Submitted to DHC Working Group Peter De Schrijver INTERNET DRAFT Yves T'Joens
<draft-ietf-dhc-pv4-reconfigure-03.txt><draft-ietf-dhc-pv4-reconfigure-04.txt> Christian Hublet Alcatel April 2001 Expires September, 2001 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. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months. Internet-Drafts may be updated, replaced, or obsoleted by other documents at any time. It is not appropriate to use Internet- Drafts as reference material or to cite them other than as a ``working draft'' or ``work in progress.'' The list of current Internet-Drafts can be accessed at http://www.ietf.org/1id-abstracts.html The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html.To view the entire list of current Internet-Drafts, please check the "1id-abstracts.txt" listing contained in the Internet-Drafts Shadow Directorieson ftp.is.co.za (Africa), ftp.nordu.net (Northern Europe), ftp.nis.garr.it (Southern Europe), munnari.oz.au(Pacific Rim), ftp.ietf.org (US East Coast), or ftp.isi.edu (US West Coast). Distribution of this memo is unlimited. 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 DHCPFORCERENEW message which forces the client to the RENEW state. The behaviour for hosts using the DHCP INFORM message to obtain configuration information is also described. 1. Introduction The procedures as described within this draft allow the dynamic reconfiguration of individual hosts. 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 renewFORCERENEW message 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 renewunicast FORCERENEW message to the client. TheUpon receipt of the unicast FORCERENEW message, the client will change its state to the RENEW state. The clientstate, and 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 renewFORCERENEW message is lost, the DHCP server will not receive a DHCP REQUEST from the client and it should retransmit the DHCPFORCERENEW 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. The procedures described above assume the server to send a unicast FORCERENEW message to the client. Receipt of a multicast FORCERENEW message by the client should be silently discarded. It can be that a client has obtained a network address through some other means (e.g., manual configuration) and has used a DHCPINFORMDHCP INFORM request to obtain other local configuration parameters. Such clients should respond to the receipt of DHCPa unicast FORCERENEW message with a new DHCP INFORM request so as to obtain a potential new set of local configuration parameters. 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 +--------+ +------+ | 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' optionsThe FORCERENEW message makes use of the normal DHCP message layout with the introduction of a new DHCP message type. DHCP option 53 (DHCP message type) is extended with a new value : DHCPFORCERENEW (TBD) 5. IANA Considerations The new value for DHCP option 53 (DHCP message type) to indicate a DHCPFORCERENEW message is TBD. 6. Security Considerations As in some network environments DHCPFORCERENEWFORCERENEW can be used to snoop and spoof traffic, the DHCPFORCERENEWFORCERENEW message MUST be authenticated using the procedures as described in [DHCP-AUTH]. FORCERENEW messages failing the authentication should be silently discarded by the client. 7. References [DHCP] R.Droms, "Dynamic Host Configuration Protocol", RFC 2131, March 1997. [DHCP-AUTH] R. Droms et al., "Authentication for DHCP Messages", RFCxxxx, yyyy 2001. [RFC2119] S. Bradner, "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 8. Acknowledgements The authors would like to thank David Allen,Allan, Nortel, for the contributionconstructive comments to these procedures. 9. Contacts Peter De Schrijver Alcatel Network Strategy Group Francis Wellesplein 1, 2018 Antwerp, Belgium Phone : +32 3 240 8569 E-mail : firstname.lastname@example.org Yves T'joens Alcatel Network Strategy Group Francis Wellesplein 1, 2018 Antwerp, Belgium Phone : +32 3 240 7890 E-mail : email@example.com Christian Hublet Alcatel Carrier Internetworking Division De Villermontstraat 28, 2550 Kontich, Belgium Phone : +32 3 450 3322 E-mail : Christian.Hublet@alcatel.be 8. 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