Recommendation for a Routing Architecture
draft-irtf-rrg-recommendation-03

Abstract

It is commonly recognized that the Internet routing and addressing architecture is facing challenges in scalability, multi-homing, and inter-domain traffic engineering. This document reports the Routing Research Group's prelimnary findings from its efforts towards developing a recommendation for a scalable routing architecture.

This document is a work in progress.

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Table of Contents

1.  Introduction
    1.1.  Structure of This Document
2.  Locator Identifier Separation Protocol (LISP)
    2.1.  Key Idea
    2.2.  Gains
    2.3.  Costs
3.  Routing Architecture for the Next Generation Internet (RANGI)
    3.1.  Key Idea
    3.2.  Gains
    3.3.  Costs
4.  Internet Vastly Improved Plumbing (Ivip)
    4.1.  Key Ideas
    4.2.  Extensions
        4.2.1.  TTR Mobility
        4.2.2.  Modified Header Forwarding
    4.3.  Gains
    4.4.  Costs
5.  hIPv4
    5.1.  Key Idea
    5.2.  Gains
    5.3.  Costs And Issues
6.  Name overlay (NOL) service for scalable Internet routing
    6.1.  Key Idea
    6.2.  Gains
    6.3.  Costs
7.  Compact routing in locator identifier mapping system
    7.1.  Key Idea
    7.2.  Gains
    7.3.  Costs
8.  Layered mapping system (LMS)
    8.1.  Key Ideas
    8.2.  Gains
    8.3.  Costs
9.  2-phased mapping
    9.1.  Considerations
    9.2.  My contribution: a 2-phased mapping
    9.3.  Gains
    9.4.  Summary
10.  Global Locator, Local Locator, and Identifier Split (GLI-Split)
    10.1.  Key Idea
    10.2.  Gains
    10.3.  Costs
11.  Tunneled Inter-domain Routing (TIDR)
    11.1.  Key Idea
    11.2.  Gains
    11.3.  Costs
12.  Identifier-Locator Network Protocol (ILNP)
    12.1.  Key Ideas
    12.2.  Benefits
    12.3.  Costs
13.  Enhanced Efficiency of Mapping Distribution Protocols in Map-and-Encap Schemes
    13.1.  Introduction
    13.2.  Management of Mapping Distribution of Subprefixes Spread Across Multiple ETRs
    13.3.  Management of Mapping Distribution for Scenarios with Hierarchy of ETRs and Multi-Homing
14.  Evolution
    14.1.  Need for Evolution
    14.2.  Relation to Other RRG Proposals
    14.3.  Aggregation with Increasing Scopes
15.  Name-Based Sockets
16.  Recommendation
17.  Acknowledgements
18.  IANA Considerations
19.  Security Considerations
20.  References
    20.1.  Normative References
    20.2.  Informative References
    20.3.  LISP References
    20.4.  RANGI References
    20.5.  Ivip References
    20.6.  hIPv4 References
    20.7.  Layered Mapping System References
    20.8.  GLI References
    20.9.  TIDR References
    20.10.  ILNP References
    20.11.  EEMDP References
    20.12.  Evolution References
    20.13.  Name Based Sockets References
§  Author's Address

1.  Introduction

It is commonly recognized that the Internet routing and addressing architecture is facing challenges in scalability, multi-homing, and inter-domain traffic engineering. The problem being addressed has been documented in [I‑D.narten‑radir‑problem‑statement] (Narten, T., “On the Scalability of Internet Routing,” February 2010.), and the design goals that we have agreed to can be found in [I‑D.irtf‑rrg‑design‑goals] (Li, T., “Design Goals for Scalable Internet Routing,” July 2007.). This document reports the Routing Research Group's (RRG's) results from its efforts towards developing a recommendation for a scalable routing architecture.

This document is a work in progress.

1.1.  Structure of This Document

This document describes a number of the different possible approaches that could be taken in a new routing architecture, as well as a summary of the current thinking of the overall group regarding each approach.

2.  Locator Identifier Separation Protocol (LISP)

2.1.  Key Idea

Implements a locator-identifier separation mechanism using encapsulation between routers at the "edge" of the Internet. Such a separation allows topological aggregation of the routeable addresses (locators) while providing stable and portable numbering of end systems (identifiers).

2.2.  Gains

• topological aggregation of numbering space (RLOCs) used for routing, which greatly reduces both the overall size and the "churn rate" of the information needed to operate the Internet global routing system
• seperate numbering space (EIDs) for end-systems, effectively allowing "PI for all" (no renumbering cost for connectivity changes) without adding state to the global routing system
• improved traffic engineering capabilities that explicitly do not add state to the global routing system and whose deployment will allow active removal of more-specific state currently used
• no changes required to end systems
• no changes to Internet "core" routers
• minimal and straightforward changes to "edge" routers
• day-one advatanges for early adopters
• defined router-to-router protocol
• defined database mapping system
• defined deployment plan
• defined interoperability/interworking mechanisms
• defined scalable end-host mobility mechanisms
• prototype implementation already exists and undergoing testing
• production implementations in progress

2.3.  Costs

• mapping system infrastructure (map servers, map resolvers, ALT routers) (new potential business opportunity)
• Interworking infrastructure (proxy ITRs) (new potential business opportunity)
• overhead for determining/maintaining locator/path liveness (common issue for all id/loc separation proposals)

3.  Routing Architecture for the Next Generation Internet (RANGI)

3.1.  Key Idea

Similar to HIP [RFC4423] (Moskowitz, R. and P. Nikander, “Host Identity Protocol (HIP) Architecture,” May 2006.), RANGI introduces a host identifier layer between the network layer and the transport layer, and the transport-layer associations (i.e., TCP connections) are no longer bound to IP addresses, but to host identifiers. The major difference from the HIP is that the host identifier in RANGI is a 128-bit hierarchical and cryptographic identifier which has organizational structure. As a result, the corresponding ID->locator mapping system for such identifiers has reasonable business model and clear trust boundaries. In addition, RANGI uses IPv4-embeded IPv6 addresses as locators. The LD ID (i.e., the leftmost 96 bits) of this locator is a provider-assigned /96 IPv6 prefix, while the last four octets of this locator is a local IPv4 address (either public or private). This special locator could be used to realize 6over4 automatic tunneling (borrowing ideas from ISATAP [RFC5214] (Templin, F., Gleeson, T., and D. Thaler, “Intra-Site Automatic Tunnel Addressing Protocol (ISATAP),” March 2008.)), which will reduce the deployment cost of this new routing architecture. Within RANGI, the mappings from FQDN to host identifiers are stored in the DNS system, while the mappings from host identifiers to locators are stored in a distributed id/locator mapping system (e.g., a hierarchical Distributed Hash Table (DHT) system, or a reverse DNS system).

3.2.  Gains

RANGI achieves almost all of goals set by RRG as follows:

1. Routing Scalability: Scalability is achieved by decoupling identifiers from locators.
2. Traffic Engineering: Hosts located in a multi-homed site can suggest the upstream ISP for outbound and inbound traffics, while the first-hop LDBR (i. e., site border router) has the final decision right on the upstream ISP selection.
3. Mobility and Multi-homing: Sessions will not be interrupted due to locator change in cases of mobility or multi-homing.
4. Simplified Renumbering: When changing providers, the local IPv4 addresses of the site do not need to change. Hence the internal routers within the site don't need renumbering.
5. Decoupling Location and Identifier: Obvious.
6. Routing Stability: Since the locators are topologically aggregatable and the internal topology within LD will not be disclosed outside, the routing stability could be improved greatly.
7. Routing Security: RANGI reuses the current routing system and does not introduce any new security risk into the routing system.
8. Incremental Deployability: RANGI allows easy transition from IPv4 network to IPv6 network. In addition, RANGI proxy allows RANGI-aware hosts to communicate to legacy IPv4 or IPv6 hosts, and vice versa.

3.3.  Costs

1. Host change is required
2. First-hop LDBR change is required to support site-controlled traffic-engineering capability.
3. The ID->Locator mapping system is a new infrastructure to be deployed.
4. Proxy needs to be deployed for communication between RANGI-aware hosts and legacy hosts.

4.  Internet Vastly Improved Plumbing (Ivip)

4.1.  Key Ideas

Ivip (pr. eye-vip, est. 2007-06-15) is a core-edge separation scheme for IPv4 and IPv6. It provides multihoming, portability of address space and inbound traffic engineering for end-user networks of all sizes and types, including those of corporations, SOHO and mobile devices.

Ivip meets all the constraints imposed by the need for widespread voluntary adoption [Ivip Constraints] (Whittle, R., “List of constraints on a successful scalable routing solution which result from the need for widespread voluntary adoption,” .).

Ivip's global fast-push mapping distribution network is structured like a cross-linked multicast tree. This pushes all mapping changes to full database query servers (QSDs) within ISPs and end-user networks which have ITRs. Each mapping change is sent to all QSDs within a few seconds.

ITRs gain mapping information from these local QSDs within a few tens of milliseconds. QSDs notify ITRs of changed mapping with similarly low latency. ITRs tunnel all traffic packets to the correct ETR without significant delay.

Ivip's mapping consists of a single ETR address for each range of mapped address space. Ivip ITRs do not need to test reachability to ETRs because the mapping is changed in real-time to that of the desired ETR.

End-user networks control the mapping, typically by contracting a specialized company to monitor the reachability of their ETRs and change the mapping to achieve multihoming and/or TE. So the mechanisms which control ITR tunneling are controlled by the end-user networks in real-time and are completely separate from the core-edge separation scheme itself.

ITRs can be implemented in dedicated servers or hardware-based routers. The ITR function can also be integrated into sending hosts. ETRs are relatively simple and only communicate with ITRs rarely - for Path MTU management with longer packets.

Ivip-mapped ranges of end-user address space need not be subnets. They can be of any length, in units of IPv4 addresses or IPv6 /64s.

Compared to conventional unscalable BGP techniques, and to the use of core-edge separation architectures with non-real-time mapping systems, end-user networks will be able to achieve more flexible and responsive inbound TE. If inbound traffic is split into several streams, each to addresses in different mapped ranges, then real-time mapping changes can be used to steer the streams between multiple ETRs at multiple ISPs.

Open ITRs in the DFZ (OITRDs, similar to LISP's PTRs) tunnel packets sent by hosts in networks which lack ITRs. So multihoming, portability and TE benefits apply to all traffic.

ITRs request mapping either directly from a local QSD or via one or more layers of caching query servers (QSCs) which in turn request it from a local QSD. QSCs are optional but generally desirable since they reduce the query load on QSDs.

ETRs may be in ISP or end-user networks. IP-in-IP encapsulation is used, so there is no UDP or any other header. PMTUD (Path MTU Discovery) management with minimal complexity and overhead will handle the problems caused by encapsulation, and adapt smoothly to jumboframe paths becoming available in the DFZ. The outer header's source address is that of the sending host - which enables existing ISP BR filtering of source addresses to be extended to encapsulated traffic packets by the simple mechanism of the ETR dropping packets whose inner and outer source address do not match.

4.2.  Extensions

4.2.1.  TTR Mobility

The TTR approach to mobility [Ivip Mobility] (Whittle, R., “TTR Mobility Extensions for Core-Edge Separation Solutions to the Internet's Routing Scaling Problem,” .) is applicable to all core-edge separation techniques and provides scalable IPv4 and IPv6 mobility in which the MN keeps its own mapped IP address(es) no matter how or where it is physically connected, including behind one or more layers of NAT.

Path-lengths are typically optimal or close to optimal and the MN communicates normally with all other non-mobile hosts (no stack or app changes), and of course other MNs. Mapping changes are only needed when the MN uses a new TTR, which would typically be if the MN moved more than 1000km. Mapping changes are not required when the MN changes its physical address(es).

4.2.2.  Modified Header Forwarding

Separate schemes for IPv4 and IPv6 enable tunneling from ITR to ETR without encapsulation. This will remove the encapsulation overhead and PMTUD problems. Both approaches involve modifying all routers between the ITR and ETR to accept a modified form of the IP header. These schemes require new FIB/RIB functionality in DFZ and some other routers but do not alter the BGP functions of DFZ routers.

4.3.  Gains

Amenable to widespread voluntary adoption due to no need for host changes, complete support for packets sent from non-upgraded networks and no significant degradation in performance.

Modular separation of the control of ITR tunneling behavior from the ITRs and the core-edge separation scheme itself: end-user networks control mapping in any way they like, in real-time.

A small fee per mapping change deters frivolous changes and helps pay for pushing the mapping data to all QSDs. End-user networks who make frequent mapping changes for inbound TE, should find these fees attractive considering how it improves their ability to utilize the bandwidth of multiple ISP links.

End-user networks will typically pay the cost of OITRD forwarding to their networks. This provides a business model for OITRD deployment and avoids unfair distribution of costs.

Existing source address filtering arrangements at BRs of ISPs and end-user networks are prohibitively expensive to implement directly in ETRs, but with the outer header's source address being the same as the sending host's address, Ivip ETRs inexpensively enforce BR filtering on decapsulated packets.

4.4.  Costs

QSDs receive all mapping changes and store a complete copy of the mapping database. However, a worst case scenario is 10 billion IPv6 mappings, each of 32 bytes, which fits on a consumer hard drive today and should fit in server DRAM by the time such adoption is reached.

The maximum number of non-mobile networks requiring multihoming etc. is likely to be ~10M, so most of the 10B mappings would be for mobile devices. However, TTR mobility does not involve frequent mapping changes since most MNs only rarely move more than 1000km.

5.  hIPv4

5.1.  Key Idea

The hierarchical IPv4 framework is adding scalability in the routing architecture by introducing hierarchy in the IPv4 address space. The hIPv4 addressing scheme is divided in two parts, the Area Locator (ALOC) address space which is globally unique and the Endpoint Locator (ELOC) address space which is only regionally unique. The ALOC and ELOC prefixes are added as an IP option to the IPv4 header as described in RFC 1385. Instead of creating a tunneling (i.e. overlay) solution a new routing element is needed in every ALOC realm, a Locator Swap Router - the current IPv4 forwarding plane remains intact, also no new routing protocols or mapping systems are required. The control plane of the ALOC realm routers needs some modification in order for ICMP to be compatible with the hIPv4 framework. When an area (one or several AS) of an ISP has become an ALOC realm only ALOC prefixes are exchanged with other ALOC realms. Directly attached ELOC prefixes are only inserted to the RIB of the local ALOC realm, ELOC prefixes are not distributed in the DFZ. Multi-homing can be achieved in two ways, either the enterprise request an ALOC prefix from the RIR (this is not recommended) or the enterprise receive the ALOC prefixes from their upstream ISPs - ELOC prefixes are PI addresses and remains intact when a upstream ISP is changed, only the ALOC prefixes is replaced. When the RIB of DFZ is compressed no longer an ingress router knows if the destination prefix is available or not, only attachment points (ALOC prefixes) of the destination prefix are advertised in the DFZ. Thus the endpoints must take more responsibility for their sessions. This can be achieved by using multipath enabled transport protocols, such as SCTP and MPTCP, at the endpoints. The multipath transport protocols also provides a session identifier, i.e. verification tag/token, thus the location and identifier split is carried out - site mobility, endpoint mobility and mobile site mobility is achieved. DNS needs to be upgraded, to resolve the location of an endpoint it must have one ELOC value (current A-record) and at least one ALOC value (in multi-homing solutions there will be several ALOC values for an endpoint). The hIPv4 framework can also be integrated to a map-and-encapsulate solution; the ITR/ETR needs to incorporate the hIPv4 stack and might use a multipath enabled transport protocol to serve the hIPv4/multipath transport protocol enabled endpoints.

5.2.  Gains

1. Improved routing scalability: Adding hierarchy in the address space enables a hierarchy in the routing architecture. Early adapters of an ALOC realm will no longer carry the RIB of the DFZ - only ELOC prefixes of directly attached networks and ALOC prefixes from other service provider that have migrated.
2. Scalable support for traffic engineering: Multipath enabled transport protocols are recommended to achieve dynamic load-balancing of a session. Support for Valiant Load-balancing schemes has been added to the framework; more research work is required around VLB switching.
3. Scalable support for multi-homing: Only attachment points of a multi-homed site are advertised in the DFZ, DNS will inform the requester how many attachment points the destination endpoint has. It is the initiating endpoints choice/responsibility which attachment point is used; endpoints using multipath enabled transport protocols can make use of several attachment points for a session.
4. Simplified Renumbering: When changing provider, the local ELOC prefixes remains intact, only the ALOC prefix is changed on the endpoints.
5. Decoupling Location and Identifier: The verification tag (SCTP) and token (MPTCP) can be considered to have the characteristics of a session identifier and thus a session layer is created between the transport and application layer in the TCP/IP model
6. Routing quality: The hIPv4 framework introduce no tunneling mechanisms, only a swap of the IPv4 header and locator header at the destination ALOC realm is required, thus current routing algorithms are preserved as such. Valiant Load-balancing might be used as a new forwarding mechanism.
7. Routing Security: Similar as with today's DFZ, except that ELOC prefixes can not be high-jacked (by injecting a longest match prefix) outside an ALOC realm (improved security)
8. Deployability: The hIPv4 framework is an evolution of the current IPv4 framework and is backwards compatible with the current IPv4 framework. Sessions in a local network and inside an ALOC realm might in the future still use the current IPv4 framework.

5.3.  Costs And Issues

1. Upgrade of the stack at an endpoint or the endpoint should make use of an ITR/XTR
2. In a multi-homing solution the border routers should be able to apply policy based routing upon the ALOC value in the locator header
3. New policies must be set by the RIRs
4. Short timeframe before the expected depletion of the IPv4 address space occurs
5. Will enterprises give up their global allocation of the current IPv4 address block they have gained?
6. Co-ordination with MPTCP is highly desirable

6.  Name overlay (NOL) service for scalable Internet routing

6.1.  Key Idea

The basic idea is to add a name overlay (NOL) on the existing TCP/IP stack.

Its functions include:

1. host names configuration, registration and authentication;
2. Initiate and manage transport connection channels (i.e., TCP/IP connections) by name;
3. keep application data transport continuity for mobility.

At the edge network, we introduce a new type of gateway NTR (Name Transfer Relay), which block the PI addresses of edge networks into upstream transit networks. NTRs performs address and/or port translation between blocked PI addresses and globally routable addresses, which seem like today's widely used NAT/NAPT devices. Both legacy and NOL applications behind a NTR can access the outside as usual. To access the hosts behind a NTR from outside, we need to use NOL traverse the NTR by name and initiate connections to the hosts behind it.

Different from proposed host-based ID/Locator split solutions, such as HIP, Shim6, and name-oriented stack, NOL doesn't need to change the existing TCP/IP stack, sockets and their packet formats. NOL can co-exist with the legacy infrastructure, the core-edges separation solutions (e.g., APT, LISP, Six/one, Ivip, etc.)

6.2.  Gains

1. Reduce routing table size: Prevent edge network PI address into transit netwok by deploying gateway NTR
2. Traffic Engineering: For legacy and NOL application initiating session, the incoming traffic can be directed to a specific NTR by DNS answer for names. In addition, for NOL application, its initial session can be redirected from one NTR to other appropriate NTRs. These mechanisms provide some support for traffic engineering.
3. Multi-homing: When a PI address network connects to Internet by multi-homing with several providers, it can deploy NTRs to block the PI addresses into provide networks.
4. And the NTRs can be allocated PA addresses from the upstream providers and store them in NTRs' address pool. By DNS query or NOL session, any session that want to access the hosts behind the NTR can be delegated to a specific PA address in the NTR address pool.
5. Mobility: NOL layer manage the traditional TCP/IP transport connections, and keeps application data transport continue by setting breakpoints and sequence numbers in data stream.
6. No need to change TCP/IP stack, sockets and DNS system.
7. No need for extra mapping system.
8. NTR can be deployed unilaterally, just like NATs
9. NOL applications can communicate with legacy applications.
10. NOL can be compatible with existing solutions, such as APT, LISP, Ivip, etc.
11. End user controlled multi-path indirect routing based on distributed NTRs. This will give benefits to the performance-aware applications, such as, MSN, Video streaming, etc.

6.3.  Costs

1. Legacy applications have trouble with initiating access to the servers behind NTR. Such trouble can be resolved by deploying NOL proxy for legacy hosts, or delegating globally routable PA addresses in NTR address pool for these servers, or deploying server proxy outside NTR.
2. It may increase the number of entries of DNS, but not drastic, because it only increases DNS entries in domains granularity not hosts. The name used in NOL, for example, just like email address hostname@domain.net. The needed DNS entries and query is just for "domain.net", and The NTR knows "hostnames". The DNS entries will not only be increased, but its dynamic might be agitated as well. However the scalability and performance of DNS is guaranteed by name hierarchy and cache mechanism.
3. Address translating/rewriting costs on NTRs.

7.  Compact routing in locator identifier mapping system

7.1.  Key Idea

Builds a highly scalable locator identity mapping system using compact routing principles. Provides means for dynamic topology adaption to facilitate efficient aggregation. Map servers are assigned as cluster heads or landmarks based on their capability to aggregate EID announcements.

7.2.  Gains

Minimizes the routing table sizes in at the system level (= map servers). Provides clear upper bounds for routing stretch that defines the packet delivery delay of the map request/first packet.

Organizes the mapping system based EID numbering space, minimizes the administrative of overhead of managing EID space. No need for administratively planned hierarchical address allocation as the system will find convergence into a sets of EID allocations.

Availability and robustness of the overall routing system (including xTRs and map servers) is improved because potential to use multiple map servers and direct routes without involvement of map servers.

7.3.  Costs

The scalability gains will materialize only in large deployments. If the stretch is required to be bound to those of compact routing (worst case stretch less or equal to 3, on average 1+epsilon) then xTRs need to have memory/cache for the mappings of its cluster.

8.  Layered mapping system (LMS)

8.1.  Key Ideas

Build a hierarchical mapping system to support scalability, analyze the design constraints and present an explicit system structure; design a two-cache mechanism on ingress tunneling router (ITR) to gain low request delay and facilitate data validation. Tunneling and mapping are done at core and no change needed on edge networks. Mapping system is run by interest groups independent of ISP, which conforms to economical model and can be voluntarily adopted by various networks. Mapping system can also be constructed stepwise, especially in the IPv6 scenario.

8.2.  Gains

1. Scalability
   1. Distributed storage of mapping data avoids central storage of massive data; restrict updates within local areas;
   2. Cache mechanism in ITR reduces request loads on mapping system reasonably.
2. Deployability
   1. No change on edge works; only tunneling in core routers; new devices in core networks;
   2. Mapping system can be constructed stepwise: a mapping node needn't be constructed if none of its responsible ELOCs is allocated. This makes sense especially for IPv6.
   3. Conform to economic model: mapping system can profit from their services; core routers and edge networks are willing to join the circle, either to avoid router upgrades or realize traffic engineering. Benefits from joining are independent of the scheme's implementation scale.
3. Low request delay: Low layer number of the mapping structure and two-stage cache can well achieve low request delay.
4. Data consistency: Two-stage cache enables ITR to update data in the map cache conveniently.
5. Traffic engineering support: Edge networks inform mapping system their mappings with all upstream routers with different priority, thus to control their ingress flows.

8.3.  Costs

1. Deployment of LMS needs to be further discussed.
2. The structure of mapping system needs to be refined according to practical circumstances.

9.  2-phased mapping

9.1.  Considerations

1. Mapping from prefixes to ETRs is an M:M mapping. Any change of (prefix, ETR) pair should be updated timely which can be a heavy burden to any mapping systems if the relation changes frequently.
2. prefix<->ETR mapping system cannot be deployed efficiently if it is overwhelmed by the worldwide dynamics. Therefore the mapping itself is not scalable with this direct mapping scheme.

9.2.  My contribution: a 2-phased mapping

1. Introduce AS number in the middle of the mapping, phase I mapping is prefix<->AS#, phase II mapping is AS#<->ETRs. We have a M:1:M mapping model now.
2. My assumption is that all ASes know better their local prefixes (in the IGP) than others. and most likely local prefixes can be aggregated when map them to the AS#, which will make the mapping entry reduction possible, ASes also know clearly their ETRs on its border between core and edge. So all mapping information can be collected locally.
3. A registry system will take care of the phase I mapping information. Each AS should have a register agent to notify the local range of IP address space to the registry. This system can be organized as a hierarchical infrastructure like DNS, or alternatively as a centralized registry like "whois" in each RIR. Phase II mapping information can be distributed between XTRs as a BGP extension.
4. A basic forwarding procedure is that ITR firstly get the destination AS# from phase I mapper (or from cache) when the packet is entering the "core". Then it will check the closest ETR of destination AS#, since phase 2 mapping information has been "pushed" to it through BGP updates. At last the ITR encap the packet and tunnel it to a corresponding ETR.

9.3.  Gains

1. Any prefixes reconfiguration (aggregation/ deaggregation) within an AS will not be notified to mapping system.
2. Possible highly efficient aggregation of the local prefixes (in the form of an IP space range).
3. Both phase I and phase II mapping can be stable.
4. A stable mapping system will reduce the update overhead introduced by topology change/routing policy dynamics.ETR.

9.4.  Summary

1. The 2-phased mapping scheme introduces AS# between the mapping prefixes and ETRs.
2. The decoupling of direct mapping makes highly dynamic updates stable, therefore it can be more scalable than any direct mapping designs.
3. The 2-phased mapping scheme is adaptable to any core/edge split based proposals.

10.  Global Locator, Local Locator, and Identifier Split (GLI-Split)

10.1.  Key Idea

GLI-Split implements a separation between global routing (in the global Internet outside edge networks) and local routing (inside edge networks) and using global and local locators (GLs, LLs). In addition, a separate static identifier (ID) is used to identify communication endpoints (e.g. nodes or services) independently of any routing information. Locators and IDs are encoded in IPv6 addresses to enable backwards-compatibility with the IPv6 Internet. The higher order bits store either a GL or a LL while the lower order bits contain the ID. A local mapping system maps IDs to LLs and a global mapping system maps IDs to GLs. The full GLI-mode requires nodes with upgraded networking stacks and special GLI-gateways. The GLI-gateways perform stateless locator rewriting in IPv6 addresses with the help of the local and global mapping system. Non-upgraded IPv6 nodes can also be accommodated in GLI-domains since an enhanced DHCP service and GLI-gateways compensate their missing GLI-functionality. This is an important feature for incremental deployability.

10.2.  Gains

The benefits of GLI-Split are

• Hierarchical aggregation of routing information in the global Internet through separation of edge and core routing
• Provider changes not visible to nodes inside GLI-domains (renumbering not needed)
• Rearrangement of subnetworks within edge networks not visible to the outside world (better support of large edge networks)
• Transport connections survive both types of changes
• Multihoming
• Improved traffic engineering for incoming and outgoing traffic
• Multipath routing and load balancing for hosts
• Improved resilience
• Improved mobility support without home agents and triangle routing
• Interworking with the classic Internet
  • without triangle routing over proxy routers
  • without stateful NAT

These benefits are available for upgraded GLI-nodes, but non-upgraded nodes in GLI-domains partially benefit from these advanced features, too. This offers multiple incentives for early adopters and they have the option to migrate their nodes gradually from non-GLI stacks to GLI-stacks.

10.3.  Costs

• Local and global mapping system
• Modified DHCP or similar mechanism
• GLI-gateways with stateless locator rewriting in IPv6 addresses
• Upgraded stacks (only for full GLI-mode)

11.  Tunneled Inter-domain Routing (TIDR)

11.1.  Key Idea

Provides a method for locator-identifier separation using tunnels between routers of the edge of the Internet transit infrastructure. It enrichs BGP protocol for distributing the identifier-to-locator mapping. Using new BGP atributes "identifier prefixes" are assigned interdomain routing locators so that they will not be installed in the RIB and will be moved to a new table called Tunnel Information Base (TIB). Afterwards, when routing a packet to the "identifier prefix", the TIB will be searched first to perform tunnel imposition, and secondly the RIB for actual routing. After the edge router performs tunnel imposition, all routers in the middle will route this packet until the router being the tail-end of the tunnel.

11.2.  Gains

• Smooth deployment
• Size Reduction of the Global RIB Table
• Deterministic Customer Traffic Engineering for Incoming Traffic
• Numerous Forwarding Decisions for a Particular Address Prefix
• TIDR Stops AS Number Space Depletion
• Improved BGP Convergence
• Protection of the Inter-domain Routing Infrastructure
• Easy Separation of Control Traffic and Transit Traffic
• Different Layer-2 Protocol-IDs for Transit and Non-Transit Traffic
• Multihoming Resilience
• New Address Families and Tunneling Techniques
• TIDR for IPv4 or IPv6, and Migration to IPv6
• Scalability, Stability and Reliability
• Faster Inter-domain Routing

11.3.  Costs

• Routers of the edge of the interdomain infrastructure will need to be upgraded to hold the mapping database (i.e. the TIB)
• "Mapping updates" will need to be treated differently from usual BGP "routing updates"

12.  Identifier-Locator Network Protocol (ILNP)

12.1.  Key Ideas

• Provide crisp separation of Identifiers from Locators.
• Identifiers name nodes, not interfaces.
• Locators name subnetworks, rather than interfaces, so they are equivalent to an IP routing prefix.
• Identifiers are never used for network-layer routing, whilst Locators are never used for Node Identity.
• Transport-layer sessions (e.g. TCP session state) use only Identifiers, never Locators, meaning that changes in location have no adverse impact on an IP session.

12.2.  Benefits

• The underlying protocol mechanisms support fully scalable site multi-homing, node multi-homing, site mobility, and node mobility.
• ILNP enables topological aggregation of location information while providing stable and topology-independent identities for nodes.
• In turn, this topological aggregation reduces both the routing prefix "churn" rate and the overall size of the Internet's global routing table, by eliminating the value and need for more-specific routing state currently carried throughout the global (default-free) zone of the routing system.
• ILNP enables improved Traffic Engineering capabilities without adding any state to the global routing system. TE capabilities include both provider-driven TE and also end-site-controlled TE.
• ILNP's mobility approach:
  • eliminates the need for special-purpose routers (e.g. Home Agent and/or Foreign Agent now required by Mobile IP & NEMO).
  • eliminates "triangle routing" in all cases.
  • supports both "make before break" and "break before make" layer-3 handoffs.
• ILNP improves resilience and network availability while reducing the global routing state (as compared with the currently deployed Internet).
• ILNP is Incrementally Deployable:
  • No changes are required to existing IPv6 (or IPv4) routers.
  • Upgraded nodes gain benefits immediately ("day one"); those benefits gain in value as more nodes are upgraded (this follows Metcalfe's Law).
  • Incremental Deployment approach is documented.
• ILNP is Backwards Compatible:
  • ILNPv6 is fully backwards compatible with IPv6 (ILNPv4 is fully backwards compatible with IPv4).
  • Reuses existing known-to-scale DNS mechanisms to provide identifier/locator mapping.
  • Existing DNS Security mechanisms are reused without change.
  • Existing IP Security mechanisms are reused with one minor change (IPsec Security Associations replace current use of IP Addresses with new use of Locator values). NB: IPsec is also backwards compatible.
  • Backwards Compatibility approach is documented.
• No new or additional overhead is required to determine or to maintain locator/path liveness.
• ILNP does not require locator rewriting (NAT); ILNP permits and tolerates NAT should that be desirable in some deployment(s).
• Changes to upstream network providers do not require node or subnetwork renumbering within end-sites.
• Compatible with and can facilitiate transition from current single-path TCP to multi-path TCP.
• ILNP can be implemented such that existing applications (e.g. applications using the BSD Sockets API) do NOT need any changes or modifications to use ILNP.

12.3.  Costs

• End systems need to be enhanced incrementally to support ILNP in addition to IPv6 (or IPv4 or both).
• DNS servers supporting upgraded end systems also should be upgraded to support new DNS resource records for ILNP. (DNS protocol & DNS security do not need any changes.)

13.  Enhanced Efficiency of Mapping Distribution Protocols in Map-and-Encap Schemes

13.1.  Introduction

We present some architectural principles pertaining to the mapping distribution protocols, especially applicable to map-and-encap (e.g., LISP) type of protocols. These principles enhance the efficiency of the map-and-encap protocols in terms of (1) better utilization of resources (e.g., processing and memory) at Ingress Tunnel Routers (ITRs) and mapping servers, and consequently, (2) reduction of response time (e.g., first packet delay). We consider how Egress Tunnel Routers (ETRs) can perform aggregation of end-point ID (EID) address space belonging to their downstream delivery networks, in spite of migration/re-homing of some subprefixes to other ETRs. This aggregation may be useful for reducing the processing load and memory consumption associated with map messages, especially at some resource-constrained ITRs and subsystems of the mapping distribution system. We also consider another architectural concept where the ETRs are organized in a hierarchical manner for the potential benefit of aggregation of their EID address spaces. The two key architectural ideas are discussed in some more detail below. A more complete description can be found in a document [EEMDP Considerations] (Sriram, K., Kim, Y., and D. Montgomery, “Architectural Considerations for Mapping Distribution Protocols,” .) that was presented at the RRG meeting in Dublin [EEMDP Presentation] (Sriram, K., Kim, Y., and D. Montgomery, “Architectural Considerations for Mapping Distribution Protocols,” .).

It will be helpful to refer to Figures 1, 2, and 3 in the document noted above for some of the discussions that follow here below.

13.2.  Management of Mapping Distribution of Subprefixes Spread Across Multiple ETRs

To assist in this discussion, we start with the high level architecture of a map-and-encap approach (it would be helpful to see Fig. 1 in the document mentioned above). In this architecture we have the usual ITRs, ETRs, delivery networks, etc. In addition, we have the ID-Locator Mapping (ILM) servers which are repositories for complete mapping information, while the ILM-Regional (ILM-R) servers can contain partial and/or regionally relevant mapping information.

While a large endpoint address space contained in a prefix may be mostly associated with the delivery networks served by one ETR, some fragments (subprefixes) of that address space may be located elsewhere at other ETRs. Let a/20 denote a prefix that is conceptually viewed as composed of 16 subnets of /24 size that are denoted as a1/24, a2/24, :::, a16/24. For example, a/20 is mostly at ETR1, while only two of its subprefixes a8/24 and a15/24 are elsewhere at ETR3 and ETR2, respectively (see Fig. 2 in the document). From the point of view of efficiency of the mapping distribution protocol, it may be beneficial for ETR1 to announce a map for the entire space a/20 (rather than fragment it into a multitude of more-specific prefixes), and provide the necessary exceptions in the map information. Thus the map message could be in the form of Map:(a/20, ETR1; Exceptions: a8/24, a15/24). In addition, ETR2 and ETR3 announce the maps for a15/24 and a8/24, respectively, and so the ILMs know where the exception EID addresses are located. Now consider a host associated with ITR1 initiating a packet destined for an address a7(1), which is in a7/24 that is not in the exception portion of a/20. Now a question arises as to which of the following approaches would be the best choice:

1. ILM-R provides the complete mapping information for a/20 to ITR1 including all maps for relevant exception subprefixes.
2. ILM-R provides only the directly relevant map to ITR1 which in this case is (a/20, ETR1).

In the first approach, the advantage is that ITR1 would have the complete mapping for a/20 (including exception subnets), and it would not have to generate queries for subsequent first packets that are destined to any address in a/20, including a8/24 and a15/24. However, the disadvantage is that if there is a significant number of exception subprefixes, then the very first packet destined for a/20 will experience a long delay, and also the processors at ITR1 and ILM-R can experience overload. In addition, the memory usage at ITR1 can be very inefficient as well. The advantage of the second approach above is that the ILM-R does not overload resources at ITR1 both in terms of processing and memory usage but it needs an enhanced map response in of the form Map:(a/20, ETR1, MS=1), where MS (more specific) indicator is set to 1 to indicate to ITR1 that not all subnets in a/20 map to ETR1. The key idea is that aggregation is beneficial and subnet exceptions must be handled with additional messages or indicators in the maps.

13.3.  Management of Mapping Distribution for Scenarios with Hierarchy of ETRs and Multi-Homing

Now we highlight another architectural concept related to mapping management (helpful here to refer to Fig. 3 in the document). Here we consider the possibility that ETRs may be organized in a hierarchical manner. For instance ETR7 is higher in hierarchy relative to ETR1, ETR2, and ETR3, and like-wise ETR8 is higher relative to ETR4, ETR5, and ETR6. For instance, ETRs 1 through 3 can relegate locator role to ETR7 for their EID address space. In essence, they can allow ETR7 to act as the locator for the delivery networks in their purview. ETR7 keeps a local mapping table for mapping the appropriate EID address space to specific ETRs that are hierarchically associated with it in the level below. In this situation, ETR7 can perform EID address space aggregation across ETRs 1 through 3 and can also include its own immediate EID address space for the purpose of that aggregation. The many details related to this approach and special circumstances involving multi-homing of subnets are discussed in detail in the detailed document noted earlier. The hierarchical organization of ETRs and delivery networks should help in the future growth and scalability of ETRs and mapping distribution networks. This is essentially recursive map-and-encap, and some of the mapping distribution and management functionality will remain local to topologically neighboring delivery networks which are hierarchically underneath ETRs.

14.  Evolution

As the Internet continues its rapid growth, router memory size and CPU cycle requirements are outpacing feasible hardware upgrade schedules. We propose to solve this problem by applying aggregation with increasing scopes to gradually evolve the routing system towards a scalable structure. At each evolutionary step, our solution is able to interoperate with the existing system and provide immediate benefits to adopters to enable deployment. This document summarizes the need for an evolutionary design, the relationship between our proposal and other revolutionary proposals and the steps of aggregation with increasing scopes. Our detailed proposal can be found in [I‑D.zhang‑evolution] (Zhang, B. and L. Zhang, “Evolution Towards Global Routing Scalability,” October 2009.).

14.1.  Need for Evolution

Multiple different views exist regarding the routing scalability problem. Networks differ vastly in goals, behavior, and resources, giving each a different view of the severity and imminence of the scalability problem. Therefore we believe that, for any solution to be adopted, it will start with one or a few early adopters, and may not ever reach the entire Internet. The evolutionary approach recognizes that changes to the Internet can only be a gradual process with multiple stages. At each stage, adopters are driven by and rewarded with solving an immediate problem. Each solution must be deployable by individual networks who deem it necessary at a time they deem it necessary, without requiring coordination from other networks, and the solution has to bring immediate relief to a single first-mover.

14.2.  Relation to Other RRG Proposals

Most proposals take a revolutionary approach that expects the entire Internet to eventually move to some new design whose main benefits would not materialize until the vast majority of the system has been upgraded; their incremental deployment plan simply ensures interoperation between upgraded and legacy parts of the system. In contrast, the evolutionary approach depicts a picture where changes may happen here and there as needed, but there is no dependency on the system as a whole making a change. Whoever takes a step forward gains the benefit by solving his own problem, without depending on others to take actions. Thus, deployability includes not only interoperability, but also the alignment of costs and gains.

The main differences between our approach and more revolutionary map-encap proposals are: (a) we do not start with a pre-defined boundary between edge and core; and (b) each step brings immediate benefits to individual first-movers. Note that our proposal neither interferes nor prevents any revolutionary host-based solutions such as ILNP from being rolled out. However, host-based solutions do not bring useful impact until a large portion of hosts have been upgraded. Thus even if a host-based solution is rolled out in the long run, an evolutionary solution is still needed for the near term.

14.3.  Aggregation with Increasing Scopes

Aggregating many routing entries to a fewer number is a basic approach to improving routing scalability. Aggregation can take different forms and be done within different scopes. In our design, the aggregation scope starts from a single router, then expands to a single network, and neighbor networks. The order of the following steps is not fixed but merely a suggestion; it is under each individual network's discretion which steps they choose to take based on their evaluation of the severity of the problems and the affordability of the solutions.

1. FIB Aggregation (FA) in a single router. A router algorithmically aggregates its FIB entries without changing its RIB or its routing announcements. No coordinations among routers is needed, nor any change to existing protocols. This brings scalability relief to individual routers with only a software upgrade.
2. Enabling 'best external' on PEs, ASBRs, and RRs, and turning on next-hop-self on RRs. For heirarchical networks, the RRs in each PoP can serve as a default gateway for nodes in the PoP, thus allowing the non-RR nodes in each PoP to maintain smaller routing tables that only include paths that egress out of that PoP. This is known as 'topology-based mode' Virtual Aggregation, and can be done with existing hardware and configuration changes only. Please see [Evolution Grow Presenatation] (Francis, P., Xu, X., Ballani, H., Jen, D., Raszuk, R., and L. Zhang, “Virtual Aggregation (VA),” .) for details.
3. Virtual Aggregation (VA) in a single network. Within an AS, some fraction of existing routers are designated as Aggregation Point Routers (APRs). These routers are either individually or collectively maintain the full FIB table. Other routers may suppress entries from their FIBs, instead forwarding packets to APRs, which will then tunnel the packets to the correct egress routers. VA can be viewed as an intra-domain map-encap system to provide the operators a control mechanism for the FIB size in their routers.
4. VA across neighbor networks. When adjacent networks have VA deployed, they can go one step further by piggybacking egress router information on existing BGP announcements, so that packets can be tunneled directly to a neighbor network's egress router. This improves packet delivery performance by performing the encapsulation/decapsulation only once across these neighbor networks, as well as reducing the stretch of the path.
5. Reducing RIB Size by separating control plane from the data plane. Although a router's FIB can be reduced by FA or VA, it usually still needs to maintain the full RIB in order for routing announcements to its neighbors. To reduce the RIB size, a network can set up special boxes, which we call controllers, to take over the eBGP sessions from border routers. The controllers receive eBGP announcements, make routing decisions, and then inform other routers in the same network of how to forward packets, while the regular routers just focus on the job of forwarding packets. The controllers, not being part of the data path, can be scaled using commodity hardware.
6. Insulating forwarding routers from routing churns. For routers with a smaller RIB, the rate of routing churns is naturally reduced. Further reduction can be achieved by not announcing failures of customer prefixes into the core, but handling these failures in a data-driven fashion, e.g., a link failure to an edge network is not reported unless and until there are data packets that are heading towards the failed link.

15.  Name-Based Sockets

Name-based sockets are an evolution of the existing address-based sockets, enabling applications to initiate and receive communication sessions by use of domain names in lieu of IP addresses. Name-based sockets move the existing indirection from domain names to IP addresses from its current position in applications down to the IP layer. As a result, applications communicate exclusively based on domain names, while the discovery, selection, and potentially in-session re-selection of IP addresses is centrally performed by the operating system.

Name-based sockets help mitigate the Internet routing scalability problem by separating naming and addressing more consistently than what is possible with the existing address-based sockets. This supports IP address aggregation because it simplifies the use of IP addresses with high topological significance, as well as the dynamic replacement of IP addresses during network-topological and host-attachment changes.

A particularly positive effect of name-based sockets on Internet routing scalability is new incentives for edge network operators to use provider-assigned IP addresses, which are better aggregatable than the typically preferred provider-independent IP addresses. Even though provider-independent IP addresses are harder to get and more expensive than provider-assigned IP addresses, many operators desire provider- independent addresses due to the high indirect cost of provider-assigned IP addresses. This indirect cost comprises both, difficulties to multi- home, and tedious and largely manual renumbering upon provider changes.

Name-based sockets reduce the indirect cost of provider-assigned IP addresses in three ways, and hence make the use of provider-assigned IP addresses more acceptable: (1) They enable fine-granular and responsive multi-homing. (2) They simplify renumbering by offering an easy means to replace IP addresses in referrals with domain names. This helps avoiding updates to application and operating system configurations, scripts, and databases during renumbering. (3) They facilitate low-cost solutions that eliminate renumbering altogether. One such low-cost solution is IP address translation, which in combination with name-based sockets loses its adverse impact on applications.

Prerequisite for a positive effect of name-based sockets on Internet routing scalability is their adoption in operating systems and applications. Operating systems should be augmented to offer name-based sockets as a new alternative to the existing address-based sockets, and applications should use name-based sockets for their communications. Neither an instantaneous, nor an eventually complete transition to name-based sockets is required, yet the positive effect on Interent routing scalability will grow with the extent of this transition.

Name-based sockets were hence designed with focus on deployment incentives, comprising both immediate deployment benefits as well as low deployment costs. Name-based sockets provide a benefit to application developers because the alleviation of applications from IP address management responsibilities simplifies and expedites application development. This benefit is immediate owing to the backwards compatibility of name-based sockets with legacy applications and legacy peers. The appeal to application developers, in turn, is an immediate benefit for operating system vendors who adopt name-based sockets.

Name-based sockets furthermore minimize deployment costs: Alternative techniques to separate naming and addressing provide applications with "surrogate IP addresses" that dynamically map onto regular IP addresses. A surrogate IP address is indistinguishable from a regular IP address for applications, but does not have the topological significance of a regular IP address. Mobile IP and the Host Identity Protocol are examples of such separation techniques. Mobile IP uses "home IP addresses" as surrogate IP addresses with reduced topological significance. The Host Identity Protocol uses "host identifiers" as surrogate IP addresses without topological significance. A disadvantage of surrogate IP addresses is their incurred cost in terms of extra administrative overhead and, for some techniques, extra infrastructure. Since surrogate IP addresses must be resolvable to the corresponding regular IP addresses, they must be provisioned in the DNS or similar infrastructure. Mobile IP uses a new infrastructure of home agents for this purpose, while the Host Identity Protocol populates DNS servers with host identities. Name-based sockets avoid this cost because they function without surrogate IP addresses, and hence without the provisioning and infrastructure requirements that accompany those.

Certainly, some edge networks will continue to use provider-independent addresses despite name-based sockets, perhaps simply due to inertia. But name-based sockets will help reduce the number of those networks, and thus have a positive impact on Internet routing scalability.

A more comprehensive description of name-based sockets can be found in [Name Based Sockets] (Vogt, C., “Simplifying Internet Applications Development With A Name-Based Sockets Interface,” .).

16.  Recommendation

17.  Acknowledgements

This document represents a small portion of the overall work product of the Routing Research Group, who have developed all of these architectural approaches and many specific proposals within this solution space.

18.  IANA Considerations

This memo includes no requests to IANA.

19.  Security Considerations

All solutions are required to provide security that is at least as strong as the existing Internet routing and addressing architecture.

20.  References

20.1. Normative References

20.2. Informative References

20.3. LISP References

20.4. RANGI References

20.5. Ivip References

20.6. hIPv4 References

20.7. Layered Mapping System References

20.8. GLI References

20.9. TIDR References

20.10. ILNP References

20.11. EEMDP References

20.12. Evolution References

20.13. Name Based Sockets References

Author's Address