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RFC 7682

Considerations for Internet Routing Registries (IRRs) and Routing Policy Configuration

Pages: 18
Informational

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Internet Engineering Task Force (IETF)                      D. McPherson
Request for Comments: 7682                                Verisign, Inc.
Category: Informational                                        S. Amante
ISSN: 2070-1721                                              Apple, Inc.
                                                            E. Osterweil
                                                          Verisign, Inc.
                                                                L. Blunk
                                                     Merit Network, Inc.
                                                             D. Mitchell
                                                    Singularity Networks
                                                           December 2015


         Considerations for Internet Routing Registries (IRRs)
                    and Routing Policy Configuration

Abstract

The purpose of this document is to catalog issues that influenced the efficacy of Internet Routing Registries (IRRs) for inter-domain routing policy specification and application in the global routing system over the past two decades. Additionally, it provides a discussion regarding which of these issues are still problematic in practice, and which are simply artifacts that are no longer applicable but continue to stifle inter-provider policy-based filtering adoption and IRR utility to this day. Status of This Memo This document is not an Internet Standards Track specification; it is published for informational purposes. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Not all documents approved by the IESG are a candidate for any level of Internet Standard; see Section 2 of RFC 5741. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc7682.
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Copyright Notice

   Copyright (c) 2015 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
   (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 2. Background . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Historical Artifacts Influencing IRR Efficacy . . . . . . . . 3 4. Accuracy and Integrity of Data Contained within the IRR . . . 4 4.1. Lack of Resource Certification . . . . . . . . . . . . . 4 4.2. Incentives to Maintain Data within the IRR . . . . . . . 5 4.3. Inability for Third Parties to Remove (Stale) Information from the IRRs . . . . . . . . . . . . . . . . . . . . . . 6 4.4. Lack of Authoritative IRR for Resources . . . . . . . . . 7 4.5. Client-Side Considerations . . . . . . . . . . . . . . . 8 4.6. Conclusions with Respect to Data in the IRR . . . . . . . 8 5. Operation of the IRR Infrastructure . . . . . . . . . . . . . 8 5.1. Replication of Resources among IRRs . . . . . . . . . . . 8 5.2. Updating Routing Policies from Updated IRR Resources . . 10 6. Historical BGP Protocol Limitations . . . . . . . . . . . . . 11 7. Historical Limitations of Routers . . . . . . . . . . . . . . 13 7.1. Incremental Updates to Policy on Routers . . . . . . . . 13 7.2. Storage Requirements for Policy on Routers . . . . . . . 13 7.3. Updating Configuration on Routers . . . . . . . . . . . . 14 8. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 9. Security Considerations . . . . . . . . . . . . . . . . . . . 15 10. Informative References . . . . . . . . . . . . . . . . . . . 16 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 18 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
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1. Introduction

The purpose of this document is to catalog issues influencing the efficacy of Internet Routing Registries (IRRs) for inter-domain routing policy specification and application in the global routing system over the past two decades. Additionally, it provides a discussion regarding which of these issues still pose problems in practice, and which are no longer obstacles, but whose perceived drawbacks continue to stifle inter-provider policy-based filtering support and IRR utility to this day.

2. Background

IRRs can be used to express a multitude of Internet number bindings and policy objectives, i.e., to include bindings between 1) an origin AS and a given prefix, 2) a given AS and its AS and community import and export policies, as well as 3) a given AS and the AS macros (as- sets in Routing Policy Specification Language (RPSL)) that convey the set of ASes that it intends to include in some common group. As quoted from Section 7 of "Routing in a Multi-Provider Internet" [RFC1787]: While ensuring Internet-wide coordination may be more and more difficult, as the Internet continues to grow, stability and consistency of the Internet-wide routing could significantly benefit if the information about routing requirements of various organizations could be shared across organizational boundaries. Such information could be used in a wide variety of situations ranging from troubleshooting to detecting and eliminating conflicting routing requirements. The scale of the Internet implies that the information should be distributed. Work is currently underway to establish depositories of this information (Routing Registries), as well as to develop tools that analyze, as well as utilize this information.

3. Historical Artifacts Influencing IRR Efficacy

The term IRR is often used, incorrectly, as a broad catch-all term to categorize issues related to the accuracy of data in the IRR, RPSL, and the operational deployment of policy (derived from RPSL contained within the IRR) to routers. It is important to classify these issues into distinct categories so that the reader can understand which categories of issues are historical artifacts that are no longer applicable and which categories of issues still exist and might be addressed by the IETF.
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   The following sections will separate out challenges related to the
   IRR into the following categories: first, accuracy and integrity of
   data contained within the IRR; second, operation of the IRR
   infrastructure, i.e., synchronization of resources from one IRR to
   other IRRs; and finally, this document covers the methods related to
   extraction of policy from the IRR and the input, plus activation of
   that policy within routers.

4. Accuracy and Integrity of Data Contained within the IRR

The following section will examine issues related to accuracy and integrity of data contained within the IRR.

4.1. Lack of Resource Certification

Internet number resources include IPv4 addresses, IPv6 addresses, Autonomous System Numbers (ASNs), and more. While these resources are generally allocated by hierarchical authorities, a general mechanism for formally verifying (such as through cryptographic mechanisms) when parties have been allocated resources remains an open challenge. We generally call such a system a Resource Certification System, and we note that some candidate examples of how such a general system might be implemented and deployed exist -- [TASRS], [RC_HotNetsX], and [RFC6480]. One of the largest weaknesses often cited with the IRR system is that the data contained within the IRRs is out of date or lacks integrity. This is largely attributable to the fact that existing IRR mechanisms do not provide ways for a relying party to (cryptographically) verify the validity of an IRR object. That is, there has never existed a resource certification infrastructure that enables a resource holder to authorize a particular autonomous system to originate network- layer reachability advertisements for a given IPv4 or IPv6 prefix. It should be noted that this is not a weakness of the underlying RPSL [RFC2622], but rather, was largely the result of no clear demand by the operator community for Internet Number Resource Registries to provide sufficient resource certification infrastructure that would enable a resource holder to develop a cryptographic binding between, for example, a given AS number and an IP prefix. Another noteworthy (but slightly different) deficiency in the IRR system is the absence of a tangible tie between the resource and the resource holder. That is, generally there is no assurance of the validity of objects at their creation time (except for a subset of, for example, the RIPE IRR where RPSS [RFC2725] attests for RIPE address holders and RIPE ASN holders). If a resource holder's authorization cannot be certified, then consumers cannot verify attestations made. In effect, without resource certification,
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   consumers are basically only certifying the assertions that the
   creator/maintainer of the resource object has made (not if that
   assertion is valid).

   The RIPE community addressed this last issue by putting in a
   foundation policy [RIPE638], which requires a contractual link
   between the RIPE NCC and the end user in direct assignment + ASN
   assignment cases, which weren't previously covered by Local Internet
   Registry (LIR) contracts for address allocations.  There were a
   couple of intentions with this policy:

   1.  There was an encumbrance placed in the policy for the LIR to
       charge the end user for provider-independent (PI) resources.
       This action created a collection mechanism for PI address
       resources (IPv4/IPv6 space, ASNs).

   2.  It guaranteed that all RIPE NCC allocated/assigned space would be
       subject to a contractual link, and that this contractual chain
       might end up actually meaning something when it came to the issue
       of who made what claim about what number resource.

   3.  It tied into the RIPE NCC's object grandfathering policy that
       ties the registration details of the end user to the object
       registered in the IRR database.

   While this policy specifically addressed PI/portable space holders,
   other regions address this issue, too.  Further, a tangible tie
   between the resource and the resource holder is indeed a prerequisite
   for resource certification, though it does not directly address the
   IRR deficiencies.

   One of the central observations of this policy was that without a
   chain-of-ownership functionality in IRR databases, the discussion of
   certifying their contents becomes moot.

4.2. Incentives to Maintain Data within the IRR

A second problem with data contained in the IRRs is that the incentives for resource holders to maintain both accurate and up-to- date information in one or more IRRs (including deletion of out-of- date or stale data from the IRRs) can diminish rapidly when changing their peering policies (such as switching transit providers). Specifically, there is a very strong incentive for an ISP's customers to register new routing information in the IRR, because some ISPs enforce a strict policy that they will only build or update a customer's prefix-lists applied to the customer's inbound eBGP sessions based off information found within the IRRs. Unfortunately, there is little incentive for an ISP's customers to remove out-of-
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   date information from an IRR, most likely attributed to the fact that
   some ISPs do not use, or enforce use of, data contained within the
   IRRs to automatically build incoming policy applied to the customer's
   eBGP sessions.  For example, if a customer is terminating service
   from one ISP that requires use of IRR data to build incoming policy
   and, at the same time, enabling service with another ISP that does
   not require use of IRR data, then that customer will likely let the
   data in the IRR become stale or inaccurate.

   Further, policy filters are almost exclusively generated based on the
   origin AS information contained within IRR route objects and used by
   providers to filter downstream transit customers.  Since providers
   only look for route objects containing the origin AS of their
   downstream customer(s), stale route objects with historical and,
   possibly, incorrect origin AS information are ignored.  Assuming that
   the downstream customer(s) do not continue to announce those routes
   with historical, or incorrect, origin AS information in BGP to the
   upstream provider, there is no significant incentive to remove them
   as they do not impact offline policy filter generation nor routing on
   the Internet.  On the other hand, the main incentive that causes the
   Service Provider to work with downstream customer(s) is when the
   resultant filter list becomes so large that it is difficult for it to
   be stored on PE routers; however, this is more practically an
   operational issue with very old, legacy PE routers, not more modern
   PE router hardware with more robust control-plane engines.

4.3. Inability for Third Parties to Remove (Stale) Information from the IRRs

A third challenge with data contained in IRRs is that it is not possible for IRR operators, and ISPs who use them, to proactively remove (perceived) out-of-date or "stale" resources in an IRR, on behalf of resource holders who may not be diligent in maintaining this information themselves. The reason is that, according to the RPSL [RFC2622], only the resource holder ('mntner') specified in a 'mnt-by' value field of an RPSL resource is authorized to add, modify, or delete their own resources within the IRR. To address this issue, the 'auth-override' mechanism [RFC2725] was later developed that would have enabled a third party to update and/or remove "stale" resources from the IRR. While it is unclear if this was ever implemented or deployed, it does provide language semantics needed to overcome this obstacle. Nevertheless, with such a mechanism in place, there is still a risk that the original RPSL resource holder would not receive notifications (via the 'notify' attribute in various RPSL resources) about the pending or actual removal of a resource from the IRR in time to halt that action if those resources were still being used.
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   In this case, if the removal of a resource was not suspended, it
   could potentially result in an unintentional denial of service for
   the RPSL resource holder when, for example, ISPs automatically
   generated and deployed a new policy based on the newly removed
   resources from the IRR, thus dropping any reachability announcement
   for the removed resource in eBGP.

4.4. Lack of Authoritative IRR for Resources

According to [RFC2622], within an RPSL resource "the source attribute specifies the registry where the object is registered." Note that this source attribute only exists within the RPSL resource itself. Unfortunately, given a specific resource (e.g., a specific IPv4 or IPv6 prefix), most of the time it is impossible to determine a priori the authoritative IRR where to query and retrieve an authoritative copy of that resource. This makes it difficult for consumers of data from the IRR to automatically know the authoritative IRR of a resource holder that will contain the most up-to-date set of resources. This is typically not a problem for an ISP that has a direct (customer) relationship with the resource holder, because the ISP will ask the resource holder which (authoritative) IRR to pull their resources from on, for example, a "Customer BGP Order Form". However, third parties that do not have a direct relationship with the resource holder have a difficult time attempting to infer the authoritative IRR, preferred by the resource holder, that likely contains the most up-to-date set of resources. As a result, it would be helpful for third parties if there were a robust referral mechanism so that a query to one IRR would be automatically redirected toward the authoritative IRR for the most up-to-date and authoritative copy of that particular resource. This problem is worked around by individual IRR operators storing a local copy of other IRRs' resources, through periodic mirroring, which allows the individual IRR to respond to a client's query with all registered instances of a particular IRR resource that exist in both the local IRR and all other IRRs. Of course, the problem with this approach is that an individual IRR operator is under no obligation to mirror all other IRRs and, in practice, some IRRs do not mirror the resources from all other IRRs. This could lead to the false impression that a particular resource is not registered or maintained at a particular IRR. Furthermore, the authentication process of accepting updates by any given IRR may or may not be robust enough to overcome impersonation attacks. As a result, there is no rigorous assurance that a mirrored RPSL statement was actually made by the authorized resource holder.
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4.5. Client-Side Considerations

There are no provisions in the IRR mode for ensuring the confidentiality component for clients issuing queries. The overall Confidentiality, Integrity, and Availability (CIA) model of the system does lack this component, because the interface to IRRs is over an unencrypted TCP connection to port 43. This leaves the transaction open to inspection such that an adversary could be able to inspect the query and the response. However, the IRR system is intended to be composed of public policy information, and protection of queries was not part of the protection calculus when it was designed, though the use of Transport Layer Security (TLS) [RFC5246] would address protections of query information.

4.6. Conclusions with Respect to Data in the IRR

All of the aforementioned issues related to integrity and accuracy of data within the IRR stem from a distinct lack of resource certification for resources contained within the IRR. Only now is an experimental testbed that reports to provide this function (under the auspices of the Resource PKI [RFC6480]) being formally discussed; this could also aid in certification of resources within the IRR. It should be noted that the RPKI is only currently able to support signing of Route Origin Authorization (ROA) resources that are the equivalent of 'route' resources in the IRR. There has been some sentiment that the RPKI currently is not scoped to address the same set of issues and the nuanced policy applications that providers leverage in RPSL. It is unclear if, in the future, the RPKI will be extended to support additional resources that already exist in the IRR, e.g., aut-num, as-net, route-set, etc. Finally, a seemingly equivalent resource certification specification for all resources in the IRR has already been developed [RFC2725]; however, it is unclear how widely it was ever implemented or deployed.

5. Operation of the IRR Infrastructure

5.1. Replication of Resources among IRRs

Currently, several IRRs [IRR_LIST] use a Near-Real-Time Mirroring (NRTM) protocol to replicate each other's contents. However, this protocol has several weaknesses. Namely, there is no way to validate that the copy of mirrored source is correct, and synchronization issues have often resulted. Furthermore, the NRTM protocol does not employ any security mechanisms. The NRTM protocol relies on a pull mechanism and is generally configured with a poll interval of 5 to 10 minutes. There is currently no mechanism to notify an IRR when an update has occurred in a mirrored IRR so that an immediate update can be made.
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   Some providers employ a process of mirroring an instance of an IRR
   that involves downloading a flat text file copy of the IRR that is
   made available via FTP [RFC959].  These FTP files are exported at
   regular intervals of typically anywhere between 2 and 24 hours by the
   IRRs.  When a provider fetches those text files, it will process them
   to identify any updates and reflect changes within its own internally
   maintained database.  The use of an internally maintained database is
   out of scope for this document but is generally used to assist with
   more straightforward access to or modification of data by the IRR
   operator.  Providers typically employ a 24-hour cycle to pull updated
   resources from IRRs.  Thus, depending on when resource holders
   submitted their changes to an IRR, it may take up to 24 hours for
   those changes to be reflected in their policy configurations.  In
   practice, it appears that the RPKI will also employ a 24-hour cycle
   whereby changes in resources are pushed out to other RPKI caches
   [RPKI_SIZING].

   IRRs originated from Section 7 of [RFC1787], specifically: "The scale
   of the Internet implies that the [routing requirements] information
   should be distributed."  Regardless, the practical effect of an
   organization maintaining its own local cache of IRR resources is an
   increase in resource resiliency (due to multiple copies of the same
   resource being geographically distributed), a reduction in query time
   for resources, and, likely, a reduction in inter-domain bandwidth
   consumption and associated costs.  This is particularly beneficial
   when, for example, an ISP is evaluating resources in an IRR just to
   determine if there are any modifications to those resources that will
   ultimately be reflected in a new routing policy that will get
   propagated to (edge) routers in the ISP's network.  Cache locality
   results in reduced inter-domain bandwidth utilization for each round
   trip.

   On the other hand, it is unclear from where the current provider
   replication interval of 24 hours originated or even whether it still
   provides enough freshness in the face of available resources,
   particularly in today's environment where a typical IRR system
   consists of a (multi-core) multi-GHz CPU connected to a network via a
   physical connection of 100 Mbps or, more likely, higher bandwidth.
   In addition, due to demand for bandwidth, circuit sizes used by ISPs
   have increased to 10 Gbps, thus eliminating bandwidth as a
   significant factor in the transfer of data between IRRs.
   Furthermore, it should be noted that Merit's Internet Routing
   Registry Daemon (IRRd) [MERIT-IRRD] uses 10 minutes as its default
   for "irr_mirror_interval".

   Lastly, it should be noted that "Routing Policy System Replication"
   [RFC2769] attempted to offer a more methodical solution for
   distributed replication of resources between IRRs.  It is unclear why
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   that RFC failed to gain traction, but it is suspected that this was
   due to its reliance on "Routing Policy System Security" [RFC2725],
   which addressed "the need to assure integrity of the data by
   providing an authentication and authorization model."  Indeed,
   [RFC2725] attempts to add an otherwise absent security model to the
   integrity of policy statements made in RPSL.  Without formal
   protections, it is possible for anyone to author a policy statement
   about an arbitrary set of resources, and publish it (as discussed
   above in Section 4.1.

5.2. Updating Routing Policies from Updated IRR Resources

Ultimately, the length of time it takes to replicate resources among IRRs is, generally, the dominant factor in reflecting changes to resources in policy that is eventually applied within the control plane of routers. The length of time to update network elements will vary considerably depending on the size of the ISP and the number of IRR resources that were updated during any given interval. However, there are a variety of common techniques, that are outside the scope of this document, that allow for this automated process to be optimized to considerably reduce the length of time it takes to update policies in the ISP's network. An ISP will begin the process of updating the policy in its network, first by fetching IRR resources associated with, for example, a customer ASN attached to its network. Next, the ISP constructs a new policy associated to that customer and then evaluates if that new policy is different from existing policy associated with that same customer. If there are no changes between the new and existing policy associated with that customer, then the ISP does not make any changes to the policy in their routers specific to that customer. On the other hand, if the new policy does reflect changes from the existing policy for that customer, then the ISP begins a process of uploading the new policy to the routers attached to that customer. The process of constructing a new policy involves use of a set of programs, e.g., IRRtoolset, that performs recursive expansion of an RPSL aut-num resource that comprises an arbitrary combination of other RPSL aut-num, as-set, route, and route-set resources, according to procedures defined by RPSL. The end result of this process is, traditionally, a vendor-dependent configuration snippet that defines the routing policy for that customer. This routing policy may consist of the set of IPv4 or IPv6 prefixes, associated prefix lengths, and AS_PATHs that are supposed to be accepted from a customer's eBGP session. However, if indicated in the appropriate RPSL resource, the policy may also set certain BGP Attributes, such
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   as MED, AS_PATH prepend value, LOCAL_PREF, etc., at either the
   incoming eBGP session from the customer or on static routes that are
   originated by the resource holder.

   An ISP's customers may not adequately plan for pre-planned
   maintenance, or, more likely, they may need to rapidly begin
   announcing a new IP prefix as a result of, for example, an emergency
   turn-up of the ISP customer's new downstream customer.
   Unfortunately, the routine, automated process employed by the ISP
   means that it may not begin updating its routing policy on its
   network for up to 24 hours, because the ISP or the IRRs the ISP uses
   might only mirror changes to IRR resources once every 24 hours.  The
   time interval for the routine/automated process is not responsive to
   the needs of directly paying customer(s) who need rapid changes in
   their policy in rare situations.  In these situations, when a
   customer has an urgent need for updates to take effect immediately,
   they will call the Network Operations Center (NOC) of their ISP and
   request that the ISP immediately fetch new IRR objects and push those
   changes out to its network.  This is often accomplished in as little
   as 5 minutes from the time a customer contacts their ISP's NOC to the
   time a new filtering policy is pushed out to the Provider Edge (PE)
   routers that are attached to that customer's Attachment Circuits
   (ACs).  It is conceivable that some ISPs automate this using out-of-
   band mechanisms as well, although the authors are unaware of any
   existing mechanisms that support this.

   Ultimately, the aforementioned latency with respect to "emergency
   changes" in IRR resources that need to be reflected in near-real-time
   in the network is compounded if the IRR resources were being used by
   third-party ISPs to perform filtering on their peering circuits,
   where typically no such policies are employed today for this very
   reason.  It is likely that the length of time that it takes IRRs to
   mirror changes will have to be dramatically reduced.  There will need
   to be a corresponding reduction in the time required by ISPs to
   evaluate whether those changes should be recompiled and reflected in
   router policies that would then get pushed out to Autonomous System
   Border Routers (ASBRs) connected to peering circuits on their
   network.

6. Historical BGP Protocol Limitations

As mentioned previously, after a resource holder made changes to their resources in an IRR, those changes would automatically be distributed to other IRRs, ISPs would then learn of those changes, generate new BGP policies, and then apply those to the appropriate subset of routers in their ASes. However, in the past, one additional step is necessary in order to have any of those new BGP policies take effect in the control plane and to allow/deny the
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   updated resource from a customer to their ISP and from their
   immediately upstream ISP to the ISP's peers.  It was necessary (often
   manually) to actually induce BGP on each router to apply the new
   policy within the control plane, thus learning of a newly announced/
   changed IP prefix (or, dropping a deleted IP prefix).  Unfortunately,
   most of these methods not only were highly impactful operationally,
   but they also affected traffic forwarding to IP destinations that
   were unrelated to the most recent changes to the BGP policy.

   Historically, a customer would have to (re-)announce the new IP
   prefix toward their ISP, but only after the ISP had put the new BGP
   policies into effect.  Alternatively, the ISP would have to reset the
   entire eBGP session from Provider Edge to Customer Edge either by: a)
   bouncing the entire interface toward the customer (e.g., shutdown /
   no shutdown) or b) clearing the eBGP session toward the customer
   (e.g., clear ip bgp neighbor <IP address of CE router>, where <IP
   address of CE router> represents a specific IP address).  The latter
   two cases were, of course, the most highly impactful impact and thus
   could generally only be performed off-hours during a maintenance
   window.

   Once the new IP prefix has been successfully announced by the
   customer and permitted by the newly updated policy at the ISP's PEs
   (attached to that customer), it would be propagated to that ISP's
   ASBRs, attached to peers, at the perimeter of the ISP network.
   Unfortunately, if those peers had either not yet learned of the
   changes to resources in the IRR or pushed out new BGP policies (and,
   reset their BGP sessions immediately afterward) incorporating those
   changes, then the newly announced route would also get dropped at the
   ingress ASBRs of the peers.

   Ultimately, either of the two scenarios above further lengthens the
   effective time it would take for changes in IRR resources to take
   effect within BGP in the network.  Fortunately, BGP has been enhanced
   over the last several years in order that changes within BGP policy
   will take effect without requiring a service-impacting reset of BGP
   sessions.  Specifically, BGP soft-reconfiguration (Section 1 of
   [RFC2918]) and, later, Route Refresh Capability for BGP-4 [RFC2918]
   were developed so that ISPs, or their customers, could induce BGP to
   apply a new policy while leaving both the existing eBGP session
   active as well as (unaffected) routes active in both the Loc-RIB and,
   more importantly, FIB of the router.  Thus, using either of these
   mechanisms, an ISP or its peers currently will deploy a newly
   generated BGP policy, based on changes to resources within the IRR,
   and immediately trigger a notification -- which does not impact
   service -- to the BGP process to have those changes take effect in
   their control plane, either allowing a new IP prefix to be announced
   or an old IP prefix to be dropped.  This dramatically reduces the
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   length of time from when changes are propagated throughout the IRRs
   to when those changes are actually operational within BGP policy in
   an ISP's network.

7. Historical Limitations of Routers

7.1. Incremental Updates to Policy on Routers

Routers in the mid 1990s rarely supported incrementally updatable prefix filters for BGP; therefore, if new information was received from a policy or internal configuration database that would impact a policy applied to a given eBGP peer, the entire prefix list or access list would need to be deleted and rewritten, compiled, and installed. This was very tedious and commonly led to leaked routes during the time when the policy was being rewritten, compiled, and applied on a router. Furthermore, application of a new policy would not automatically result in new ingress or egress reachability advertisements from that new policy, because routers at the time would require a reset of the eBGP sessions for routing information to be evaluated by the new policy. Of course, resetting of an eBGP session had implications on traffic forwarding during the time the eBGP session was reestablished and new routing information was learned. Routers now support the ability to perform incremental, and in situ, updates to filter lists consisting of IP prefixes and/or AS_PATHs that are used within an ingress or egress BGP policy. In addition, routers also can apply those incremental updates to policy, with no traffic disruption, using BGP soft-reconfiguration or BGP Route Refresh, as discussed in the previous section.

7.2. Storage Requirements for Policy on Routers

Historically, routers had very limited storage capacity and would have difficulty in storing an extremely large BGP policy on-board. This was typically the result of router hardware vendors using an extremely limited amount of NVRAM for storage of router configurations. Another challenge with historical router hardware was that writing to NVRAM was extremely slow. For example, when the router configuration had changed as a result of updating a BGP policy that needed to accommodate changes in IRR resources, this would result in extremely long times to write out these configuration changes. Sometimes, due to bugs, this would result in loss of protocol keep-alives. This would cause an impact to routing or forwarding of packets through the platform.
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   The above limitations have largely been resolved with equipment from
   the last few years that ships with increasing amounts of non-volatile
   storage such as PCMCIA or USB flash cards, hard disk drives, or
   solid-state disk drives.

   However, as capacities and technologies have evolved on modern
   routing hardware, so have some of the scaling requirements of the
   data.  In some large networks, configuration growth has begun to
   "pose challenges" [IEPG89_NTT].  While the enhancements of hardware
   have overcome some historical limitations, evidence suggests that
   further optimizations in configuration processing may be needed in
   some cases.  Some of the more recent operational issues include
   scheduler slips and protracted commit times.  This suggests that even
   though many historical hurdles have been overcome, there are still
   motivations to optimize and modernize IRR technologies.

7.3. Updating Configuration on Routers

Historically, there has not been a standardized modeling language for network configuration or an associated method to update router configurations. When an ISP detected a change in resources within the IRR, it would fashion a vendor-dependent BGP policy and upload that to the router usually via the following method. First, an updated BGP policy configuration snippet is generated via processes running on an out-of-band server. Next, the operator uses either telnet or SSH [RFC4253] to log in to the CLI of a target router and issue vendor-dependent CLI commands that will trigger the target router to fetch the new configuration snippet via TFTP, FTP, or Secure Copy (SCP) stored on the out-of-band server. The target router will then perform syntax checking on that configuration snippet and, if that passes, merge that configuration snippet into the running configuration of the router's control software. At this point, the new BGP policy configuration snippet is active within the control plane of the router. One last step remains -- the operator will issue a CLI command to induce the router to perform a "soft reset", via BGP soft-reconfiguration or BGP Route Refresh, of the associated BGP session in order to trigger the router to apply the new policy to routes learned from that BGP session without disrupting traffic forwarding. More recently, operators have the ability to use NETCONF [RFC6241] / SSH (or, TLS) from an out-of-band server to push a BGP configuration snippet from an out-of-band server toward a target router that has that capability. However, this activity is still dependent on generating, via the out-of-band server, a vendor-dependent XML configuration snippet that would get uploaded via SSH or TLS to the target router.
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   In the future, the ability to upload new Route Origin Authorization
   (ROA) information may be provided from the RPKI to routers via the
   RPKI-RTR [RFC6810] protocol.  However, this will not allow operators
   the ability to upload other configuration information such as BGP
   policy information (AS_PATHs, BGP communities, etc.) that might be
   associated with that ROA information, as they can from IRR-generated
   BGP policies.

8. Summary

As discussed above, many of the problems that have traditionally stifled IRR deployment have, themselves, become historical. However, there are still real operational considerations that limit IRR usage from realizing its full effectiveness. The potential for IRRs to express inter-domain routing policy, and to allow relying parties to learn policy, has always positioned them as a strong candidate to aid the security postures of operators. However, while routing density and complexity have grown, so have some of the challenges facing IRRs (even today). Because of this state increase, the potential to model all policies for all ASes in all routers may still remain illusive. In addition, without an operationally deployed resource certification framework that can tie policies to resource holders, there is a fundamental limitation that still exists.

9. Security Considerations

One of the central concerns with IRRs is the ability of an IRR operator to remotely influence the routing operations of an external consumer. Specifically, if the processing of IRR contents can become burdensome, or if the policy statements can be crafted to introduce routing problems or anomalies, then operators may want to be circumspect about ingesting contents from external parties. A resource certification framework should be used to address the authorization of IRR statements to make attestations and assertions (as mentioned in Section 4.1, and discussed in Section 5.1). Additionally, the external and systemic dependencies introduced by IRRs and other such systems employed to inform routing policy, and how tightly or loosely coupled those systems are to the global routing system and operational networks, introduce additional vectors that operators and system architects should consider when evaluating attack surface and service dependencies associated with those elements. These attributes and concerns are certainly not unique to IRRs, and operators should evaluate the implications of external systems and the varying degrees of coupling and operational buffers that might be installed in their environments.
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10. Informative References

[IEPG89_NTT] Mauch, J., "NTT BGP Configuration Size and Scope", IEPG meeting before IETF 89, March 2014, <http://iepg.org/2014-03-02-ietf89/ ietf89_iepg_jmauch.pdf>. [IRR_LIST] Merit Network, Inc., "List of Routing Registries", <http://www.irr.net/docs/list.html>. [MERIT-IRRD] Merit, "IRRd - Internet Routing Registry Daemon", <http://www.irrd.net>. [RC_HotNetsX] Osterweil, E., Amante, S., Massey, D., and D. McPherson, "The Great IPv4 Land Grab: Resource Certification for the IPv4 Grey Market", DOI 10.1145/2070562.2070574, <http://dl.acm.org/citation.cfm?id=2070574>. [RFC959] Postel, J. and J. Reynolds, "File Transfer Protocol", STD 9, RFC 959, DOI 10.17487/RFC0959, October 1985, <http://www.rfc-editor.org/info/rfc959>. [RFC1787] Rekhter, Y., "Routing in a Multi-provider Internet", RFC 1787, DOI 10.17487/RFC1787, April 1995, <http://www.rfc-editor.org/info/rfc1787>. [RFC2622] Alaettinoglu, C., Villamizar, C., Gerich, E., Kessens, D., Meyer, D., Bates, T., Karrenberg, D., and M. Terpstra, "Routing Policy Specification Language (RPSL)", RFC 2622, DOI 10.17487/RFC2622, June 1999, <http://www.rfc-editor.org/info/rfc2622>. [RFC2725] Villamizar, C., Alaettinoglu, C., Meyer, D., and S. Murphy, "Routing Policy System Security", RFC 2725, DOI 10.17487/RFC2725, December 1999, <http://www.rfc-editor.org/info/rfc2725>. [RFC2769] Villamizar, C., Alaettinoglu, C., Govindan, R., and D. Meyer, "Routing Policy System Replication", RFC 2769, DOI 10.17487/RFC2769, February 2000, <http://www.rfc-editor.org/info/rfc2769>. [RFC2918] Chen, E., "Route Refresh Capability for BGP-4", RFC 2918, DOI 10.17487/RFC2918, September 2000, <http://www.rfc-editor.org/info/rfc2918>.
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   [RFC4253]  Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
              Transport Layer Protocol", RFC 4253, DOI 10.17487/RFC4253,
              January 2006, <http://www.rfc-editor.org/info/rfc4253>.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <http://www.rfc-editor.org/info/rfc5246>.

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
              <http://www.rfc-editor.org/info/rfc6241>.

   [RFC6480]  Lepinski, M. and S. Kent, "An Infrastructure to Support
              Secure Internet Routing", RFC 6480, DOI 10.17487/RFC6480,
              February 2012, <http://www.rfc-editor.org/info/rfc6480>.

   [RFC6810]  Bush, R. and R. Austein, "The Resource Public Key
              Infrastructure (RPKI) to Router Protocol", RFC 6810,
              DOI 10.17487/RFC6810, January 2013,
              <http://www.rfc-editor.org/info/rfc6810>.

   [RIPE638]  RIPE NCC, "Autonomous System (AS) Number Assignment
              Policies", March 2015,
              <https://www.ripe.net/publications/docs/ripe-638>.

   [RPKI_SIZING]
              Osterweil, E., Manderson, T., White, R., and D. McPherson,
              "Sizing Estimates for a Fully Deployed RPKI", Verisign
              Labs Technical Report 1120005 version 2, December 2012,
              <http://techreports.verisignlabs.com/
              tr-lookup.cgi?trid=1120005&rev=2>.

   [TASRS]    Osterweil, E., Amante, S., and D. McPherson, "TASRS:
              Towards a Secure Routing System Through Internet Number
              Resource Certification", Verisign Labs Technical
              Report 1130009, February 2013,
              <http://techreports.verisignlabs.com/
              tr-lookup.cgi?trid=1130009&rev=1>.
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Acknowledgements

The authors would like to acknowledge and thank Chris Morrow, Jeff Haas, Wes George, and John Curran for their help and constructive feedback.

Authors' Addresses

Danny McPherson Verisign, Inc. Email: dmcpherson@verisign.com Shane Amante Apple, Inc. Email: amante@apple.com Eric Osterweil Verisign, Inc. Email: eosterweil@verisign.com Larry J. Blunk Merit Network, Inc. Email: ljb@merit.edu Dave Mitchell Singularity Networks Email: dave@singularity.cx