Internet DRAFT - draft-chen-bess-evpn-df-algorithm-selection
draft-chen-bess-evpn-df-algorithm-selection
BESS Workgroup J. Chen
Internet Draft
Intended status: Standards Track H3C
Expires: May 20, 2018 Nov 27, 2017
EVPN DF Election Algorithm Selection
draft-chen-bess-evpn-df-algorithm-selection-00
Abstract
This document describes a new EVPN Designated Forwarder Election (DF)
method which can be used to select a proper DF Election algorithm.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Specification of Requirements . . . . . . . . . . . . . . . . . 3
3. Solution requirements . . . . . . . . . . . . . . . . . . . . 3
4. EVPN BGP Attributes for DF Election . . . . . . . . . . . . . . 3
5. Solution description . . . . . . . . . . . . . . . . . . . . . 4
5.1 Use of the DF Type Priority . . . . . . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
7. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 5
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5
9.1 Normative References . . . . . . . . . . . . . . . . . . . . 5
9.2 Informative References . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
IN RFC7432, the Designated Forwarder (DF) in (PBB-)EVPN networks is
the PE responsible for ccertain actions:
o Sending multicast and broadcast traffic, on a given Ethernet tag on
a particular Ethernet segment, to the CE.
o Flooding unknown unicast traffic (i.e., traffic for which a PE does
not know the destination MAC address), on a given Ethernet tag on a
particular Ethernet segment to the CE, if the environment requires
flooding of unknown unicast traffic.
The DF is selected out of a candidate list of PEs at the granularity
of <ES, VLAN> or <ES, VLAN bundle> as the default procedure. This is
refereed to as "service carving".
Besides 'service-carving', there are also many other efficient and
automated way of selecting the DF.
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This document proposes an extension to the current RFC7432 DF
election procedures to select a proper way for DF election.
2. Specification of Requirements
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 [RFC2119].
3. Solution requirements
This document proposes an extension for 'service-carving' with the
following requirements:
a) An administrative priority option provided for controlling the
order of candidate DF Election Algorithms MAY be used.
4. EVPN BGP Attributes for DF Election
This solution reuses and extends the DF Election Extended Community
defined in [EVPN-HRW-DF] that is advertised along with the ES route:
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=0x06 | Sub-Type(TBD) | DF Type | Reserved = 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DF Type Prio | Reserved = 0 | Reserved = 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o The definition of DF Type is outside the scope of this document and
can have the following values :
- Type 0 - Default, mod based DF election as per RFC7432.
- Type 1 - HRW algorithm as per [EVPN-HRW-DF]
- Type 2 and so on - To be determined
o DF Type Prio or DF Type Priority defines a 1-octect value indicates
the priority that PE uses the DF Type. The allowed values are
within the range 0-255 inclusive, and default value MUST be 0. This
value stands for lowest priority. If PEs advertise different
priority for one ES, the minimum will be used.
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5. Solution description
Figure 1 gives an example that will be used in the description of the
solution.
+-------------------+
| +-------+
| | PE1 | <---ESI1, DF type 1, Priority 100
| | | <---ESI1, DF type 2, Priority 200
| | |
+-----+ | |
CEs--+PEs | +-------+
+-----+ |
| |
| +-----+
| | PE2 | <---ESI1, DF type 1, Priority 50
| +-----+ <---ESI1, DF type 2, Priority 100
| |
| +-----+
| | PE3 + <---ESI1, DF type 1, Priority 100
| +-----+
--------------------+
Figure 1 DF Election Method
Figure 1 shows three PEs that are connecting to the same ES in the
EVPN network.
If all the PEs use the DF election method described in this document,
DF type 1 will become the DF election algorithm. The following
sections provide some examples of the new defined procedures and how
they are applied in the use-case in Figure 1.
5.1 Use of the DF Type Priority
Assuming the operator wants to control globally - in a flexible way -
what DF election algorithm to be used for a given ES . The following
procedure may be used:
a) PEs (or ES1 in PEs) are now configurable with two optional
parameters that are signaled in the DF Election extended
community. These parameters are the DF algorithm type and
Priority. We will represent these parameters as [(DF Type, DF Type
Priority), (DF Type, DF Type Priority) ...]. Let's assume PE1 is
configured as [(1, 100), (2, 200)], [(1, 50), (2, 100)] in PE2 and
[(1, 100)] in PE3.
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b) The PEs will advertise an ES route for each ES (here ESI 1),
including the 2 parameters in one or more DF Election Extended
Community. Each DF type needs one DF Election Extended Community
except the DF type 0 with the priority 0.
c) According to RFC7432, each PE will wait for the DF timer to expire
before running the DF election algorithm. After the timer expires,
each PE runs the DF election method as follows:
o Each PE builds a list of candidate DF election algorithms that
are supported by all PEs, ordered based on the Priority. E.g.
PE1 will build a list of candidate DF election algorithms for
ESI1 by the Priority, from high to low: (DF type 1, 50), (DF
type 0, 0). Hence the DF type 1 will be used as DF election
algorithm.
o Each PE uses the selected DF election algorithm to elect a
proper DF for ESI1.
d) In case of equal Priority for two or more DF types, the tie-
breakers will be the highest DF type number in that order. For
instance:
o If the DF list is [(2, 50), (1, 50), (0, 0)], DF type 2 will be
used.
e) The DF type and Priority are administrative options that may be
configured on a per-ES/per-device basis from the management plane
or fixed by device capability. The definition of the actual local
policies is out of scope of this document.
6. IANA Considerations
This document solicits the addition of DFT Priority field in the
registry created by [EVPN-HRW-DF].
7. Security Considerations
This section will be added in future versions.
8. Acknowledgments
TBD.
9. References
9.1 Normative References
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[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>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March
1997, <http://www.rfc-editor.org/info/rfc2119>.
9.2 Informative References
[EVPN-HRW-DF] Mohanty S. et al. "A new Designated Forwarder Election
for the EVPN", draft-mohanty-bess-evpn-df-election-02, work-in-
progress, October 19, 2015.
[EVPN-PREF-DF] Rabadan J., Ed. et al. "Preference-based EVPN DF
Election", draft-ietf-bess-evpn-pref-df-00, work-in- progress, June
21, 2017.
Authors' Addresses
Jian Chen
H3C
Email: jian_chen@h3c.com
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