IPv6 Segment Routing
Header (SRH)Cisco Systems, Inc.BrusselsBEcfilsfil@cisco.comHuaweiItalystefano@previdi.netIndividualUSjohn@leddy.netSoftbanksatoru.matsushima@g.softbank.co.jpBell Canadadaniel.voyer@bell.caNetwork Working GroupSegment Routing can be applied to the IPv6 data plane using a new
type of Routing Extension Header. This document describes the Segment
Routing Extension Header and how it is used by Segment Routing capable
nodes.The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP 14
when, and only when,
they appear in all capitals, as shown here.Segment Routing can be applied to the IPv6 data plane using a new
type of Routing Extension Header (SRH). This document describes the
Segment Routing Extension Header and how it is used by Segment Routing
capable nodes.The Segment Routing Architecture describes
Segment Routing and its instantiation in two data planes MPLS and
IPv6.SR with the MPLS data plane is defined in .SR with the IPv6 data plane is defined in .The encoding of MPLS labels and label stacking are defined in .The encoding of IPv6 segments in the Segment Routing Extension Header
is defined in this document.Terminology used within this document is defined in detail in . Specifically, these terms: Segment Routing, SR
Domain, SRv6, Segment ID (SID), SRv6 SID, Active Segment, and SR
Policy.Routing Headers are defined in . The Segment
Routing Header has a new Routing Type (suggested value 4) to be assigned
by IANA.The Segment Routing Header (SRH) is defined as follows:Next Header: Defined in Hdr Ext Len: Defined in Routing Type: TBD, to be assigned by IANA (suggested value:
4).Segments Left: Defined in Last Entry: contains the index (zero based), in the Segment List,
of the last element of the Segment List.Flags: 8 bits of flags. Following flags are defined:U: Unused and for future use. MUST be 0 on transmission and
ignored on receipt.Tag: tag a packet as part of a class or group of packets, e.g.,
packets sharing the same set of properties. When tag is not used at
source it MUST be set to zero on transmission. When tag is not used
during SRH Processing it SHOULD be ignored. The allocation and use
of tag is outside the scope of this document.Segment List[n]: 128 bit IPv6 addresses representing the nth
segment in the Segment List. The Segment List is encoded starting
from the last segment of the SR Policy. I.e., the first element of
the segment list (Segment List [0]) contains the last segment of the
SR Policy, the second element contains the penultimate segment of
the SR Policy and so on.Type Length Value (TLV) are described in .This section defines TLVs of the Segment Routing Header.Type: An 8 bit value. Unrecognized Types MUST be ignored on
receipt.Length: The length of the Variable length data. It is RECOMMENDED
that the total length of new TLVs be multiple of 8 bytes to avoid the
use of Padding TLVs.Variable length data: Length bytes of data that is specific to the
Type.Type Length Value (TLV) contain OPTIONAL information that may be
used by the node identified in the Destination Address (DA) of the
packet.Each TLV has its own length, format and semantic. The code-point
allocated (by IANA) to each TLV Type defines both the format and the
semantic of the information carried in the TLV. Multiple TLVs may be
encoded in the same SRH.TLVs may change en route at each segment. To identify when a TLV
type may change en route the most significant bit of the Type has the
following significance: 0: TLV data does not change en route1: TLV data does change en routeIdentifying which TLVs change en route, without having to
understand the Type, is required for Authentication Header Integrity
Check Value (ICV) computation. Any TLV that changes en route is
considered mutable for the purpose of ICV computation, the Type Length
and Variable Length Data is ignored for the purpose of ICV Computation
as defined in .The "Length" field of the TLV is used to skip the TLV while
inspecting the SRH in case the node doesn't support or recognize the
Type. The "Length" defines the TLV length in octets, not including the
"Type" and "Length" fields.The following TLVs are defined in this document:Padding TLVHMAC TLVAdditional TLVs may be defined in the future.There are two types of padding TLVs, pad0 and padN, the following
applies to both:Padding TLVs are used to pad the TLVs to a multiple of 8
octets.More than one Padding TLV MUST NOT appear in the SRH.The Padding TLVs are used to align the SRH total length on
the 8 octet boundary.When present, a single Pad0 or PadN TLV MUST appear as the
last TLV.When present, a PadN TLV MUST have a length from 0 to 5 in
order to align the SRH total length on a 8-octet boundary.Padding TLVs are ignored by a node processing the SRH TLV,
even if more than one is present.Padding TLVs are ignored during ICV calculation.Type: to be assigned by IANA (Suggested value 128)A single Pad0 TLV MUST be used when a single byte of padding is
required. If more than one byte of padding is required a Pad0 TLV
MUST NOT be used, the PadN TLV MUST be used.Type: to be assigned by IANA (suggested value 129).Length: 0 to 5Padding: Length octets of padding. Padding bits have no
semantics. They MUST be set to 0 on transmission and ignored
on receipt.The PadN TLV MUST be used when more than one byte of padding is
required.The keyed Hashed Message Authentication Code (HMAC) TLV is
OPTIONAL and has the following format: Type: to be assigned by IANA (suggested value 5).Length: 38.RESERVED: 2 octets. MUST be 0 on transmission and ignored on
receipt.HMAC Key ID: A 4 octet opaque number which uniquely
identifies the pre-shared key and algorithm used to generate the
HMAC. If 0, the HMAC is not included.HMAC: 32 octets of keyed HMAC, not present if Key ID is
0.The HMAC TLV is used to verify the source of a packet is
permitted to use the current segment in the destination address of
the packet, and ensure the segment list is not modified in
transit.The HMAC field is the output of the HMAC computation as defined
in , using:key: the pre-shared key identified by HMAC Key IDHMAC algorithm: identified by the HMAC Key IDText: a concatenation of the following fields from the IPv6
header and the SRH, as it would be received at the node
verifying the HMAC:IPv6 header: source address (16 octets)IPv6 header: destination address (16 octets)SRH: Segments Left (1 octet)SRH: Last Entry (1 octet)SRH: Flags (1 octet)SRH: HMAC Key-id (4 octets)SRH: all addresses in the Segment List (variable
octets)The HMAC digest is truncated to 32 octets and placed in the
HMAC field of the HMAC TLV.For HMAC algorithms producing digests less than 32 octets, the
digest is placed in the lowest order octets of the HMAC field.
Remaining octets MUST be set to zero.Local policy determines when to check for an HMAC and
potentially a requirement on where the HMAC TLV must appear (e.g.
first TLV). This local policy is outside the scope of this
document. It may be based on the active segment at an SR Segment
endpoint node, the result of an ACL that considers incoming
interface, or other packet fields.If HMAC verification is successful, the packet is forwarded to
the next segment.If HMAC verification fails, an ICMP error message (parameter
problem, error code 0, pointing to the HMAC TLV) SHOULD be
generated (but rate limited) and SHOULD be logged.The HMAC Key ID field allows for the simultaneous existence of
several hash algorithms (SHA-256, SHA3-256 ... or future ones) as
well as pre-shared keys.The HMAC Key ID field is opaque, i.e., it has neither syntax
nor semantic except as an identifier of the right combination of
pre-shared key and hash algorithm, and except that a value of 0
means that there is no HMAC field.At the HMAC TLV verification node the Key ID uniquely
identifies the pre-shared key and HMAC algorithm.At the HMAC TLV generating node the Key ID and destination
address uniquely identify the pre-shared key and HMAC algorithm.
Utilizing the destination address with the Key ID allows for
overlapping key IDs amongst different HMAC verification nodes. The
Text for the HMAC computation is set to the IPv6 header fields and
SRH fields as they would appear at the verification node, not
necessarily the same as the source node sending a packet with the
HMAC TLV.Pre-shared key roll-over is supported by having two key IDs in
use while the HMAC TLV generating node and verifying node converge
to a new key.SRH implementations can support multiple hash functions but
MUST implement SHA-2 in its SHA-256
variant.The selection of pre-shared key and algorithm, and their
distribution is outside the scope of this document, some options
may include: in the configuration of the HMAC generating or verifying
nodes, either by static configuration or any SDN oriented
approachdynamically using a trusted key distribution protocol such
as There are different types of nodes that may be involved in segment
routing networks: source SR nodes originate packets with a segment in
the destination address of the IPv6 header, transit nodes that forward
packets destined to a remote segment, and SR segment endpoint nodes that
process a local segment in the destination address of an IPv6
header.A Source SR Node is any node that originates an IPv6 packet with a
segment (i.e. SRv6 SID) in the destination address of the IPv6 header.
The packet leaving the source SR Node may or may not contain an SRH.
This includes either: A host originating an IPv6 packet.An SR domain ingress router encapsulating a received packet in
an outer IPv6 header, followed by an optional SRH.The mechanism through which a segment in the destination address of
the IPv6 header and the Segment List in the SRH, is derived is outside
the scope of this document.A transit node is any node forwarding an IPv6 packet where the
destination address of that packet is not locally configured as a
segment nor a local interface. A transit node is not required to be
capable of processing a segment nor SRH.A SR segment endpoint node is any node receiving an IPv6 packet
where the destination address of that packet is locally configured as
a segment or local interface.This section describes SRv6 packet processing at the SR source,
Transit and SR segment endpoint nodes.A Source node steers a packet into an SR Policy. If the SR Policy
results in a segment list containing a single segment, and there is no
need to add information to SRH flag or TLV, the DA is set to the
single segment list entry and the SRH MAY be omitted.When needed, the SRH is created as follows:Next Header and Hdr Ext Len fields are set as specified in
.Routing Type field is set as TBD (to be allocated by IANA,
suggested value 4).The DA of the packet is set with the value of the first
segment.The first element of the SRH Segment List is the ultimate
segment. The second element is the penultimate segment and so
on.The Segments Left field is set to n-1 where n is the number of
elements in the SR Policy.The Last Entry field is set to n-1 where n is the number of
elements in the SR Policy.HMAC TLV may be set according to .The packet is forwarded toward the packet's Destination Address
(the first segment).When a source does not require the entire SID list to be
preserved in the SRH, a reduced SRH may be used.A reduced SRH does not contain the first segment of the related
SR Policy (the first segment is the one already in the DA of the
IPv6 header), and the Last Entry field is set to n-2 where n is the
number of elements in the SR Policy.As specified in , the only node allowed to
inspect the Routing Extension Header (and therefore the SRH), is the
node corresponding to the DA of the packet. Any other transit node
MUST NOT inspect the underneath routing header and MUST forward the
packet toward the DA according to its IPv6 routing table.When a SID is in the destination address of an IPv6 header of a
packet, it's routed through an IPv6 network as an IPv6 address. SIDs,
or the prefix(es) covering SIDs, and their reachability may be
distributed by means outside the scope of this document. For example,
or may be used to
advertise a prefix covering the SIDs on a node.Without constraining the details of an implementation, the SR
segment endpoint node creates Forwarding Information Base (FIB)
entries for its local SIDs.When an SRv6-capable node receives an IPv6 packet, it performs a
longest-prefix-match lookup on the packets destination address. This
lookup can return any of the following:This document, and section, defines a single SRv6 SID called END.
Future documents may define additional SRv6 SIDs. In which case, the
entire content of this section will be defined in that document.If the FIB entry represents a locally instantiated SRv6 SID,
process the next header of the IPv6 header as defined in section 4
of The following sections describe the actions to take while
processing next header fields.Local policy determines how TLV's are to be processed when
the Active Segment is a local END SID. The definition of local
policy is outside the scope of this document.For illustration purpose only, two example local policies
that may be associated with an END SID are provided below.Send an ICMP parameter problem message to the Source Address
and discard the packet. Error code (TBD by IANA) "SR Upper-layer
Header Error", pointer set to the offset of the upper-layer
header.A unique error code allows an SR Source node to recognize an
error in SID processing at an endpoint.If the FIB entry represents a local interface, not locally
instantiated as an SRv6 SID, the SRH is processed as follows:If Segments Left is zero, the node must ignore the Routing
header and proceed to process the next header in the packet,
whose type is identified by the Next Header field in the Routing
Header.If Segments Left is non-zero, the node must discard the
packet and send an ICMP Parameter Problem, Code 0, message to
the packet's Source Address, pointing to the unrecognized
Routing Type.Processing is not changed by this document.Processing is not changed by this document.Within an SR domain, an SR source node encapsulates a packet in
an outer IPv6 header for transport to an endpoint. The SR source
node MUST impose a flow label computed based on the inner packet.
The computation of the flow label is as recommended in for the sending Tunnel End Point.At any transit node within an SR domain, the flow label MUST be
used as defined in to calculate the ECMP
hash toward the destination address. If flow label is not used, the
transit node may hash all packets between a pair of SR Edge nodes to
the same link.At an SR segment endpoint node, the flow label MUST be used as
defined in to calculate any ECMP hash used
to forward the processed packet to the next segment.This section provides illustrations of SRv6 packet processing at SR
source, transit and SR segment endpoint nodes.For a node k, its IPv6 address is represented as Ak, its SRv6 SID
is represented as Sk.IPv6 headers are represented as the tuple of (source, destination).
For example, a packet with source address A1 and destination address
A2 is represented as (A1,A2). The payload of the packet is
omitted.An SR Policy is a list of segments. A list of segments is
represented as <S1,S2,S3> where S1 is the first SID to visit, S2
is the second SID to visit and S3 is the last SID to visit.(SA,DA) (S3, S2, S1; SL) represents an IPv6 packet with:Source Address is SA, Destination Addresses is DA, and
next-header is SRH.SRH with SID list <S1, S2, S3> with SegmentsLeft =
SL.Note the difference between the <> and () symbols.
<S1, S2, S3> represents a SID list where the leftmost
segment is the first segment. Whereas, (S3, S2, S1; SL) represents
the same SID list but encoded in the SRH Segment List format where
the leftmost segment is the last segment. When referring to an SR
policy in a high-level use-case, it is simpler to use the <S1,
S2, S3> notation. When referring to an illustration of detailed
behavior, the (S3, S2, S1; SL) notation is more convenient.At its SR Policy headend, the Segment List <S1,S2,S3> results
in SRH (S3,S2,S1; SL=2) represented fully as: The following topology is used in examples below: 3 and 4 are SR Domain edge routers5, 6, and 7 are all SR Domain routers8 and 9 are hosts within the SR Domain1 and 2 are hosts outside the SR DomainWhen host 8 sends a packet to host 9 via an SR Policy
<S7,A9> the packet isP1: (A8,S7)(A9,S7; SL=1)When host 8 sends a packet to host 9 via an SR Policy
<S7,A9> and it wants to use a reduced SRH, the packet isP2: (A8,S7)(A9; SL=1)When host 1 sends a packet to host 2, the packet isP3: (A1,A2)The SR Domain ingress router 3 receives P3 and steers it to SR
Domain egress router 4 via an SR Policy <S7, S4>. Router 3
encapsulates the received packet P3 in an outer header with an SRH.
The packet isP4: (A3, S7)(S4, S7; SL=1)(A1, A2)If the SR Policy contains only one segment (the egress router 4),
the ingress Router 3 encapsulates P3 into an outer header (A3, S4).
The packet isP5: (A3, S4)(A1, A2)The SR Domain ingress router 3 receives P3 and steers it to SR
Domain egress router 4 via an SR Policy <S7, S4>. If router
3 wants to use a reduced SRH, Router 3 encapsulates the received
packet P3 in an outer header with a reduced SRH. The packet isP6: (A3, S7)(S4; SL=1)(A1, A2)Nodes 5 acts as transit nodes for packet P1, and sends packetP1: (A8,S7)(A9,S7;SL=1)on the interface toward node 7.Node 7 receives packet P1 and, using the logic in section 4.3.1,
sends packetP7: (A8,A9)(A9,S7; SL=0)on the interface toward router 6.SR Source Nodes within an SR Domain are trusted to generate IPv6
packets with SRH. SR segment endpoint nodes receiving packets on
interface that are part of the SR Domain may process any packet
destined to a local segment, containing an SRH.A SR Source Node connected to the SR Domain via a secure tunnel,
e.g. IPSec tunnel mode or Ethernet pseudowire
, may be considered trusted and directly
connected. Some types of tunnels may result in additional processing
overhead that should be considered in a deployment.Nodes outside the SR Domain cannot be trusted. SR Domain Ingress
routers SHOULD discard packets destined to SIDs within the SR Domain
(regardless of the presence of an SRH) to avoid attacks on the SR
Domain as described and referenced in . As an
additional layer of protection, SR Segment Endpoint nodes SHOULD
discard packets destined to local SIDs from source addresses not part
of the SR Domain.For example, using the example topology from section 5, all SIDs in
the SR Domain (SIDS S1-S9) are assigned within a single IPv6 prefix,
Prefix-S. All SIDs assigned to a node k are assigned within a single
IPv6 prefix Prefix-Sk, all addresses permitted to source packets
destined to SIDs in the SR Domain are assigned within a single IPv6
prefix Prefix-A.An Infrastructure Access List (IACL), applied to the external
interfaces of SR Domain ingress nodes 3 and 4, that discards packets
destined to a SID covered by Prefix-S is used to discard packets
destined to SIDs within the SR Domain.An IACL, applied to each interface of SR Segment Endpoint Nodes k,
that discards packets destined to a SID covered by Prefix-Sk with a
source address not covered by Prefix-A.Failure to implement a method of ingress filtering, as defined
above, exposes the SR domain to source routing attacks from nodes
outside the SR Domain, as described and referenced in .Nodes outside the SR Domain may request, by some trusted means
outside the scope of this document, a complete SRH including an HMAC
TLV which is computed correctly for the SRH.SR Domain ingress routers permit traffic destined to select SIDs
with local policy requiring HMAC TLV processing for those select
SIDs, i.e. those SIDs provide a gateway to the SR Domain for a set
of segment lists.If HMAC verification is successful, the packet is forwarded to
the next segment. Within the SR Domain no further HMAC check need be
performed.If HMAC verification fails, an ICMP error message (parameter
problem, error code 0, pointing to the HMAC TLV) SHOULD be generated
(but rate limited) and SHOULD be logged.For example, extending the topology defined in , consider node 3 offering access to a premium SLA
service to node 20. Node 20 is a trusted SR Source not directly
connected to the SR Domain. In order to access the SLA service, node 20 must be able to
access segments within the SR Domain. To provide a secure entry
point for the SLA service, SIDs with local policy requiring HMAC
verification at node k are defined as Hk and assigned from a prefix
Prefix-H. Prefix-H is disjoint with Prefix-S and Prefix-A defined
earlier.Prefix-H is not part of the IACLs applied at the external facing
interfaces of node 3 and 4, allowing external nodes access to
it.SID H3 is a SID covered by Prefix-H at node 3.Node 20 requests the premium SLA service to node 2 and is
provided a pre-computed SRH and HMAC with destination address
H3.Node 20 sends a packet with destination addresses set to H2, SRH
and HMAC TLV are as provided for the premium SLA service.Node 3 receives the packet and verifies the HMAC as defined in
section 4.3, forwarding the packet to the next segment in the
segment list or dropping it based on the HMAC result.This use of an HMAC is particularly valuable within an enterprise
based SR Domain to authenticate a host which is using SRv6 segment
routing as documented in . In that example, the
HMAC is used to validate a source node is using a permitted segment
list.This section reviews security considerations related to the SRH,
given the SRH processing and deployment models discussed in this
document.As describe in , it is necessary to filter
packets ingress to the SR Domain destined to segments within the SR
Domain. This ingress filtering is via an IACL at SR Domain ingress
border nodes. Additional protection is applied via an IACL at each SR
Segment Endpoint node, filtering packets not from within the SR Domain,
destined to SIDs in the SR Domain. ACLs are easily supported for small
numbers of prefixes, making summarization important, and when the
prefixes requiring filtering is kept to a seldom changing set.Additionally, ingress filtering of IPv6 source addresses as
recommended in BCP38 SHOULD be used.SR Source Nodes not directly connected to the SR Domain may access
specific sets of segments within the SR Domain when secured with the SRH
HMAC TLV. The SRH HMAC TLV provides a means of verifying the validity of
ingress packets SRH, limiting access to the segments in the SR Domain to
only those source nodes with permission. deprecates the Type 0 Routing header due
to a number of significant attacks that are referenced in that
document. Such attacks include bypassing filtering devices, reaching
otherwise unreachable Internet systems, network topology discovery,
bandwidth exhaustion, and defeating anycast.Because this document specifies that the SRH is for use within an
SR domain protected by ingress filtering via IACLs, and by
cryptographically authenticated SR source nodes not directly connected
to the SR Domain; such attacks cannot be mounted from outside an SR
Domain. As specified in this document, SR Domain ingress edge nodes
drop packets entering the SR Domain destined to segments within the SR
Domain.Aditionally, this document specifies the use of IACL on SR Segment
Endpoint nodes within the SR Domain to limit the source addresses
permitted to send packets to a SID in the SR Domain.Such attacks may, however, be mounted from within the SR Domain,
from nodes permitted to source traffic to SIDs in the domain. As such,
these attacks and other known attacks on an IP network (e.g. DOS/DDOS,
topology discovery, man-in-the-middle, traffic
interception/siphoning), can occur from compromised nodes within an SR
Domain.Service theft is defined as the use of a service offered by the SR
Domain by a node not authorized to use the service.Service theft is not a concern within the SR Domain as all SR
Source nodes and SR segment endpoint nodes within the domain are able
to utilizing the services of the Domain. If a node outside the SR
Domain learns of segments or a topological service within the SR
domain, IACL filtering denies access to those segments.Nodes outside the SR Domain, capable of intercepting packets from
SR Source nodes not directly connected to the SR Domain utilizing the
SRH HMAC, may steel the outer IP header SRH and HMAC TLV. If such an
attacker is capable of spoofing the source address of the original
sender it may use the IP header and HMAC to access services of the SR
Domain intended for the original SR Source node.Frequent rekeying of the HMAC TLV helps mitigate against this
attack but cannot prevent it.However, as described in , there exist use
cases where the risk of service threat is of minimum concern and the
HMAC TLV is used primarily to validate that the source is permitted to
use the segment list in the SRH.The SRH may contains SIDs of some intermediate SR-nodes in the path
towards the destination, this reveals those addresses to attackers if
they are able to intercept packets containing SRH.This is applicable within an SR Domain but the disclosure is less
relevant as an attacker has other means of learning topology.For an SR Source node not directly connected to the SR Domain this
disclosure is applicable. While the segments within the SR domain
disclosed in SRH are protected by ingress filtering, they may be
learned by an attacker external to the SR Domain.As described in , there exist use cases
where the risk of topology disclosure is of minimum concern when the
HMAC TLV is used primarily to validate that the source is permitted to
use the segment list in the SRH.The generation of ICMPv6 error messages may be used to attempt
denial-of-service attacks by sending an error-causing destination
address or SRH in back-to-back packets. An implementation that
correctly follows Section 2.4 of would be
protected by the ICMPv6 rate-limiting mechanism.This document makes the following registrations in the Internet
Protocol Version 6 (IPv6) Parameters "Routing Type" registry maintained
by IANA:This document request IANA to create and maintain a new Registry:
"Segment Routing Header TLVs"This document requests the creation of a new IANA managed registry
to identify SRH Flags Bits. The registration procedure is "Expert
Review" as defined in . Suggested registry
name is "Segment Routing Header Flags". Flags is 8 bits, the following
bits are defined in this document: This document requests the creation of a new IANA managed registry
to identify SRH TLVs. The registration procedure is "Expert Review" as
defined in . Suggested registry name is
"Segment Routing Header TLVs". A TLV is identified through an unsigned
8 bit codepoint value. The following codepoints are defined in this
document: This section is to be removed prior to publishing as an RFC.Name: Linux Kernel v4.14Status: ProductionImplementation: adds SRH, performs END processing, supports HMAC
TLVDetails: https://irtf.org/anrw/2017/anrw17-final3.pdf and Name: IOS XR and IOS XEStatus: Pre-productionImplementation: adds SRH, performs END processing, no TLV
processingDetails: Name: VPP/Segment Routing for IPv6Status: ProductionImplementation: adds SRH, performs END processing, no TLV
processingDetails: https://wiki.fd.io/view/VPP/Segment_Routing_for_IPv6 and
Name: Barefoot Networks Tofino NPUStatus: PrototypeImplementation: performs END processing, no TLV processingDetails: Name: Juniper Networks Trio and vTrio NPU'sStatus: Prototype & ExperimentalImplementation: SRH insertion mode, Process SID where SID is an
interface address, no TLV processingName: Huawei Systems VRP PlatformStatus: ProductionImplementation: adds SRH, performs END processing, no TLV
processingKamran Raza, Darren Dukes, Brian Field, Daniel Bernier, Ida Leung,
Jen Linkova, Ebben Aries, Tomoya Kosugi, Eric Vyncke, David Lebrun, Dirk
Steinberg, Robert Raszuk, Dave Barach, John Brzozowski, Pierre Francois,
Nagendra Kumar, Mark Townsley, Christian Martin, Roberta Maglione, James
Connolly, Aloys Augustin contributed to the content of this
document.The authors would like to thank Ole Troan, Bob Hinden, Ron Bonica,
Fred Baker, Brian Carpenter, Alexandru Petrescu, Punit Kumar Jaiswal,
and David Lebrun for their comments to this document.FIPS 180-4 Secure Hash Standard (SHS)National Institute of Standards and
TechnologySoftware Resolved Networks: Rethinking Enterprise Networks
with IPv6 Segment Routing