Individual Submission Internet Draft Jaehoon Paul Jeong Kyeong-Jin Lee Jung-Soo Park Hyoung-Jun Kim ETRI Expires: April 2004 2 October 2003 ND-Proxy based Route and DNS Optimizations for Mobile Nodes in Mobile Network Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026 except that the right to produce derivative works is not granted [1]. 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. Abstract This document specifies a mechanism for enabling mobile nodes in IPv6 mobile network to perform route optimization. The route optimization is possible because mobile router relays the prefix of its Care-of address to its mobile nodes by playing the role of ND-proxy. Through binding updates associated with the network prefix of an access network, the mobile nodes can perform route optimization. In addition, this document explains how mobile nodes can optimize its DNS name resolution through RA-based DNS discovery. By announcing the address of local recursive DNS server, mobile router allows mobile nodes to optimize their DNS name resolution. Conventions used in this document Jeong, et al. Expires - April 2004 [Page 1] Internet-Draft ND-Proxy based Route Optimization for MN October 2003 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 [2]. Table of Contents 1. Terminology...................................................2 2. Introduction..................................................3 3. Overview......................................................3 4. Neighbor Discovery extension..................................4 4.1 RO Prefix Information option format.......................4 4.2 Neighbor Solicitation (NS) message format.................5 4.3 DNS Server option format..................................6 5. Mobile Router.................................................8 5.1 Process of RO Prefix Information option...................8 5.2 Process of DNS Server option..............................8 5.3 Delivery of Data Packets..................................8 6. Mobile Node...................................................9 6.1 Procedure of Route Optimization...........................9 6.1.1 Generation of a new CoA.............................9 6.1.2 DAD for the new CoA.................................9 6.1.3 Return Routability and Binding Update..............10 6.2 Procedure of DNS Optimization............................10 6.2.1 RDNSS Configuration................................10 6.2.2 RDNSS Selection....................................10 7. Security Considerations......................................11 8. Copyright....................................................11 9. Normative References.........................................12 10. Informative References......................................12 11. Acknowledgements............................................13 12. Authors' Addresses..........................................13 1. Terminology This document uses the terminology described in [3]-[7]. Especially four important terms are as follows [5][7]: Multilink Subnet (MS) A collection of independent links, connected by routers, but sharing a common subnet prefix. ND-Proxy A router proxying and relaying for all nodes on its router-mode interfaces except proxy-mode interfaces among its network interfaces. Multilink-Subnet Router (MSR) Jeong, et al. Expires - April 2004 [Page 2] Internet-Draft ND-Proxy based Route Optimization for MN October 2003 A router which has interfaces attached to different links in a MS, and which plays the role of ND-Proxy. Recursive DNS Server (RDNSS) A Recursive DNS Server is a name server that offers the recursive service of DNS name resolution. 2. Introduction The basic support of mobile network (NEMO) enables mobile network nodes and correspondent nodes to communicate through bi-directional tunnels. The deeper multi-level network this NEMO gets, the longer the delay becomes by dog-legged routing. This document specifies how to optimize the routes between mobile nodes and correspondent nodes. Also, this document provides a way to optimize DNS name resolution of mobile nodes, through the autoconfiguration of recursive DNS server. 3. Overview +---+ ******************* +---+ |CN1+---* Internet *---+CN2| +---+ ******************* +---+ | | +-+-+ |AR1| RA(AR1_P)| +-+-+ V | ----------+---------------+---------------+----------- Link1 |Proxy-mode |Proxy-mode +-+-+ +------+ +-+-+ +------+ |MR1+--+RDNSS1| |MR2+--+RDNSS2| RA(AR1_P)| +-+-+ +------+ RA(AR1_P)| +-+-+ +------+ V |Router-mode V |Router-mode ---+-----+-----+--- Link2 ---+------+-----+--- Link3 | | | Proxy-mode| +-+-+ +-+-+ +-+-+ +-+-+ |MN1| |MN2| |MN3| |MR3| +---+ +---+ +---+ +-+-+ | RA(AR1_P) Router-mode| V ---+-----+-----+--- Link4 | | +-+-+ +-+-+ |MN4| |MN5| +---+ +---+ Figure 1. Multilink Subnet for Route Optimization Jeong, et al. Expires - April 2004 [Page 3] Internet-Draft ND-Proxy based Route Optimization for MN October 2003 The route optimization is possible by mobile router's performing ND- Proxy, which makes a Care-of Address (CoA) with the prefix advertised by access router and delivers the prefix of access network into the NEMO. Each mobile node can make its new CoA with router advertisement message including access network prefix and perform the return routability and binding update procedure. As ND-Proxy, the mobile router performs neighbor discovery instead of the mobile nodes within its NEMO. Like this, through mobile router that performs ND- Proxy, access network and NEMO are configured into a multilink subnet. Figure 1 shows an example of a multilink subnet comprised of four links from Link1 to Link4. Three mobile routers from MR1 to MR3 relay the prefix information of access network (AR1_P) that was sent by an access router, AR1. Let's assume that the mobile nodes MN1 and MN2 move into the mobile network managed by mobile router MR1 like Figure 1. Also, let's assume that these visiting mobile nodes communicate with the correspondent nodes, CN1 and CN2, respectively. If these visiting mobiles can get the prefix of access network and make their new CoA, through the binding update with their correspondent node, they can communicate each other via optimized path. This dissemination of access network's prefix is performed by mobile router which becomes attached to a foreign access network, not its home network. Likewise, MN3 can optimize the route through MR2. MN4 and MN5 can perform route optimization through MR2 and MR3, too. The optimization of DNS name resolution is possible by mobile router's announcing the address of local recursive DNS server as well as the prefix information of access network. In Figure 1, by DNS Server option included in RA message, MR1 announces the address of Recursive DNS Server, RDNSS1, within its mobile network to its router-mode link, Link2. Therefore, mobile nodes within Link2, MN1 and MN2, can optimize their DNS name resolution by using local DNS server, RDNSS1. 4. Neighbor Discovery extension 4.1 RO Prefix Information option format The mechanism of this document needs the addition of a new flag within prefix information option for route optimization [3]. When this flag is set, it indicates that the prefix included in the option can be used by mobile nodes within a NEMO for the route optimization. Figure 2 shows the format of the modified prefix information option, RO Prefix Information option, which is included in RA message. Jeong, et al. Expires - April 2004 [Page 4] Internet-Draft ND-Proxy based Route Optimization for MN October 2003 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Prefix Length |L|A|O|Reserved1| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Valid Lifetime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Preferred Lifetime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + Prefix + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2. Prefix Information Option Format for Route Optimization Field: O 1-bit route-optimization flag. When set indicates that this prefix can be used for the route optimization of mobile nodes within NEMO. The RO Prefix Information option provides a mobile node with the network prefix of access network and allows it to autoconfigure its new CoA through stateless address autoconfiguration and to perform binding update. The Prefix Information option appears in RA message and MUST be silently ignored for other messages. L (On-link) flag MAY be either 0 or 1. Namely, this route optimization can be either on-link or off-link model [5]. A (Autonomous address-configuration) flag MUST be 1, indicating IPv6 stateless address autoconfiguration. 4.2 Neighbor Solicitation (NS) message format NS message MUST be extended for Duplicate Address Detection (DAD) for the address based on RO prefix of access network. Therefore, there is a need to discriminate between the normal NS message and extended NS message for route optimization [3]. Figure 3 shows the format of the modified NS message. Jeong, et al. Expires - April 2004 [Page 5] Internet-Draft ND-Proxy based Route Optimization for MN October 2003 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Code | Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |M| Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + Target IPv6 Address + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Options ... +-+-+-+-+-+-+-+-+-+-+-+- Figure 3. Extended Neighbor Solicitation Message Format Fields: M 1-bit multi-hop flag. When set indicates that this NS message SHOULD be relayed to the other links of multilink subnet. Target IPv6 Address The IPv6 address of the target of the solicitation that will be used as CoA. It MUST NOT be a multicast address. 4.3 DNS Server option format DNS Server option contains the IPv6 address of the recursive DNS server. When more than one DNS Server option are advertised, as many DNS Server options as DNS servers are included in an RA message. Figure 4 shows the format of DNS Server option [7]. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Pref | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Valid Lifetime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Jeong, et al. Expires - April 2004 [Page 6] Internet-Draft ND-Proxy based Route Optimization for MN October 2003 | | + + | | + IPv6 Address of DNS Server + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 4. DNS Server Option Format Fields: Type 8-bit identifier of the option type (TBD: IANA) Option Name Type DNS Server (TBD) Length 8-bit unsigned integer. The length of the option (including the type and length fields) in units of 8 octets. The value 0 is invalid. Mobile nodes MUST silently discard a Neighbor Discovery (ND) packet that contains an option with length zero. Pref The preference of a DNS server. A 4-bit unsigned integer. A decimal value of 15 indicates the highest preference. A decimal value of 0 indicates that the DNS server can not be used. The field can be used for selecting an RDNSS among multiple RDNSSes. Valid Lifetime 32-bit unsigned integer. The maximum time, in seconds, over which this DNS server is used for name resolution. Mobile nodes should contact the source of this information, mobile router, before expiry of this time interval. A value of all one bits (0xffffffff) represents infinity. IPv6 Address of DNS Server Recursive DNS Server's address for DNS name resolution. "Pref"=0 SHOULD require a "Valid Lifetime"=0 because the corresponding DNS server SHOULD not be used any more. Jeong, et al. Expires - April 2004 [Page 7] Internet-Draft ND-Proxy based Route Optimization for MN October 2003 5. Mobile Router Mobile router MUST process Prefix Information option for Route Optimization (RO) and DNS Server option for DNS Optimization, which are included in RA message. 5.1 Process of RO Prefix Information option Only if the prefix announced by an access router is different from the prefix of a mobile router's Home Address (HoA), the mobile router MUST perform the role of ND-Proxy and relay the prefix information. Before mobile router advertises the prefix information through Router Advertisement (RA) message, it MUST set route-optimization flag indicating that this prefix can be used for route optimization of mobile nodes, which are either local mobile nodes or visiting mobile nodes within the mobile network. If a mobile node within a mobile network receives the new prefix information option through RA message and can recognize this option, it MAY prefer this new prefix information option to the normal prefix information option that contains the mobile network prefix assigned by the mobile router's home network. By performing binding update with the prefix of the access network, the mobile node can optimize the routes between its correspondent nodes and itself. ND-Proxy MUST join the solicited-node multicast address(es) that correspond to the IP address(es) assigned to the mobile node for which it is proxying [3]. 5.2 Process of DNS Server option If mobile router has its own local RDNSS like MR1 and MR2 in Figure 1, it SHOULD announce the address of RDNSS to its router-mode link(s). If mobile router receives DNS Server option from its proxy-mode link(s), it SHOULD relay the option to its router-mode link(s) through its RA message. In case that mobile router has its own local RDNSS, it announces the DNS Server option of its RDNSS with higher precedence than those of other RDNSSes. 5.3 Delivery of Data Packets After a mobile node gets a new CoA within a mobile network and performs binding update associated with the address, the data packets of correspondent node toward the mobile node are delivered to the access network to which the NEMO containing the mobile node is attached, via optimal path between the mobile and correspondent nodes. Jeong, et al. Expires - April 2004 [Page 8] Internet-Draft ND-Proxy based Route Optimization for MN October 2003 When the access router of the access network receives the data packets, it multicasts normal Neighbor Solicitation (NS) message to the solicited-node multicast address of the destination IPv6 address in order to find out the link-layer address of the destination mobile node. The mobile router, knowing the link-layer address of the target, responds to the NS message by returning its own link-layer address in a unicast Neighbor Advertisement (NA) message as ND-Proxy, which knows the IPv6 addresses and link-layer addresses of mobile nodes within its mobile network during the DAD of each CoA of each mobile node. When the access router knows the link-layer address to the destination, it forwards the IPv6 data packets to the mobile router corresponding to the link-layer address. The mobile router relays the packets to the destination mobile node. In case that the NEMO where the destination node is placed is multi-level, the packets are relayed to the destination node by more than one mobile router. 6. Mobile Node Mobile node MUST process Prefix Information option for Route Optimization (RO) and DNS Server option for DNS Optimization, which are included in RA message. 6.1 Procedure of Route Optimization For route optimization, mobile node generates a new CoA based on the access network prefix and performs binding update for the CoA. 6.1.1 Generation of a new CoA Whenever a mobile node receives RA message containing RO prefix information option that includes a new network prefix of access network, it makes a new CoA. 6.1.2 DAD for the new CoA The mobile node performs DAD for the new CoA through the extended NS message. The NS message of DAD for the new address is relayed to the other links by a mobile router, acting as ND-Proxy, on the link where the mobile node is placed [5]. The mobile router memorizes the DAD for returning NA message to the sender of the extended NS message. If there is no NA returned and the DAD is successful, the mobile node configures the verified address as its new CoA in its network interface. Jeong, et al. Expires - April 2004 [Page 9] Internet-Draft ND-Proxy based Route Optimization for MN October 2003 Notice that the DAD for the link-local addresses and global addresses based on mobile network prefix assigned by home network is performed through normal NS message only within a link and the DAD for the global addresses based on access network prefix is performed through extended NS message within a multilink subnet, which is relayed by ND-Proxies. 6.1.3 Return Routability and Binding Update After configuring the new CoA, the mobile node performs the return routability and binding update procedure of Mobile IPv6 [8]. If the mobile node is visiting mobile node (VMN) for the mobile network where it is present, or as local mobile node (LMN), moves into another link of the mobile network to which its home link belongs to, it SHOULD perform binding updates with both its home agent and correspondent nodes. In case that as LMN, the mobile node is present at home link and receives RO prefix information option, namely when the mobile node's HoA and CoA belong to the same link, it SHOULD perform not deregistration with its home agent which is its mobile router simultaneously, but binding updates with both its home agent and correspondent nodes. 6.2 Procedure of DNS Optimization The optimization of DNS name resolution is possible by mobile router's announcing the address of local recursive DNS server as well as RO prefix information through RA message [7]. The DNS server can exist either within mobile network or within access network. The address of recursive DNS server is delivered to mobile nodes through DNS Server option, one of RA options. Especially, visiting mobile nodes will optimize their DNS name resolution effectively by using local recursive DNS server. 6.2.1 RDNSS Configuration The addresses of DNS servers are announced by DNS Server options in RA message. These addresses can be used for recursive DNS service providing DNS name resolution. If mobile node receives DNS Server option, it SHOULD store RDNSS's address in the configuration file for its DNS resolver; i.e., /etc/resolv.conf in UNIX. 6.2.2 RDNSS Selection When mobile node perceives multiple RDNSSes through RA message, it stores the RDNSS addresses in order into the configuration file which its DNS resolver uses for DNS name resolution on the basis of the value of "Pref" field in the DNS Server option. The following algorithm is simply based on the rule of selecting an RDNSS in the Jeong, et al. Expires - April 2004 [Page 10] Internet-Draft ND-Proxy based Route Optimization for MN October 2003 order from the most preferred RDNSS, provided that its preference value is not zero. The processing of the DNS Server option received in RA message by a mobile node is as follows: For each DNS Server option: Step (a) : Receive and parse all DNS Server options. Step (b) : Arrange the addresses of RDNSSes in a descending order, in the respect of preference value, namely starting with the biggest value of "Pref" field of the DNS Server option and store them in the configuration file used by resolver for DNS name Resolution (DNS configuration). Step (c) : For each DNS Server option, check the following: If the Value of "Pref" or "Valid Lifetime" field is set to zero, exclude the corresponding RDNSS entry from the list of RDNSSes of DNS configuration in order to let the RDNSS not used any more. Whenever the DNS resolver on the mobile node performs the name resolution, it refers to the address of RDNSS in order from the first RDNSS stored in its DNS configuration. Like this, in case that there are several mobile routers advertising RDNSS in a multilink subnet, "Pref" field is used to select RDNSS. 7. Security Considerations The route optimization and DNS optimization in this document does not add any other security problems to the NEMO, Mobile IPv6, or Neighbor Discovery (ND) protocols. Security issues regarding the ND protocol are being discussed in IETF SEND (Securing Neighbor Discovery) working group [9]. 8. Copyright The following copyright notice is copied from RFC 2026 [Bradner, 1996], Section 10.4, and describes the applicable copyright for this document. Copyright (C) The Internet Society July 12, 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 Jeong, et al. Expires - April 2004 [Page 11] Internet-Draft ND-Proxy based Route Optimization for MN October 2003 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 assignees. 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. 9. Normative References [1] Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9, RFC 2026, October 1996. [2] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [3] T. Narten, E. Nordmark and W. Simpson, "Neighbour Discovery for IP version 6", RFC 2461, December 1998. [4] S. Thomson and T. Narten, "IPv6 Stateless Address Autoconfiguration", RFC 2462, December 1998. [5] Dave Thaler and Chistian Huitema, "Multi-link Subnet Support in IPv6", draft-ietf-ipv6-multilink-subnets-00.txt, June 2002. [6] Thierry Ernst, "Network Mobility Support Terminology", draft- ietf-nemo-terminology-00.txt, May 2003. [7] Jaehoon Jeong, Soohong D. Park, Luc Beloeil and Syam Madanapalli, "IPv6 DNS Discovery based on Router Advertisement", draft-jeong- dnsop-ipv6-dns-discovery-00.txt, July 2003. 10. Informative References [8] D. Johnson, C. Perkins and J. Arkko, "Mobility Support in IPv6", draft-ietf-mobileip-ipv6-22.txt, May 2003. Jeong, et al. Expires - April 2004 [Page 12] Internet-Draft ND-Proxy based Route Optimization for MN October 2003 [9] J. Arkko, J. Kempf, B. Sommerfeld, B. Zill and P. Nikander, "SEcure Neighbor Discovery (SEND)", draft-ietf-send-ipsec-01.txt, June 2003. 11. Acknowledgements The authors would like to acknowledge the previous contribution of Dave Thaler and Christian Huitema. 12. Authors' Addresses Jaehoon Paul Jeong ETRI / PEC 161 Gajong-Dong, Yusong-Gu Daejon 305-350 Korea Phone: +82 42 860 1664 EMail: paul@etri.re.kr Kyeong-Jin Lee ETRI / PEC 161 Gajong-Dong, Yusong-Gu Daejon 305-350 Korea Phone: +82 42 860 6484 EMail: leekj@etri.re.kr Jung-Soo Park ETRI / PEC 161 Gajong-Dong, Yusong-Gu Daejon 305-350 Korea Phone: +82 42 860 6514 EMail: pjs@etri.re.kr Hyoung-Jun Kim ETRI / PEC 161 Gajong-Dong, Yusong-Gu Daejon 305-350 Korea Phone: +82 42 860 6576 EMail: khj@etri.re.kr Jeong, et al. Expires - April 2004 [Page 13]