Submitted to DHC Working Group Peter De Schrijver
INTERNET DRAFT Yves T'Joens
<draft-ietf-dhc-pv4-reconfigure-00.txt> Christian Hublet
Alcatel
March 2000
Expires September 2000
Dynamic host configuration : DHCP reconfigure extension
Status of this memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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Abstract
This draft defines extensions to DHCP [DHCP] to allow dynamic
reconfiguration of a single host triggered by the DHCP server (eg. a
new IP address). This is achieved by introducing a unicast DHCP
FORCERENEW message which forces the client to the RENEW state.
1. Introduction
The procedures as described within this draft allow the dynamic
reconfiguration of individual hosts.
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Internet Draft draft-ietf-dhc-pv4-reconfigure-01 March 2000
1.1 Conventions
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. DHCP force renew
This section describes the DHCP force renew extension.
2.1 Terminology
DHCP client : host to be reconfigured using DHCP.
DHCP server : server which configured the DHCP client.
2.2 Force renew procedures
The DHCP server sends a force renew message to the client. The client
will change its state to the RENEW state. The client will then try to
renew its lease according to normal DHCP procedures. If the server
wants to assign a new IP address to the client, it will reply to the
DHCP REQUEST with a DHCP NAK. The client will then go back to the
init state and broadcast a DHCP DISCOVER message. The server can now
assign a new IP address to the client by replying with a DHCP OFFER.
If the force renew message is lost, the DHCP server will not receive
a DHCP REQUEST from the client and it should retransmit the DHCP
FORCERENEW message using an exponential backoff algorithm. Depending
on the bandwidth of the network between server and client, the server
should choose a delay. This delay grows exponentially as
retransmissions fail. The amount of retransmissions should be
limited.
2.3 Rationale
This approach has a number of advantages. It does not require new
states to be added to the DHCP client implementation. This minimizes
the amount of code to be changed. It also allows lease RENEWAL to be
driven by the server, which can be used to optimize network usage or
DHCP server load.
3. Extended DHCP state diagram
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Internet Draft draft-ietf-dhc-pv4-reconfigure-01 March 2000
+--------+ +------+
| Init / | +-->+ Init +<---------------+-------------------+
| Reboot | | +--+---+ | |
+---+----+ DHCPNAK/ -/Send DHCPDISCOVER | |
| Restart | (broadcast) | |
| | v v-------------+ | |
-/Send DHCPREQUEST | +----+------+ DHCPOFFER/DHCPDECLINE |
| (broadcast) | | Selecting |----------+ | |
v | +----+------+ | |
+---+----+ | DHCPOFFER/DHCPREQUEST | |
| Reboot +--------------+ (broadcast) | |
+---+----+ v | |
| +----+-------+ DHCPNAK /halt network
| + Requesting | | lease expired
DHCPACK/ +----+-------+ | |
Record lease | | |
set timers DHCPACK/Record lease | |
| v Set T1 & T2 | |
| +--+----+DHCPFORCE +---+---+ +---+----+
+---------------------->+ Bound +---------->+ Renew +---------->+ Rebind |
+--+-+--+T1 expires +-+-+---+ T2 expires+--+--+--+
^ /DHCPREQUEST | | /broadcast |
DHCPACK to leasing | | DHCPREQUEST |
| server | | |
+------------------------------------------+
4. Message layout
Field DHCPFORCERENEW
----- ---------------
'op' BOOTREPLY
'htype' (From "Assigned Numbers" RFC)
'hlen' (Hardware address length in octets)
'hops' 0
'xid' selected by server
'secs' 0
'ciaddr' 0
'yiaddr' 0
'siaddr' 0
'flags' 0
'giaddr' 0
'chaddr' client's hardware address
'sname' 0
'file' 0
'options' options
DHCP option 53 (DHCP message type) is extended with a new value :
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DHCPFORCERENEW
5. Failover Considerations
A DHCP server should only send a DHCPFORCERENEW when it's fully aware
of the current state of the DHCP client. In practice this means it
should only send a DHCPFORCERENEW when in "PARTNER DOWN",
"COMMUNICATIONS INTERRUPTED" or "NORMAL" state, and only for DHCP
clients of which the state is synchronised.
6. IANA Considerations
A new value for DHCP option 53 (DHCP message type) should be added to
indicate a DHCPFORCERENEW message.
7. Security Considerations
Depending on layer 2 characteristics, DHCP force renew can be used to
snoop and spoof traffic. To prevent this, the DHCPFORCERENEW message
should be authenticated using a shared secret based mechanism as
described in [DHCP-AUTH].
8. References
[DHCP] R.Droms, "Dynamic Host Configuration Protocol", RFC 2131,
March 1997.
[DHCP-AUTH] R. Droms, "Authentication for DHCP Messages", draft-
ietf-dhc-euthentication-12, October 1999.
9. Contacts
Peter De Schrijver
Alcatel Corporate Research Center
Francis Wellesplein 1, 2018 Antwerp, Belgium
Phone : +32 3 240 8569
E-mail : peter.de_schrijver@alcatel.be
Yves T'joens
Alcatel Corporate Research Center
Francis Wellesplein 1, 2018 Antwerp, Belgium
Phone : +32 3 240 7890
E-mail : yves.tjoens@alcatel.be
Christian Hublet
Alcatel Carrier Internetworking Division
De Villermontstraat 28, 2550 Kontich, Belgium
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Internet Draft draft-ietf-dhc-pv4-reconfigure-01 March 2000
Phone : +32 3 450 3322
E-mail : Christian.Hublet@alcatel.be
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