draft-ietf-bess-evpn-df-election-01.txt   draft-ietf-bess-evpn-df-election-02.txt 
BESS Working Group S. Mohanty BESS Working Group S. Mohanty
Internet-Draft K. Patel Internet-Draft K. Patel
Intended status: Standards Track A. Sajassi Intended status: Standards Track A. Sajassi
Expires: April 05, 2017 Cisco Systems, Inc. Expires: October 06, 2017 Cisco Systems, Inc.
J. Drake J. Drake
Juniper Networks, Inc. Juniper Networks, Inc.
A. Przygienda A. Przygienda
Ericsson Juniper
October 07, 2016 April 09, 2017
A new Designated Forwarder Election for the EVPN A new Designated Forwarder Election for the EVPN
draft-ietf-bess-evpn-df-election-01 draft-ietf-bess-evpn-df-election-02
Abstract Abstract
This document describes an improved EVPN Designated Forwarder This document describes an improved EVPN Designated Forwarder
Election (DF) algorithm which can be used to enhance operational Election (DF) algorithm which can be used to enhance operational
experience in terms of convergence speed and robustness over a WAN experience in terms of convergence speed and robustness over a WAN
deploying EVPN deploying EVPN
Status of This Memo Status of This Memo
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 05, 2017. This Internet-Draft will expire on October 06, 2017.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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The applicability of HRW to DF Election can be described here. Let The applicability of HRW to DF Election can be described here. Let
DF(v) denote the Designated Forwarder and BDF(v) the Backup DF(v) denote the Designated Forwarder and BDF(v) the Backup
Designated forwarder for the ethernet tag V, where v is the vlan, Si Designated forwarder for the ethernet tag V, where v is the vlan, Si
is the IP address of server i and weight is a pseudorandom function is the IP address of server i and weight is a pseudorandom function
of v and Si. In case of a vlan bundle service, v denotes the lowest of v and Si. In case of a vlan bundle service, v denotes the lowest
vlan similar to the 'lowest vlan in bundle' logic of [RFC7432]. vlan similar to the 'lowest vlan in bundle' logic of [RFC7432].
1. DF(v) = Si: Weight(v, Si) >= Weight(V, Sj) , for all j. In case 1. DF(v) = Si: Weight(v, Si) >= Weight(V, Sj) , for all j. In case
of a tie, choose the PE whose IP address is numerically the of a tie, choose the PE whose IP address is numerically the
least. least. Note 0 <= i,j <= Number of PEs in the redundancy group.
2. BDF(v) = Sk: Weight(v, Si) >= Weight(V, Sk) and Weight(v, Sk) >= 2. BDF(v) = Sk: Weight(v, Si) >= Weight(V, Sk) and Weight(v, Sk) >=
Weight(v, Sj). in case of tie choose the PE whose IP address is Weight(v, Sj). in case of tie choose the PE whose IP address is
numerically the least. numerically the least.
Since the Weight is a Pseudorandom function with domain as a Since the Weight is a Pseudorandom function with domain as a
concatenation of (v, S), it is an efficient deterministic algorithm concatenation of (v, S), it is an efficient deterministic algorithm
which is independent of the Ethernet Tag V sample space distribution. which is independent of the Ethernet Tag V sample space distribution.
Choosing a good hash function for the pseudorandom function is an Choosing a good hash function for the pseudorandom function is an
important consideration for this algorithm to perform provably better important consideration for this algorithm to perform provably better
than the existing algorithm. As mentioned previously, such functions than the existing algorithm. As mentioned previously, such functions
are described in the HRW paper. We take as candidate hash functions are described in the HRW paper. We take as candidate hash functions
two of the ones that are preferred in [HRW1999]. two of the ones that are preferred in [HRW1999].
1. Wrand(v, Si) = (1103515245((1103515245.Si+12345)XOR 1. Wrand(v, Si) = (1103515245((1103515245.Si+12345)XOR
D(v))+12345)(mod 2^31) and D(v))+12345)(mod 2^31) and
2. Wrand2(v, Si) = (1103515245((1103515245.D(v)+12345)XOR 2. Wrand2(v, Si) = (1103515245((1103515245.D(v)+12345)XOR
Si)+12345)(mod 2^31) Si)+12345)(mod 2^31)
Here D(v) is the 31-bit digest of the ethernet-tag v and Si is Here D(v) is the 31-bit digest (CRC-32 and discarding the MSB as in
[HRW1999] ) of the ethernet-tag v and Si is
address of the ith server. The server's IP address length does not address of the ith server. The server's IP address length does not
matter as only the low-order 31 bits are modulo significant. matter as only the low-order 31 bits are modulo significant.
Eventually we plan to choose one of the two candidate hash functions Although both the above hash functions perform similarly, we will
as the preferred one. select the first hash function (1), as the hash function has to be
the same in all the PEs.
A point to note is that the the domain of the Weight function is a A point to note is that the the domain of the Weight function is a
concatenation of the ethernet-tag and the PE IP-address, and the concatenation of the ethernet-tag and the PE IP-address, and the
actual length of the server IP address (whether V4 or V6) is not actual length of the server IP address (whether V4 or V6) is not
really relevant, so long as the actual hash algorithm takes into really relevant, so long as the actual hash algorithm takes into
consideration the concatenated string. The existing algorithm in consideration the concatenated string. The existing algorithm in
[RFC7432] as is cannot employ both V4 and V6 neighbor peering [RFC7432] as is cannot employ both V4 and V6 neighbor peering
address. address.
HRW solves the disadvantage pointed out in Section 3 and ensures HRW solves the disadvantage pointed out in Section 3 and ensures
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John Drake John Drake
Juniper Networks, Inc. Juniper Networks, Inc.
1194 N. Mathilda Drive 1194 N. Mathilda Drive
Sunnyvale, CA 95134 Sunnyvale, CA 95134
USA USA
Email: jdrake@juniper.com Email: jdrake@juniper.com
Antoni Przygienda Antoni Przygienda
Ericsson Juniper Networks, Inc.
300 Holger Way 1194 N. Mathilda Drive
San Jose, CA 95134 Sunnyvale, CA 95134
USA USA
Email: antoni.przygienda@ericsson.com Email: prz@juniper.net
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