Internet DRAFT - draft-ietf-bess-evpn-ac-df
draft-ietf-bess-evpn-ac-df
BESS Workgroup J. Rabadan, Ed.
Internet Draft K. Nagaraj
S. Sathappan
Intended status: Informational V. Prabhu
Nokia
A. Liu
Ciena
W. Lin
Juniper Networks
Expires: July 22, 2018 January 18, 2018
AC-Influenced Designated Forwarder Election for EVPN
draft-ietf-bess-evpn-ac-df-03
Abstract
The Designated Forwarder (DF) in EVPN networks is the PE responsible
for sending multicast, broadcast and unknown unicast traffic to a
multi-homed CE, on a given Ethernet Tag on a particular Ethernet
Segment (ES). The DF is selected based on the list of PEs that
advertise the Ethernet Segment Identifier (ESI) to the EVPN network.
While PE node or link failures trigger the DF re-election for a given
<ESI, EVI>, individual Attachment Circuit (AC) or MAC-VRF failures do
not trigger such DF re-election and the traffic may therefore be
permanently impacted, even though there is an alternative path. This
document improves the DF election algorithm so that the AC status can
influence the result of the election and this type of "logical"
failures can be protected too.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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Copyright (c) 2018 IETF Trust and the persons identified as the
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Table of Contents
1. Problem Statement . . . . . . . . . . . . . . . . . . . . . . . 3
2. Solution Description . . . . . . . . . . . . . . . . . . . . . 4
2.1. Current DF Election Procedure And AC Failures . . . . . . . 5
2.2. The Attachment Circuit (AC) Influenced DF Election . . . . 6
2.3. AC-Influenced DF Election For VLAN-Aware Bundle Services . 7
3. Solution benefits . . . . . . . . . . . . . . . . . . . . . . . 8
4. Conventions used in this document . . . . . . . . . . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 9
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 9
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
7.1. Normative References . . . . . . . . . . . . . . . . . . . 9
7.2. Informative References . . . . . . . . . . . . . . . . . . 9
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 9
9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
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1. Problem Statement
[RFC7432] defines the Designated Forwarder (DF) as the EVPN PE
responsible for:
o Flooding Broadcast, Unknown unicast and Multicast traffic (BUM), on
a given Ethernet Tag on a particular Ethernet Segment (ES), to the
CE. This is valid for single-active and all-active EVPN
multi-homing.
o Sending unicast traffic on a given Ethernet Tag on a particular ES
to the CE. This is valid for single-active multi-homing.
The default DF election algorithm defined by [RFC7432] is called
service-carving and, for a given ES, is based on a (V mod N)= i
function that provides a local DF election of a PEi at <ESI, EVI>
level. V is the Ethernet Tag associated to the EVI (the numerically
lowest Ethernet Tag value in case of multiple Ethernet Tags), whereas
N is the number of PEs for which ES routes have been successfully
imported. In other words, EVPN's service-carving takes into account
only two variables in the DF election for a given ESI: the existence
of the PE's IP address on the candidate list and the locally
provisioned Ethernet Tags.
If the DF for an <ESI, EVI> fails (due to physical link/node
failures) an ES route withdrawn will make the Non-DF (NDF) PEs re-
elect the DF for that <ESI, EVI> and the service will be recovered.
However the current DF election procedure does not provide a
protection against "logical" failures or human errors that may occur
at service level on the DF, while the list of active PEs for a given
ES does not change. These failures may have an impact not only on the
local PE where the issue happens, but also on the rest of the PEs of
the ES. Some examples of such logical failures are listed below:
a) A given individual Attachment Circuit (AC) defined in an ES is
accidentally shutdown or even not provisioned yet (hence the
Attachment Circuit Status - ACS - is DOWN), while the ES is
operationally active (since the ES route is active).
b) A given MAC-VRF - with an ES defined - is shutdown or not
provisioned yet, while the ES is operationally active (since the
ES route is active). In this case, the ACS of all the AC defined
in that MAC-VRF is considered to be DOWN.
Neither (a) nor (b) will trigger the DF re-election on the remote PEs
for a given ES since the ACS is not taken into account in the DF
election procedures. While the ACS is used as a DF election tie-
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breaker and trigger in [VPLS-MH], there is no procedure defined in
[RFC7432] to trigger the DF re-election based on the ACS change on
the DF.
This document improves the [RFC7432] service-carving procedure so
that the ACS may be taken into account as a variable in the DF
election, and therefore EVPN can provide protection against logical
failures.
2. Solution Description
The ACS for a given Ethernet Tag on an ES is implicitly conveyed in
the corresponding EVPN A-D per EVI route for that given <ESI,
Ethernet Tag>. This section describes how to use the A-D per EVI
routes to improve the DF election algorithm.
Figure 1 illustrates an example EVPN network that will be used to
describe the proposed solution.
EVI-1 is defined in PE-1, PE-2, PE-3 and PE-4. CE12 is a multi-homed
CE connected to ESI12 in PE-1 and PE-2. Similarly CE23 is multi-homed
to PE-2 and PE-3 using ESI23. Both, CE12 and CE23, are connected to
EVI-1 through VLAN-based service interfaces: CE12-VID 1 (VLAN ID 1 on
CE12) is associated to AC1 and AC2 in EVI-1, whereas CE23-VID 1 is
associated to AC3 and AC4 in EVI-1. Note that there are other ACs
defined on these ES mapped to different EVIs.
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+---+
|CE4|
+---+
|
PE-4 |
+-----+-----+
+---------------| +-----+ |---------------+
| | |EVI-1| | |
| +-----------+ |
| |
| EVPN |
| |
| PE-1 PE-2 PE-3 |
| (NDF) (DF) (NDF)|
+-----------+ +-----------+ +-----------+
| |EVI-1| | | |EVI-1| | | |EVI-1| |
| +-----+ |-------| +-----+ |-------| +-----+ |
+-----------+ +-----------+ +-----------+
AC1\ ESI12 /AC2 AC3\ ESI23 /AC4
\ / \ /
\ / \ /
+----+ +----+
|CE12| |CE23|
+----+ +----+
Figure 1 EVPN network example
2.1. Current DF Election Procedure And AC Failures
After running the service-carving DF election algorithm, PE-2 turns
out to be the DF for ESI12 and ESI23 in EVI-1. The following two
examples illustrate the issues with the existing defined procedure in
[RFC7432]:
a) If AC2 is accidentally shutdown or even not configured, CE12
traffic will be impacted. In case of all-active multi-homing, the BUM
traffic to CE12 will be "black-holed", whereas for single-active
multi-homing all the traffic to/from CE12 will be discarded. This is
due to the fact that a logical failure in PE-2 AC2 may not trigger an
ES route withdrawn for ESI12 (since there are still other ACs active
on ESI12) and therefore PE-1 will not re-run the DF election
procedures.
b) If EVI-1 is administratively shutdown or even not configured yet
on PE-2, CE12 and CE23 will both be impacted: BUM traffic to both CEs
will be discarded in case of all-active multi-homing and all traffic
will be discarded to/from the CEs in case of single-active
multi-homing. This is due to the fact that PE-1 and PE-3 will not
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re-run the DF election procedures and will keep assuming PE-2 is the
DF.
According to [RFC7432], "when an Ethernet tag is decommissioned on an
Ethernet segment, then the PE MUST withdraw the Ethernet A-D per EVI
route(s) announced for the <ESI, Ethernet tags> that are impacted by
the decommissioning", however, while this A-D per EVI route
withdrawal is used at the remote PEs performing aliasing or backup
procedures, it is not used to influence the DF election for the
affected EVIs.
2.2. The Attachment Circuit (AC) Influenced DF Election
Modifying the service-carving DF election procedure in the following
way solves the issue:
1. When PE-1 and PE-2 discover ESI12, they advertise an ES route for
ESI12 with the associated ES-import extended community, starting a
timer at the same time. Likewise, PE-2 and PE-3 advertise an ES
route for ESI23 and start a timer.
2. Similarly, PE-1 and PE-2 advertise an Ethernet A-D per ES route
for ESI12, and PE-2/PE-3 advertise an Ethernet A-D per ES route
for ESI23.
3. In addition, PE-1/PE-2/PE-3 advertise an Ethernet A-D per EVI
route for AC1, AC2, AC3 and AC4 as soon as the ACs are enabled.
Note that the AC can be associated to a single customer VID (e.g.
VLAN-based service interfaces) or a bundle of customer VIDs (e.g.
VLAN-bundle service interfaces).
4. When the timer expires, each PE builds an ordered "candidate" list
of the IP addresses of all the PE nodes connected to the Ethernet
Segment (including itself), in increasing numeric order. The
candidate list is based on the Originator Router's IP addresses of
the ES routes, excluding all the PEs for which no Ethernet A-D per
ES route has been received.
5. When electing the DF for a given EVI, a PE will not be considered
candidate until an Ethernet A-D per EVI route has been received
from that PE. In other words, the ACS on the ESI for a given PE
must be UP so that the PE is considered as candidate for a given
EVI. For example, PE-1 will not consider PE-2 as candidate for DF
election for <ESI12, EVI-1> until an Ethernet A-D per EVI route is
received from PE-2 for <ESI12, EVI-1>.
6. Once the PEs with ACS = DOWN for a given EVI have been eliminated
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from the candidate list, the (V mod N) = i function can be applied
for the remaining N candidates, as per [RFC7432].
Note that this procedure does not modify the existing EVPN control
plane whatsoever. It only modifies the candidate list of PEs taken
into account for the DF election algorithm defined in [RFC7432].
In addition to the procedure described above, the following events
SHALL modify the candidate PE list and trigger the DF re-election in
a PE for a given <ESI,EVI>:
a) Local ES going DOWN due to a physical failure or reception of an
ES route withdraw for that ESI.
b) Local ES going UP due to its detection/configuration or reception
of a new ES route update for that ESI.
c) Local AC going DOWN/UP.
d) Reception of a new Ethernet A-D per EVI update/withdraw for the
<ESI, EVI>.
e) Reception of a new Ethernet A-D per ES update/withdraw for the
ESI.
This procedure is backwards compatible with the DF election
procedures described in [RFC7432] since it does not add any new
extension in the control plane, however, a PE not supporting the
procedures in this document SHOULD NOT share a multi-homed ES with a
PE following this solution since both PEs may end up with an
inconsistent view on who the DF is. The AC influenced DF election
procedures SHOULD be enabled by an administrative option and only
used when all the PEs in the ES support it.
The procedure discussed in this section is applicable to the DF
Election in EVPN Services [RFC7432] and EVPN Virtual Private Wire
Services [RFC8214].
2.3. AC-Influenced DF Election For VLAN-Aware Bundle Services
The procedure described section 2.2 works for VLAN-based and VLAN-
bundle service interfaces since, for those service types, a PE
advertises only one Ethernet A-D per EVI route per <ESI,EVI>. The
withdrawal of such route means that the PE cannot forward traffic on
that particular <ESI,EVI>.
In VLAN-aware bundle services, the PE advertises multiple Ethernet A-
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D per EVI routes per <ESI,EVI> (one route per Ethernet Tag). The
withdrawal of an individual route only indicates the unavailability
of a specific AC but not necessarily all the ACs in the <ESI,EVI>.
For the specific case of VLAN-aware bundle services, the DF election
will be influenced by the update/withdraw of any of the Ethernet A-D
per EVI routes in the <ESI,EVI>.
For example, assuming three bridge tables in PE-1 for the same MAC-
VRF (each one associated to a different Ethernet Tag), PE-1 will
advertise three Ethernet A-D per EVI routes for <ESI12,EVI1>. Each of
the three routes will indicate the status of each AC in <ESI12,EVI1>.
PE-1 will be considered as a valid candidate PE for DF election as
long as the three routes are active. If PE-1 withdraws one or more of
the Ethernet A-D per EVI routes for <ESI12,EVI1>, the PEs in ESI12
will not consider PE-1 as a suitable DF candidate for <ESI12,EVI1>.
3. Solution benefits
The solution described in this document provides the following
benefits:
a) Improves the DF election procedures for EVPN so that failures due
to human errors, logical failures or even delay in provisioning of
Attachment Circuits can be protected by multi-homing.
b) It does not modify or add any BGP new attributes or NLRI changes.
c) It is backwards compatible with the procedures defined in RFC7432.
4. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119 [RFC2119].
In this document, these words will appear with that interpretation
only when in ALL CAPS. Lower case uses of these words are not to be
interpreted as carrying RFC-2119 significance.
In this document, the characters ">>" preceding an indented line(s)
indicates a compliance requirement statement using the key words
listed above. This convention aids reviewers in quickly identifying
or finding the explicit compliance requirements of this RFC.
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5. Security Considerations
The same Security Considerations described in [RFC7432] are valid for
this document.
6. IANA Considerations
There are no new IANA considerations in this document.
7. References
7.1. Normative References
[RFC7432] Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A.,
Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based Ethernet
VPN", RFC 7432, DOI 10.17487/RFC7432, February 2015, <http://www.rfc-
editor.org/info/rfc7432>.
[RFC8214] Boutros, S., Sajassi, A., Salam, S., Drake, J., Rabadan,
J., "Virtual Private Wire Service Support in Ethernet VPN", RFC 8214,
DOI 10.17487/RFC8214, August 2017, <http://www.rfc-
editor.org/info/rfc8214>.
7.2. Informative References
[VPLS-MH] Kothari, Henderickx et al., "BGP based Multi-homing in
Virtual Private LAN Service", draft-ietf-bess-vpls-multihoming-
01.txt, work in progress, January, 2016.
8. Acknowledgments
The authors want to thank Sriram Venkateswaran, Laxmi Padakanti,
Ranganathan Boovaraghavan and Ali Sajassi for their review and
contributions.
9. Contributors
In addition to the authors listed on the front page, the following
coauthors have also contributed to this document:
Wim Henderickx
Nokia
Email: wim.henderickx@nokia.com
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Patrice Brissette
Cisco Systems
Email: pbrisset@cisco.com
Authors' Addresses
Jorge Rabadan
Nokia
777 E. Middlefield Road
Mountain View, CA 94043 USA
Email: jorge.rabadan@nokia.com
Kiran Nagaraj
Nokia
Email: kiran.nagaraj@nokia.com
Senthil Sathappan
Nokia
Email: senthil.sathappan@nokia.com
Vinod Prabhu
Nokia
Email: vinod.prabhu@nokia.com
Autumn Liu
Ciena
Email: hliu@ciena.com
Wen Lin
Juniper Networks, Inc.
Email: wlin@juniper.net
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