Internet DRAFT - draft-filsfils-spring-srv6-net-pgm-illustration
draft-filsfils-spring-srv6-net-pgm-illustration
SPRING C. Filsfils
Internet-Draft P. Camarillo, Ed.
Intended status: Informational Cisco Systems, Inc.
Expires: October 1, 2021 Z. Li
Huawei Technologies
S. Matsushima
SoftBank
B. Decraene
Orange
D. Steinberg
Lapishills Consulting Limited
D. Lebrun
Google
R. Raszuk
Bloomberg LP
J. Leddy
Individual Contributor
March 30, 2021
Illustrations for SRv6 Network Programming
draft-filsfils-spring-srv6-net-pgm-illustration-04
Abstract
This document illustrates how SRv6 Network Programming [RFC8986] can
be used to create interoperable and protected overlays with underlay
optimization and service programming.
Requirements Language
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 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
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 https://datatracker.ietf.org/drafts/current/.
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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."
This Internet-Draft will expire on October 1, 2021.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Illustration . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Simplified SID allocation . . . . . . . . . . . . . . . . 3
2.2. Reference diagram . . . . . . . . . . . . . . . . . . . . 4
2.3. Basic security . . . . . . . . . . . . . . . . . . . . . 4
2.4. SR-L3VPN . . . . . . . . . . . . . . . . . . . . . . . . 5
2.5. SR-Ethernet-VPWS . . . . . . . . . . . . . . . . . . . . 6
2.6. SR-EVPN-FXC . . . . . . . . . . . . . . . . . . . . . . . 7
2.7. SR-EVPN . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.7.1. EVPN Bridging . . . . . . . . . . . . . . . . . . . . 7
2.7.2. EVPN Multi-homing with ESI filtering . . . . . . . . 9
2.7.3. EVPN Layer-3 . . . . . . . . . . . . . . . . . . . . 11
2.7.4. EVPN Integrated Routing Bridging (IRB) . . . . . . . 11
2.8. SR TE for Underlay SLA . . . . . . . . . . . . . . . . . 12
2.8.1. SR policy from the Ingress PE . . . . . . . . . . . . 12
2.8.2. SR policy at a midpoint . . . . . . . . . . . . . . . 13
2.9. End-to-End policy with intermediate BSID . . . . . . . . 14
2.10. TI-LFA . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.11. SR TE for Service programming . . . . . . . . . . . . . . 16
3. Benefits . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.1. Seamless deployment . . . . . . . . . . . . . . . . . . . 18
3.2. Integration . . . . . . . . . . . . . . . . . . . . . . . 19
3.3. Security . . . . . . . . . . . . . . . . . . . . . . . . 19
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 19
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5. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 19
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
1. Introduction
Segment Routing leverages the source routing paradigm. An ingress
node steers a packet through a ordered list of instructions, called
segments. Each one of these instructions represents a function to be
called at a specific location in the network. A function is locally
defined on the node where it is executed and may range from simply
moving forward in the segment list to any complex user-defined
behavior. The network programming consists in combining segment
routing functions, both simple and complex, to achieve a networking
objective that goes beyond mere packet routing.
[RFC8986] defines the SRv6 Network Programming concept and the main
segment routing behaviors.
This document illustrates how these concepts can be used to enable
the creation of interoperable overlays with underlay optimization and
service programming.
The terminology for this document is defined in [RFC8986].
2. Illustration
We introduce a simplified SID allocation technique to ease the
reading of the text. We document the reference diagram. We then
illustrate the network programming concept through different use-
cases. These use-cases have been thought to allow straightforward
combination between each other.
2.1. Simplified SID allocation
To simplify the illustration, we assume:
2001:db8::/32 is an IPv6 block allocated by a RIR to the operator
2001:db8:0::/48 is dedicated to the internal address space
2001:db8:cccc::/48 is dedicated to the internal SRv6 SID space
We assume a location expressed in 64 bits and a function expressed
in 16 bits
Node k has a classic IPv6 loopback address 2001:db8::k/128 which
is advertised in the IGP
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Node k has 2001:db8:cccc:k::/64 for its local SID space. Its SIDs
will be explicitly assigned from that block
Node k advertises 2001:db8:cccc:k::/64 in its IGP
Function :1:: (function 1, for short) represents the End function
with PSP support
Function :C2:: (function C2, for short) represents the End.X
function towards neighbor 2
Each node k has:
An explicit SID instantiation 2001:db8:cccc:k:1::/128 bound to an
End function with additional support for PSP
An explicit SID instantiation 2001:db8:cccc:k:Cj::/128 bound to an
End.X function to neighbor J with additional support for PSP
2.2. Reference diagram
Let us assume the following topology where all the links have IGP
metric 10 except the link 3-4 which is 100.
Nodes A, B and 1 to 8 are considered within the network domain while
nodes CE-A, CE-B and CE-C are outside the domain.
CE-B
\
3------4---5
| \ /
| 6
| /
A--1--- 2------7---8--B
/ \
CE-A CE-C
Tenant100 Tenant100 with
IPv4 203.0.113.0/24
Figure 1: Reference topology
2.3. Basic security
Any edge node such as 1 would be configured with an ACL on any of its
external interface (e.g. from CE-A) which drops any traffic with SA
or DA in 2001:db8:cccc::/48. See SEC-1.
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Any core node such as 6 could be configured with an ACL with the
SEC-2 behavior "IF (DA == LocalSID) && (SA is not in 2001:db8:0::/48
or 2001:db8:cccc::/48) THEN drop".
SEC-3 protection is a default property of SRv6. A SID must be
explicitly instantiated. In our illustration, the only available
SIDs are those explicitly instantiated.
2.4. SR-L3VPN
Let us illustrate the SR-L3VPN use-case applied to IPv4.
Nodes 1 and 8 are configured with a tenant 100, each respectively
connected to CE-A and CE-C.
Node 8 is configured with a locally instantiated End.DT4 SID
2001:db8:cccc:8:D100:: bound to tenant IPv4 table 100.
Via BGP signaling or an SDN-based controller, Node 1's tenant-100
IPv4 table is programmed with an IPv4 SR-VPN route 203.0.113.0/24 via
SRv6 policy <2001:db8:cccc:8:D100::>.
When 1 receives a packet P from CE-A destined to 203.0.113.20, 1
looks up 203.0.113.20 in its tenant-100 IPv4 table and finds an SR-
VPN entry 203.0.113.0/24 via SRv6 policy <2001:db8:cccc:8:D100::>.
As a consequence, 1 pushes an outer IPv6 header with SA=2001:db8::1,
DA=2001:db8:cccc:8:D100:: and NH=4. 1 then forwards the resulting
packet on the shortest path to 2001:db8:cccc:8::/64.
When 8 receives the packet, 8 matches the DA in its "My SID Table",
finds the bound function End.DT4(100) and confirms NH=4. As a
result, 8 decaps the outer header, looks up the inner IPv4 DA in
tenant-100 IPv4 table, and forward the (inner) IPv4 packet towards
CE-C.
The reader can easily infer all the other SR-IPVPN instantiations:
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+---------------------------------+----------------------------------+
| Route at ingress PE(1) | SR-VPN Egress SID of egress PE(8)|
+---------------------------------+----------------------------------+
| IPv4 tenant route with egress | End.DT4 function bound to |
| tenant table lookup | IPv4-tenant-100 table |
+---------------------------------+----------------------------------+
| IPv4 tenant route without egress| End.DX4 function bound to |
| tenant table lookup | CE-C (IPv4) |
+---------------------------------+----------------------------------+
| IPv6 tenant route with egress | End.DT6 function bound to |
| tenant table lookup | IPv6-tenant-100 table |
+---------------------------------+----------------------------------+
| IPv6 tenant route without egress| End.DX6 function bound to |
| tenant table lookup | CE-C (IPv6) |
+---------------------------------+----------------------------------+
2.5. SR-Ethernet-VPWS
Let us illustrate the SR-Ethernet-VPWS use-case.
Node 8 is configured a locally instantiated End.DX2 SID
2001:db8:cccc:8:DC2C:: bound to local attachment circuit {ethernet
CE-C}.
Via BGP signalling or an SDN controller, node 1 is programmed with an
Ethernet VPWS service for its local attachment circuit {ethernet CE-
A} with remote endpoint 2001:db8:cccc:8:DC2C::.
When 1 receives a frame F from CE-A, node 1 pushes an outer IPv6
header with SA=2001:db8::1, DA=2001:db8:cccc:8:DC2C:: and NH=143.
Note that no additional header is pushed. 1 then forwards the
resulting packet on the shortest path to 2001:db8:cccc:8::/64.
When 8 receives the packet, 8 matches the DA in its "My SID Table"
and finds the bound function End.DX2. After confirming that next-
header=143, 8 decaps the outer IPv6 header and forwards the inner
Ethernet frame towards CE-C.
The reader can easily infer the Ethernet VPWS use-case:
+------------------------+-----------------------------------+
| Route at ingress PE(1) | SR-VPN Egress SID of egress PE(8) |
+------------------------+-----------------------------------+
| Ethernet VPWS | End.DX2 function bound to |
| | CE-C (Ethernet) |
+------------------------+-----------------------------------+
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2.6. SR-EVPN-FXC
Let us illustrate the SR-EVPN-FXC use-case (Flexible cross-connect
service).
Node 8 is configured with a locally instantiated End.DX2V SID
2001:db8:cccc:8:DC2C:: bound to the L2 table T1. Node 8 is also
configured with local attachment circuits {ethernet CE1-C VLAN:100}
and {ethernet CE2-C VLAN:200} in table T1.
Via an SDN controller or derived from a BGP-based sginalling, the
node 1 is programmed with an EVPN-FXC service for its local
attachment circuit {ethernet CE-A} with remote endpoint
2001:db8:cccc:8:DC2C::. For this purpose, the EVPN Type-1 route is
used.
When node 1 receives a frame F from CE-A, it pushes an outer IPv6
header with SA=2001:db8::1, DA=2001:db8:cccc:8:DC2C:: and NH=143.
Note that no additional header is pushed. Node 1 then forwards the
resulting packet on the shortest path to 2001:db8:cccc:8::/64.
When node 8 receives the packet, it matches the IP DA in its "My SID
Table" and finds the bound function End.DX2V. After confirming that
next-header=143, node 8 decaps the outer IPv6 header, performs a VLAN
loopkup in table T1 and forwards the inner Ethernet frame to matching
interface e.g. for VLAN 100, packet is forwarded to CE1-C and for
VLAN 200, frame is forwarded to CE2-C.
The reader can easily infer the Ethernet FXC use-case:
+---------------------------------+------------------------------------+
| Route at ingress PE (1) | SR-VPN Egress SID of egress PE (8) |
+---------------------------------+------------------------------------+
| EVPN-FXC | End.DX2V function bound to |
| | CE1-C / CE2-C (Ethernet) |
+---------------------------------+------------------------------------+
2.7. SR-EVPN
The following section details some of the particular use-cases of SR-
EVPN. In particular bridging (unicast and multicast), multi-homing
ESI filtering, L3 EVPN and EVPN-IRB.
2.7.1. EVPN Bridging
Let us illustrate the SR-EVPN unicast and multicast bridging.
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Nodes 1, 3 and 8 are configured with a EVPN bridging service (E-LAN
service).
Node 1 is configured with a locally instantiated End.DT2U SID
2001:db8:cccc:1:D2AA:: bound to a local L2 table T1 where EVPN is
enabled. This SID will be used to attract unicast traffic.
Additionally, Node 1 is configured with a locally instantiated
End.DT2M SID 2001:db8:cccc:1:D2AF:: bound to the same local L2 table
T1. This SID will be used to attract multicast traffic. Node 1 is
also configured with local attachment circuit {ethernet CE-A
VLAN:100} associated to table T1.
A similar instantiation is done at Node 3 and Node 8 resulting in:
- Node 1 - My SID table:
- End.DT2U SID: 2001:db8:cccc:1:D2AA:: table T1
- End.DT2M SID: 2001:db8:cccc:1:D2AF:: table T1
- Node 3 - My SID table:
- End.DT2U SID: 2001:db8:cccc:3:D2BA:: table T3
- End.DT2M SID: 2001:db8:cccc:3:D2BF:: table T3
- Node 8 - My SID table:
- End.DT2U SID: 2001:db8:cccc:8:D2CA:: table T8
- End.DT2M SID: 2001:db8:cccc:8:D2CB:: table T8
Nodes 1, 4 and 8 are going to exchange the End.DT2M SIDs via BGP-
based EVPN Type-3 route. Upon reception of the EVPN Type-3 routes,
each node build its own replication list per L2 table that will be
used for ingress BUM traffic replication. The replication lists are
the following:
- Node 1 - replication list: {2001:db8:cccc:3:D2BF:: and
2001:db8:cccc:8:D2CF::}
- Node 3 - replication list: {2001:db8:cccc:1:D2AF:: and
2001:db8:cccc:8:D2CF::}
- Node 8 - replication list: {2001:db8:cccc:1:D2AF:: and
2001:db8:cccc:3:D2CF::}
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When node 1 receives a BUM frame F from CE-A, it replicates that
frame to every node in the replication list. For node 3, it pushes
an outer IPv6 header with SA=2001:db8::1, DA=2001:db8:cccc:3:D2BF::
and NH=143. For node 8, it performs the same operation but
DA=2001:db8:cccc:8:D2CF::. Note that no additional headers are
pushed. Node 1 then forwards the resulting packets on the shortest
path for each destination.
When node 3 receives the packet, it matches the DA in its "My SID
Table" and finds the bound function End.DT2M with its related layer2
table T3. After confirming that next-header=143, node 3 decaps the
outer IPv6 header and forwards the inner Ethernet frame to all
layer-2 output interface found in table T3. Similar processing is
also performed by node 8 upon packet reception. This example is the
same for any BUM stream coming from CE-B or CE-C.
Node 1,3 and 8 are also performing software MAC learning to exchange
MAC reachability information (unicast traffic) via BGP among
themselves.
Each MAC being learnt is exchanged using BGP-based EVPN Type-2 route.
When node 1 receives an unicast frame F from CE-A, it learns its MAC-
SA=CEA in software. Node 1 transmits that MAC and its associated SID
2001:db8:cccc:1:D2AA:: using BGP-based EVPN route-type 2 to all
remote nodes.
When node 3 receives an unicast frame F from CE-B destinated to MAC-
DA=CEA, it performs a L2 lookup on T3 to find the associated SID. It
pushes an outer IPv6 header with SA=2001:db8::3,
DA=2001:db8:cccc:1:D2AA:: and NH=143. Node 3 then forwards the
resulting packet on the shortest path to 2001:db8:cccc:1::/64.
Similar processing is also performed by node 8.
2.7.2. EVPN Multi-homing with ESI filtering
In L2 network, support for traffic loop avoidance is mandatory. In
EVPN all-active multi-homing scenario enforces that requirement using
ESI filtering. Let us illustrate how it works:
Nodes 3 and 4 are peering partners of a redundancy group where the
access CE-B, is connected in an all-active multi-homing way with
these two nodes. Hence, the topology is the following:
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CE-B
/ \
3------4---5
| \ /
| 6
| /
A--1--- 2------7---8--B
/ \
CE-A CE-C
Tenant100 Tenant100 with
IPv4 203.0.113.0/24
EVPN ESI filtering - Reference topology
Nodes 3 and 4 are configured with an EVPN bridging service (E-LAN
service).
Node 3 is configured with a locally instantiated End.DT2M SID
2001:db8:cccc:3:D2BF:: bound to a local L2 table T1 where EVPN is
enabled. This SID is also configured with the optional argument
Arg.FE2 that specifies the attachment circuit. Particularly, node 3
assigns identifier 0xC1 to {ethernet CE-B}.
Node 4 is configured with a locally instantiated End.DT2M SID
2001:db8:cccc:4:D2BF:: bound to a local L2 table T1 where EVPN is
enabled. This SID is also configured with the optional argument
Arg.FE2 that specifies the attachment circuit. Particularly, node 4
assigns identifier 0xC2 to {ethernet CE-B}.
Both End.DT2M SIDs are exchanged between nodes via BGP-based EVPN
Type-3 routes. Upon reception of EVPN Type-3 routes, each node build
its own replication list per L2 table T1.
On the other hand, the End.DT2M SID arguments (Arg.F2) are exchanged
between nodes via SRv6 VPN SID attached to the BGP-based EVPN Type-1
route. The BGP ESI-filtering extended community label is set to
implicit-null [I-D.ietf-bess-srv6-services].
Upon reception of EVPN Type-1 route and Type-3 route, node 3 merges
merges the End.DT2M SID (2001:db8:cccc:4:D2BF:) with the
Arg.FE2(0:0:0:C2::) from node 4 (its peering partner). This is done
by a simple OR bitwise operation. As a result, the replication list
on node 3 for the PEs 1,4 and 8 is: {2001:db8:cccc:1:D2AF::;
2001:db8:cccc:4:D2BF:C2::; 2001:db8:cccc:8:D2CF::}.
In a similar manner, the replication list on node 4 for the PEs 1,3
and 8 is: {2001:db8:cccc:1:D2AF::; 2001:db8:cccc:3:D2BF:C1::;
2001:db8:cccc:8:D2CF::}. Note that in this case the SID for PE3
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contains the OR bitwise operation of SIDs 2001:db8:cccc:3:D2BF:: and
0:0:0:C1::.
When node 3 receives a BUM frame F from CE-B, it replicates that
frame to remote PEs. For node 4, it pushes an outer IPv6 header with
SA=2001:db8::3, DA=2001:db8:cccc:4:D2BF:C2:: and NH=143. Note that
no additional header is pushed. Node 3 then forwards the resulting
packet on the shortest path to node 4, and once the packet arrives to
node 4, the End.DT2M function is executed forwarding to all L2 OIFs
except the ones corresponding to identifier 0xC2.
2.7.3. EVPN Layer-3
EVPN layer-3 works exactly in the same way than L3VPN. Please refer
to section Section 2.4
2.7.4. EVPN Integrated Routing Bridging (IRB)
EVPN IRB brings Layer-2 and Layer-3 together. It uses BGP-based EVPN
Type-2 route to achieve Layer-2 intra-subnet and Layer-3 inter-subnet
forwarding. The EVPN Type-2 route-2 maintains the MAC/IP
association.
Node 8 is configured with a locally instantiated End.DT2U SID
2001:db8:cccc:8:D2C:: used for unicast L2 traffic. Node 8 is also
configured with locally instantiated End.DT4 SID
2001:db8:cccc:8:D100:: bound to IPv4 tenant table 100.
Node 1 is going to be configured with the EVPN IRB service.
Node 8 signals to other remote PEs (1, 3) each ARP/ND request learned
via BGP-based EVPN Type-2 route. For example, when node 8 receives
an ARP/ND packet P from a host (203.0.113.20) on CE-C destined to
192.0.2.10, it learns its MAC-SA=CEC in software. It also learns the
ARP/ND entry (IP SA=203.0.113.20) in its cache. Node 8 transmits
that MAC/IP and its associated L3 SID (2001:db8:cccc:8:D100::) and L2
SID (2001:db8:cccc:8:D2C::).
When node 1 receives a packet P from CE-A destined to 203.0.113.20
from a host (192.0.2.10), node 1 looks up its tenant-100 IPv4 table
and finds an SR-VPN entry for that prefix. As a consequence, node 1
pushes an outer IPv6 header with SA=2001:db8::1,
DA=2001:db8:cccc:8:D100:: and NH=4. Node 1 then forwards the
resulting packet on the shortest path to 2001:db8:cccc:8::/64. EVPN
inter-subnet forwarding is then achieved.
When node 1 receives a packet P from CE-A destined to 203.0.113.20
from a host (192.0.2.11), P looks up its L2 table T1 MAC-DA lookup to
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find the associated SID. It pushes an outer IPv6 header with
SA=2001:db8::1, DA=2001:db8:cccc:8:D2C:: and NH=143. Note that no
additional header is pushed. Node 8 then forwards the resulting
packet on the shortest path to 2001:db8:cccc:8::/64. EVPN intra-
subnet forwarding is then achieved.
2.8. SR TE for Underlay SLA
2.8.1. SR policy from the Ingress PE
Let's assume that node 1's tenant-100 IPv4 route "203.0.113.0/24 via
2001:db8:cccc:8:D100::" is programmed with a color/community that
requires low-latency underlay optimization
[I-D.ietf-spring-segment-routing-policy].
In such case, node 1 either computes the low-latency path to the
egress node itself or delegates the computation to a PCE.
In either case, the location of the egress PE can easily be found by
looking for who originates the locator comprising the SID
2001:db8:cccc:8:D100::. This can be found in the IGP's LSDB for a
single domain case, and in the BGP-LS LSDB for a multi-domain case.
Let us assume that the TE metric encodes the per-link propagation
latency. Let us assume that all the links have a TE metric of 10,
except link 27 which has TE metric 100.
The low-latency path from 1 to 8 is thus 1234678.
This path is encoded in a SID list as: first a hop through
2001:db8:cccc:3:C4:: and then a hop to 8.
As a consequence the SR-VPN entry 203.0.113.0/24 installed in the
Node1's Tenant-100 IPv4 table is: H.Encaps with SRv6 Policy
<2001:db8:cccc:3:C4::, 2001:db8:cccc:8:D100::>.
When 1 receives a packet P from CE-A destined to 203.0.113.20, P
looks up its tenant-100 IPv4 table and finds an SR-VPN entry
203.0.113.0/24. As a consequence, 1 pushes an outer header with
SA=2001:db8::1, DA=2001:db8:cccc:3:C4::, NH=SRH followed by SRH
(2001:db8:cccc:8:D100::, 2001:db8:cccc:3:C4::; SL=1; NH=4). 1 then
forwards the resulting packet on the interface to 2.
2 forwards to 3 along the path to 2001:db8:cccc:3::/64.
When 3 receives the packet, 3 matches the DA in its "My SID Table"
and finds the bound function End.X to neighbor 4. 3 notes the PSP
capability of the SID 2001:db8:cccc:3:C4::. 3 sets the DA to the next
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SID 2001:db8:cccc:8:D100::. As 3 is the penultimate segment hop, it
performs PSP and pops the SRH. 3 forwards the resulting packet to 4.
4, 6 and 7 forwards along the path to 2001:db8:cccc:8::/64.
When 8 receives the packet, 8 matches the DA in its "My SID Table"
and finds the bound function End.DT(100). As a result, 8 decaps the
outer header, looks up the inner IPv4 DA (203.0.113.20) in tenant-100
IPv4 table, and forward the (inner) IPv4 packet towards CE-B.
2.8.2. SR policy at a midpoint
Let us analyze a policy applied at a midpoint on a packet without
SRH.
Packet P1 is (2001:db8::1, 2001:db8:cccc:8:D100::).
Let us consider P1 when it is received by node 2 and let us assume
that that node 2 is configured to steer 2001:db8:cccc:8::/64 in a
H.Insert.Red behavior associated with SR policy
<2001:db8:cccc:3:C4::>.
In such a case, node 2 would send the following modified packet P1 on
the link to 3:
(2001:db8::1, 2001:db8:cccc:3:C4::)(2001:db8:cccc:8:D100::; SL=1).
The rest of the processing is similar to the previous section.
Let us analyze a policy applied at a midpoint on a packet with an
SRH.
Packet P2 is (2001:db8::1,
2001:db8:cccc:7:1::)(2001:db8:cccc:8:D100::; SL=1).
Let us consider P2 when it is received by node 2 and let us assume
that node 2 is configured to steer 2001:db8:cccc:7::/64 in a
H.Insert.Red behavior associated with SR policy
<2001:db8:cccc:3:C4::, 2001:db8:cccc:5:1::>.
In such a case, node 2 would send the following modified packet P2 on
the link to 4:
(2001:db8::1, 2001:db8:cccc:3:C4::)(2001:db8:cccc:7:1::,
2001:db8:cccc:5:1::; SL=2)(2001:db8:cccc:8:D100::; SL=1)
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Node 3 would send the following packet to 4: (2001:db8::1,
2001:db8:cccc:5:1::)(2001:db8:cccc:7:1::, 2001:db8:cccc:5:1::;
SL=1)(2001:db8:cccc:8:D100::; SL=1)
Node 4 would send the following packet to 5: (2001:db8::1,
2001:db8:cccc:5:1::)(2001:db8:cccc:7:1::, 2001:db8:cccc:5:1::;
SL=1)(2001:db8:cccc:8:D100::; SL=1)
Node 5 would send the following packet to 6: (2001:db8::1,
2001:db8:cccc:7:1::)(2001:db8:cccc:8:D100::; SL=1)
Node 6 would send the following packet to 7: (2001:db8::1,
2001:db8:cccc:7:1::)(2001:db8:cccc:8:D100::; SL=1)
Node 7 would send the following packet to 8: (2001:db8::1,
2001:db8:cccc:8:D100::)
2.9. End-to-End policy with intermediate BSID
Let us now describe a case where the ingress VPN edge node steers the
packet destined to 203.0.113.20 towards the egress edge node
connected to the tenant100 site with 203.0.113.0/24, but via an
intermediate SR Policy represented by a single routable Binding SID.
Let us illustrate this case with an intermediate policy which both
encodes underlay optimization for low-latency and the service
programming via two SR-aware container-based apps.
Let us assume that the End.B6.Insert SID 2001:db8:cccc:2:B1:: is
configured at node 2 and is associated with midpoint SR policy
<2001:db8:cccc:3:C4::, 2001:db8:cccc:9:A1::, 2001:db8:cccc:6:A2::>.
2001:db8:cccc:3:C4:: realizes the low-latency path from the ingress
PE to the egress PE. This is the underlay optimization part of the
intermediate policy.
2001:db8:cccc:9:A1:: and 2001:db8:cccc:6:A2:: represent two SR-aware
NFV applications residing in containers respectively connected to
node 9 and 6.
Let us assume the following ingress VPN policy for 203.0.113.0/24 in
tenant 100 IPv4 table of node 1: H.Encaps with SRv6 Policy
<2001:db8:cccc:2:B1::, 2001:db8:cccc:8:D100::>.
This ingress policy will steer the 203.0.113.0/24 tenant-100 traffic
towards the correct egress PE and via the required intermediate
policy that realizes the SLA and NFV requirements of this tenant
customer.
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Node 1 sends the following packet to 2: (2001:db8::1,
2001:db8:cccc:2:B1::) (2001:db8:cccc:8:D100::, 2001:db8:cccc:2:B1::;
SL=1)
Node 2 sends the following packet to 4: (2001:db8::1,
2001:db8:cccc:3:C4::) (2001:db8:cccc:6:A2::, 2001:db8:cccc:9:A1::,
2001:db8:cccc:3:C4::; SL=2)(2001:db8:cccc:8:D100::,
2001:db8:cccc:2:B1::; SL=1)
Node 4 sends the following packet to 5: (2001:db8::1,
2001:db8:cccc:9:A1::) (2001:db8:cccc:6:A2::, 2001:db8:cccc:9:A1::,
2001:db8:cccc:3:C4::; SL=1)(2001:db8:cccc:8:D100::,
2001:db8:cccc:2:B1::; SL=1)
Node 5 sends the following packet to 9: (2001:db8::1,
2001:db8:cccc:9:A1::) (2001:db8:cccc:6:A2::, 2001:db8:cccc:9:A1::,
2001:db8:cccc:3:C4::; SL=1)(2001:db8:cccc:8:D100::,
2001:db8:cccc:2:B1::; SL=1)
Node 9 sends the following packet to 6: (2001:db8::1,
2001:db8:cccc:6:A2::) (2001:db8:cccc:8:D100::, 2001:db8:cccc:2:B1::;
SL=1)
Node 6 sends the following packet to 7: (2001:db8::1,
2001:db8:cccc:8:D100::)
Node 7 sends the following packet to 8: (2001:db8::1,
2001:db8:cccc:8:D100::) which decaps and forwards to CE-B.
The benefits of using an intermediate Binding SID are well-known and
key to the Segment Routing architecture: the ingress edge node needs
to push fewer SIDs, the ingress edge node does not need to change its
SR policy upon change of the core topology or re-homing of the
container-based apps on different servers. Conversely, the core and
service organizations do not need to share details on how they
realize underlay SLA's or where they home their NFV apps.
2.10. TI-LFA
Let us assume two packets P1 and P2 received by node 2 exactly when
the failure of link 27 is detected.
P1: (2001:db8::1, 2001:db8:cccc:7:1::)
P2: (2001:db8::1, 2001:db8:cccc:7:1::)(2001:db8:cccc:8:D100::;
SL=1)
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Node 2's pre-computed TI-LFA backup path for the destination
2001:db8:cccc:7::/64 is <2001:db8:cccc:3:C4::>. It is installed as a
H.Insert.Red transit behavior.
Node 2 protects the two packets P1 and P2 according to the pre-
computed TI-LFA backup path and send the following modified packets
on the link to 4:
P1: (2001:db8::1, 2001:db8:cccc:3:C4::)(2001:db8:cccc:7:1::; SL=1)
P2: (2001:db8::1, 2001:db8:cccc:3:C4::)(2001:db8:cccc:7:1::; SL=1)
(2001:db8:cccc:8:D100::; SL=1)
Node 4 then sends the following modified packets to 5:
P1: (2001:db8::1, 2001:db8:cccc:7:1::)
P2: (2001:db8::1, 2001:db8:cccc:7:1::)(2001:db8:cccc:8:D100::;
SL=1)
Then these packets follow the rest of their post-convergence path
towards node 7 and then go to node 8 for the VPN decaps.
2.11. SR TE for Service programming
We have illustrated the service programming through SR-aware apps in
a previous section.
We illustrate the use of End.AS function
[I-D.ietf-spring-sr-service-programming] to service chain an IP flow
bound to the internet through two SR-unaware applications hosted in
containers.
Let us assume that servers 20 and 70 are respectively connected to
nodes 2 and 7. They are respectively configured with SID spaces
2001:db8:cccc:20::/64 and 2001:db8:cccc:70::/64. Their connected
routers advertise the related prefixes in the IGP. Two SR-unaware
container-based applications App2 and App7 are respectively hosted on
server 20 and 70. Server 20 (70) is configured explicitly with an
End.AS SID 2001:db8:cccc:20:2:: for App2 (2001:db8:cccc:70:7:: for
App7).
Let us assume a broadband customer with a home gateway CE-A connected
to edge router 1. Router 1 is configured with an SR policy which
encapsulates all the traffic received from CE-A into a H.Encaps
policy <2001:db8:cccc:20:2::, 2001:db8:cccc:70:7::,
2001:db8:cccc:8:D0::> where 2001:db8:cccc:8:D0:: is an End.DT4 SID
instantiated at node 8.
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P1 is a packet sent by the broadband customer to 1: (X, Y) where X
and Y are two IPv4 addresses.
1 sends the following packet to 2: (A1::,
2001:db8:cccc:20:2::)(2001:db8:cccc:8:D0::, 2001:db8:cccc:70:7::,
2001:db8:cccc:20:2::; SL=2; NH=4)(X, Y).
2 forwards the packet to server 20.
20 receives the packet (A1::,
2001:db8:cccc:20:2::)(2001:db8:cccc:8:D0::, 2001:db8:cccc:70:7::,
2001:db8:cccc:20:2::; SL=2; NH=4)(X, Y) and forwards the inner IPv4
packet (X,Y) to App2. App2 works on the packet and forwards it back
to 20. 20 pushes the outer IPv6 header with SRH (A1::,
2001:db8:cccc:70:7::)(2001:db8:cccc:8:D0::, 2001:db8:cccc:70:7::,
2001:db8:cccc:20:2::; SL=1; NH=4) and sends the (whole) IPv6 packet
with the encapsulated IPv4 packet back to 2.
2 and 7 forward to server 70.
70 receives the packet (A1::,
2001:db8:cccc:70:7::)(2001:db8:cccc:8:D0::, 2001:db8:cccc:70:7::,
2001:db8:cccc:20:2::; SL=1; NH=4)(X, Y) and forwards the inner IPv4
packet (X,Y) to App7. App7 works on the packet and forwards it back
to 70. 70 pushes the outer IPv6 header with SRH (A1::,
2001:db8:cccc:8:D0::)(2001:db8:cccc:8:D0::, 2001:db8:cccc:70:7::,
2001:db8:cccc:20:2::; SL=0; NH=4) and sends the (whole) IPv6 packet
with the encapsulated IPv4 packet back to 7.
7 forwards to 8.
8 receives (A1::, 2001:db8:cccc:8:D0::)(2001:db8:cccc:8:D0::,
2001:db8:cccc:70:7::, 2001:db8:cccc:20:2::; SL=0; NH=4)(X, Y) and
performs the End.DT4 function and sends the IP packet (X, Y) towards
its internet destination.
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3. Benefits
3.1. Seamless deployment
The VPN use-case can be realized with SRv6 capability deployed solely
at the ingress and egress PE's.
All the nodes in between these PE's act as transit routers as per
[RFC8200]. No software/hardware upgrade is required on all these
nodes. They just need to support IPv6 per [RFC8200].
The SRTE/underlay-SLA use-case can be realized with SRv6 capability
deployed at few strategic nodes.
It is well-known from the experience deploying SR-MPLS that
underlay SLA optimization requires few SIDs placed at strategic
locations. This was illustrated in our example with the low-
latency optimization which required the operator to enable one
single core node with SRv6 (node 4) where one single and End.X SID
towards node 5 was instantiated. This single SID is sufficient to
force the end-to-end traffic via the low-latency path.
The TI-LFA benefits are collected incrementally as SRv6 capabilities
are deployed.
It is well-know that TI-LFA is an incremental node-by-node
deployment. When a node N is enabled for TI-LFA, it computes TI-
LFA backup paths for each primary path to each IGP destination.
In more than 50% of the case, the post-convergence path is loop-
free and does not depend on the presence of any remote SRv6 SID.
In the vast majority of cases, a single segment is enough to
encode the post-convergence path in a loop-free manner. If the
required segment is available (that node has been upgraded) then
the related back-up path is installed in FIB, else the pre-
existing situation (no backup) continues. Hence, as the SRv6
deployment progresses, the coverage incrementally increases.
Eventually, when the core network is SRv6 capable, the TI-LFA
coverage is complete.
The service programming use-case can be realized with SRv6 capability
deployed at few strategic nodes.
The service-programming deployment is again incremental and does
not require any pre-deployment of SRv6 in the network. When an
NFV app A1 needs to be enabled for inclusion in an SRv6 service
chain, all what is required is to install that app in a container
or VM on an SRv6-capable server (Linux 4.10 or FD.io 17.04
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release). The app can either be SR-aware or not, leveraging the
proxy functions.
By leveraging the various End functions it can also be used to
support any current VNF/CNF implementations and their forwarding
methods (e.g. Layer 2).
The ability to leverage SR TE policies and BSIDs also permits
building scalable, hierarchical service-chains.
3.2. Integration
The SRv6 network programming concept allows integrating all the
application and service requirements: multi-domain underlay SLA
optimization with scale, overlay VPN/Tenant, sub-50msec automated
FRR, security and service programming.
3.3. Security
The combination of well-known techniques (SEC-1, SEC-2) and carefully
chosen architectural rules (SEC-3) ensure a secure deployment of SRv6
inside a multi-domain network managed by a single organization.
Inter-domain security will be described in a companion document.
4. Acknowledgements
The authors would like to acknowledge Stefano Previdi, Dave Barach,
Mark Townsley, Peter Psenak, Thierry Couture, Kris Michielsen, Paul
Wells, Robert Hanzl, Dan Ye, Gaurav Dawra, Faisal Iqbal, Jaganbabu
Rajamanickam, David Toscano, Asif Islam, Jianda Liu, Yunpeng Zhang,
Jiaoming Li, Narendra A.K, Mike Mc Gourty, Bhupendra Yadav, Sherif
Toulan, Satish Damodaran, John Bettink, Kishore Nandyala Veera Venk,
Jisu Bhattacharya, Saleem Hafeez and Michael Huang.
5. Contributors
Daniel Bernier
Bell Canada
Canada
Email: daniel.bernier@bell.ca
Daniel Voyer
Bell Canada
Canada
Email: daniel.voyer@bell.ca
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Bart Peirens
Proximus
Belgium
Email: bart.peirens@proximus.com
Hani Elmalky
Ericsson
United States of America
Email: hani.elmalky@gmail.com
Prem Jonnalagadda
Barefoot Networks
United States of America
Email: prem@barefootnetworks.com
Milad Sharif
Barefoot Networks
United States of America
Email: msharif@barefootnetworks.com
Stefano Salsano
Universita di Roma "Tor Vergata"
Italy
Email: stefano.salsano@uniroma2.it
Ahmed AbdelSalam
Gran Sasso Science Institute
Italy
Email: ahmed.abdelsalam@gssi.it
Gaurav Naik
Drexel University
United States of America
Email: gn@drexel.edu
Arthi Ayyangar
Arista
United States of America
Email: arthi@arista.com
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Satish Mynam
Innovium Inc.
United States of America
Email: smynam@innovium.com
Wim Henderickx
Nokia
Belgium
Email: wim.henderickx@nokia.com
Shaowen Ma
Juniper
Singapore
Email: mashao@juniper.net
Ahmed Bashandy
Individual
United States of America
Email: abashandy.ietf@gmail.com
Francois Clad
Cisco Systems, Inc.
France
Email: fclad@cisco.com
Kamran Raza
Cisco Systems, Inc.
Canada
Email: skraza@cisco.com
Darren Dukes
Cisco Systems, Inc.
Canada
Email: ddukes@cisco.com
Patrice Brissete
Cisco Systems, Inc.
Canada
Email: pbrisset@cisco.com
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Zafar Ali
Cisco Systems, Inc.
United States of America
Email: zali@cisco.com
6. References
[I-D.ietf-bess-srv6-services]
Dawra, G., Filsfils, C., Talaulikar, K., Raszuk, R.,
Decraene, B., Zhuang, S., and J. Rabadan, "SRv6 BGP based
Overlay services", draft-ietf-bess-srv6-services-05 (work
in progress), November 2020.
[I-D.ietf-spring-segment-routing-policy]
Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and
P. Mattes, "Segment Routing Policy Architecture", draft-
ietf-spring-segment-routing-policy-09 (work in progress),
November 2020.
[I-D.ietf-spring-sr-service-programming]
Clad, F., Xu, X., Filsfils, C., daniel.bernier@bell.ca,
d., Li, C., Decraene, B., Ma, S., Yadlapalli, C.,
Henderickx, W., and S. Salsano, "Service Programming with
Segment Routing", draft-ietf-spring-sr-service-
programming-03 (work in progress), September 2020.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
[RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
<https://www.rfc-editor.org/info/rfc8754>.
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[RFC8986] Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
(SRv6) Network Programming", RFC 8986,
DOI 10.17487/RFC8986, February 2021,
<https://www.rfc-editor.org/info/rfc8986>.
Authors' Addresses
Clarence Filsfils
Cisco Systems, Inc.
Belgium
Email: cf@cisco.com
Pablo Camarillo Garvia (editor)
Cisco Systems, Inc.
Spain
Email: pcamaril@cisco.com
Zhenbin Li
Huawei Technologies
China
Email: lizhenbin@huawei.com
Satoru Matsushima
SoftBank
1-9-1,Higashi-Shimbashi,Minato-Ku
Tokyo 105-7322
Japan
Email: satoru.matsushima@g.softbank.co.jp
Bruno Decraene
Orange
France
Email: bruno.decraene@orange.com
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Dirk Steinberg
Lapishills Consulting Limited
Cyprus
Email: dirk@lapishills.com
David Lebrun
Google
Belgium
Email: david.lebrun@uclouvain.be
Robert Raszuk
Bloomberg LP
United States of America
Email: robert@raszuk.net
John Leddy
Individual Contributor
United States of America
Email: john@leddy.net
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