Internet DRAFT - draft-wang-bess-evpn-ac-df-per-evi
draft-wang-bess-evpn-ac-df-per-evi
BESS WG Y. Wang
Internet-Draft ZTE Corporation
Intended status: Standards Track 11 July 2021
Expires: 12 January 2022
AC-Influenced DF Election per EVI
draft-wang-bess-evpn-ac-df-per-evi-01
Abstract
The AC-influenced DF Election (AC-DF) per [RFC8584] is too dependent
on EAD/EVI routes. For example, when no failures occured on an ESI,
that AC-DF procedures will give incorrect results if no EAD/EVI
routes are advertised. But in some light-weighted EVPNs (i.e. PBB
EVPNs), no EAD/EVI routes will be advertised at all.
This draft proposes some new extensions to support AC-influenced DF
Election without any EAD/EVI routes advertised in advance of any
<ESI, EVI> failures.
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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This Internet-Draft will expire on 12 January 2022.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. AC-DF per EVI . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Use Case . . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. AC-DF per EVI Capability . . . . . . . . . . . . . . . . 4
2.2.1. Capability Negotiation Procedures . . . . . . . . . . 4
2.2.2. AC-DF Capability vs AC-DF per EVI Capability . . . . 4
2.3. DF Election Procedures . . . . . . . . . . . . . . . . . 4
2.3.1. Initiation of AC-DF per EVI Mode . . . . . . . . . . 4
2.3.2. Reverse EAD/EVI Route . . . . . . . . . . . . . . . . 5
2.3.3. DF Election Rules . . . . . . . . . . . . . . . . . . 5
2.3.4. Route Filtering and RT Constraints Mechanism . . . . 6
3. Other considerations . . . . . . . . . . . . . . . . . . . . 6
3.1. Reverse EAD/EVI Route in PBB EVPNs . . . . . . . . . . . 6
3.2. Why no EAD/EVI Routes Advertised . . . . . . . . . . . . 6
4. Comparison with other solutions . . . . . . . . . . . . . . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6.1. New DF Election Capability . . . . . . . . . . . . . . . 8
6.2. New EVPN Layer 2 Attributes Control Flags . . . . . . . . 8
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
8. Normative References . . . . . . . . . . . . . . . . . . . . 8
9. Informative References . . . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
When the EAD/EVI route is not advertised before the corresponding ESI
sub-interface fails, The AC-influenced DF Election procedures should
elect the right DF before and after that failure.
Note that according to [RFC8584], the AC-influenced DF Election will
be incorrect when no EAD/EVI route is advertised, even if no ESI sub-
interface has failed at all.
This draft proposes some extension to DF-Capability negotiation and
DF-Election procedures to support AC-influenced DF-election when no
EAD/EVI routes are advertised.
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1.1. Terminology
Most of the terminology used in this documents comes from [RFC8584]
and [RFC7623] except for the following:
* Light-weighted EVPN: The EVPN solution without EAD/EVI Route
advertisedment.
* EAD/ES: Ethernet A-D route per EVI, or RT-1 per ES route.
* EAD/EVI: Ethernet A-D route per EVI, or RT-1 per EVI route.
2. AC-DF per EVI
2.1. Use Case
The ethernet segment ES1's ESI is ESI1, AC1/AC2 is two sub-interfaces
on ES1, and AC3/AC4 is two sub-interfaces on ES2. AC1 and AC3 are
attached to EVPN Instance EVI1, while AC2 and AC4 are attached to
EVI2. The redundancy mode of ES1 is all-active.
+----------+
PE1 | |
+-------------+ | |
| AC1 | | | PE3
/| AC2 |----| | +-------------+
/ | | | | | |
LAG / +-------------+ | | | AC3 |---CE2
CE1===== | PSN | | AC4 |
\ +-------------+ | |---| |
\ | | | | +-------------+
\| AC2 |----| |
| AC1 | | |
+-------------+ | |
PE2 | |
+----------+
Figure 1: AC-DF per EVI Usecase
EVI1 and EVI2 are two EVPN Instances, and there are no EAD/EVI routes
advertised for them. Such EVPN Instances are called Light-weighted
EVPNs in this draft. For example, EVI1 and EVI2 can be the
I-Components of PBB EVPNs, because no EAD/EVI routes are advertised
for these I-Components.
Initially PE1 is the DF for <ESI1, EVI1>, and PE2 is the DF for
<ESI1, EVI2>. When the AC1 of PE1 fails (but ESI1 and AC2 of PE1
still works well), the DF for <ESI1, EVI1> should switch to PE2.
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The DF-election should be done without any EAD/EVI routes advertised
before any ESI sub-interface fails. Otherwise those EAD/EVI routes
are advertised just for the adaptation of AC-influenced DF-election
procedures per [RFC8584], but will do nothing good for the unicast
packet forwarding in data plane (because data plane MAC learning
don't use EAD/EVI routes).
2.2. AC-DF per EVI Capability
We introduce a new bit named "AC-DF per EVI" in the "bitmap" field of
the DF Election extended community. The "AC-DF per EVI" bit means
that the DF-Election for an <ESI, EVI> will not take EAD/EVI routes
into considerations untill a Reverse EAD/EVI route for that <ESI,
EVI> is received from any of the PEs.
2.2.1. Capability Negotiation Procedures
Only when all RT-4 routes of the same ESI indicate the "AC-DF per
EVI" Capability, The DF Election will be executed in "AC-DF per EVI"
mode. We can say that the DF Election mode for that ESI is
negotiated as "AC-DF per EVI" mode.
Note that when any of the PEs on that ES is an old PE that don't
support "AC-DF per EVI" mode, the RT-4 route from that PE will not
indicate the "AC-DF per EVI" Capability, So the DF election will not
be executed in "AD-DF per EVI" mode. This is for compatibility
purpose.
2.2.2. AC-DF Capability vs AC-DF per EVI Capability
When all RT-4 routes of the same ESI indicate both the "AC-DF per
EVI" Capability and the old AC-DF Capability, The DF Election will be
executed in "AD-DF per EVI" mode.
Note that when any of the PEs on that ES is an old PE that don't
support "AC-DF per EVI" mode, the RT-4 route from that PE may
indicate the "old AC-DF" Capability only, So the DF election will
still be executed in old AD-DF mode per [RFC8584]. This is for
compatibility purpose.
2.3. DF Election Procedures
2.3.1. Initiation of AC-DF per EVI Mode
According to [RFC8584], the AC-influenced DF Election will be
incorrect when no EAD/EVI route is advertised, even if no ESI sub-
interface has failed at all.
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But when the DF Election mode for an ESI is negotiated as AC-DF per
EVI mode, no normal EAD/EVI routes can impact the DF Election
procedures. The DF election will be done following that ESI's RT-4
routes only until at least one reverse EAD/EVI route is received.
2.3.2. Reverse EAD/EVI Route
In order to do AC-influenced DF election after a sub-interface of
that ES fails, we introduce the "Reverse EAD/EVI Route". The reverse
EAD/EVI Route is a special type of EAD/EVI Route that is advertised
on the failure of corresponding <ESI, EVI>, not on the activation of
that <ESI, EVI>.
Reverse EAD/EVI routes can use the same format as EAD/EVI Routes
except for the following differences:
* A Reverse EAD/EVI Route carries an EVPN Layer 2 Attributes
Extended Community whose "Control Flags" field includes a new flag
named "AC Down". The "AC Down" flag means that the corresponding
AC (for which the Reverse EAD/EVI route is advertised) is down.
* It is recommended to carry an ES-Import RT ([RFC7432]) and an EVI-
RT ([I-D.ietf-bess-evpn-igmp-mld-proxy]) along with a reverse EAD/
EVI route, no traditional Route-Targets have to be carried for DF-
election purpose.
* A Reverse EAD/EVI Route should make its MPLS label field be set to
zero.
Note that when the corresponding sub-interface fails, the
MP_REACH_NLRI of the reverse EAD/EVI route is advertised, and when
the corresponding sub-interface recovers, the MP_UNREACH_NLRI of the
reverse EAD/EVI route is sent. This is the opposite of normal EAD/
EVI route. So it is called as reverse EAD/EVI route.
2.3.3. DF Election Rules
When a Reverse EAD/EVI Route for an <ESI, EVI> is received from a
remote PE X, the RT-4 Route of that PE x are expelled from that <ESI,
EVI>'s DF election. Then the DF election for that <ESI, EVI> will be
updated according to the corresponding DF Alg.
Note that the DF election for other <ESI, EVI>s will not be affected
by that Reverse EAD/EVI Route.
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2.3.4. Route Filtering and RT Constraints Mechanism
When PE Y receives a reverse EAD/EVI route from PE X, and the ES-
Import RT of that route can't match any local ES of PE Y, PE Y will
not import that route into the EVI that is identified by that route's
EVI-RT.
When RT Constraints Mechanism is enabled, each reverse EAD/EVI route
will be distributed to the adjacent PEs of its ES only. Because that
only the ES-Import RT are visible to the RT Constraints Mechanism,
The EVI-RT is not visible to the RT Constraints Mechanism.
3. Other considerations
3.1. Reverse EAD/EVI Route in PBB EVPNs
The AC-DF per EVI mode is not confined to PBB EVPN which is just an
example of light-weighted EVPNs. But in PBB EVPN, the construction
of reverse EAD/EVI route need some special considerations.
* It's EVI-RT should be the export route-target of the B-Component,
not the C-Component.
* It's Ethernet Tag ID (ETI) should be the I-SID of the I-Component.
Note that when PE Z receives a reverse EAD/EVI route whose EVI-RT
matches a local B-Component but whose ETI matches none of the
I-Components of that B-Component, PE Z may not import that reverse
EAD/EVI route.
Note that the reverse EAD/EVI route don't have to carry any B-MAC
along with it. Because that the B-MAC can do nothing helpful for the
DF election.
3.2. Why no EAD/EVI Routes Advertised
When no RT-2 Routes advertised, no EAD/EVI routes need to be
advertised either. PBB EVPN is an example of that. In PBB EVPN, the
C-MACs are learnt in the data plane.
Other light-weighted EVPNs also do data plane C-MAC learning, so they
don't have to advertise EAD/EVI routes either. In such EVPNs, AC-DF
per EVI will help.
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4. Comparison with other solutions
PBB EVPN can assign a deicated vES to each sub-interface, in such
case, the RT-4 routes are advertised per each sub-interface (or
vESI). But this will bring out some other disadvantages:
* The uniformity of service carving can't be achieved without
careful configuring.
With service carving, it is possible to elect multiple DFs per ES
(one per EVI) in order to perform load balancing of traffic
destined to a given ES. The objective is that the load-balancing
procedures should carve up the BD space among the redundant PE
nodes evenly, in such a way that every PE is the DF for a distinct
set of EVIs.
When each EVI use a dedicated vESI to advertise the corresponding
Ethernet Segment Routes for that <ES, EVI>, The service carving
mechanisms can not work without manual configuration.
* The amount of B-MACs will be greatly increased.
The brief comparisons are listed as the following table:
+====================+================+=======================+
| Items | AC-DF per EVI | vESI |
+====================+================+=======================+
| ESIs | one per port | one per sub-interface |
+--------------------+----------------+-----------------------+
| RT-4 Routes | one per port | one per sub-interface |
+--------------------+----------------+-----------------------+
| B-MACs | one per port | one per sub-interface |
+--------------------+----------------+-----------------------+
| Service Carving | auto | manual-configured |
+--------------------+----------------+-----------------------+
| EAD per EVI routes | none | none |
+--------------------+----------------+-----------------------+
| Reverse EAD per | one per failed | none |
| EVI routes | sub-interfaces | |
+--------------------+----------------+-----------------------+
Table 1: Comparisons with vESI for PBB-EVPN
Using AC-DF per EVI mode, the service-carving is automatically
achieved, and no extra B-MACs should be configured and advertised.
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5. Security Considerations
Security considerations will be added in future versions.
6. IANA Considerations
6.1. New DF Election Capability
IANA will be requested to allocate a new DF Election Capability in
the "DF Election Capabilities" Registry. This capability is called
"AC-DF per EVI Capability".
Bit Name Reference
---- ---------------- -------------
4 AC-DF per EVI Capability This draft
Figure 2: AC-DF per EVI Capability
6.2. New EVPN Layer 2 Attributes Control Flags
IANA will be requested to allocate a new Control Flag in the "EVPN
Layer 2 Attributes Control Flags" Registry. This Control Flag is
called "D" Flag, where "D" means AC-Down.
Bit Name Reference
---- ---------------- -------------
D AC-Down on Advertising PE This Draft
Figure 3: AC Failure Flag
7. Acknowledgements
The authors would like to thank the following for their comments and
review of this document:
Chunning Dai.
8. Normative References
[I-D.ietf-bess-evpn-igmp-mld-proxy]
Sajassi, A., Thoria, S., Mishra, M. P., Patel, K., Drake,
J., and W. Lin, "IGMP and MLD Proxy for EVPN", Work in
Progress, Internet-Draft, draft-ietf-bess-evpn-igmp-mld-
proxy-09, 19 April 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-bess-
evpn-igmp-mld-proxy-09>.
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[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", Work in Progress, Internet-Draft,
draft-ietf-bess-srv6-services-07, 11 April 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-bess-
srv6-services-07>.
[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, <https://www.rfc-editor.org/info/rfc7432>.
[RFC7623] Sajassi, A., Ed., Salam, S., Bitar, N., Isaac, A., and W.
Henderickx, "Provider Backbone Bridging Combined with
Ethernet VPN (PBB-EVPN)", RFC 7623, DOI 10.17487/RFC7623,
September 2015, <https://www.rfc-editor.org/info/rfc7623>.
[RFC8584] Rabadan, J., Ed., Mohanty, S., Ed., Sajassi, A., Drake,
J., Nagaraj, K., and S. Sathappan, "Framework for Ethernet
VPN Designated Forwarder Election Extensibility",
RFC 8584, DOI 10.17487/RFC8584, April 2019,
<https://www.rfc-editor.org/info/rfc8584>.
9. Informative References
[RFC7041] Balus, F., Ed., Sajassi, A., Ed., and N. Bitar, Ed.,
"Extensions to the Virtual Private LAN Service (VPLS)
Provider Edge (PE) Model for Provider Backbone Bridging",
RFC 7041, DOI 10.17487/RFC7041, November 2013,
<https://www.rfc-editor.org/info/rfc7041>.
[RFC7348] Mahalingam, M., Dutt, D., Duda, K., Agarwal, P., Kreeger,
L., Sridhar, T., Bursell, M., and C. Wright, "Virtual
eXtensible Local Area Network (VXLAN): A Framework for
Overlaying Virtualized Layer 2 Networks over Layer 3
Networks", RFC 7348, DOI 10.17487/RFC7348, August 2014,
<https://www.rfc-editor.org/info/rfc7348>.
[RFC8365] Sajassi, A., Ed., Drake, J., Ed., Bitar, N., Shekhar, R.,
Uttaro, J., and W. Henderickx, "A Network Virtualization
Overlay Solution Using Ethernet VPN (EVPN)", RFC 8365,
DOI 10.17487/RFC8365, March 2018,
<https://www.rfc-editor.org/info/rfc8365>.
Author's Address
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Yubao Wang
ZTE Corporation
No.68 of Zijinghua Road, Yuhuatai Distinct
Nanjing
China
Email: wang.yubao2@zte.com.cn
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