaka KDDI Japan Email: ta-miyasaka@kddi.com Kentaro Ebisawa Toyota Motor Corporation Japan Email: ebisawa@toyota-tokyo.tech Yukito Ueno NTT Communications Corporation Japan Email: yukito.ueno@ntt.com