Network Working Group T. Boot Internet-Draft Infinity Networks B.V. Intended status: Informational A. Holtzer Expires: August 4, 2011 TNO ICT January 31, 2011 BRDP Framework draft-boot-brdp-framework-00.txt Abstract This document describes the Border Router Discovery Protocol (BRDP) framework. This framework enables multi-homing for small to medium sites, using Provider Aggregatable IPv6 addresses. It describes a mechanism for automated IP address configuration and renumbering, a mechanism for optimized source address selection and a new paradigm for packet forwarding. The BRDP framework prevents ingress filtering problems with multi-homed sites and supports load-balancing for multi-path transport protocols. This work also prevents routing scalability problems in the provider network and Internet Default Free Zone because small to medium multi-homed size sites would not need to request Provider Independent address blocks. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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." This Internet-Draft will expire on August 4, 2011. Copyright Notice Copyright (c) 2011 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 Boot & Holtzer Expires August 4, 2011 [Page 1]
Internet-Draft BRDP Framework January 2011 (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 5 2. Reference Scenarios . . . . . . . . . . . . . . . . . . . . . 6 2.1. Small multi-homed site or DMZ . . . . . . . . . . . . . . 6 2.2. Medium multi-homed site . . . . . . . . . . . . . . . . . 7 2.3. Medium multi-homed site with ULAs and DHCP server . . . . 11 2.4. MANET site . . . . . . . . . . . . . . . . . . . . . . . . 13 3. Border Router Discovery Protocol (BRDP) . . . . . . . . . . . 15 4. BRDP based Address Configuration and Prefix Delegation . . . . 17 5. BRDP based Source Address Selection . . . . . . . . . . . . . 18 6. BRDP based Routing . . . . . . . . . . . . . . . . . . . . . . 18 7. BRDP and IRTF RRG goals . . . . . . . . . . . . . . . . . . . 19 7.1. Scalability . . . . . . . . . . . . . . . . . . . . . . . 20 7.2. Traffic engineering . . . . . . . . . . . . . . . . . . . 20 7.3. Multi-homing . . . . . . . . . . . . . . . . . . . . . . . 20 7.4. Loc/id separation . . . . . . . . . . . . . . . . . . . . 20 7.5. Mobility . . . . . . . . . . . . . . . . . . . . . . . . . 20 7.6. Simplified renumbering . . . . . . . . . . . . . . . . . . 20 7.7. Modularity . . . . . . . . . . . . . . . . . . . . . . . . 21 7.8. Routing quality . . . . . . . . . . . . . . . . . . . . . 21 7.9. Routing security . . . . . . . . . . . . . . . . . . . . . 21 7.10. Deployability . . . . . . . . . . . . . . . . . . . . . . 21 8. Currently unaddressed issues . . . . . . . . . . . . . . . . . 22 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 22 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22 11. Security Considerations . . . . . . . . . . . . . . . . . . . 22 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22 12.1. Normative References . . . . . . . . . . . . . . . . . . . 22 12.2. Informative References . . . . . . . . . . . . . . . . . . 22 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 24 Boot & Holtzer Expires August 4, 2011 [Page 2]
Internet-Draft BRDP Framework January 2011 1. Introduction IPv6 provides basic functionality for multi-homing, since nodes can have multiple addresses configured on their interfaces. However, it is difficult to utilize the advantages of this, as there is a strong tendency among network administrators for shielding the network topology from hosts. As a result, it is difficult or impossible for a host to utilize available facilities of the network, such as multi- path. Also scalability of the Internet routing system is getting a problem due to a high demand of Provider Independent (PI) addresses. The Border Router Discovery Protocol (BRDP) enhances the IPv6 model by enabling automated renumbering in dynamically changing multi-homed environments, such that routers and hosts cooperate on address configuration and path selection. BRDP utilizes Provider Aggregatable (PA) addresses and uses them as locator. Mapping identifiers to locators is out of scope of the BRDP framework, also because many solutions exists or are being worked on. All these solutions work fine with BRDP, as long as they don't break IPv6. The BRDP framework can be applied to edge networks. These networks can be fixed, for example enterprise networks, small offices / home offices (SOHO) or home sites. BRDP also can be used in wireless access networks, for example wireless access networks such as 3G or 4G, wireless LANs or mobile ad hoc networks (MANETs). A nice attribute of BRDP is that it supports multi-homing in heterogeneous networks, meaning that e.g. a SOHO network can have multiple wired broadband and 3G connections or a mixture of wireless access networks and MANET. In a multi-homed network, nodes are connected to the Internet via multiple exit points, possibly via multiple providers. [RFC5887] argues that if a site is multi-homed using multiple PA routing prefixes, then the interior routers need a mechanism to learn which upstream providers and corresponding PA prefixes are currently reachable and valid. Next to that, these upstream providers or PA prefixes may change over time. This requires a dynamic renumbering mechanism that can handle planned or unplanned changes in the prefixes used. BRDP proposes a mechanism for automated renumbering in larger networks that goes beyond hosts in a single subnet. The BRDP framework uses the following key elements: o Propagation of available Border Routers and corresponding prefixes; o Address autoconfiguration and prefix delegation, using BRDP provided hints; Boot & Holtzer Expires August 4, 2011 [Page 3]
Internet-Draft BRDP Framework January 2011 o Source address selection, using BRDP provided hints; o Packet forwarding to the Border Router that corresponds with the source address prefix, in case the destination address is not found in the routing domain. The propagation of available Border Routers and corresponding prefixes is implemented as an extension on the Neighbor Discovery Protocol [RFC4861]. Border Router Information Options (BRIOs) are sent with Router Advertisements, and contain information about the Border Routers, such as the Border Router address, the prefix that corresponds with that Border Router, and the costs of the path via that Border Router to the Internet Default Free Zone (DFZ). BRIOs are disseminated downstream through the network and all nodes store the information from BRIOs they receive in a BRIO cache. When a node is multi-homed it will receive multiple prefix information, from multiple upstream Border Routers. BRIOs contain a Border Router prefix and routers can generate an IPv6 address based on this prefix [I-D.boot-autoconf-brdp], just like in regular SLAAC [RFC4862]. Routers can set up reachability to this address automatically, by adding the generated address in the routing protocol. Routers automatically learn Border Routers that act as DHCP server or relay agent [RFC3633]. When routers detect an alternate path to the DFZ, a new prefix is requested from this newly learned Border Router. Prefixes, of which the path to the DFZ is no longer available, are put 'out of service' by routers, meaning they are not used for address assignments anymore. Optionally, if the cost to the DFZ through a Border Router is far higher than via other available paths, a router can put the corresponding prefix out of service. Prefixes that are out of service are released. Prefixes that are in service are configured on interfaces with a 64- bit prefix length and advertised with a Prefix Information Option in Router Advertisements. The Prefix Information lifetime is copied from lifetime information in the BRIO cache. Hosts can use the BRDP provided information together with the Prefix Information to autoconfigure addresses, based on IPv6 Stateless Address Autoconfiguration [RFC4862]. A host may also use DHCPv6 to get addresses or "Other configuration". Nodes with multiple configured addresses need to select a source address for outgoing connections. Default Address Selection for IPv6 [RFC3484] defines a mechanism, used as default behavior. It is open to more advanced mechanisms or site policies. BRDP provided information can be used for a more advanced mechanism, where the Boot & Holtzer Expires August 4, 2011 [Page 4]
Internet-Draft BRDP Framework January 2011 hosts select automatically a source address that corresponds with a path with the lowest cost to the DFZ. When multiple Border Routers are available, automatic load distribution and multi-path transport becomes available. Hosts can use information in the BRIO cache to select a default router. For selecting the best paths, hosts may use next hop selection based on source address and path costs to the corresponding Border Router, if such information is available to the host. Network Ingress Filtering [RFC2827] describes the need for ingress filtering, to limit the impact of distributed denial of service attacks, by denying traffic with spoofed source addresses access. It also helps ensure that traffic is traceable to its correct source network. Ingress Filtering for Multihomed Networks [RFC3704] provides solutions for multi-homed sites. However, the proposal applicable for PA addresses requires careful planning and configuration. It suggests routing based on source address, and a path on each Border Router to all ISPs in use, either with a direct connection or with tunnels between all Border Routers. It is hard to make such mechanisms work in an automated fashion, or mechanisms are not supported on Border Routers used today. As an evolutionary approach, BRDP provided information is to be used to forward packets to their destination without ingress filtering problems. The BRIO cache contains a mapping between Border Routers and the addresses that do pass ingress filtering. So the packet forwarding heuristic can be straightforward: send packets, where the destination is not in the routing domain itself to the Border Router that owns the prefix of the source address. Enabling BRDP in an existing network is straightforward. First, all routers have to be updated for BRDP support. At this step, Border Router information is propagated in the network enabling BRDP assisted address autoconfiguration and prefix delegation and BRDP assisted source address selection. The second step is updating all routers with the BRDP based routing mechanism. To enable this mechanism the default gateway is removed from the routing table. This second step is a flag day operation. Rolling back is easy, by just re-inserting the default gateway. 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]. Boot & Holtzer Expires August 4, 2011 [Page 5]
Internet-Draft BRDP Framework January 2011 2. Reference Scenarios This section describes the use of BRDP in four different scenarios: a small multi-homed site or DMZ, a medium multi-homed site, a medium multi-homed site with ULA with DHCP server and a MANET site. 2.1. Small multi-homed site or DMZ This scenario discusses BRDP operation for multi-homed Small Office - Home Office (SOHO) networks and De-Militarized Zones (DMZ). The scenario is shown in Figure 1. Each provider assigns a PA /48 prefix to its customers. All addresses and prefixes are configured completely automatically. The feature of BRDP that adds value in this scenario is BRDP based Border Router selection for multi-homed hosts. This is enabled by using BRDP based forwarding. /^^^^^^^^^^^^^^^^^^^^^^\ / \ { The Internet } \ / \______________________/ / \ /(2001:08db:100::/40) \(2001:8DB:200::/40) +=======+ +=======+ [ ISP_1 ] [ ISP_2 ] +=======+ +=======+ | | |(2001:8DB:101::/48) |(2001:8DB:201::/48) +--------+ +--------+ | BR_101 | | BR_201 | +--------+ +--------+ | FE80::101/64 | FE80::201/64 | 2001:8DB:101:1::101/64 | 2001:8DB:201:1::201/64 | | -+---------------------+---+- | 2001:8DB:101:1::1234/64 | 2001:8DB:201:1::1234/64 FE80::1234/64 | +-----------+ | Host_1234 | +-----------+ Figure 1: Scenario 1: multi-homed Small Office - Home Office (SOHO) network or DMZ In this scenario, Host_1234 has configured two addresses using SLAAC [RFC4862], one with prefix 2001:8DB:101:1::/64 from Border Router BR_101 and one with prefix 2001:8DB:201:1::/64 from Border Router Boot & Holtzer Expires August 4, 2011 [Page 6]
Internet-Draft BRDP Framework January 2011 BR_201. Host_1234 has learned these prefixes from Prefix Information Options sent by both Border Routers according to [RFC4861]. The host has learned via BRIOs that these prefixes belong to Border Routers. The host can use optimal paths by selecting BR_101 as default router for all packets with a source address with prefix 2001:8DB:101:1::/64 and default gateway BR_201 for all packets with a source address with prefix 2001:8DB:201:1::/64. Non-optimal default router selection on hosts is handled by the routers, "misdirected" packets are forwarded to the correct Border Router. BRDP enables routers to deliver non-optimal directed packets from attached hosts towards a Border Router that owns the prefix of the source address, if such a Border Router exists. In the above scenario, a packet sent from Host_1234 with source address 2001:8DB: 201:1::1234 to default router BR_101 would be dropped due to on an ingress filter, when no mechanism is in place to redirect the packet. BRDP based forwarding provides such a mechanism automatically. Instead of dropping the packet, BR_101 forwards it to BR_201. 2.2. Medium multi-homed site This scenario discusses BRDP operation for medium sized multi-homed networks. The difference with the previous scenario is that the network paths between hosts and the Border Routers have intermediate routers. The scenario is shown in Figure 2. The added value of BRDP in this scenario is the discovery of Border Routers for hosts and routers beyond the first hop as well as Border Router Selection for hosts and routers. Boot & Holtzer Expires August 4, 2011 [Page 7]
Internet-Draft BRDP Framework January 2011 /^^^^^^^^^^^^^^^^^^^^^^\ / \ { The Internet } \ / \______________________/ / \ /(2001:8DB:100::/40) \(2001:8DB:200::/40) +=======+ +=======+ [ ISP_1 ] [ ISP_2 ] +=======+ +=======+ | | |(2001:8DB:101::/48) |(2001:8DB:201::/48) +--------+ +--------+ | BR_101 | | BR_201 | +--------+ +--------+ | FE80::101/64 | FE80::201/64 | 2001:8DB:101:1::101/64 | 2001:8DB:201:1::201/64 | | -+-+-----------------------+-+- | | | 2001:8DB:201:1::1/64 | | 2001:8DB:101:1::1/64 | 2001:8DB:201:1::2/64 | FE80::1/64 | FE80::2/64 +--------+ +--------+ | R_1 | | R_2 | +--------+ +--------+ |FE80 | FE80::1/64 | FE80::2/64 |::1 | | |/64 -+--------------------+-+- | | | 2001:8DB:101:2::1234/64 | | 2001:8DB:201:3::1234/64 | | FE80::1234/64 | +-----------+ | 2001:8DB:101:3::ABCD/64 | Host_1234 | | FE80::ABCD/64 +-----------+ +-----------+ | Host_ABCD | +-----------+ Figure 2: Scenario 2: medium sized multi-homed network Routers can learn advertised on-link prefixes automatically via the Prefix Information Option in IPv6 ND RAs. In this scenario, routers R_1 and R_2 learn prefix 2001:8DB:101:1::/64 from BR_101 and prefix 2001:8DB:201:1::/64 from BR_201. Routers may autoconfigure addresses on their interfaces. In this example, R_1 has configured addresses from both providers on its upstream interface, R_2 only configured an address based on the prefix of BR_201. If the routers run a routing Boot & Holtzer Expires August 4, 2011 [Page 8]
Internet-Draft BRDP Framework January 2011 protocol, the learned prefixes are made reachable in the network. In the next steps of the autoconfiguration proces, the prefixes and addresses on the other links are automatically configured, but first we discuss the BRDP messages that are disseminated through the network. Routers automatically learn Border Routers and mapping between prefixes and Border Routers using BRDP. The diagram in Figure 3 depicts BRIO message dissemination in scenario 2. The two Border Routers advertise their own address and corresponding prefix with an address prefix. Nothing prevents them from forwarding each other's BRIO message, although resending BRIO information on non-MANET interfaces is not useful. Both routers R_1 and R_2 forward both Border Router address prefixes, using separate BRIOs in RAs, on downstream interfaces. In this way all routers and hosts in the network are aware of all reachable Border Routers and corresponding prefixes. Boot & Holtzer Expires August 4, 2011 [Page 9]
Internet-Draft BRDP Framework January 2011 /^^^^^^^^^^^^^^^^^^^^^^\ / \ { The Internet } \ / \______________________/ / \ /(2001:8DB:100::/40) \(2001:8DB:200::/40) +=======+ +=======+ [ ISP_1 ] [ ISP_2 ] +=======+ +=======+ | | |(2001:8DB:101::/48) |(2001:8DB:201::/48) +--------+ +--------+ | BR_101 | | BR_201 | +--------+ +--------+ | : | : | V 2001:8DB:101:1::101/48 | V 2001:8DB:201:1::201/48 | | -+-+-------------------------+-+- | | | | +--------+ +--------+ | R_1 | | R_2 | +--------+ +--------+ | : | : | : | : | : 2001:8DB:101:1::101/48 | : 2001:8DB:101:1::101/48 | : | V 2001:8DB:201:1::201/48 | V 2001:8DB:201:1::201/48 | : | | | : -+--------------------------+- | : | : 2001:8DB:101:1::101/48 | V 2001:8DB:201:1::201/48 | -+---- Figure 3: BRIO dissemination in Scenario 2 Routers are not required to configure global addresses on each interface. In the example, only the interface pointing to the Internet has configured global addresses. Routers may also use a (logical) management interface for global reachability. So, the one-hop neighbours of BR_101 and BR_201, being R_1 and R_2, have learned the prefixes and configured addresses on their upstream interfaces. And all nodes in the network have learned the Border Router prefixes. The next step is to get configured addresses on the hosts in Figure 2. This is done by using DHCP Prefix Delegation. R_1 and R_2 request a prefix from either or both BR_101 and BR_201 Boot & Holtzer Expires August 4, 2011 [Page 10]
Internet-Draft BRDP Framework January 2011 for binding as on-link prefix on the links, and advertise those using Prefix Information Options to the hosts. This will result in a maximum of four prefixes that are advertised on the downlink of R_1 and R_2. Having multiple prefixes from the same ISP bound on a link is not useful. So a router requests a prefix from a Border Router only if no other prefix of that Border Router is advertised already by another router on this network segment. In this example, R_1 has been delegated two prefixes by DHCP PD for the link with host Host_1234; 2001:8DB:101:2::/64 and 2001:8DB:201: 3::/64. No other router is on this link. R_1 or R_2 has also been delegated a prefix on the link to host Host_ABCD; 2001:8DB:101: 3::/64. It cannot be seen in Figure 2 which router has been delegated the prefix, nor if another prefix for this link has been delegated. No redundant prefix is delegated, as the routers learned with RA PIO already delegated prefixes for known Border Routers. Now, Host_1234 and Host_ABCD can autoconfigure addresses for their interfaces. Host_1234 configures two addresses, one for each Border Router. Host_ABCD chooses not to use ISP_2. Nodes R_1 and Host_1234 can use both providers, by using two configured global addresses. Any multi-path facility can be used, either on an application layer or with a multi-path transport protocol. Host_ABCD may forward packets to the Internet via router R_1 or R_2. If R_2 is selected as default router, R_2 forwards the packets to BR_101 as this Border Router corresponds to the prefix of the source address 2001:8DB:101:3::ABCD. This works well, even in this case where R_2 hasn't configured an address with a BR_101 prefix for itself, and selected a global address from the BR_201 prefix only. 2.3. Medium multi-homed site with ULAs and DHCP server In this example, the scenario 2 is extended by adding Unique Local Addresses (ULA) for communication within the site itself. For simplicity there is only one ISP present. The ULA IP configuration, with prefix FD00:8DB::/48, is managed by DHCPv6 server DHCP_201. The scenario is shown in Figure 4. Boot & Holtzer Expires August 4, 2011 [Page 11]
Internet-Draft BRDP Framework January 2011 /^^^^^^^^^^^^^^^^^^^^^^\ / \ { The Internet } \ / \______________________/ / /(2001:8DB:100::/40) +=======+ [ ISP_1 ] +=======+ | |(2001:8DB:101::/48) +--------+ +---------+ | BR_101 | | DHCP_201| +--------+ +---------+ | FE80::101/64 | FE80::201/64 | 2001:8DB:101:1::101/64 | FD00:8DB:201:1::201/64 | FD00:8DB:201:1::101/64 | (acme.com,FD00:8DB:201:1:201:/48) | | -+-+-----------------------+-+- | | | FD00:8DB:201:1::1/64 | FD00:8DB:201:1::2/64 | 2001:8DB:101:1::1/64 | 2001:8DB:101:1::2/64 | FE80::1/64 | FE80::2/64 +--------+ +--------+ | R_1 | | R_2 | +--------+ +--------+ |FE80 | FE80::1/64 | FE80::2/64 |::1 | | |/64 -+--------------------+-+- | | | 2001:8DB:101:2::1234/64 | | FD00:8DB:201:3::1234/64 | | FE80::1234/64 | +-----------+ | 2001:8DB:101:3::ABCD/64 | Host_1234 | | FD00:8DB:201:3::ABCD/64 +-----------+ | FE80::ABCD/64 +-----------+ | Host_ABCD | +-----------+ Figure 4: Scenario 3: a medium sized multi-homed site with ULAs and DHCP server. In this scenario, all nodes have configured a ULA and a Global Unicast Address using prefix delegation in the way that was described in Section 2.2. ULA prefix delegation is automated just like PA addresses. The DHCP server is therefore implemented on a router, in Boot & Holtzer Expires August 4, 2011 [Page 12]
Internet-Draft BRDP Framework January 2011 this case DHCP_201. This router advertises the ULA prefix with BRDP, here FD00:8DB:201::/48. Although BRDP provides automatic prefix and address configuration for ULA, a network administrator is free to configure it manually, along using BRDP for global addresses. BRDP based ULA configuration with BRDP based routing would result in routing packets with ULA destinations outside the site to the originator of the ULA prefix, in this case router DHCP_201. DHCP_201 is not connected to the Internet or another site owning the ULA, so packets to non-existing destinations are dropped. DHCP_201 indicates such with the BRIO F-bit set, meaning the Border Router is floating. This scenario, it is demonstrated that BRDP and DHCPv6 cooperate in address configuration. BRDP provides announcements of Border Routers and DHCP servers. Routers request prefixes with DHCP, and can request other parameters also. Such parameters are disseminated to other nodes, either with router advertisements or acting as DHCP server itself. Routers may also act as DHCP relay, redirecting address requests to the Border Router(s). The Router Advertisement M-bit and O-bit indicates availability of DHCPv6 services to attached nodes. Difficulties may arise when both ULA and global addresses are used for Internet connectivity, e.g. when address translation is used. To distinguish, the Border Router not providing Internet connectivity informs nodes in the network using Service Selection suboption, similar to "Service Selection for Mobile IPv6" [RFC5149]. This procedure helps also for extranet connectivity. In this scenario, the ULA is used within the ACME Corporation, nodes are made aware by adding "acme.com" in the BRIO Service Selection Option. It is for the reader to work out extensions for this scenario, where the ULA prefix originator is a Border Router to another site, e.g. a link from a branch office to a head quarter, or a ULA-only side connected to the Internet with NAT66. 2.4. MANET site BRDP was developed for address autoconfiguration in MANETs. This scenario, see Figure 5 demonstrates the powerful multi-homing facilities provided to the MANET nodes. Boot & Holtzer Expires August 4, 2011 [Page 13]
Internet-Draft BRDP Framework January 2011 /^^^^^^^^^^^^^^^^^^^^^^\ / \ { The Internet } \ / \______________________/ / \ /(2001:8DB:100::/40) \(2001:8DB:200::/40) +=======+ +=======+ [ ISP_1 ] [ ISP_2 ] +=======+ +=======+ | | |c=1 |c=1 |(2001:8DB:101::/48) |(2001:8DB:201::/48) +--------+ +--------+ | BR_101 | | BR_201 | +-+------+ +---+----+ | FE80::101/64 | FE80::201/64 | 2001:8DB:101:1::101/128 | 2001:8DB:201:1::201/128 /|\ /|\ : . c=5 . : : . . . . . . . . . :c=1 :c=2 . : : . . . . . . . . . . \|/ : . c=5 | 2001:8DB:201:1::2/128 \|/ | 2001:8DB:201:1::2/128 | 2001:8DB:201:1::1/128 | FE80::2/64 | 2001:8DB:101:1::1/128+--+--+ | FE80::102/64 . .| R_2 | +--+--+ . . . . +-----+. | R_1 |. . . . c=5 : . c=4 +-----+. . . . . . . :c=1 . . . . . c=4 . : . \|/ \|/ 2001:8DB:201:1::3/128 | 2001:8DB:201:1::4/128 | 2001:8DB:101:1::3/128 | 2001:8DB:201:1::4/128 | FE80::3/64 | FE80::4/64 | +--+--+ +--+--+ | R_3 | . . . . . . . . .| R_4 | +-----+ c=4 +-----+ Figure 5: Scenario 4: a MANET site On the MANET interfaces, addresses are configured using a 64-bit prefix provided by BRDP, appending it with a 64-bit Interface Identifier according to BRDP based address autoconfiguration. This creates a 128-bit prefix length as recommended in IP Addressing Model in Ad Hoc Networks [RFC5889]. Each MANET node has configured two global addresses, one for each ISP. With BRDP, the nodes are aware Boot & Holtzer Expires August 4, 2011 [Page 14]
Internet-Draft BRDP Framework January 2011 of the cost of the path to the DFZ, defined as dimensionless metric for both directions of the patch. This enables optimized source address selection, and as an implicit result a Border Router and ISP selection. In the scenario, R_1 is near to BR_101 and the cost via this Border Router is lower than via BR_201. The table below shows costs to the DFZ for all nodes, via both ISPs. Paths with lowest costs are marked with *. +---------+-------+-------+ | Costs | Via | Via | | to DFZ | ISP_1 | ISP_2 | +---------+-------+-------+ | BR_101 | 1* | 7 | | BR_201 | 7 | 1* | | R_1 | 3* | 6 | | R_2 | 6 | 2* | | R_3 | 7 | 3* | | R_4 | 10 | 6* | +---------+-------+-------+ The optimized source address selection facility is also of utility in the other scenarios. For example, the cost of the link to the ISP could be set depending of bandwidth and optionally on utilization. Nodes would use a near uplink to an ISP, and as a result some form of load distribution is enabled. Note that nodes still can use the alternative addresses, in fact it is recommended to use multi-path transport protocols for better load balancing and improved robustness. For isolated MANETs, a DHCP server election mechanism can be used. Nodes may initiate to advertise a self-generated ULA. In such cases, it is recommended that a prefix is used with a 56-bit random ULA identifier (including random 16-bit Subnet ID) and 64-bit prefix length. Other nodes join this prefix, although some may wish to start or continue using their own prefix. The latter would occur in cases of a merge of previous isolated MANETs. 3. Border Router Discovery Protocol (BRDP) BRDP is an extension to the IPv6 ND mechanism [RFC4861] that provides information about the reachability, availability, prefix information, quality and cost of upstream providers, and enables automated (re)numbering of possibly multi-homed routers and hosts. BRDP adds the Border Router Information Option (BRIO) to the Router Advertisement (RA) of IPv6 ND. A BRIO contains all relevant information of an upstream Border Router and the corresponding Boot & Holtzer Expires August 4, 2011 [Page 15]
Internet-Draft BRDP Framework January 2011 provider. Border Routers initiate sending BRIO messages, other routers in the network disseminate the messages downstream through the network. Nodes store the information from received BRIOs in a BRIO cache, to be used for address generation, DHCP server discovery, address selection or packet forwarding. A BRIO cache entry records reception of a BRIO for a single advertised prefix, received via a neighbor router. Border Routers that need to advertise multiple prefixes simply use multiple BRIOs, each with its own address prefix. For further processing of BRIO entries, only the entry with the lowest cost to a Border Router is used. When a node is multi-homed, it will receive BRIOs from multiple upstream Border Routers. BRIO may have options to indicate connectivity to networks other than the Internet, or indications that usage of the Border Router needs authentication and authorization. A BRIO message contains informational elements listed below. A more detailed description is provided in BRDP based Address Autoconfiguration [I-D.boot-autoconf-brdp]. Border Router Address: 128-bit address of the Border Router. The Border Router should make this address reachable in the IGP, if a site use an IGP. Prefix Length: 8-bit unsigned integer. The number of leading bits in the Border Router Address, that indicates the assigned prefix for that Border Router. The Prefix Length is used for BRDP Based Routing [I-D.boot-brdp-based-routing]. The Border Router address prefix specifies the source address ingress filter, if ingress filtering is implemented on this Border Router. Uniform Path Metric (UPM): A dimensionless cost measure for the quality of the bi-directional path between the upstream router to the Border Router and the DFZ of the Internet, or to the Border Router itself in case it is floating. UPM is set to some initial value by the Border Router and is incremented by each Router that propagates the BRIO. Boot & Holtzer Expires August 4, 2011 [Page 16]
Internet-Draft BRDP Framework January 2011 Floating(F) flag: When the F-flag is set, the Border Router does not provide access to the Internet. BRIOs with an ULA prefix SHOULD have the F-bit set. DHCP (D) flag: When the D-flag is set, the Border Router is acting as a DHCP server or DHCP relay agent [RFC3315]. Service Selection Identifier: An option for a variable length UTF-8 encoded Service Selection Identifier string used to identify the Border Routers' type of service. A valid example is 'acme.com'. A Border Router MAY offer multiple services using multiple BRIOs. However, each of those BRIOs MUST use a unique Border Router address. A detailed description of BRDP message processing is found in [I-D.boot-autoconf-brdp]. 4. BRDP based Address Configuration and Prefix Delegation BRDP supports stateless address autoconfiguration [RFC4862], DHCP managed IP configuration [RFC3315] and DHCP prefix delegation [RFC3633]. MANET routers can also use a variant of stateless address autoconfiguration, where BRDP provided information is used to configure off-link addresses, used in ad hoc networks [RFC5889]. BRDP adds topology awareness in address configuration. Nodes can configure multiple addresses, each to support a different facility. ULAs can be used for site internal traffic or for Extranets. Global addresses are mandatory for access to the Internet, assuming address translation is not used. A node that is offered multiple prefixes for stateless address autoconfiguration or multiple addresses by DHCP chooses to configure one or more addresses. BRDP provides information for the candidate addresses. An important criterion is the costs of the path to the Internet DFZ. A node would select an address with the lowest costs. Another criterion is the Service Selection Identifier, to be used for access to private networks. The BRDP framework does not modify stateless address autoconfiguration and DHCP protocols, except that in a MANET, MANET Boot & Holtzer Expires August 4, 2011 [Page 17]
Internet-Draft BRDP Framework January 2011 routers perform stateless address autoconfiguration from the Border Router Information Option (BRIO) instead of the Prefix Information Option (PIO) [I-D.boot-autoconf-brdp]. This enables MANET-wide address configuration, because BRIOs are disseminated over multiple hops in the MANET, while PIOs are link local messages only. When a BRIO is stored in the BRIO cache table, the node checks if a corresponding address already exists for the Border Router from which this BRIO originates. If not, and a corresponding address for that Border Router is beneficial, address generation for that Border Router is triggered. 5. BRDP based Source Address Selection As a next step, multi-homed nodes perform source address selection for new, self-initiated connections. The algorithm described in Default Address Selection for IPv6 [RFC3484] uses the concept of a "candidate set" of potential source addresses. Rule 8 of source address selection is "Uses longest match prefix". The goal of this rule is to select the address with good communications performance. If other means of choosing among source addresses for better performance is available, that should be used. BRDP provides attributes for prefix, such as a cost metric to the Internet or a Service Selection Identifier. This information van be used to select the "best" source address. For multi-path transport protocols, it is also important to have a mechanism to select alternative addresses. For example, rule 4 gives preference to a Home Address. Alternate addresses can be used for route optimization and to avoid overhead of the Mobile IP tunnel. BRDP provided information can also be utilized by address lookup protocols such as DNS. A node can register its addresses dynamically, with support of preference and load balancing if the mechanism used support such. 6. BRDP based Routing The BRDP framework introduces a new paradigm for packet forwarding for multi-homed sites, where forwarding to a default gateway is replaced by source address based forwarding towards a corresponding Border Router [I-D.boot-brdp-based-routing]. This enforces that packets will be sent via the selected upstream provider, without the need of tunneling. As such, it prevents problems with ingress filters in multi-homed edge networks [RFC3704]. Boot & Holtzer Expires August 4, 2011 [Page 18]
Internet-Draft BRDP Framework January 2011 The BRDP Based Routing mechanism provides basic support for load distribution over multiple Border Routers. BRDP Based Routing forwards the packets to the Border Router that corresponds with the source address. As a result, nodes can utilize multiple paths, if available. Standardization of this load balancing functionality is work in progress in the IETF MPTCP working group. When a router forwards a packet to a next-hop node, via the interface where this packet was received, and the next-hop address was selected using BRDP based routing, then the router should not send an ICMP redirect message to the upstream host. This is because the upstream node would cache the redirect for the destination address, while the forwarding decision was based on the source address. 7. BRDP and IRTF RRG goals The IRTF Routing Research Group (RRG) was chartered to explore solutions for problems on routing and addressing, when the Internet continues to evolve. It has explored a number of proposed solutions, but did not reach consensus on a single, best approach [I-D.irtf-rrg-recommendation]. In fulfillment of the routing research group's charter, the co-chairs recommend that the IETF pursue work in three areas, "Evolution" [I-D.zhang-evolution], "Identifier/Locator Network Protocol (ILNP) [I-D.rja-ilnp-intro] and "Renumbering" [RFC5887] . BRDP fits in all three approaches. BRDP is an evolution in IPv6 address configuration and address selection, as well as forwarding to destinations outside the routing domain. As a result, it removes a demand for Provider Independent addresses for (small) multi-homed edge networks. BRDP enables sites to use multiple Provider Aggregatable address blocks, while being able to utilize multi-homing for improved redundancy of communications and enlarged capacity. Each site that continues to use Provider Aggregatable addresses when getting multi-homed, instead of using its own Provider Independent address space, reduces the growth of the routing tables in the Default Free Zone. BRDP can cooperate or live next many other solutions. ILNP is a good example for cooperation, BRDP provides multi-path transport capabilities to ILNP nodes. This multi-path transport capability applies to many other approaches also, such as map&encap and nat66. Because BRDP provides automatic address and prefix configuration, Renumbering is far less problematic. That said, legacy (IPv4) hosts, applications and network equipment is not BRDP enabled and manual address configuration will be used for many years to come. Boot & Holtzer Expires August 4, 2011 [Page 19]
Internet-Draft BRDP Framework January 2011 In Design Goals for Scalable Internet Routing [I-D.irtf-rrg-design-goals], a number of design goals are defined. The role BRDP can play for these goals are briefly described in the next sections. 7.1. Scalability Because BRDP is implemented in edge networks, and not in the core, scalability of BRDP is less an issue. BRDP solves the Internet routing problem at the source, by reducing the demand for PI addresses. 7.2. Traffic engineering BRDP provides traffic engineering options to end-nodes. End-nodes can configure multiple addresses and use these for utilizing multi- path capabilities of the network. Using multi-path is being worked on by the IETF MPTCP working group. 7.3. Multi-homing The core function of BRDP is providing support for IPv6 multi-homing, without any problems caused by ingress filtering [RFC3704]. 7.4. Loc/id separation BRDP does not mandate any approach for location / identification. For packet forwarding, addresses are used as locator. If addresses are used as identifiers also, for example in Mobile IP, BRDP supports route optimization where traffic uses the Home Address as identifier and care-of addresses as locator. MPTCP provides the route optimization capability. 7.5. Mobility BRDP was defined as a solution for address autoconfiguration for ad hoc networks. With BRDP, nodes can easily configure topology correct addresses in a multi-homes ad hoc network. BRDP does not provide session continuity functions. Mobility solutions are already in place or new approaches are proposed. All approaches should work well with BRDP, as BRDP does not modify the IPv6 protocol. 7.6. Simplified renumbering BRDP makes site renumbering fully automatic. This applies to node address configuration on the IPv6 stack and prefix delegation and configuration on routers. IP addresses could be configured on many other places, either manually or using specific protocols for such Boot & Holtzer Expires August 4, 2011 [Page 20]
Internet-Draft BRDP Framework January 2011 purpose. Complete automatic numbering is possible if all mechanisms in use support dynamic addresses. There is definitely more work to do [RFC5887]. 7.7. Modularity BRDP is a small, but important piece of the puzzle. It applies to edge networks only. It helps other mechanisms to work well in a multi-homed network using PA addresses, but also provides multi-path capabilities in multi-homed networks with PI addresses or multi- homing with connections to Extranets. 7.8. Routing quality BRDP is not a routing protocol, so it has no influence on routing quality. But the functionality of routing to a default gateway is changed. BRDP based routing supports paths to multiple Border Routers, where hosts can select which Border Router to use. In such scheme, nodes can select the route to use, based on quality of available routes. MPTCP provides this route selection functionality. 7.9. Routing security BRDP doesn't update any routing protocols. BRDBP based routing modifies the default gateway heuristic, the route to prefix ::/0 is replaced by a route to a Border Router, which corresponds with the source address of a packet. As a result, ingress filtering is distributed over all routers in the edge network and invalid packets are dropped as near to the source as possible. The BRDP protocol runs on IPv6 NDP and inherits all security aspects. BRDP messages are disseminated in the edge network, which may enlarge the needs for protection. Implementing SeND [RFC3971] is recommended. 7.10. Deployability BRDP deployment takes place edge network by edge network. Each network that migrates to BRDP, instead of getting a PI address bock, reduces the load on the Internet routing infrastructure. For implementing BRDP on an edge network, all routers in the network must support BRDP. BRDP support for hosts is optional. Enterprise networks can migrate site by site. Boot & Holtzer Expires August 4, 2011 [Page 21]
Internet-Draft BRDP Framework January 2011 8. Currently unaddressed issues BRDP based routing may have impact on multicast routing, e.g. selecting the route to a RP. It is not fully understood how BRDP may influence host behavior on RA M and O bits, and may bypass a 1-hop router DHCP relay server for getting information for a BRDP-learned DHCP server. Currently unaddressed issues are addressed in a next version of this document. 9. Acknowledgements TBD 10. IANA Considerations This memo includes no request to IANA. 11. Security Considerations No new security considerations arise. 12. References 12.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, September 2007. [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless Address Autoconfiguration", RFC 4862, September 2007. 12.2. Informative References [I-D.boot-autoconf-brdp] Boot, T. and A. Holtzer, "Border Router Discovery Protocol (BRDP) based Address Autoconfiguration", draft-boot-autoconf-brdp-02 (work in progress), July 2009. Boot & Holtzer Expires August 4, 2011 [Page 22]
Internet-Draft BRDP Framework January 2011 [I-D.boot-brdp-based-routing] Boot, T., "Border Router Discovery Protocol (BRDP) Based Routing", draft-boot-brdp-based-routing-00 (work in progress), November 2008. [I-D.irtf-rrg-design-goals] Li, T., "Design Goals for Scalable Internet Routing", draft-irtf-rrg-design-goals-06 (work in progress), January 2011. [I-D.irtf-rrg-recommendation] Li, T., "Recommendation for a Routing Architecture", draft-irtf-rrg-recommendation-16 (work in progress), November 2010. [I-D.rja-ilnp-intro] Atkinson, R., "ILNP Concept of Operations", draft-rja-ilnp-intro-09 (work in progress), January 2011. [I-D.zhang-evolution] Zhang, B. and L. Zhang, "Evolution Towards Global Routing Scalability", draft-zhang-evolution-02 (work in progress), October 2009. [RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering: Defeating Denial of Service Attacks which employ IP Source Address Spoofing", BCP 38, RFC 2827, May 2000. [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and M. Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3315, July 2003. [RFC3484] Draves, R., "Default Address Selection for Internet Protocol version 6 (IPv6)", RFC 3484, February 2003. [RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic Host Configuration Protocol (DHCP) version 6", RFC 3633, December 2003. [RFC3704] Baker, F. and P. Savola, "Ingress Filtering for Multihomed Networks", BCP 84, RFC 3704, March 2004. [RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure Neighbor Discovery (SEND)", RFC 3971, March 2005. [RFC5149] Korhonen, J., Nilsson, U., and V. Devarapalli, "Service Selection for Mobile IPv6", RFC 5149, February 2008. Boot & Holtzer Expires August 4, 2011 [Page 23]
Internet-Draft BRDP Framework January 2011 [RFC5887] Carpenter, B., Atkinson, R., and H. Flinck, "Renumbering Still Needs Work", RFC 5887, May 2010. [RFC5889] Baccelli, E. and M. Townsley, "IP Addressing Model in Ad Hoc Networks", RFC 5889, September 2010. Authors' Addresses Teco Boot Infinity Networks B.V. Email: teco@inf-net.nl Arjen Holtzer TNO Information and Communication Technology Email: arjen.holtzer@tno.nl Boot & Holtzer Expires August 4, 2011 [Page 24]