IPv6 Segment Routing
Header (SRH)Cisco Systems, Inc.BrusselsBEcfilsfil@cisco.comCisco Systems, Inc.OttawaCAddukes@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 called the Segment Routing Header. This
document describes the Segment Routing Header and how it is used by
Segment Routing capable nodes.Segment Routing can be applied to the IPv6 data plane using a new
type of Routing Header called the Segment Routing Header. This document
describes the Segment Routing 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.The encoding of IPv6 segments in the Segment Routing Header is
defined in this document.This document uses the terms Segment Routing, SR Domain, SRv6,
Segment ID (SID), SRv6 SID, Active Segment, and SR Policy as defined in
.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.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 Section 4.4Hdr Ext Len: Defined in Section 4.4Routing Type: TBD, to be assigned by IANA (suggested value:
4).Segments Left: Defined in Section
4.4Last Entry: contains the index (zero based), in the Segment List,
of the last element of the Segment List.Flags: 8 bits of flags. creates an
IANA registry for new flags to be defined. The 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. Tag is not used when
processing the SID defined in . It may be
used when processing other SIDs which are not defined in this
document. 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 .In the SRH, the Next Header, Hdr Ext Len, Routing Type, and Segments
Left fields are defined in Section 4.4 of .
Based on the constraints in that section Next Header, Header Ext Len,
and Routing Type are not mutable while Segments Left is mutable.The mutability of the TLV value is defined by the most significant
bit in the type, as specified in . defines the mutability of the remaining
fields in the SRH (Flags, Tag, Segment List) in the context of the SID
defined in this document.New SIDs defined in the future MUST specify the mutability properties
of the Flags, Tag, and Segment List and indicate how the HMAC TLV () verification works. Note, that in effect these
fields are mutable.Consistent with the source routing model, the source of the SRH
always knows how to set the segment list, Flags, Tag and TLVs of the SRH
for use within the SR Domain. How it achieves this is outside the scope
of this document, but may be based on topology, available SIDs and their
mutability properties, the SRH mutability requirements of the
destination, or any other information.This section defines TLVs of the Segment Routing Header.A TLV provides meta-data for segment processing. The only TLVs
defined in this document are the HMAC () and
PAD () TLVs. While processing the SID
defined in , all TLVs are ignored unless
local configuration indicates otherwise ().
Thus, TLV and HMAC support is optional for any implementation, however
an implementation adding or parsing TLVs MUST support PAD TLVs. Other
documents may define additional TLVs and processing rules for
them.TLVs are present when the Hdr Ext Len is greater than (Last
Entry+1)*2.While processing TLVs at a segment endpoint, TLVs MUST be fully
contained within the SRH as determined by the Hdr Ext Len. Detection
of TLVs exceeding the boundary of the SRH Hdr Ext Len results in an
ICMP Parameter Problem, Code 0, message to the Source Address,
pointing to the Hdr Ext Len field of the SRH, and the packet being
discarded.An implementation MAY limit the number and/or length of TLVs it
processes based on local configuration. It MAY:Limit the number of consecutive Pad1 ()
options to 1, if padding of more than one byte is required then
PadN () should be used.Limit the length in PadN to 5.Limit the maximum number of non-Pad TLVs to be processed.Limit the maximum length of all TLVs to be processed. The implementation MAY stop processing additional TLVs in
the SRH when these configured limits are exceeded.Type: An 8 bit value. Unrecognized Types MUST be ignored on
receipt.Length: The length of the Variable length data.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.The highest-order bit of the TLV type specifies whether or not the
TLV data of that type can change en route to the packet's final
destination: 0: TLV data does not change en route1: TLV data does change en routeAll TLVs specify their alignment requirements using an xn+y format.
The xn+y format is defined as per . The SR
Source nodes use the xn+y alignment requirements of TLVs and Padding
TLVs when constructing an SRH.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 TLVsHMAC TLVAdditional TLVs may be defined in the future.There are two types of Padding TLVs, pad1 and padN, the following
applies to both:Padding TLVs are used for meeting the alignment requirement
of the subsequent TLVs.Padding TLVs are used to pad the SRH to a multiple of 8
octets.Padding TLVs are used for alignment.Padding TLVs are ignored by a node processing the SRH
TLV.Multiple Padding TLVs MAY be used in one SRHAlignment requirement: noneType: to be assigned by IANA (Suggested value 0)A single Pad1 TLV MUST be used when a single byte of padding is
required. If more than one byte of padding is required a Pad1 TLV
MUST NOT be used, the PadN TLV MUST be used.Alignment requirement: noneType: to be assigned by IANA (suggested value 4).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.Alignment requirement: 8nThe 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.HMAC: 32 octets of keyed HMAC.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.Local configuration determines when to check for an HMAC and
potentially indicates what the HMAC protects, and a requirement on
where the HMAC TLV must appear (e.g. first TLV), and whether or
not to verify the destination address is equal to the current
segment. This local configuration 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, HMAC Key ID, or other packet fields.An implementation that supports the generation and verification
of the HMAC SHOULD support the following default behavior as
defined in the remainder of this section.The HMAC verification begins by checking the current segment is
equal to the destination address of the IPv6 header, i.e.
destination address is equal to Segment List [Segments Left] and
Segments Left is less than or equal to Last Segment+1.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)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.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 and the packet discarded.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.An implementation supporting HMAC can support multiple hash
functions. An implementation supporting HMAC 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. 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 chain of the IPv6 header as defined in
section 4 of .
describes how to process an SRH,
describes how to process an upper layer header or no next
header.Processing this SID modifies the Segments Left and, if configured
to process TLVs, it may modify the "variable length data" of TLV
types that change en route. Therefore Segments Left is mutable and
TLVs that change en route are mutable. The remainder of the SRH
(Flags, Tag, Segment List, and TLVs that do not change en route) are
immutable while processing this SID.Local configuration determines how TLVs are to be processed
when the Active Segment is a local SID defined in this document.
The definition of local configuration is outside the scope of
this document.For illustration purpose only, two example local
configurations that may be associated with a SID are provided
below.When processing the Upper-layer header of a packet matching a
FIB entry locally instantiated as an SRv6 SID defined in this
document.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.The use of the SIDs exclusively within the SR Domain and solely for
packets of the SR Domain is an important deployment model.This enables the SR Domain to act as a single routing system.This section covers:securing the SR Domain from external attempt to use its SIDsSR Domain as a single system with delegation between
componentshandling packets of the SR DomainNodes outside the SR Domain are not trusted: they cannot directly
use the SID's of the domain. This is enforced by two levels of access
control lists: Any packet entering the SR Domain and destined to a SID within
the SR Domain is dropped. This may be realized with the following
logic, other methods with equivalent outcome are considered
compliant: allocate all the SID's from a block S/sconfigure each external interface of each edge node of the
domain with an inbound infrastructure access list (IACL) which
drops any incoming packet with a destination address in
S/sFailure to implement this method of ingress filtering
exposes the SR Domain to source routing attacks as described
and referenced in The distributed protection in #1 is complemented with per node
protection, dropping packets to SIDs from source addresses outside
the SR Domain. This may be realized with the following logic,
other methods with equivalent outcome are considered compliant:
assign all interface addresses from prefix A/aat node k, all SIDs local to k are assigned from prefix
Sk/skconfigure each internal interface of each SR node k in the
SR Domain with an inbound IACL which drops any incoming packet
with a destination address in Sk/sk if the source address is
not in A/a.All intra SR Domain packets are of the SR Domain. The IPv6 header
is originated by a node of the SR Domain, and is destined to a node of
the SR Domain.All inter domain packets are encapsulated for the part of the
packet journey that is within the SR Domain. The outer IPv6 header is
originated by a node of the SR Domain, and is destined to a node of
the SR Domain.As a consequence, any packet within the SR Domain is of the SR
Domain.The SR Domain is a system in which the operator may want to
distribute or delegate different operations of the outer most header
to different nodes within the system.An operator of an SR domain may choose to delegate SRH addition to
a host node within the SR domain, and validation of the contents of
any SRH to a more trusted router or switch attached to the host.
Consider a top of rack switch (T) connected to host (H) via interface
(I). H receives an SRH (SRH1) with a computed HMAC via some SDN method
outside the scope of this document. H classifies traffic it sources
and adds SRH1 to traffic requiring a specific SLA. T is configured
with an IACL on I requiring verification of the SRH for any packet
destined to the SID block of the SR Domain (S/s). T checks and
verifies that SRH1 is valid, contains an HMAC TLV and verifies the
HMAC.An operator of the SR Domain may choose to have all segments in the
SR Domain verify the HMAC. This mechanism would verify that the SRH
segment list is not modified while traversing the SR Domain.An SR Domain ingress edge node encapsulates packets traversing the
SR Domain, and needs to consider the MTU of the SR Domain. Within the
SR Domain, well known mitigation techniques are RECOMMENDED, such as
deploying a greater MTU value within the SR Domain than at the ingress
edges.ICMP error packets generated within the SR Domain are sent to
source nodes within the SR Domain. The invoking packet in the ICMP
error message may contain an SRH. Since the destination address of a
packet with an SRH changes as each segment is processed, it may not be
the destination used by the socket or application that generated the
invoking packet.For the source of an invoking packet to process the ICMP error
message, the correct destination address must be determined. The
following logic is used to determine the destination address for use
by protocol error handlers.Walk all extension headers of the invoking IPv6 packet to the
routing extension header preceding the upper layer header.If routing header is type 4 (SRH)Use the SID at Segment List[0] as the destination
address of the invoking packet.ICMP errors are then processed by upper layer transports as defined
in .For IP packets encapsulated in an outer IPv6 header, ICMP error
handling is as defined in .For any inter domain packet, 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.For any intra domain packet, the SR Source node SHOULD impose a
flow label computed as described in to assist
ECMP load balancing at transit nodes incapable of computing a 5-tuple
beyond the SRH.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 would likely 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.Other deployment models and their implications on security, MTU,
HMAC, ICMP error processing and interaction with other extension
headers are outside the scope of this document.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 DomainThe SR domain is secured as per
and no external packet can enter the domain with a destination
address equal to a segment of the domain.When 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)When host 8 sends a packet to host 1, the packet is encapsulated
for the portion of its journey within the SR Domain. From 8 to 3 the
packet isP7: (A8,S3)(A8,A1)In the opposite direction, the packet generated from 1 to 8
isP8: (A1,A8)At node 3 P8 is encapsulated for the portion of its journey
within the SR domain, with the outer header destined to segment S8.
Resulting inP9: (A3,S8)(A1,A8)At node 8 the outer IPv6 header is removed by S8 processing, then
processed again when received by A8.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 , sends packetP7: (A8,A9)(A9,S7; SL=0)on the interface toward router 6.This section describes how a function may be delegated within the
SR Domain to non SR source nodes. In the following sections consider a
host 8 connected to a top of rack 5.An operator may prefer to add the SRH at source 8, while 5
verifies the SID list is valid.For illustration purpose, an SDN controller provides 8 an SRH
terminating at node 9, with segment list <S5,S7,S6,A9>, and
HMAC TLV computed for the SRH. The HMAC key is shared with 5, node 8
does not know the key. Node 5 is configured with an IACL applied to
the interface connected to 8, requiring HMAC verification for any
packet destined to S/s.Node 8 originates packets with the received SRH with HMAC
TLV.P15:(A8,S5)(A9,S6,S7,S5;SL=3;HMAC)Node 5 receives and verifies the HMAC for the SRH, then forwards
the packet to the next segmentP16:(A8,S7)(A9,S6,S7,S5;SL=2;HMAC)Node 6 receivesP17:(A8,S6)(A9,S6,S7,S5;SL=1;HMAC)Node 9 receivesP18:(A8,A9)(A9,S6,S7,S5;SL=0;HMAC)This use of an HMAC is particularly valuable within an enterprise
based SR Domain .This section reviews security considerations related to the SRH,
given the SRH processing and deployment models discussed in this
document.As described in , it is necessary to filter
packets ingress to the SR Domain, destined to SIDs within the SR Domain
(i.e., bearing a SID in the destination address). 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. 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; 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.Additionally, 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 utilize 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.The SRH is unencrypted and may contain SIDs of some intermediate
SR-nodes in the path towards the destination within the SR Domain. If
packets can be snooped within the SR Domain, the SRH may reveal
topology, traffic flows, and service usage.This is applicable within an SR Domain but the disclosure is less
relevant as an attacker has other means of learning topology, flows,
and service usage.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.The SR Domain is a trusted domain, as defined in Section 2 and Section 8.2. The SR Source is trusted
to add an SRH (optionally verified via the HMAC TLV in this document),
and segments advertised within the domain are trusted to be accurate
and advertised by trusted sources via a secure control plane. As such
the SR Domain does not rely on the Authentication Header (AH) as
defined in to secure the SRH.The use of SRH with AH by an SR source node, and processing at a SR
segment endpoint node, is not defined in this document. Future
documents may define use of SRH with AH and its processing.This document makes the following registrations in the Internet
Protocol Version 6 (IPv6) Parameters "Routing Type" registry maintained
by IANA:This document makes the following registrations in "Type 4 -
Parameter Problem" message of the "Internet Control Message Protocol
version 6 (ICMPv6) Parameters" registry maintained by IANA:This section provides guidance to the Internet Assigned Numbers
Authority (IANA) regarding registration of values related to the SRH, in
accordance with BCP 26, .The following terms are used here with the meanings defined in BCP
26: "namespace", "assigned value", "registration".The following policies are used here with the meanings defined in BCP
26: "Private Use", "First Come First Served", "Expert Review",
"Specification Required", "IETF Consensus", "Standards Action".For registration requests where a Designated Expert should be
consulted, the responsible IESG area director should appoint the
Designated Expert. The intention is that any allocation will be
accompanied by a published RFC. In order to allow for the allocation of
values prior to the RFC being approved for publication, the Designated
Expert can approve allocations once it seems clear that an RFC will be
published. The Designated expert will post a request to the 6man WG
mailing list (or a successor designated by the Area Director) for
comment and review, including an Internet-Draft. Before a period of 30
days has passed, the Designated Expert will either approve or deny the
registration request and publish a notice of the decision to the 6man WG
mailing list or its successor, as well as informing IANA. A denial
notice must be justified by an explanation, and in the cases where it is
possible, concrete suggestions on how the request can be modified so as
to become acceptable should be provided.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.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, with assigned values 0-127 for TLVs that do not
change en route, and 128-255 for TLVs that may change en route. The
following codepoints are defined in this document: Values 1,2,3,6 were defined in draft versions of this specification
and are Reserved for backwards compatibility with early
implementations and should not be reassigned. Values 127 and 255 are
Reserved to allow for expansion of the Type field in future
specifications if needed.This section is to be removed prior to publishing as an RFC.See for
updated deployment and interoperability reports.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: Production (IOS XR), Pre-production (IOS XE)Implementation: 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, Zafar Ali, 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