DHC Working Group D. Miles, Ed. Internet-Draft S. Ooghe Intended status: Standards Track Alcatel-Lucent Expires: April 16, 2010 W. Dec Cisco Systems S. Krishnan A. Kavanagh Ericsson October 13, 2009 Lightweight DHCPv6 Relay Agent draft-ietf-dhc-dhcpv6-ldra-01 Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. 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 and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on April 16, 2010. Copyright Notice Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Miles, et al. Expires April 16, 2010 [Page 1] Internet-Draft LDRA October 2009 Abstract This document proposes a Lightweight DHCPv6 Relay Agent (LDRA) that is used to insert relay agent options in DHCPv6 message exchanges identifying client-facing interfaces. The LDRA can be implemented in existing access nodes (such as DSLAMs and Ethernet switches) that do not support IPv6 control or routing functions. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 2. Background . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. Server Considerations . . . . . . . . . . . . . . . . . . . . 4 5. Message Format . . . . . . . . . . . . . . . . . . . . . . . . 5 5.1. Relay-Forward Message . . . . . . . . . . . . . . . . . . 5 5.2. Relay-Reply Message . . . . . . . . . . . . . . . . . . . 5 5.3. Mandatory DHCP Options . . . . . . . . . . . . . . . . . . 6 5.3.1. Relay-Message Option . . . . . . . . . . . . . . . . . 6 5.3.2. Interface-ID Option . . . . . . . . . . . . . . . . . 6 6. Agent Behaviour . . . . . . . . . . . . . . . . . . . . . . . 7 6.1. Relaying a Client Message . . . . . . . . . . . . . . . . 7 6.1.1. Client Message Validation . . . . . . . . . . . . . . 7 6.1.2. Trusted and Untrusted Interfaces . . . . . . . . . . . 8 6.2. Relaying a Relay-Reply message from the network . . . . . 8 7. Network Topology . . . . . . . . . . . . . . . . . . . . . . . 9 7.1. Client and Server on Same Link . . . . . . . . . . . . . . 10 7.2. Client and Server behind Relay Agent . . . . . . . . . . . 10 7.3. Relay Agent in Front of LDRA . . . . . . . . . . . . . . . 11 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 13 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 10. Security Considerations . . . . . . . . . . . . . . . . . . . 13 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13 11.1. Normative References . . . . . . . . . . . . . . . . . . . 13 11.2. Informative References . . . . . . . . . . . . . . . . . . 13 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14 Miles, et al. Expires April 16, 2010 [Page 2] Internet-Draft LDRA October 2009 1. Introduction DHCPv6 Relay-Agents [RFC3315] are deployed to forward DHCPv6 messages between clients and servers when they are not on the same IPv6 link and are often implemented alongside a routing function in a common node. A Lightweight DHCPv6 Relay Agent (LDRA) allows Relay Agent Information to be inserted by an access node that performs a link- layer bridging (i.e. non-routing) function. A LDRA resides on the same IPv6 link as the client and a DHCPv6 Relay Agent or Server and is functionally the equivalent of the Layer 2 DHCP Relay draft[L2RA] proposed for DHCPv4 operation. Unlike a DHCPv6 Relay-Agent specified in [RFC3315], a LDRA does not implement any IPv6 control functions (e.g. ICMPv6) or have any routing capability in the node. 1.1. Requirements Language 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 A variety of different link-layer network topologies exist for the aggregation of IPv6 nodes into one or more routers. In Layer 2 aggregation networks (IEEE 802.1D bridging or similar) that have many nodes on a single link, a DHCPv6 server or DHCP relay agent would normally be unaware of how a DHCP client is attached to the network. The LDRA allows Relay Agent Information, including the Interface-ID option [RFC3315], to be inserted by the access node so that it may be used by the DHCPv6 server for client identification. A typical application in a broadband service provider may be as an equivalent to the Broadband Forum TR-101 Layer 2 DHCP Relay Agent[TR-101] described in [L2RA] 3. Terminology Access Node A device that combines many interfaces onto one link. An access node is not IP-aware in the data path Address An IP layer identifier for an interface or set of interfaces Miles, et al. Expires April 16, 2010 [Page 3] Internet-Draft LDRA October 2009 Client-facing An interface on the access node that carries traffic towards the DHCPv6 client Host A non-routing IPv6 node that is participating in DHCPv6 message exchange IP Internet Protocol Version 6 (IPv6) LDRA Lightweight DHCPv6 Relay Agent Lightweight Relay Agent A function on the access node that intercepts DHCP messages between clients and servers. The function exists as a bump in the wire on the IP link. Link A communication facility or medium over which nodes can communicate at the link layer Link-local address An IP address having only local-scope, indicated by having the address prefix FE80::/10, that can be used to reach neighbouring nodes attached to the same link. Every interface has a link-local address. Network-facing An interface on the access node that carries traffic towards the DHCPv6 server(s) Node A device that implements IPv6 Router A node that forwards packets not directly addressed to itself Relay Agent A node that acts as an intermediary to deliver DHCP messages between clients and servers and being on the same link as the client Unspecified address An IP address that is comprised entirely of zeros 4. Server Considerations This document updates the behavior specified in section 11 of DHCP for IPv6 [RFC3315]. RFC3315 states, in part: Miles, et al. Expires April 16, 2010 [Page 4] Internet-Draft LDRA October 2009 o If the server receives the message from a forwarding relay agent, then the client is on the same link as the one to which the interface, identified by the link-address field in the message from the relay agent, is attached. DHCP server implementations conforming to this specification must, for the purposes of address selection, ignore any link-address field whose value is zero. In the text from RFC3315 above, "link-address" refers both to the link-address field of the Relay-forward message, and also the link-address fields in any Relay-forward messages that may be nested within the Relay-forward message. 5. Message Format The Lightweight DHCPv6 Relay Agent (LDRA) exchanges DHCP messages between clients and servers using the message formats established in [RFC3315]. To maintain interoperability with existing DHCP relays and servers the message format is unchanged from [RFC3315]. The LDRA implements the same message types as a normal DHCPv6 Relay Agent. They are: o Relay-Forward Messages o Relay-Reply Messages 5.1. Relay-Forward Message The Relay-Forward message is created by any DHCPv6 Relay Agent, including an LDRA, to forward messages between clients and servers or other relay agents. These messages are built as specified in [RFC3315] The Relay-Forward message contains relay agent parameters that identify the client-facing interface on which any reply messages should be forwarded. These parameters are link-address, peer-address and Interface-ID. The link-address parameter MUST be set to the unspecified address. The Interface-ID Relay Agent Option MUST be included in the Relay-Forward message. The LDRA MAY insert additional relay agent options. 5.2. Relay-Reply Message The Relay-Reply message is constructed by a DHCPv6 server to send parameters to a DHCP client when a relay agent is present between the server and the client. The Relay-Reply message may be sent after an initial Relay-Forward message as the parameters link-address, peer- Miles, et al. Expires April 16, 2010 [Page 5] Internet-Draft LDRA October 2009 address, Interface-ID and the relay agent's IP address are learnt from the Relay-Forward message. The server MUST include the Interface-ID option in the Relay-Reply Message to indicate to the LDRA the interface on which the de- capsulated message should be forwarded. 5.3. Mandatory DHCP Options Parameters are exchanged between DHCP client, relay-agent and server through the use of DHCP options. There are a set of mandatory DHCP options that MUST be included by the LDRA in all Relay-Forward and Relay-Reply messages. These are the: o Relay-Message Option o Interface-ID Option 5.3.1. Relay-Message Option A DHCPv6 Relay Agent relays messages between clients and servers or other relay agents through Relay-Forward and Relay-Reply message types. The original client DHCP message (i.e. the packet payload, excluding UDP and IP headers) is encapsulated in a Relay Message option [RFC3315]. As an LDRA does not implement ICMPv6, fragmentation of Relay-Messages is not supported. If a Relay-Message would exceed the MTU of the outgoing interface it MUST be discarded and an error condition SHOULD be logged. 5.3.2. Interface-ID Option The LDRA MUST include the Interface-ID option [RFC3315] in all Relay- Forward messages. When a LDRA receives a Relay-reply message with an Interface-ID option present and link-address unspecified, the LDRA MUST relay the decapsulated message to the client on the interface identified in the Interface-ID option. Servers MAY use the Interface-ID for parameter assignment policies. The format of the Interface-ID is outside the scope of this contribution. The Interface-ID SHOULD be considered an opaque value, i.e. the server SHOULD NOT try to parse the contents of the Interface-ID option. The LDRA SHOULD use the same Interface-ID value for a given interface, and this value SHOULD be retained across restarts. This is because, if the Interface-ID changes, a server will not be able to use it reliably in parameter assignment policies. Miles, et al. Expires April 16, 2010 [Page 6] Internet-Draft LDRA October 2009 6. Agent Behaviour The LDRA MUST have each of its interfaces configured as either client-facing or network (DHCPv6 server) facing. The LDRA uses the notion of client-facing and network-facing interfaces to process the DHCPv6 messages. 6.1. Relaying a Client Message When a DHCPv6 message (defined in [RFC3315]) is received on any client-facing interface, the LDRA MUST intercept and process the message. The LDRA MUST also prevent the original message from being forwarded on the network facing interface. The lightweight relay agent adds any other options it is configured or required to include in the Relay-Forward message. The LDRA MUST set the link-address field of the Relay-forward message to the Unspecified Address (::) and MUST include the Interface-ID option in all DHCP Relay-Forward messages. If the message received on the client-facing interface is a Relay- Forward message, the LDRA MUST set the Hop-Count field in the newly created Relay-Forward message to the value of the hop-count field in the received message incremented by 1 as specified in [RFC3315]. The LDRA MUST copy the IP destination and link-layer destination addresses from the client-originated message into the IP destination address and link-layer destination address of the Relay-forward message. The LDRA MUST copy the IP source address from the client-originated message into the peer-address field of the Relay-forward message. The LDRA MUST copy the link-layer source address from the client- originated message into the link-layer source address of the Relay- forward message. 6.1.1. Client Message Validation On receipt of a DHCP message on the client facing interface, the LDRA MUST discard a message if it is of one of following message types: o ADVERTISE (2) o REPLY (7) o RECONFIGURE (10) Miles, et al. Expires April 16, 2010 [Page 7] Internet-Draft LDRA October 2009 o RELAY-REPLY (13) Options contained in the DHCPv6 message MUST NOT be validated by the LDRA, making it the responsibility of the DHCP server to check message option validity and allow new options to be introduced without changes on the LDRA. 6.1.2. Trusted and Untrusted Interfaces In [RFC3046] DHCPv4 relay-agents had their client-facing interfaces set to trusted and untrusted. An LDRA MUST implement a configuration setting for all client-facing interfaces, marking them either as trusted or as untrusted. This setting SHOULD be configurable per interface. When a client-facing interface is deemed untrusted the LDRA MUST discard any message received from the client-facing interface of type RELAY-FORWARD (12). In DHCPv4 it was not possible for a DHCP server to determine whether the client or an intermediate relay agent had added relay agent options and thus trusted interfaces (relay-agent interfaces that would allow any DHCP options to be present on incoming messages) and untrusted interfaces (relay-agent interfaces that would ensure there are no relay-agent options on incoming messages) were defined. In DHCPv6, relay agents encapsulate the received message into the Relay- Message Option in addition to adding any relay-agent options. This nested message behaviour allows a server to identify the options each relay-agent has inserted along the path, whenever the data path between LDRA and server falls within a protected or operator controlled environment. When an LDRA is deployed, DHCPv6 servers MAY be configured with the Relay-Forward hop-count of the LDRA to instruct at which level of nesting the relay-agent options should be parsed. This removes the need for an interface to be configured as trusted or untrusted by providing the DHCPv6 server with an awareness of the LDRA logical location in the DHCP relay path. This behaviour is dependent on the interception of all DHCP messages by the LDRA and the incrementing of the Relay-Forward hop-count if a Relay-Forward message is received from the client-facing LDRA interface. 6.2. Relaying a Relay-Reply message from the network The LDRA MUST intercept and process all IP traffic received on the network-facing interface that has: o a link-local scoped source address; Miles, et al. Expires April 16, 2010 [Page 8] Internet-Draft LDRA October 2009 o a link-local scoped destination address; o protocol type UDP; and o destination port 547 An LDRA MUST inspect the DHCP message type and MUST silently discard any DHCP message that is not type Relay-Reply or is otherwise an invalid DHCPv6 packet. The LDRA SHOULD ignore any message that does not meet this criteria and subject it to normal packet forwarding. In addition to the validity checks performed by a relay agent in [RFC3315] , the Relay-Reply message is considered valid by the LDRA if: - The Interface-ID Option is present and the value corresponds to a valid interface in the access node, - the Relay-Reply peer-address and the destination IP address MUST be identical and MUST be a link-local scoped address when no IP address is configured on the LDRA, and - the link-address is the Unspecified Address when no IP address is configured on the LDRA The LDRA copies the peer-address into to the destination IP address field. The LDRA SHOULD forward the packet to the correct client- facing interface using the destination link-layer (MAC) address or the Interface-Id in the Relay-Reply. The LDRA SHOULD NOT retransmit the packet on any other interface. The contents of the Relay Message Option is put into an IP/UDP packet and then forwarded to the client. The LDRA MUST copy the link-layer and IP source address from the Relay-Reply message into the IP/UDP packet that is forwarded to the client. 7. Network Topology The LDRA intercepts any DHCPv6 message received on client-facing interfaces with a destination IP address of All_DHCP_Relay_Agents_and_Servers (FF02::1:2). The LDRA MUST NOT forward the original client message to a network-facing interface, it MUST process the message and add the appropriate Relay-Forward options as described in previous sections. Miles, et al. Expires April 16, 2010 [Page 9] Internet-Draft LDRA October 2009 7.1. Client and Server on Same Link The access node acts as a bridge; it has no information about any IP prefixes that are valid on the link, thus a server should consider address and parameter assignment as if the client DHCP message was not relayed. +--------+ Client -------| | | Access | Client -------| Node |-----+ | (LDRA) | | Client -------| | | +--------+ | | +--------+ |------| Server | | +--------+ +--------+ | Client -------| | | | Access | | Client -------| Node |-----+ | (LDRA) | Client -------| | +--------+ <------IPv6 Link-----> For example, if a client sent a DHCP solicit message that was relayed by the LDRA and then to the server, the server would receive the following Relay-Forward message from the LDRA: src-ip: client link-local address dst-ip: All_DHCP_Relay_Agents_and_Servers msg-type: RELAY-FORWARD hop-count: 0 link-address: Unspecified_Address peer-address: client link-local address Interface-ID Option: interface-id: LDRA-inserted interface-id Relay-Message Option, which contains: msg-type: SOLICIT Solicit Message Options: 7.2. Client and Server behind Relay Agent The client and server are on different IPv6 links, separated by one or more relay agents that will typically act as a router. The LDRA will send Relay-Forward messages upstream towards the second relay agent which in turn will process the messages. Miles, et al. Expires April 16, 2010 [Page 10] Internet-Draft LDRA October 2009 +--------+ Client -------| | | Access | Client -------| Node |-----+ | (LDRA) | | Client -------| | | +--------+ | | +--------+ +--------+ |------| RelayB |---------| Server | | +--------+ +--------+ +--------+ | Client -------| | | | Access | | Client -------| Node |-----+ | (LDRA) | Client -------| | +--------+ <--IPv6 Link A--> <--IPv6 Link B--> For example, if a client sent a DHCP solicit message that was relayed by the LDRA to another relay agent and then to the server, the server would receive the following Relay-Forward message from the LDRA: src-ip: relayB dst-ip: server msg-type: RELAY-FORWARD hop-count: 1 link-address: relayB address from link A peer-address: client link-local address Relay-Message Option, which contains: msg-type: RELAY-FORWARD hop-count: 0 link-address: Unspecified_Address peer-address: client link-local address Interface-ID Option: interface-id: LDRA-inserted interface-id Relay-Message Option, which contains: msg-type: SOLICIT Solicit Message Options: 7.3. Relay Agent in Front of LDRA The client and server are on different IPv6 links, separated by one or more relay agents that will typically act as a router and there is an [RFC3315] Relay Agent on the client-facing Interface of the LDRA. The LDRA will send Relay-Forward messages upstream towards the second relay agent which in turn will process the messages. Miles, et al. Expires April 16, 2010 [Page 11] Internet-Draft LDRA October 2009 +--------+ RelayC -------| | | Access | RelayC -------| Node |-----+ | (LDRA) | | RelayC -------| | | +--------+ | | +--------+ +--------+ |------| RelayB |---------| Server | | +--------+ +--------+ +--------+ | RelayC -------| | | | Access | | RelayC -------| Node |-----+ | (LDRA) | RelayC -------| | +--------+ <--IPv6 Link A--> <--IPv6 Link B--> For example, if a client sent a DHCP solicit message that was relayed by the LDRA to another relay agent and then to the server, the server would receive the following Relay-Forward message from the LDRA: src-ip: relayB dst-ip: server msg-type: RELAY-FORWARD hop-count: 2 link-address: relayB address from link A peer-address: relayC Relay-Message Option, which contains: msg-type: RELAY-FORWARD hop-count: 1 link-address: Unspecified_Address peer-address: relayC Interface-ID Option: interface-id: LDRA-inserted interface-id Relay-Message Option, which contains: msg-type: RELAY-FORWARD hop-count: 0 link-address: global or unspecified address peer-address: end client address Interface-ID Option: (if required) interface-id: relayC inserted Interface-ID Relay-Message Option, which contains: msg-type: SOLICIT Solicit Message Options: Miles, et al. Expires April 16, 2010 [Page 12] Internet-Draft LDRA October 2009 8. Contributors The authors would like to thank the following for their support, Lieven Levrau, Alastair Johnson, Robert Haylock, Mickey Vucic, Ludwig Pauwels, Fernando Cuervo, John Kaippallimalil, Fredrik Garneij, Alfred Hoenes and Ted Lemon. Comments are solicited and should be addressed to the DHC WG mailing list (dhcwg@ietf.org) and/or the author. 9. IANA Considerations This document does not introduce any new namespaces for the IANA to manage. 10. Security Considerations Although the LDRA only listens to client-originated IPv6 traffic sent to the All_DHCPv6_Servers_and_Relay_Agents address on UDP port 547, the LDRA SHOULD implement some form of rate-limiting on received messages to prevent excessive process utilisation. As DHCP is session-oriented, messages in excess of the rate-limit may be silently discarded. The hop count based determination of the trustworthiness of the LDRA can be easily defeated by a rogue relay agent on the network-facing interface of the LDRA. 11. References 11.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, March 1997. [RFC3315] Droms, R., "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3315, July 2003. 11.2. Informative References [L2RA] Joshi, B., "Layer 2 Relay Agent Information", IETF Draft draft-ietf-dhc-l2ra-02, May 2008. [RFC3046] Patrick, M., "DHCP Relay Agent Information Option", RFC 3046, January 2001. Miles, et al. Expires April 16, 2010 [Page 13] Internet-Draft LDRA October 2009 [TR-101] The Broadband Forum, "Migration to Ethernet-Based DSL Aggregation", Technical Report TR-101, April 2006. Authors' Addresses David Miles (editor) Alcatel-Lucent L3 / 215 Spring St Melbourne, Victoria 3000 Australia Phone: +61 3 9664 3308 Email: david.miles@alcatel-lucent.com Sven Ooghe Alcatel-Lucent Copernicuslaan 50 2018 Antwerp, Belgium Phone: Email: sven.ooghe@alcatel-lucent.com Wojciech Dec Cisco Systems Haarlerberdweg 13-19 1101 CH Amsterdam, The Netherlands Phone: Email: wdec@cisco.com Suresh Krishnan Ericsson 8400 Blvd Decarie Town of Mount Royal, Quebec Canada Email: suresh.krishnan@ericsson.com Miles, et al. Expires April 16, 2010 [Page 14] Internet-Draft LDRA October 2009 Alan Kavanagh] Ericsson 8400 Blvd Decarie Town of Mount Royal, Quebec Canada Email: alan.kavanagh@ericsson.com Miles, et al. Expires April 16, 2010 [Page 15]