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Internet Dynamic Host Configuration Internet-Draft This document defines a method to inform a DHCPv6 server that a device has a self-generated or statically configured address. About This Document The latest revision of this draft can be found at . Status information for this document may be found at . Discussion of this document takes place on the Dynamic Host Configuration Working Group mailing list (), which is archived at . Subscribe at . Source for this draft and an issue tracker can be found at .

Introduction It is very common operational practice, especially in enterprise networks, to use IPv4 DHCP logs for troubleshooting or security purposes. Examples of this include a helpdesk dealing with a ticket such as "The CEO's laptop cannot connect to the printer"; if the MAC address of the printer is known (for example from an inventory system), the IPv4 address can be retrieved from the DHCP logs and the printer pinged to determine if it is reachable. Another common example is a Security Operations team discovering suspicious events in outbound firewall logs and then consulting DHCP logs to determine which employee's laptop had that IPv4 address at that time so that they can quarantine it and remove the malware. This operational practice relies on the DHCP server knowing the IP address assignments. Therefore, the practice does not work if static IP addresses are manually configured on devices or self-assigned addresses (such as when self-configuring an IPv6 address using SLAAC ) are used. The lack of this parity with IPv4 is one of the reasons that some enterprise networks are unwilling to deploy IPv6. This document provides a mechanism for a device to inform the DHCPv6 server that it has a self-configured IPv6 address (or has a statically configured address), and thus provides parity with IPv4 in this aspect.

Conventions and Definitions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here.

Description of Mechanism After successfully assigning a self-generated IPv6 address on one of its interfaces, an end-host implementing this specification SHOULD multicast an ADDR-REG-INFORM message in order to inform the DHCPv6 server that this address is in use.

Address Registration Procedure | | | | | | | ADDR-REG-INFORM | |------------------------------------------------->| | | |Register / log | | REPLY (optional) |address |<------------------------------------------------- ]]>

DHCPv6 ADDR-REG-INFORM Message The DHCPv6 client sends an ADDR-REG-INFORM message to inform that an IPv6 address is in use. The format of the ADDR-REG-INFORM message is described as follows:

DHCPv6 ADDR-REG-INFORM message

The ADDR-REG-INFORM message MUST NOT contain server-identifier option and MUST contain the IA Address option. The ADDR-REG-INFORM message is dedicated for clients to initiate an address registration request toward an address registration server. Consequently, clients MUST NOT put any Option Request Option(s) in the ADDR-REG-INFORM message. Clients MAY include other options, such as the Client FQDN Option . Clients MUST discard any received ADDR-REG-INFORM messages. Servers MUST discard any ADDR-REG-INFORM messages that meet any of the following conditions:

• the address is not appropriate for the link;
• the message does not include a Client Identifier option;
• the message includes a Server Identifier option;
• the message does not include the IA Address option;
• the message includes an Option Request Option.

DHCPv6 Address Registration Procedure The DHCPv6 protocol is used as the address registration protocol when a DHCPv6 server performs the role of an address registration server. The DHCPv6 IA Address option is adopted in order to fulfill the address registration interactions.

DHCPv6 Address Registration Request The end-host sends a DHCPv6 ADDR-REG-INFORM message to the address registration server to the All_DHCP_Relay_Agents_and_Servers multicast address (ff02::1:2). The host MUST only send the packet on the network interface that has the address being registered (i.e. if the host has multiple interfaces with different addresses, it should only send the packet on the interface with the address being registered). The host MUST send the packet from the address being registered. This is primarily for "fate sharing" purposes - for example, if the network implements some form of L2 security to prevent a client from spoofing other clients' addresses this prevents an attacker from spoofing ADDR-REG-INFORM messages. The host MUST send separate messages for each address being registered. The end-host MUST include a Client Identifier option in the ADDR-REG-INFORM message. The host MUST only send the ADDR-REG-INFORM message for valid () addresses of global scope (). The host MUST NOT send the ADDR-REG-INFORM message for addresses configured by DHCPv6. The host MUST NOT send the ADDR-REG-INFORM message if it has not received any Router Advertisement message with either M or O flags set to 1. After receiving this ADDR-REG-INFORM message, the address registration server SHOULD verify that the address being registered is "appropriate to the link" as defined by . If the server believes that  address being registered is not appropriate to the link , it MUST drop the message, and SHOULD log this fact. If the address is appropriate, the server:

• SHOULD register or update a binding between the provided Client Identifier and IPv6 address in its database;
• SHOULD log the address registration information (as is done normally for clients which have requested an address), unless configured not to do so;
• SHOULD mark the address as unavailable for use and not include it in future ADVERTISE messages.
• MAY send back a REPLY message.

If the DHCPv6 server does not support the address registration function, it MUST drop the message, and SHOULD log this fact. DHCPv6 relay agents that relay address registration messages directly from clients SHOULD include the client's link-layer address in the relayed message using the Client Link-Layer Address option ()

DHCPv6 Address Registration Acknowledgement The server MAY choose to acknowledge receipt of an ADDR-REG-INFORM message by sending a REPLY message back. The REPLY message only indicates that the ADDR-REG-INFORM message has been received. It MUST NOT be considered as any indication of the address validity.

Registration Expiry and Refresh The client MUST refresh the registration every AddrRegRefresh seconds, where AddrRegRefresh is min(1/3 of the Valid Lifetime filed in the very first PIO received to form the address; 4 hours ). Registration refresh packets SHOULD be retransmitted using the same logic as described in the 'Retransmission' section below. In particular, retransmissions SHOULD be jittered to avoid synchronization causing a large number of registrations to expire at the same time. If the address registration server does not receive such a refresh after the preferred lifetime has passed, it SHOULD remove the record of the Client-Identifier-to-IPv6-address binding. The client MAY choose to notify the server when an address is no longer being used (the client is disconnecting from the network, the address lifetime expired or the address is being removed from the interface). To indicate that the address is not being used anymore the client MUST set the preferred-lifetime and valid-lifetime fields of the IA Address option to zero.

Retransmission The client can not rely on the server acknowledging recipt of the registration message with a REPLY, as the server might not support address registration or choose not to acknowledge. To reduce the effects of packet loss on registration, the client SHOULD send each registration message ADDREG_XMIT times. If the acknowledgement is received, the client SHOULD stop retransmission. The minimal interval between retransmissions ADDRREG_XMIT be at least ADDREG_RT_DELAY second and should be jittered to prevent overloading the DHCP infrastructure when a new prefix is announced to the link via Router Advertisement. It should be noted that ADDR-REG-INFORM is the first and the only DHCPv6 message which does not require acknowledgement from the server, so the retransmission logic described in Section 15 of RFC8415 is not really applicable. The default values for the variables:

• ADDRREG_XMIT 3
• ADDREG_RT_DELAY 3 secs

The client SHOULD allow those variables to be configured by the administrator.

Security Considerations An attacker may attempt to register a large number of addresses in quick succession in order to overwhelm the address registration server and / or fill up log files. These attacks may be mitigated by using generic DHCPv6 protection such as the AUTH option . The similar attack vector exist today, e.g. an attacker can DoS the server with messages contained spoofed DUIDs. If a network is using FCFS SAVI [RFC6620], then the DHCPv6 server can trust that the ADDR-REG-INFORM message was sent by the legitimate owner of the address. This prevents a host from registering an address owned by another host. One of the use-cases for the mechanism described in this document is to identify sources of malicious traffic after the fact. Note, however, that as the device itself is responsible for informing the DHCPv6 server that it is using an address, a malicious or compromised device can simply not send the ADDR-REG-INFORM message. This is an informational, optional mechanism, and is designed to aid in troubleshooting and forensics. On its own, it is not intended to be a strong security access mechanism.

IANA Considerations This document defines a new DHCPv6 message, the ADDR-REG-INFORM message (TBA1) described in Section 4, that requires an allocation out of the registry of Message Types defined at http://www.iana.org/assignments/dhcpv6-parameters/

Normative References In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. This document specifies the architectural characteristics, expected behavior, textual representation, and usage of IPv6 addresses of different scopes. According to a decision in the IPv6 working group, this document intentionally avoids the syntax and usage of unicast site-local addresses. [STANDARDS-TRACK] This document specifies the steps a host takes in deciding how to autoconfigure its interfaces in IP version 6. The autoconfiguration process includes generating a link-local address, generating global addresses via stateless address autoconfiguration, and the Duplicate Address Detection procedure to verify the uniqueness of the addresses on a link. [STANDARDS-TRACK] This document specifies the format and mechanism that is to be used for encoding the client link-layer address in DHCPv6 Relay-Forward messages by defining a new DHCPv6 Client Link-Layer Address option. This document describes the Dynamic Host Configuration Protocol for IPv6 (DHCPv6): an extensible mechanism for configuring nodes with network configuration parameters, IP addresses, and prefixes. Parameters can be provided statelessly, or in combination with stateful assignment of one or more IPv6 addresses and/or IPv6 prefixes. DHCPv6 can operate either in place of or in addition to stateless address autoconfiguration (SLAAC). This document updates the text from RFC 3315 (the original DHCPv6 specification) and incorporates prefix delegation (RFC 3633), stateless DHCPv6 (RFC 3736), an option to specify an upper bound for how long a client should wait before refreshing information (RFC 4242), a mechanism for throttling DHCPv6 clients when DHCPv6 service is not available (RFC 7083), and relay agent handling of unknown messages (RFC 7283). In addition, this document clarifies the interactions between models of operation (RFC 7550). As such, this document obsoletes RFC 3315, RFC 3633, RFC 3736, RFC 4242, RFC 7083, RFC 7283, and RFC 7550. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. This document specifies a new Dynamic Host Configuration Protocol for IPv6 (DHCPv6) option that can be used to exchange information about a DHCPv6 client's Fully Qualified Domain Name (FQDN) and about responsibility for updating DNS resource records (RRs) related to the client's address assignments. [STANDARDS-TRACK]

Acknowledgments Much thanks to Bernie Volz for significant review and feedback, as well as Stuart Cheshire, Alan DeKok, Ryan Globus, Erik Kline, Ted Lemon, Eric Levy-Abegnoli, Mark Smith, Eric Vynke, Timothy Winter for their feedback, comments and guidance. This document borrows heavily from a previous document, draft-ietf-dhc-addr-registration, which defined "a mechanism to register self-generated and statically configured addresses in DNS through a DHCPv6 server". That document was written Sheng Jiang, Gang Chen, Suresh Krishnan, and Rajiv Asati.

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