RFC 3203
DHCP reconfigure extension
DHCP reconfigure extension 🎀
okay bestie, this is RFC 3203 🦋 It's a Standards Track doc from December 2001, written by Y. T'Joens and C. Hublet (both at Alcatel) and P. De Schrijver (at Mind). It came out of the Network Working Group, and it doesn't obsolete or update any other RFCs, since the title block doesn't list any. 💅
Status of this Memo ✨
This is an Internet standards track protocol for the Internet community, and the authors want discussion and suggestions for improvements 💬 For the current standardization state and status, check the "Internet Official Protocol Standards" (STD 1). Distribution of this memo is unlimited. 🌸
Copyright Notice 💜
Copyright (C) The Internet Society (2001). All Rights Reserved.
Abstract 🔥
this doc extends DHCP (Dynamic Host Configuration Protocol) so the DHCP server can dynamically reconfigure one single host, like giving it a new IP address and/or new local configuration parameters 🧚 The trick is a unicast FORCERENEW message that forces the client into the RENEW state. It also covers how hosts that use the DHCP INFORM message to get configuration info should behave. ✨
1. Introduction 🌈
The procedures in this document let you dynamically reconfigure 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 is all about the FORCERENEW message extension. 💖
2.1 Terminology
DHCP client: a host that gets reconfigured using DHCP. 🎀
DHCP server: the server that configured the DHCP client. 🎀
2.2 Force renew procedures
Okay so the DHCP server sends a unicast FORCERENEW message to the client. When the client gets that unicast FORCERENEW, it switches to the RENEW state and tries to renew its lease the normal DHCP way 🦋 If the server wants to give the client a brand new IP address, it replies to the DHCP REQUEST with a DHCP NAK. The client then goes back to the init state and broadcasts a DHCP DISCOVER message, and the server can now assign a new IP address by replying with a DHCP OFFER. 💅
If the FORCERENEW message gets lost, the DHCP server won't receive a DHCP REQUEST from the client, so it should retransmit the FORCERENEW message using an exponential backoff algorithm. ⏳ The server should pick a delay based on the bandwidth of the network between server and client, and that delay grows exponentially as retransmissions fail. The number of retransmissions should be limited. 🙈
The procedures above assume the server sends a unicast FORCERENEW message to the client. A client that receives a multicast FORCERENEW message should silently discard it. 🚫
Here's a fun one 🧚 A client might have gotten its network address some other way (like manual configuration) and then used a DHCP INFORM request to grab other local configuration parameters. Clients like that should respond to a unicast FORCERENEW message by sending a new DHCP INFORM request, so they can pick up a possibly new set of local configuration parameters. Just note that these procedures are limited to the options that are eligible for configuration by DHCP, and they should not override manually configured parameters. 🍓
Also, using FORCERENEW to reconfigure a client address or local configuration parameters can interrupt active sessions, so these procedures should be used in controlled circumstances. ⚠️
2.3 Example usage
2.3.1 Embedded DHCP clients
Home gateways (more generically Network Termination equipment) can be autoconfigured for public networking through DHCP, as described in [DSL_autoconf]. To allow service changes or service interruptions, FORCERENEW can trigger the home gateway to contact the DHCP server before its lease expires. 🏠✨
2.3.2 Hospitality service scenario
In self provisioned networks, like hotel rooms, the hotel-owned DHCP server can hand out limited use IP addresses. That lets the customer use local services or pick external services from a web browser interface. 🏨 To reach external services through other service providers, like global internet services or enterprise VPN services, the DHCP server can trigger the client to start a new DHCP initialization session, so it can get something like a globally routed IP address. 🌍
2.3.3 Network renumbering
Under tightly controlled conditions, the FORCERENEW procedures can be used to brute force the renumbering of entire subnets, one client at a time, under the control of a DHCP server. 🔧
2.4 Rationale
This approach has a few big advantages 👑 It doesn't require new states in the DHCP client implementation, which keeps the amount of code that has to change pretty small. It also lets the server drive lease RENEWAL, which can help 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 🎀
The FORCERENEW message uses the normal DHCP message layout, plus one new DHCP message type. DHCP option 53 (DHCP message type) gets a new value: DHCPFORCERENEW (9) ✨
5. IANA Considerations 📋
The new value for DHCP option 53 (DHCP message type) that indicates a DHCPFORCERENEW message is 9. 🔢
6. Security Considerations 🚨
🚨 This section is serious business, bestie. 🚨
In some network environments FORCERENEW can be used to snoop and spoof traffic, so the FORCERENEW message MUST be authenticated using the procedures described in [DHCP-AUTH]. FORCERENEW messages that fail authentication should be silently discarded by the client. 🔐
6.1 Protocol vulnerabilities
The mechanism in this document is vulnerable to a denial of service attack where a client gets flooded with bogus FORCERENEW messages 😭 The calculations needed to authenticate those bogus FORECERENEW messages may overwhelm the device the client is running on. 💀
7. References 📚
- [DHCP] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March 1997.
- [DHCP-AUTH] Droms, R. and W. Arbaugh, "Authentication for DHCP Messages", RFC 3118, June 2001.
- [DSL_autoconf] Technical Report TR-044, "Auto-Configuration for Basic Internet (IP-based) Services", DSL Forum, November 2001.
- [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
8. Acknowledgements 🫶
The authors thank David Allan, Nortel, for the constructive comments on these procedures. 💖
9. Authors' Addresses 💌
Yves T'joens
Alcatel Network Strategy Group
Francis Wellesplein 1, 2018 Antwerp, Belgium
Phone: +32 3 240 7890
EMail: yves.tjoens@alcatel.be
Peter De Schrijver
Mind NV
Vaartkom 11
3000 Leuven
EMail: p2@mind.be
Alcatel Broadband Networking Division
Veldkant 33b, 2550 Kontich, Belgium
Phone: +32 3 450 3322
EMail: Christian.Hublet@alcatel.be10. Full Copyright Statement 💜
Copyright (C) The Internet Society (2001). All Rights Reserved.
This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English.
The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgement 🌸
Funding for the RFC Editor function is currently provided by the Internet Society. 🎉
📦 where this page comes from
- ietf: rfc3203 2001-12
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms