DHC A. Kostur
Internet-Draft Incognito
Intended status: Standards Track March 02, 2014
Expires: September 01, 2014
DHC Load Balancing Algorithm for DHCPv6
draft-ietf-dhc-dhcpv6-load-balancing-01
Abstract
This document proposes a method of algorithmic load balancing for
IPv6 Dynamic Host Configuration Protocol (DHCPv6) traffic. It
enables multiple, cooperating servers to decide which one should
service a client, without necessarily exchanging any information
between the servers. The server selection is based on the servers
hashing client DHCP Unique Identifiers (DUIDs) when multiple DHCPv6
servers are available to service DHCPv6 clients. The proposed
technique provides for efficient server selection when multiple
DHCPv6 servers offer services on a network without requiring any
changes to existing DHCPv6 clients. This algorithm is an extension
of an already defined and proven algorithm used for DHCPv4, as
described in RFC 3074.
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 September 01, 2014.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2
2. Background and External Requirements . . . . . . . . . . . . . 3
3. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Messages with a Server Identifier . . . . . . . . . . . . 3
3.2. RENEWs with the DHCPv6 servers sharing lease information . 3
3.3. RENEWs with the DHCPv6 servers not sharing lease informatio 4
3.4. Selecting the STID . . . . . . . . . . . . . . . . . . . . 4
3.5. Replacing the secs field . . . . . . . . . . . . . . . . . 5
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5
7.1. Normative References . . . . . . . . . . . . . . . . . . . 5
7.2. Informative References . . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
This document is intended to extend the algorithm described in DHC
Load Balancing Algorithm [RFC3074] to apply to DHCPv6 [RFC3315]
traffic. Most of the terminology and procedures are identical to the
ones specified in RFC 3074. As a short summary: servers which are
participating in load balancing calculate hash values for the Service
Transaction ID (STID) based on client-specific values (the client
DUID for DHCPv6, the Client ID or CHADDR field for DHCPv4) for each
incoming UDP packet. This hash is then used to select a hash bucket.
Servers are assigned to service particular buckets.
Load balancing is not the same as failover, as load balancing is not
attempting to address any redundancy concerns [RFC6853]. Load
balancing does not attempt to address the issues of configuration or
data synchronization between DHCPv6 servers. However, load balancing
may be desirable in a failover set of servers in order to reduce the
load on the servers in normal operations (see Section 5.3 of
[RFC6853]), and certain desirable behaviors can occur if load
balancing is aware that data synchronization is occurring.
1.1. Requirements Language
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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].
2. Background and External Requirements
The requirements for DHCPv6 are substantially the same as for DHCPv4,
replacing DHCPDISCOVER with SOLICIT, DHCPREQUEST with REQUEST,
CONFIRM, RENEW, or REBIND (as appropriate), etc.
3. Operation
A DHCPv6 server performing this load balancing will operate in
substantially the same manner as if it were a DHCPv4 server load
balancing an incoming DHCPv4/BOOTP packet with the following
differences.
Load balancing only applies to incoming UDP DHCPv6 messages that
servers would normally process: SOLICIT, REQUEST, CONFIRM, RENEW,
REBIND, RELEASE, DECLINE, INFORMATION-REQUEST, and RECONFIGURE-
REQUEST [RFC6977]. RELAY-FORWARDs are processed based on the content
of the most encapsulated packet (ie: the above listed message types).
Future message types will have to be considered as they are proposed
as to how they may be load balanced.
LEASEQUERY [RFC5007] messages with a query based on IP SHOULD NOT
have load balancing applied to them. The Client DUID that is
supplied in a LEASEQUERY message identifies the requestor, and not an
actual client device. This could result in the server which answered
the client device deciding that it should not answer the requestor.
LEASEQUERY messages with a query based on Client ID SHOULD have load
balancing applied to them, using the Client DUID contained in the
OPTION_LQ_QUERY option for the STID.
DHCPV4-QUERY [I-D.ietf-dhc-dhcpv4-over-dhcpv6] messages SHOULD NOT be
load balanced, but should be subject to DHCPv4 load balncing, if the
server supports it.
ADVERTISE, REPLY, RELAY-REPL, LEASEQUERY-REPLY, LEASEQUERY-DONE,
LEASEQUERY-DATA, and RECONFIGURE-REPLY are messages which should not
be received by a DHCPv6 server and thus are not considered in this
document.
3.1. Messages with a Server Identifier
Messages which contain a Server Identifier to direct that message to
a specific server SHOULD be processed as if load balancing were not
in play, with the exception of RENEWs.
3.2. RENEWs with the DHCPv6 servers sharing lease information
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A DHCPv6 server receiving a RENEW with the server's Server Identifier
specified MAY choose to ignore the request if the load balancing
algorithm decides that this server should not process this message.
Let us assume the following sequence of events:
1. There is a pair of DHCPv6 servers that are known to be exchanging
lease information with each other
2. The first server fails and is no longer servicing DHCPv6 clients
3. Some number of DHCPv6 clients are bound to the second DHCPv6
server (whether by performing a SOLCIT-ADVERTISE-REQUEST-REPLY
sequence, or by REBINDing to the second server)
4. The first server is restored to service and is able to service
DHCPv6 clients
At this point, a disproportionate set of DHCPv6 clients are now bound
to the second DHCPv6 server. If the second DHCPv6 server is
permitted to ignore the RENEW even though the Server Identifier would
indicate that it should respond, then the clients which should be
answered by the first server will get no response to the RENEW that
contains the second server's Server Identifier and will perform the
normal retry mechanisms. At some point the client will transition
into the REBIND state and will attempt to REBIND. That REBIND will
not have a Server Identifier and will be received by both DHCPv6
servers. Since the servers were exchanging lease information, the
first DHCPv6 server would have sufficient information to be able to
REPLY to the client to extend the lease and those clients would now
be bound to the first DHCPv6 server again. Over time this would
result in the DHCPv6 population being rebalanced.
3.3. RENEWs with the DHCPv6 servers not sharing lease information
A DHCPv6 server receiving a RENEW with the server's Server Identifier
specified SHOULD be processed as if load balancing were not in play.
If the server ignored these RENEWs, the requesting device would
eventually transition to REBIND, and the other servers may not have
any lease information to answer the REBIND with, forcing the client
to eventually drop its lease and start again from SOLICIT.
3.4. Selecting the STID
DHCPv6 servers MUST use the client's DUID in its entirety as the
STID. This is different than RFC 3074 which limited the STID to 16
bytes.
An INFORMATION-REQUEST may have no client DUID in the message.
Calculate the hash as if a 0-length DUID were supplied, effectively
assigning those messages to hash bucket 0.
A LEASEQUERY based on Client ID MUST use the Client ID contained in
the OPTION_LQ_QUERY option.
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3.5. Replacing the secs field
A DHCPv6 server providing the capability of Delayed Service SHOULD
use the value in the OPTION_ELAPSED_TIME wherever RFC 3074 makes
reference to the secs field.
4. Acknowledgements
Thanks to Bernie Volz, Steve Gonczi, Ted Lemon, and Rob Stevens as
this document heavily borrows from their previous work on RFC 3074,
as well as Bernie and Tomek Mrugalski's additional comments during
the discussions.
5. IANA Considerations
This memo includes no request to IANA.
6. Security Considerations
This proposal in and by itself provides no security, nor does it
impact existing security. Servers using this algorithm are
responsible for ensuring that if the contents of the HBA are
transmitted over the network as part of the process of configuring
any server, that message be secured against tampering, since
tampering with the HBA could result in denial of service for some or
all clients.
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3074] Volz, B., Gonczi, S., Lemon, T. and R. Stevens, "DHC Load
Balancing Algorithm", RFC 3074, February 2001.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C. and
M. Carney, "Dynamic Host Configuration Protocol for IPv6
(DHCPv6)", RFC 3315, July 2003.
[RFC5007] Brzozowski, J., Kinnear, K., Volz, B. and S. Zeng, "DHCPv6
Leasequery", RFC 5007, September 2007.
[RFC6977] Boucadair, M. and X. Pougnard, "Triggering DHCPv6
Reconfiguration from Relay Agents", RFC 6977, July 2013.
7.2. Informative References
[I-D.ietf-dhc-dhcpv4-over-dhcpv6]
Sun, Q., Cui, Y., Siodelski, M., Krishnan, S. and I.
Farrer, "DHCPv4 over DHCPv6 Transport", Internet-Draft
draft-ietf-dhc-dhcpv4-over-dhcpv6-05, February 2014.
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[RFC6853] Brzozowski, J., Tremblay, J., Chen, J. and T. Mrugalski,
"DHCPv6 Redundancy Deployment Considerations", BCP 180,
RFC 6853, February 2013.
Author's Address
Andre Kostur
Incognito Software Inc.
Suite 500 - 375 Water St.
Vancouver, BC V6B 5C6
CA
Phone: +1 604 678 2864
Email: akostur@incognito.com
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