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Versions: 00 01 RFC 6382
INTERNET-DRAFT Danny McPherson
Ryan Donnelly
Frank Scalzo
VeriSign, Inc.
Expires: May 2011 November 15, 2010
Intended Status: Best Current Practice
Unique Per-Node Origin ASNs for Globally Anycasted Services
<draft-ietf-grow-unique-origin-as-00.txt>
Status of this Memo
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McPherson, et al. [Page 1]
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Copyright Notice
Copyright (C) (2010) The IETF Trust and the persons identified as the
document authors. All rights reserved.
Abstract
This document makes recommendations regarding the use of per-node
unique origin ASNs for globally anycasted critical infrastructure
services in order to provide routing system discriminators for a
given anycasted prefix. Network managment and monitoring techniques,
or other operational mechanisms may employ this new discriminator in
whatever manner fits their operating environment.
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Table of Contents
1. Terminology. . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Recommendation for Unique Origin ASNs. . . . . . . . . . . . . 6
4. Additional Recommendations for Globally Anycasted
Services. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5. Security Considerations. . . . . . . . . . . . . . . . . . . . 8
6. Deployment Considerations. . . . . . . . . . . . . . . . . . . 9
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
8. IANA Considerations. . . . . . . . . . . . . . . . . . . . . . 10
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
9.1. Normative References. . . . . . . . . . . . . . . . . . . . 11
9.2. Informative References. . . . . . . . . . . . . . . . . . . 11
10. Authors' Addresses. . . . . . . . . . . . . . . . . . . . . . 11
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1. Terminology
This document employs much of the following terminology, which was
taken in full from Section 2 of [RFC 4786].
Anycast: the practice of making a particular Service Address
available in multiple, discrete, autonomous locations, such that
datagrams sent are routed to one of several available locations.
Anycast Node: an internally-connected collection of hosts and
routers that together provide service for an anycast Service
Address. An Anycast Node might be as simple as a single host
participating in a routing system with adjacent routers, or it
might include a number of hosts connected in some more elaborate
fashion; in either case, to the routing system across which the
service is being anycast, each Anycast Node presents a unique path
to the Service Address. The entire anycast system for the service
consists of two or more separate Anycast Nodes.
Catchment: in physical geography, an area drained by a river, also
known as a drainage basin. By analogy, as used in this document,
the topological region of a network within which packets directed
at an Anycast Address are routed to one particular node.
Local-Scope Anycast: reachability information for the anycast
Service Address is propagated through a routing system in such a
way that a particular anycast node is only visible to a subset of
the whole routing system.
Local Node: an Anycast Node providing service using a Local-Scope
Anycast Address.
Global Node: an Anycast Node providing service using a Global-Scope
Anycast Address.
Global-Scope Anycast: reachability information for the anycast
Service Address is propagated through a routing system in such a
way that a particular anycast node is potentially visible to the
whole routing system.
Service Address: an IP address associated with a particular service
(e.g., the destination address used by DNS resolvers to reach a
particular authority server).
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2. Introduction
IP anycasting [RFC 4786] has been deployed for an array of network
services since the early 1990s. It provides a mechanism for a given
network resource to be available in a more distributed manner,
locally and/or globally, with a more robust and resilient footprint,
commonly yielding better localization and absorption of systemic
query loads, as well as better protections in the face of DDoS
attacks, network partitions, and other similar incidents. A large
part of the Internet root DNS infrastructure, as well as many other
resources, has been anycasted for nearly a decade.
While the benefits realized by anycasting network services is proven,
some issues do emerge with asserting routing system reachability for
a common network identifier from multiple locations. Specifically,
anycasting in BGP requires injection of reachability information in
the routing system for a common IP address prefix from multiple
locations. These anycasted prefixes and network services have
traditionally employed a common origin autonomous system number (ASN)
in order to preserve historically scarce 16-bit AS number space
utilized by BGP for routing domain identifiers in the global routing
system. Additionally, a common origin AS number was used in order to
ease management overhead of resource operations associated with
acquiring and maintaining multiple discrete AS numbers, as well as to
avoid triggering various operations- oriented reporting functions
aimed at identifying "inconsistent origin AS announcements" observed
in the routing system. As a result, the representation of routing
system path attributes associated with those service instances, and
that anycasted prefix itself, typically bear no per-instance
discriminators in the routing system (i.e., within the network
control plane itself).
Service level query capabilities may or may not provide a mechanism
to identify which anycast node responded to a particular query,
although this is likely both service (e.g., DNS or NTP) and
implementation dependent. For example, NSD, Unbound, and BIND all
provide 'hostname.bind or hostname.id' [HNAME] query support that
enables service-level identification of a given server. Tools such
as traceroute are also used to determine which location a given query
is being routed to, although it may not reveal local-scope anycast
instances, or if there are multiple servers within a given anycast
node, which of the servers responded to a given query, in particular
when multiple servers within an anycast node are connected to a
single IP router. When utilizing these service level capabilities,
query responses are typically both deterministic and inherently
topology-dependent, however, these service level identifiers at the
data plane provide no control plane (routing system) uniqueness.
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As more services are globally anycasted, and existing anycasted
services realize wider deployment of anycast nodes for a given
service address in order to accommodate growing system loads, the
difficulty of providing safeguards and controls to better protect
those resources expands. Intuitively, the more widely distributed a
given anycasted service address is, the more difficult it becomes for
network operators to detect operational and security issues that
affect that service. Some examples of such security and operational
issues include BGP route leaks affecting the anycasted service, rogue
anycast nodes appearing for the service, or the emergence of other
aberrant behavior in either the routing system, the forward query
datapath, or query response datapath. Diagnosis of the routing
system issues is complicated by the fact that no unique
discriminators exist in the routing system to identify a given local
or global anycast node. Furthermore, both datapath and routing
system problem identification is compounded by the fact that either
incident type can be topologically-dependent.
Additionally, while it goes without saying that anycasted services
should always strive for exact synchronization across all instances
of an anycasted service address, if local policies or data plane
response manipulation techniques were to "influence" responses within
a given region in such a way that those response are no longer
authentic or that they diverge from what other nodes within an
anycasted service were providing, then it should be an absolute
necessity that those modified resources only be utilized by service
consumers within that region or influencer's jurisdiction.
Mechanisms should exist at both the network and service layer to make
it abundantly apparent to operators and users alike whether any of
the query responses are not authentic. For DNS, DNSSEC [RFC 4033]
provides this capability at the service layer with object level
integrity, assuming validation is being enforced by recursive name
servers, and DNSSEC deployment at the root and top level domain (TLD)
levels is well underway [DNSSEC-DEPLOY]. Furthermore, control plane
discriminators should exist to enable operators to know toward which
of a given set of instances a query is being directed, and to enable
detection and alerting capabilities when this changes. Such
discriminators may also be employed to enable anycast node preference
or filtering keys, should local operational policy require it.
3. Recommendation for Unique Origin ASNs
In order to be able to better detect changes to routing information
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associated with crtical anycasted resources, globally anycasted
services with partitioned origin ASNs SHOULD utilize a unique origin
ASN per node where possible.
Discrete origin ASNs per node provide a discriminator in the routing
system that would enable detection of leaked or hijacked instances
more quickly, and would also enable operators that so choose to
proactively develop routing policies that express preferences or
avoidance for a given node or set of nodes associated with an
anycasted service. This is particularly useful when it is observed
that local policy or known issues exist with the performance or
authenticity of responses returned from a specific anycast node, or
that enacted policies meant to affect service within a particular
region are affecting users outside of that region as a result of a
given anycast catchment expanding beyond its intended scope.
Furthermore, inconsistent origin AS announcements associated with
anycasted services for critical infrastructure SHOULD NOT be deemed
undesirable by routing system reporting functions, but should instead
be embraced in order to better identify the connectedness and
footprint of a given anycasted service.
While namespace conservation and reasonable use of AS number
resources should always be a goal, the introduction of 32-bit ASNs
significantly lessens concerns in this space. Globally anycasted
resources, in particular those associated with critical
infrastructure-enabling services such as root and TLD name servers,
SHOULD warrant special consideration with regard to AS number
allocation practices during policy development by the constituents of
those responsible organizations (e.g., the Regional Internet
Registries). Additionally, defining precisely what constitutes
"critical infrastructure services" or "special consideration" (e.g.,
some small range of 32-bit AS numbers might be provided) is left to
the constituents of those organizations. Additionally, critical
infrastructure employment of 32-bit ASNs for new nodes might well
help to foster adoption of native 32-bit ASN support by network
operators.
One additional benefit of unique origin AS numbers per anycast node
is that Resource PKI (RPKI) Secure Inter-domain Routing [SIDR]
machinery, and in particular, that of Route Origin Authorizations
(ROAs), and routing policies that may be derived based on those ROAs,
can be employed with per anycast node resolution, rather than relying
on a single ROA and common origin AS to cover all instantiations of
an anycasted prefix (possibly hundreds) within the global routing
system. For example, deployments that incorporate partitioned ASN
anycast models that have a single ASN bound to all nodes but cross
organizational or political boundaries, a situation may arise where
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nobody would be deemed appropriate to hold the key for the ROA.
Additionally, a globally anycasted service within a given IP prefix
that shares a common ASN might be taken totally offline because of
the revocation of a ROA for that origin.
4. Additional Recommendations for Globally Anycasted Services
Two additional recommendations for globally anycasted critical
infrastructure services are related to publication of information
associated with a given node's physical location, and which adjacent
upstream ASNs an origin AS interconnects with. The former would
allow operators to better define and optimize preferences associated
with a given node to align with local policy and service
optimizations. The latter would allow expression through policy such
as Routing Policy Specification Language [RFC 4012] specified in
Internet Routing Registries (IRRs) in a manner that illustrates a
discrete set of upstream ASNs for each anycast node, rather than the
current model where all upstream ASNs associated with a common origin
AS may or may not be expressed. This information would provide an
additional level of static AS path validation or monitoring and
detection models by network operators, and perhaps explicit network
layer source address validation in the datapath.
5. Security Considerations
The recommendations made in this memo aim to provide more flexibility
for network operators hoping to better monitor and prevent issues
related to globally anycasted critical infrastructure resources.
Anycast itself provides considerable benefit in the face of certain
attacks, yet if a given instance of a service can appear at many
points in the routing system and legitimate instances are difficult
to distinguish from malicious ones, then anycast expands the
service's attack surface rather than reducing it.
The recommendations made in this document are expressed to assist
with visibility and policy specification capabilities in order to
improve the availability of critical Internet resources. Use cases
where the recommendations outlined in this memo may have helped to
more easily detect or scope the impact of a particular incident are
illustrated in [RENESYS-BLOG].
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Furthermore, while application layer protection mechanisms such as
DNSSEC provide object level integrity and authentication, they often
do so at the cost of introducing more failure conditions. For
example, if a recursive name server is performing DNSSEC validator
functions and receives a bogus response to a given query as a result
of a man-in-the-middle (MITM) or injected spoofed response packet
such as a cache poisoning attempt, the possibility might exist that
that packet is processed by the server and results in some temporal
or persistent DoS condition on the recursuve name server and for its
customer set. The unique origin AS mechanism outlined in this
document provides the capability for network operators to expressly
avoid anycast node catchments known to regularly elicit bogus
responses, while allowing the anycasted service address to remain
available otherwise.
6. Deployment Considerations
Maintenance of unique ASNs for each node within an anycasted service
may be challenging for some critical infrastructure service operators
initially, but for globally anycasted resources there needs to be
some type of per-node discriminator in the control plane to enable
detection, remediation, and optimally, preventative controls for
dealing with routing system anomalies that are intensified by the
application of IP anycasting. Additionally, this technique sets the
stage to employ RPKI-enabled machinery and more secure and explicit
routing policies, which all network operators should be considering.
The granularity of data publication related to anycast node location
should be left to the devises of each services operator, but some
reasonable level of detail to enable operators to make informed
decisions that align with their security and operational objectives
as outlined herein should be provided by each critical services
operator.
Adjacent AS information for a given origin AS can be obtained through
careful routing system analysis already when prefixes are advertised
via a given set of AS adjacencies, and therefore should present no
new threat. However, network interconnection and peering policies
may well present some challenges in this area. For example, if a
technique such as unique origin AS per node is employed then a single
orgnaizaton may no longer have a single AS for interconnection at
each location, and interconnection policies should expressly consider
this. That said, interconnection with networks that provide critical
infrastructure services should certainly be given due consideration
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as such by network operators when evaluating interconnection
strategies.
Some root and TLD operators today identify erroneous anycast prefix
announcements by detecting prefix announcements with an origin AS
other than the common origin AS shared via all nodes. This detection
model would need to be expanded to account for unique origin ASNs per
node if a given service operators chooses to employ such as a model,
and given that AS paths are trivial to manipulate, the above
technique would only assist in the event of unintentional
configuration errors that reoriginate the route (e.g., it doesn't
even detect leaks that preserve the initial path elements).
Finally, anycast node presence at exchange points that employs route
servers may make enumeration of adjacent ASNs for a given node
challenging. While this is understood, service operators should make
every effort to enumerate the set of adjacent ASNs associated with a
given anycast node's origin AS. Without express understanding of
legitimate AS interconnection and authorized origin AS information,
more secure routing is difficult to acheive.
7. Acknowledgements
Thanks to David Conrad, Steve Kent, Mark Kosters, Andrei Robachevsky,
Paul Vixie, Brad Verd, Andrew Herrmann, Gaurab Raj Upadhaya, Joe
Abley, Benson Schliesser, Shane Amante, and Randy Bush for review and
comments on this concept.
Others? Your name could be here.......
8. IANA Considerations
This document requires no direct IANA actions, although it does
provide general guidance to number resource allocation and policy
development organizations, and in particular Regional Internet
Registries, regarding allocation of AS numbers for globally anycasted
services.
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9. References
9.1. Normative References
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC 4786] Abley, J., and Lindqvist, K., "Operation of Anycast
Services", RFC 4786, BCP 126, December 2006.
9.2. Informative References
[RFC 4012] Blunk, et al., "Routing Policy Specification Language
next generation (RPSLng)", RFC 4012, March 2005.
[RFC 4033] Arends, et al., "DNS Security Introduction and
Requirements", RFC 4033, March 2005.
[DNSSEC-DEPLOY] "Root DNSSEC", <http://www.root-dnssec.org/>
[HNAME] ISC, "Which F-root node am I using?"
<http://www.isc.org/community/f-root/which_node>
[RENESYS-BLOG] Zmijewski, E., "Accidentally Importing Censorship",
Renesys Blog, March 30, 2010.
<http://www.renesys.com/blog/2010/03/fouling-the-global-nest.shtml>
[SIDR] Lepinski, M., Kent, S., "An Infrastructure to Support Secure
Internet Routing", October 2009, Internet-Draft, "Work in
Progress".
10. Authors' Addresses
McPherson, et al. Section 10. [Page 11]
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Danny McPherson
Verisign, Inc.
Email: dmcpherson@verisign.com
Ryan Donnelly
Verisign, Inc.
Email: rdonnelly@verisign.com
Frank Scalzo
Verisign, Inc.
Email: fscalzo@verisign.com
Copyright Statement
Copyright (C) (2010) The 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.
McPherson, et al. Section 10. [Page 12]
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