SPRING Working Group Z. Ali
Internet-Draft C. Filsfils
Intended status: Standards Track N. Kumar
Expires: August 30, 2018 C. Pignataro
F. Iqbal
R. Gandhi
Cisco Systems, Inc.
J. Leddy
Comcast
S. Matsushima
SoftBank
R. Raszuk
Bloomberg LP
B. Peirens
Proximus
G. Naik
Drexel University
February 26, 2018
Operations, Administration, and Maintenance (OAM) in Segment
Routing Networks with IPv6 Data plane (SRv6)
draft-ali-spring-srv6-oam-00.txt
Abstract
This document describes mechanisms for Operations, Administration,
and Maintenance (OAM) in Segment Routing with IPv6 data plane (SRv6)
network.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
Ali, et al. Expires August 30, 2018 [Page 1]
Internet-Draft OAM for SRv6 February 26, 2018
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used in This Document . . . . . . . . . . . . . . 3
2.1. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Terminology and Reference Topology . . . . . . . . . . . . 3
3. OAM Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Ping . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1.1. Classic Ping . . . . . . . . . . . . . . . . . . . . . 5
3.1.2. Pinging SID Function . . . . . . . . . . . . . . . . . 6
3.1.2.1. End-to-end Ping Using END.OTP . . . . . . . . . . 7
3.1.2.2. Segment-by-segment Ping Using O-bit (Proof of
Transit) . . . . . . . . . . . . . . . . . . . . . 8
3.2. Error Reporting . . . . . . . . . . . . . . . . . . . . . 9
3.3. Traceroute . . . . . . . . . . . . . . . . . . . . . . . . 10
3.3.1. Classic Traceroute . . . . . . . . . . . . . . . . . . 10
3.3.2. Traceroute to a SID Function . . . . . . . . . . . . . 11
3.3.2.1. Hop-by-hop Traceroute Using END.OTP . . . . . . . 12
3.3.2.2. Tracing SRv6 Overlay . . . . . . . . . . . . . . . 14
4. In-situ OAM Applicability . . . . . . . . . . . . . . . . . . 15
5. Seamless BFD Applicability . . . . . . . . . . . . . . . . . . 16
6. Monitoring of SRv6 Paths . . . . . . . . . . . . . . . . . . . 16
7. Security Considerations . . . . . . . . . . . . . . . . . . . 17
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
9.1. Normative References . . . . . . . . . . . . . . . . . . . 17
9.2. Informative References . . . . . . . . . . . . . . . . . . 18
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20
Ali, et al. Expires August 30, 2018 [Page 2]
Internet-Draft OAM for SRv6 February 26, 2018
1. Introduction
This document describes mechanisms for Operations, Administrations,
and Maintenance (OAM) in Segment Routing using IPv6 data plane (SRv6)
networks.
Additional mechanisms will be added in a future revision of the
document.
2. Conventions Used in This Document
2.1. Abbreviations
ECMP: Equal Cost Multi-Path.
SID: Segment ID.
SL: Segment Left.
SR: Segment Routing.
SRH: Segment Routing Header.
SRv6: Segment Routing with IPv6 Data plane.
TC: Traffic Class.
UCMP: Unequal Cost Multi-Path.
2.2. Terminology and Reference Topology
In this document, the simple topology shown in Figure 1 is used for
illustration.
--------
+------------------------| N100 |------------------------+
| -------- |
| |
====== link1====== link3------ link5====== link9------
||N1||======||N2||======| N3 |======||N4||======| N5 |
|| ||------|| ||------| |------|| ||------| |
====== link2====== link4------ link6======link10------
| |
| ------ |
+--------| N6 |--------+
link7 | | link8
------
Ali, et al. Expires August 30, 2018 [Page 3]
Internet-Draft OAM for SRv6 February 26, 2018
Figure 1: Reference Topology
In the reference topology:
Nodes N1, N2, and N4 are SRv6 capable nodes.
Nodes N3, N5 and N6 are classic IPv6 nodes.
Node 100 is a controller.
Node Nk has a classic IPv6 loopback address Bk::/128
Node Nk has Ak::/48 for its local SID space from which Local SIDs are
explicitly allocated.
The IPv6 address of the nth Link between node X and Y at the X side
is represented as 2001:DB8:X:Y:Xn::, e.g., the IPv6 address of link6
(the 2nd link) between N3 and N4 at N3 in Figure 1 is
2001:DB8:3:4:32::. Similarly, the IPv6 address of link5 (the 1st
link between N3 and N4) at node 3 is 2001:DB8:3:4:31::.
Ak::0 is explicitly allocated as the END function at Node k.
Ak::Cij is explicitly allocated as the END.X function at node k
towards neighbor node i via jth Link between node i and node j. e.g.,
A2::C31 represents END.X at N2 towards N3 via link3 (the 1st link
between N2 and N3). Similarly, A4::C52 represents the END.X at N4
towards N5 via link10.
<S1, S2, S3> represents a SID list where S1 is the first SID and S3
is the last SID. (S3, S2, S1; SL) represents the same SID list but
encoded in the SRH format where the rightmost SID (S1) in the SRH is
the first SID and the leftmost SID (S3) in the SRH is the last SID.
(SA, DA) (S3, S2, S1; SL) represents an IPv6 packet, SA is the IPv6
Source Address, DA the IPv6 Destination Address, (S3, S2, S1; SL) is
the SRH header that includes the SID list <S1, S2, S3>.
SR policy is defined in Section 3 of
[I-D.spring-segment-routing-policy].
3. OAM Mechanisms
This section describes how ping and traceroute mechanisms can be used
in an SRv6 network. Additional OAM mechanisms will be added in a
future revision of the document.
Ali, et al. Expires August 30, 2018 [Page 4]
Internet-Draft OAM for SRv6 February 26, 2018
3.1. Ping
[RFC4443] describes Internet Control Message Protocol for IPv6
(ICMPv6) that is used by IPv6 devices for network diagnostic and
error reporting purposes. As Segment Routing with IPv6 data plane
(SRv6) simply adds a new type of Routing Extension Header, existing
ICMPv6 mechanisms can be used in an SRv6 network. This section
describes the applicability of ICMPv6 in the SRv6 network and how the
existing ICMPv6 mechanisms can be used for providing OAM
functionality.
Throughout this document, unless otherwise specified, the acronym
ICMPv6 refers to multi-part ICMPv6 messages [RFC4884]. The document
does not propose any changes to the standard ICMPv6 [RFC4443],
[RFC4884] or standard ICMPv4 [RFC792].
There is no hardware or software change required for ping operation
at the classic IPv6 nodes in an SRv6 network. This includes the
classic IPv6 node with ingress, egress or transit roles.
Furthermore, no protocol changes are required to the standard ICMPv6
[RFC4443], [RFC4884] or standard ICMPv4 [RFC792]. In other words,
existing ICMP ping mechanisms work seamlessly in SRv6 networks.
The following subsections outline some use cases of the ICMP ping in
SRv6 networks.
3.1.1. Classic Ping
The existing mechanism to ping a remote IP prefix, along the shortest
path, continues to work without any modification. The initiator may
be an SRv6 node or a classic IPv6 node. Similarly, the egress or
transit may be an SRv6 capable node or a classic IPv6 node.
If an SRv6 capable ingress node wants to ping an IPv6 prefix via an
arbitrary segment list <S1, S2, S3>, it needs to initiate ICMPv6 ping
with an SR header containing the SID list <S1, S2, S3>. This is
illustrated using the topology in Figure 1. Assume all the links
have IGP metric 10 except both links between node N2 and node N3,
which have IGP metric set to 100. User issues a ping from node N1 to
a loopback of node N5, via via segment list <A2::C31, A4::C52>.
Figure 2 contains sample output for a ping request initiated at node
N1 to the loopback address of node N5 via a segment list <A2::C31,
A4::C52>.
> ping B5:: via segment-list A2::C31, A4::C52
Sending 5, 100-byte ICMP Echos to B5::, timeout is 2 seconds:
Ali, et al. Expires August 30, 2018 [Page 5]
Internet-Draft OAM for SRv6 February 26, 2018
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 0.625
/0.749/0.931 ms
Figure 2: A sample ping output at an SRv6 capable node
All transit nodes process the echo request message like any other
data packet carrying SR header and hence do not require any change.
Similarly, the egress node (IPv6 classic or SRv6 capable) does not
require any change to process the ICMPv6 echo request. For example,
in the ping example of Figure 2:
o Node N1 initiates an ICMPv6 ping packet with SRH as follows
(B1::,A2::C31)(B1::, A4::C52, A2::C31, SL=2, NH: ICMPv6)(ICMPv6
Echo Request).
o Node N2, which is an SRv6 capable node, performs the standard SRH
processing. Specifically, it executes the END.X function
(A2::C31) on the echo request packet.
o Node N3, which is a classic IPv6 node, performs the standard IPv6
processing. Specifically, it forwards the echo request based on
DA A4::C52 in the IPv6 header.
o Node N4, which is an SRv6 capable node, performs the standard SRH
processing. Specifically, it observes the END.X function
(A4::C52) with PSP (Penultimate Segment Popping) on the echo
request packet and removes the SRH and forwards the packet across
link10 to N5.
o The echo request packet at N5 arrives as an IPv6 packet without a
SRH. Node N5, which is a classic IPv6 node, performs the standard
IPv6/ICMPv6 processing on the echo request and responds,
accordingly.
3.1.2. Pinging SID Function
The classic ping described in the previous section cannot be used to
ping a remote SID function, as explained using an example in the
following.
Consider the case where the user wants to ping the remote SID
function A4::C52, via A2::C31, from node N1. Node N1 constructs the
ping packet (B1::0, A2::C31)( A4::C52, A2::C31,
SL=1;NH=ICMPv6)(ICMPv6 Echo Request). When the node N4 receives the
ICMPv6 echo request with DA set to A4::C52 and next header set to
ICMPv6, it silently drops it (as per
[I-D.filsfils-spring-srv6-network-programming]). To solve this
Ali, et al. Expires August 30, 2018 [Page 6]
Internet-Draft OAM for SRv6 February 26, 2018
problem, the initiator needs to mark the ICMPv6 echo request as an
OAM packet.
The OAM packets are identified either by setting the O-bit in SRH
[I-D.6man-segment-routing-header] or by inserting the SID Function
END.OTP at an appropriate place in the SRH
[I-D.filsfils-spring-srv6-network-programming].
In an SRv6 network, the user can exercise two flavors of the ping:
end-to-end ping or segment-by-segment ping, as outlined in the
following.
3.1.2.1. End-to-end Ping Using END.OTP
Consider the same example where the user wants to ping a remote SID
function A4::C52 , via A2::C31, from node N1. To force a punt of the
ICMPv6 echo request at the node N4, node N1 inserts the SID function
END.OTP just before the target SID A4::C52 in the SRH. The ICMPv6
echo request is processed at the individual nodes along the path as
follows:
o Node N1 initiates an ICMPv6 ping packet with SRH as follows
(B1::0, A2::C31)(A4::C52, A4::OTP, A2::C31; SL=2;
NH=ICMPv6)(ICMPv6 Echo Request).
o Node N2, which is an SRv6 capable node, performs the standard SRH
processing. Specifically, it executes the END.X function
(A2::C31) on the echo request packet.
o Node N3 receives the packet as follows (B1::0, A4::OTP)(A4::C52,
A4::OTP, A2::C31 ; SL=1; NH=ICMPv6)(ICMPv6 Echo Request). Node
N3, which is a classic IPv6 node, performs the standard IPv6
processing. Specifically, it forwards the echo request based on
DA A4::OTP in the IPv6 header.
o When node N4 receives the packet (B1::0, A4::OTP)(A4::C52,A4::OTP,
A2::C31 ; SL=1; NH=ICMPv6)(ICMPv6 Echo Request), it processes the
SID Function END.OTP, as described in the pseudocode in
[I-D.filsfils-spring-srv6-network-programming]. The packet gets
punted to the ICMPv6 process for processing. The ICMPv6 process
checks if the next SID in SRH (the target SID A4::C52) is locally
programmed.
o If the target SID is not locally programmed, N4 responses with the
ICMPv6 message (Type: "SRv6 OAM (TBA1 by IANA)", Code: "SID not
locally implemented (TBA2 by IANA)"); otherwise a success is
returned.
Ali, et al. Expires August 30, 2018 [Page 7]
Internet-Draft OAM for SRv6 February 26, 2018
3.1.2.2. Segment-by-segment Ping Using O-bit (Proof of Transit)
Consider the same example where the user wants to ping a remote SID
function A4::C52 , via A2::C31, from node N1. However, in this ping,
the node N1 wants to get a response from each segment node in the
SRH. In other words, in the segment-by-segment ping case, the node
N1 expects a response from node N2 and node N4 for their respective
local SID function.
To force a punt of the ICMPv6 echo request at node N2 and node N4,
node N1 sets the O-bit in SRH [I-D.6man-segment-routing-header]. The
ICMPv6 echo request is processed at the individual nodes along the
path as follows:
o Node N1 initiates an ICMPv6 ping packet with SRH as follows
(B1::0, A2::C31)(A4::C52, A2::C31; SL=1, Flags.O=1;
NH=ICMPv6)(ICMPv6 Echo Request).
o When node N2 receives the packet (B1::0, A2::C31)(A4::C52,
A2::C31; SL=1, Flags.O=1; NH=ICMPv6)(ICMPv6 Echo Request) packet,
it processes the O-bit in SRH, as described in the pseudo code in
[I-D.filsfils-spring-srv6-network-programming]. A time-stamped
copy of the packet is punted to the ICMPv6 process in control
plane for processing. Node N2 continues to apply the A2::C31 SID
function on the original packet and forwards it, accordingly. Due
to SRH.Flags.O=1, Node N2 also disables the PSP behaviour, i.e.,
does not remove the SRH. The ICMPv6 process at node N2 checks if
its local SID (A2::C31) is locally programmed or not and responds
to the ICMPv6 Echo Request.
o If the target SID is not locally programmed, N4 responses with the
ICMPv6 message (Type: "SRv6 OAM (TBA1 by IANA)", Code: "SID not
locally implemented (TBA2 by IANA)"); otherwise a success is
returned. Note that, as mentioned in
[I-D.filsfils-spring-srv6-network-programming], if node N2 does
not support the O-bit, it simply ignores it and process the local
SID, A2::C31.
o Node N3, which is a classic IPv6 node, performs standard IPv6
processing. Specifically, it forwards the echo request based on
DA A4::C52 in the IPv6 header.
o When node N4 receives the packet (B1::0, A4::C52)(A4::C52,
A2::C31; SL=0, Flags.O=1; NH=ICMPv6)(ICMPv6 Echo Request), it
processes the O-bit in SRH, as described in the pseudo code in
[I-D.filsfils-spring-srv6-network-programming]. A time-stamped
copy of the packet is punted to the ICMPv6 process in control
plane for processing. The ICMPv6 process at node N4 checks if its
Ali, et al. Expires August 30, 2018 [Page 8]
Internet-Draft OAM for SRv6 February 26, 2018
local SID (A2::C31) is locally programmed or not and responds to
the ICMPv6 Echo Request.
If the target SID is not locally programmed, N4 responses with the
ICMPv6 message (Type: "SRv6 OAM (TBA1 by IANA)", Code: "SID not
locally implemented (TBA2 by IANA)"); otherwise a success is
returned.
Support for O-bit is part of node capability advertisement. This
enables node N1 to know which segment nodes are capable of responding
to the ICMPv6 echo request. Node N1 processes the echo responses and
presents the data to the user, accordingly.
Please note that segment-by-segment ping described in this Section
can be used to address proof of transit use-case.
3.2. Error Reporting
Any IPv6 node can use ICMPv6 control messages to report packet
processing errors to the source that originated the datagram packet.
To name a few such scenarios:
- If the router receives an undeliverable IP datagram, or
- If the router receives a packet with a Hop Limit of zero, or
- If the router receives a packet such that if the router decrements
the packet's Hop Limit it becomes zero, or
- If the router receives a packet with problem with a field in the
IPv6 header or the extension headers such that it cannot complete
processing the packet, or
- If the router cannot forward a packet because the packet is larger
than the MTU of the outgoing link.
In the scenarios listed above, the ICMPv6 response also contains the
IP header, IP extension headers and leading payload octets of the
"original datagram" to which the ICMPv6 message is a response.
Specifically, the "Destination Unreachable Message", "Time Exceeded
Message", "Packet Too Big Message" and "Parameter Problem Message"
ICMPV6 messages can contain as much of the invoking packet as
possible without the ICMPv6 packet exceeding the minimum IPv6 MTU
[RFC4443], [RFC4884]. In an SRv6 network, the copy of the invoking
packet contains the SR header. The packet originator can use this
information for diagnostic purposes. For example, traceroute can use
this information as detailed in the following.
Ali, et al. Expires August 30, 2018 [Page 9]
Internet-Draft OAM for SRv6 February 26, 2018
3.3. Traceroute
There is no hardware or software change required for traceroute
operation at the classic IPv6 nodes in an SRv6 network. That
includes the classic IPv6 node with ingress, egress or transit roles.
Furthermore, no protocol changes are required to the standard
traceroute operations. In other words, existing traceroute
mechanisms work seamlessly in the SRv6 networks.
The following subsections outline some use cases of the traceroute in
the SRv6 networks.
3.3.1. Classic Traceroute
The existing mechanism to traceroute a remote IP prefix, along the
shortest path, continues to work without any modification. The
initiator may be an SRv6 node or a classic IPv6 node. Similarly, the
egress or transit node may be an SRv6 node or a classic IPv6 node.
If an SRv6 capable ingress node wants to traceroute to IPv6 prefix
via an arbitrary segment list <S1, S2, S3>, it needs to initiate
traceroute probe with an SR header containing the SID list <S1, S2,
S3>. This is illustrated using the topology in Figure 1. Assume all
the links have IGP metric 10 except both links between node N2 and
node N3, which have IGP metric set to 100. User issues a traceroute
from node N1 to a loopback of node N5, via segment list <A2::C31,
A4::C52>. Figure 3 contains sample output for the traceroute
request.
> traceroute B5:: via segment-list A2::C31, A4::C52
Tracing the route to B5::
1 2001:DB8:1:2:21:: 0.512 msec 0.425 msec 0.374 msec
SRH: (B5::, A4::C52, A2::C31, SL=2)
2 2001:DB8:2:3:31:: 0.721 msec 0.810 msec 0.795 msec
SRH: (B5::, A4::C52, A2::C31, SL=1)
3 2001:DB8:3:4:41:: 0.921 msec 0.816 msec 0.759 msec
SRH: (B5::, A4::C52, A2::C31, SL=1)
4 2001:DB8:4:5:52:: 0.879 msec 0.916 msec 1.024 msec
Figure 3: A sample traceroute output at an SRv6 capable node
Please note that information for hop2 is returned by N3, which is a
classic IPv6 node. Nonetheless, the ingress node is able to display
Ali, et al. Expires August 30, 2018 [Page 10]
Internet-Draft OAM for SRv6 February 26, 2018
SR header contents as the packet travels through the IPv6 classic
node. This is because the "Time Exceeded Message" ICMPv6 message can
contain as much of the invoking packet as possible without the ICMPv6
packet exceeding the minimum IPv6 MTU [RFC4443]. The SR header is
also included in these ICMPv6 messages initiated by the classic IPv6
transit nodes that are not running SRv6 software. Specifically, a
node generating ICMPv6 message containing a copy of the invoking
packet does not need to understand the extension header(s) in the
invoking packet.
The segment list information returned for hop1 is returned by N2,
which is an SRv6 capable node. Just like for hop2, the ingress node
is able to display SR header contents for hop1.
There is no difference in processing of the traceroute probe at an
IPv6 classic node and an SRv6 capable node. Similarly, both IPv6
classic and SRv6 capable nodes use the address of the interface on
which probe was received as the source address in the ICMPv6
response. ICMP extensions defined in [RFC5837] can be used to also
display information about the IP interface through which the datagram
would have been forwarded had it been forwardable, and the IP next
hop to which the datagram would have been forwarded, the IP interface
upon which a datagram arrived, the sub-IP component of an IP
interface upon which a datagram arrived.
The information about the IP address of the incoming interface on
which the traceroute probe was received by the reporting node is very
useful. This information can also be used to verify if SID functions
A2::C31 and A4::C52 are executed correctly by N2 and N4,
respectively. Specifically, the information displayed for hop2
contains the incoming interface address 2001:DB8:2:3::31 at N3. This
matches with the expected interface bound to END.X function A2::C31
(link3). Similarly, the information displayed for hop5 contains the
incoming interface address 2001:DB8:4:5::52 at N5. This matches with
the expected interface bound to the END.X function A4::C52 (link10).
3.3.2. Traceroute to a SID Function
The classic traceroute described in the previous Section cannot be
used to traceroute a remote SID function, as explained using an
example as follows.
Consider the case where the user wants to traceroute the remote SID
function A4::C52, via A2::C31, from node N1. Node N1 constructs the
traceroute packet (B1::0, A2::C31, HC=1) (A4::C52, A2::C31, SL=1;
NH=UDP) (traceroute probe). Even though Hop Count of the packet is
set to 1, when the node N4 receives the traceroute probe with DA set
to A4::C52 and next header set to UDP, it silently drops it (as per
Ali, et al. Expires August 30, 2018 [Page 11]
Internet-Draft OAM for SRv6 February 26, 2018
[I-D.filsfils-spring-srv6-network-programming]). To solve this
problem, the initiator node needs to mark the traceroute probe as an
OAM packet.
The OAM packets are identified either by setting the O-bit in SRH
[I-D.6man-segment-routing-header] or by inserting the SID Function
END.OTP at an appropriate place in the SRH
[I-D.filsfils-spring-srv6-network-programming].
In SRv6 networks, the user can exercise two flavors of the
traceroute: hop-by-hop traceroute or overlay traceroute.
o In hop-by-hop traceroute, user gets responses from all nodes
including classic IPv6 transit nodes, SRv6 capable transit nodes
as well as SRv6 capable segment endpoints. E.g., consider the
example where the user wants to traceroute to a remote SID
function A4::C52, via A2::C31, from node N1. The traceroute
output will also display information about node N3, which is a
transit (underlay) node.
o The overlay traceroute, on the other hand, does not trace the
underlay nodes. In other words, the overlay traceroute only
displays the nodes that acts as SRv6 segments along the route.
I.e., in the example where the user wants to traceroute to a
remote SID function A4::C52, via A2::C31, from node N1, the
overlay traceroute would only display the traceroute information
from node N2 and node N4 and will not display information from
node N3.
3.3.2.1. Hop-by-hop Traceroute Using END.OTP
In this Section, hop-by-hop traceroute to a SID function is
exemplified using UDP probes. However, the procedure is equally
applicable to other implementation of traceroute mechanism.
Consider the same example where the user wants to traceroute to a
remote SID function A4::C52 , via A2::C31, from node N1. To force a
punt of the traceroute probe only at the node N4, node N1 inserts the
SID Function END.OTP just before the target SID A4::C52 in the SRH.
The traceroute probe is processed at the individual nodes along the
path as follows:
o Node N1 initiates a traceroute probe packet with a monotonically
increasing value of hop count and SRH as follows
(B1::0,A2::C31)(A4::C52, A4::OTP, A2::C31; SL=2;
NH=UDP)(Traceroute probe).
o When node N2 receives the packet with hop-count = 1, it processes
Ali, et al. Expires August 30, 2018 [Page 12]
Internet-Draft OAM for SRv6 February 26, 2018
the hop count expiry. Specifically, the node N2 responses with
the ICMPv6 message (Type: "Time Exceeded", Code: "Time to Live
exceeded in Transit").
o When Node N2 receives the packet with hop-count > 1, it performs
the standard SRH processing. Specifically, it executes the END.X
function (A2::C31) on the traceroute probe.
o When node N3, which is a classic IPv6 node, receives the packet
(B1::0, A4::OTP)(A4::C52, A4::OTP, A2::C31 ; HC=1, SL=1;
NH=UDP)(Traceroute probe) with hop-count = 1, it processes the hop
count expiry. Specifically, the node N3 responses with the ICMPv6
message (Type: "Time Exceeded", Code: "Time to Live exceeded in
Transit").
o When node N3, which is a classic IPv6 node, receives the packet
with hop-count > 1, it performs the standard IPv6 processing.
Specifically, it forwards the traceroute probe based on DA A4::OTP
in the IPv6 header.
o When node N4 receives the packet (B1::0, A4::OTP)(A4::C52,
A4::OTP, A2::C31 ; SL=1; HC=1, NH=UDP)(Traceroute probe), it
processes the SID Function END.OTP, as described in the pseudocode
in [I-D.filsfils-spring-srv6-network-programming]. The packet
gets punted to the traceroute process for processing. The
traceroute process checks if the next SID in SRH (the target SID
A4::C52) is locally programmed. If the target SID A4::C52 is
locally programmed, node N4 responses with the ICMPv6 message
(Type: Destination unreachable, Code: Port Unreachable). If the
target SID A4::C52 is not a local SID, node N4 silently drops the
traceroute probe.
Figure 4 displays a sample traceroute output for this example.
> traceroute srv6 A4::C52 via segment-list A2::C31
Tracing the route to SID function A4::C52
1 2001:DB8:1:2::21 0.512 msec 0.425 msec 0.374 msec SRH:
(A4::C52, A4::OTP, A2::C31; SL=2)
2 2001:DB8:2:3::31 0.721 msec 0.810 msec 0.795 msec SRH:
(A4::C52, A4::OTP, A2::C31; SL=1)
3 2001:DB8:3:4::41 0.921 msec 0.816 msec 0.759 msec SRH:
(A4::C52, A4::OTP, A2::C31; SL=1)
Figure 4: A sample output for hop-by-hop traceroute to a SID function
Ali, et al. Expires August 30, 2018 [Page 13]
Internet-Draft OAM for SRv6 February 26, 2018
3.3.2.2. Tracing SRv6 Overlay
The overlay traceroute does not trace the underlay nodes, i.e., only
displays the nodes that acts as SRv6 segments along the path. This
is achieved by setting the SRH.Flags.O bit.
In this section, overlay traceroute to a SID function is exemplified
using UDP probes. However, the procedure is equally applicable to
other implementation of traceroute mechanism.
Consider the same example where the user wants to traceroute to a
remote SID function A4::C52 , via A2::C31, from node N1.
o Node N1 initiates a traceroute probe with SRH as follows
(B1::0,A2::C31)(A4::C52, A2::C31; HC=64, SL=1, Flags.O=1;
NH=UDP)(Traceroute Probe). Please note that the hop-count is set
to 64 to skip the underlay nodes from tracing. The O-bit in SRH
is set to make the overlay nodes (nodes processing the SRH)
respond.
o When node N2 receives the packet (B1::0, A2::C31)(A4::C52,A2::C31;
SL=1, HC=64, Flags.O=1; NH=UDP)(Traceroute Probe), it processes
the O-bit in SRH, as described in the pseudocode in
[I-D.filsfils-spring-srv6-network-programming]. A time-stamped
copy of the packet gets punted to the traceroute process for
processing. Node N2 continues to apply the A2::C31 SID function on
the original packet and forwards it, accordingly. As
SRH.Flags.O=1, Node N2 also disables the PSP flavor, i.e., does
not remove the SRH. The traceroute process at node N2 checks if
its local SID (A2::C31) is locally programmed. If the SID is not
locally programmed, it silently drops the packet. Otherwise, it
performs the egress check by looking at the SL value in SRH.
o As SL is not equal to zero (i.e., it's not egress node), node N2
responses with the ICMPv6 message (Type: "SRv6 OAM (TBA1 by
IANA)", Code: "O-bit punt at Transit (TBA3 by IANA)"). Note that,
as mentioned in [I-D.filsfils-spring-srv6-network-programming], if
node N2 does not support the O-bit, it simply ignores it and
processes the local SID, A2::C31.
o When node N3 receives the packet (B1::0, A4::C52)(A4::C52,
A2::C31; SL=0, HC=63, Flags.O=1; NH=UDP)(Traceroute Probe),
performs the standard IPv6 processing. Specifically, it forwards
the traceroute probe based on DA A4::C52 in the IPv6 header.
Please note that there is no hop-count expiration at the transit
nodes.
o When node N4 receives the packet (B1::0, A4::C52)(A4::C52,A2::C31;
Ali, et al. Expires August 30, 2018 [Page 14]
Internet-Draft OAM for SRv6 February 26, 2018
SL=0, HC=62, Flags.O=1; NH=UDP)(Traceroute Probe), it processes
the O-bit in SRH, as described in the pseudocode in
[I-D.filsfils-spring-srv6-network-programming]. A time-stamped
copy of the packet gets punted to the traceroute process for
processing. The traceroute process at node N4 checks if its local
SID (A2::C31) is locally programmed. If the SID is not locally
programmed, it silently drops the packet. Otherwise, it performs
the egress check by looking at the SL value in SRH. As SL is
equal to zero (i.e., N4 is the egress node), node N4 tries to
consume the UDP probe. As UDP probe is set to access an invalid
port, the node N4 responses with the ICMPv6 message (Type:
Destination unreachable, Code: Port Unreachable).
Figure 5 displays a sample overlay traceroute output for this
example. Please note that the underlay node N3 does not appear in
the output.
> traceroute srv6 A4::C52 via segment-list A2::C31
Tracing the route to SID function A4::C52
1 2001:DB8:1:2::21 0.512 msec 0.425 msec 0.374 msec
SRH: (A4::C52, A4::OTP, A2::C31; SL=2)
2 2001:DB8:3:4::41 0.921 msec 0.816 msec 0.759 msec
SRH: (A4::C52, A4::OTP, A2::C31; SL=1)
Figure 5: A sample output for overlay traceroute to a SID function
4. In-situ OAM Applicability
[I-D.brockners-inband-oam-requirements] describes motivation and
requirements for In-situ OAM (iOAM). iOAM records operational and
telemetry information in the data packet while the packet traverses
the network of telemetry domain. iOAM complements out-of-band probe
based OAM mechanisms such ICMP ping and traceroute by directly
encoding tracing and the other kind of telemetry information to the
regular data traffic.
[I-D.brockners-inband-oam-transport] describes transport mechanisms
for iOAM data including IPv6 and Segment Routing traffic.
Furthermore, [I-D.brockners-inband-oam-data] defines information
encoding for iOAM data.
One of the application of iOAM is to perform inband traceroute. In
SRv6 network, iOAM traceroute feature can be used to trace the order
set of segment ID executed by SRv6 nodes for packet forwarding along
Ali, et al. Expires August 30, 2018 [Page 15]
Internet-Draft OAM for SRv6 February 26, 2018
the packet path. This is achieved by recording the node details that
the packet traversed in the packet header itself.
Another important application of iOAM is to perform delay measurement
in anycast server scenarios. Anycast server deployment is commonly
seen for redundancy and load balancing purpose. In SRv6 network,
iOAM can be used to collect the timestamp from different anycats
servers to measure the delay induced by each server within the
anycast cluster that helps to provide SLA constrained services.
One of the other applications of iOAM is to provide the Proof of
Transit (POT). Among other features of iOAM, SRv6 networks can use
the POT feature of iOAM to verify that all the function SIDs in SRH
have been executed before the packet is delivered to the destination.
It can also ensure that the order of execution of the SID function
has been consistent with the SRH contents.
More details on various applications of iOAM in SRv6 networks will be
included in future versions of this document.
5. Seamless BFD Applicability
[RFC7880] defines Seamless BFD (S-BFD) architecture that simplifies
BFD mechanism and enables it to perform path monitoring in a
controlled and scalable manner. [RFC7881] describes the procedure to
perform continuity check using S-BFD in different environments
including IPv6 networks. Section 5.1 of [RFC7881] explains the
SBFDInitiator specification and procedure to initiate S-BFD control
packet in IP and MPLS network. The specification described for
IP-routed S-BFD control packet is also directly applicable to the
SRv6 network.
S-BFD has a fast bootstrapping capability. Furthermore, in S-BFD,
only the ingress is required to keep BFD states; the egress and
transit node does not have any knowledge of the BFD session. These
attributes of S-BFD make it an excellent candidate for rapid failure
detection in the SRv6 network. More details on various S-BFD usage
on the SRv6 network will be included in a future version.
6. Monitoring of SRv6 Paths
In the recent past, network operators are interested in performing
network OAM functions in a centralized manner. Various data models
like YANG are available to collect data from the network and manage
it from a centralized entity.
The SR technology enables a centralized OAM entity to perform path
monitoring without control plane intervention on monitored nodes.
Ali, et al. Expires August 30, 2018 [Page 16]
Internet-Draft OAM for SRv6 February 26, 2018
[I-D.ietf-spring-oam-usecase] describes such centralized OAM
mechanism. Specifically, it describes a procedure that can be used
to perform path continuity check between any nodes within an SR
domain from a centralized monitoring system, with minimal or no
control plane intervention on the nodes. However, the document
focuses on SR networks with MPLS data plane. The same concept is
also applicable to the SRv6 networks. This document describes how
the concept can be used to perform path monitoring in an SRv6 network
as follows.
In the reference topology in Figure 1, N100 is the controller
implementing an END function A100::. In order to verify a segment
list <A2::C31, A4::C52>, N100 generates a probe packet with SRH set
to (A100::, A4::C52, A2::C31, SL=2). The controller routes the probe
packet towards the first segment, which is A2::C31. N2 performs the
standard SRH processing and forwards it over link3 with the DA of
IPv6 packet set to A4::C52. N4 also performs the normal SRH
processing and forwards it over link10 with the DA of IPv6 packet set
to A100::. This makes the probe packet loop back to the controller.
In our reference topology in Figure 1, N100 uses an IGP protocol like
OSPF or ISIS to get the topology view within the IGP domain. N100
can also use BGP-LS to get the complete view of an inter-domain
topology. In other words, the controller leverages the visibility of
the topology to monitor the paths between the various endpoints
without control plane intervention required at the monitored nodes.
7. Security Considerations
This document does not define any new protocol extensions and relies
on existing procedures defined for ICMP. This document does not
impose any additional security challenges to be considered beyond
security considerations described in [RFC4884], [RFC4443], [RFC792]
and RFCs that updates these RFCs.
8. IANA Considerations
This document requests IANA to allocate a new Type for ICMPv6 message
for "SRv6 OAM".
9. References
9.1. Normative References
[RFC792] J. Postel, "Internet Control Message Protocol", RFC 792,
September 1981.
[RFC4443] A. Conta, S. Deering, M. Gupta, Ed., "Internet Control
Ali, et al. Expires August 30, 2018 [Page 17]
Internet-Draft OAM for SRv6 February 26, 2018
Message Protocol (ICMPv6) for the Internet Protocol
Version 6 (IPv6) Specification", RFC 4443, March 2006.
[RFC4884] R. Bonica, D. Gan, D. Tappan, C. Pignataro, "Extended ICMP
to Support Multi-Part Messages", RFC 4884, April 2007.
[RFC5837] A. Atlas, Ed., R. Bonica, Ed., C. Pignataro, Ed., N. Shen,
JR. Rivers, "Extending ICMP for Interface and Next-Hop
Identification", RFC 5837, April 2010.
[RFC7880] C.Pignataro, D.Ward, N.Akiya, M.Bhatia, S.Pallagatti,
"Seamless Bidirectional Forwarding Detection (S-BFD)", RFC
7880, July 2016.
[RFC7881] C.Pignataro, D.Ward, N.Akiya, "Seamless Bidirectional
Forwarding Detection (S-BFD) for IPv4, IPv6, and MPLS",
RFC 7881 July 2016.
[I-D.filsfils-spring-srv6-network-programming] C. Filsfils, et al.,
"SRv6 Network Programming",
draft-filsfils-spring-srv6-network-programming, work in
progress.
[] Previdi, S., Filsfils, et al,
"IPv6 Segment Routing Header (SRH)",
draft-ietf-6man-segment-routing-header, work in progress.
9.2. Informative References
[I-D.ietf-spring-oam-usecase] A Scalable and Topology-Aware MPLS
Dataplane Monitoring System. R. Geib, C. Filsfils, C.
Pignataro, N. Kumar, draft-ietf-spring-oam-usecase, work
in progress.
[I-D.brockners-inband-oam-data] F. Brockners, et al., "Data Formats
for In-situ OAM", draft-brockners-inband-oam-data, work in
progress.
[I-D.brockners-inband-oam-transport] F.Brockners, at al.,
"Encapsulations for In-situ OAM Data",
draft-brockners-inband-oam-transport, work in progress.
[I-D.brockners-inband-oam-requirements] F.Brockners, et al.,
"Requirements for In-situ OAM",
draft-brockners-inband-oam-requirements, work in progress.
[I-D.spring-segment-routing-policy] Filsfils, C., et al., "Segment
Routing Policy for Traffic Engineering",
Ali, et al. Expires August 30, 2018 [Page 18]
Internet-Draft OAM for SRv6 February 26, 2018
draft-filsfils-spring-segment-routing-policy, work in
progress.
Ali, et al. Expires August 30, 2018 [Page 19]
Internet-Draft OAM for SRv6 February 26, 2018
10. Acknowledgments
To be added.
Authors' Addresses
Clarence Filsfils
Cisco Systems, Inc.
Email: cfilsfil@cisco.com
Zafar Ali
Cisco Systems, Inc.
Email: zali@cisco.com
Nagendra Kumar
Cisco Systems, Inc.
Email: naikumar@cisco.com
Carlos Pignataro
Cisco Systems, Inc.
Email: cpignata@cisco.com
Faisal Iqbal
Cisco Systems, Inc.
Email: faiqbal@cisco.com
Rakesh Gandhi
Cisco Systems, Inc.
Canada
Email: rgandhi@cisco.com
John Leddy
Comcast
Email: John_Leddy@cable.comcast.com
Robert Raszuk
Bloomberg LP
731 Lexington Ave
New York City, NY10022, USA
Email: robert@raszuk.net
Ali, et al. Expires August 30, 2018 [Page 20]
Internet-Draft OAM for SRv6 February 26, 2018
Satoru Matsushima
SoftBank
Japan
Email: satoru.matsushima@g.softbank.co.jp
Bart Peirens
Proximus
Email: bart.peirens@proximus.com
Gaurav Naik
Drexel University
United States of America
Email: gn@drexel.edu
Ali, et al. Expires August 30, 2018 [Page 21]