Network Working Group R. Bush
Internet-Draft Internet Initiative Japan
Intended status: BCP October 19, 2011
Expires: April 21, 2012
BGPsec Operational Considerations
draft-ietf-sidr-bgpsec-ops-01
Abstract
Deployment of the BGPsec architecture and protocols has many
operational considerations. This document attempts to collect and
present them. It is expected to evolve as BGPsec is formalized and
initially deployed.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on April 21, 2012.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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carefully, as they describe your rights and restrictions with respect
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Suggested Reading . . . . . . . . . . . . . . . . . . . . . . . 3
3. RPKI Distribution and Maintenance . . . . . . . . . . . . . . . 3
4. AS/Router Certificates . . . . . . . . . . . . . . . . . . . . 4
5. Within a Network . . . . . . . . . . . . . . . . . . . . . . . 4
6. Considerations for Edge Sites . . . . . . . . . . . . . . . . . 5
7. Beaconing Considerations . . . . . . . . . . . . . . . . . . . 5
8. Routing Policy . . . . . . . . . . . . . . . . . . . . . . . . 6
9. Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
10. Security Considerations . . . . . . . . . . . . . . . . . . . . 8
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 8
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
13.1. Normative References . . . . . . . . . . . . . . . . . . . 8
13.2. Informative References . . . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 9
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1. Introduction
BGPsec is a new protocol with many operational considerations. It is
expected to be deployed incrementally over a number of years. As
core BGPsec-capable routers may require large memory and crypto
assist, it is thought that origin validation based on the RPKI will
occur over the next two to five years and that BGPsec will start to
deploy late in that window.
BGPsec relies on widespread propagation of the Resource Public Key
Infrastructure (RPKI) [I-D.ietf-sidr-arch]. How the RPKI is
distributed and maintained globally and within an operator's
infrastructure may be different for BGPsec than for origin
validation.
BGPsec need be spoken only by a AS's eBGP speaking, AKA border,
routers, and is designed so that it can be used to protect
announcements which are originated by small edge routers, and this
has special operational considerations.
Different prefixes have different timing and replay protection
considerations.
2. Suggested Reading
It is assumed that the reader understands BGP, [RFC4271], BGPsec,
[I-D.lepinski-bgpsec-overview], the RPKI, see [I-D.ietf-sidr-arch],
the RPKI Repository Structure, see [I-D.ietf-sidr-repos-struct], and
ROAs, see [I-D.ietf-sidr-roa-format].
3. RPKI Distribution and Maintenance
The RPKI is a distributed database containing certificates, CRLs,
manifests, ROAs, and Ghostbuster Records as described in
[I-D.ietf-sidr-repos-struct]. Policies and considerations for RPKI
object generation and maintenance are discussed elsewhere.
A local valid cache containing all RPKI data may be gathered from the
global distributed database using the rsync protocol and a validation
tool such as rcynic.
Validated caches may also be created and maintained from other
validated caches. Network operators SHOULD take maximum advantage of
this feature to minimize load on the global distributed RPKI
database.
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As RPKI-based origin validation relies on the availability of RPKI
data, operators SHOULD locate caches close to routers that require
these data and services. A router can peer with one or more nearby
caches.
For redundancy, a router SHOULD peer with more than one cache at the
same time. Peering with two or more, at least one local and others
remote, is recommended.
If an operator trusts upstreams to carry their traffic, they SHOULD
also trust the RPKI data those upstreams cache, and SHOULD peer with
those caches. Note that this places an obligation on those upstreams
to maintain fresh and reliable caches.
A transit provider or a network with peers SHOULD validate NLRI in
announcements made by upstreams, downstreams, and peers. To minimize
impact on the global RPKI, they SHOULD fetch from and then revalidate
data from caches provided by their upstreams.
An environment where private address space is announced in eBGP the
operator MAY have private RPKI objects which cover these private
spaces. This will require a trust anchor created and owned by that
environment, see [I-D.ietf-sidr-ltamgmt].
4. AS/Router Certificates
A site/operator MAY use a single certificate/key in all their
routers, one certificate/key per router, or any granularity in
between.
A large operator, concerned that a compromise of one router's key
would make many routers vulnerable, MAY accept a more complex
certificate/key distribution burden to reduce this exposure.
On the other extreme, an edge site with one or two routers MAY use a
single certificate/key.
Routers MAY be capable of generating their own keys and having their
certificates signed and published in the RPKI by their NOC. This
would mean that a router's private key need never leave the router.
5. Within a Network
BGPsec is spoken by edge routers in a network, those which border
other networks/ASs.
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In a fully BGPsec enabled AS, Route Reflectors MUST have BGPsec
enabled if and only if there are eBGP speakers in their client cone.
A BGPsec capable router MAY use the data it receives to influence
local policy within its network, see Section 8. In deployment this
policy should fit into the AS's existing policy, preferences, etc.
This allows a network to incrementally deploy BGPsec capable border
routers.
eBGP speakers which face more critical peers or up/downstreams would
be candidates for the earliest deployment. Both securing one's own
announcements and validating received announcements should be
considered in partial deployment.
An eBGP listener MUST NOT trust non-BGPsec markings such as
communities received across a trust boundary.
6. Considerations for Edge Sites
An edge site which does not provide transit and trusts its
upstream(s) SHOULD only originate a signed prefix announcement and
need not validate received announcements.
BGPsec protocol capability negotiation provides for a speaker signing
the data it sends but being unable to accept signed data. Thus a
smallish edge router may hold only its own signing key(s) and sign
it's announcement but not receive signed announcements and therefore
not need to deal with the majority of the RPKI.
As the vast majority (84%) of ASs are stubs, and they announce the
majority of prefixes, this allows for simpler and cheaper early
incremental deployment. It may also mean that edge sites concerned
with routing security will be attracted to upstreams which support
BGPsec.
7. Beaconing Considerations
The BGPsec protocol attempts to reduce exposure to replay attacks by
allowing the route originator to sign an announcement with a validity
period and re-announce well within that period.
This re-announcement is termed 'beaconing'. All timing values are,
of course, jittered.
It is only the originator of an NLRI which signs the announcement
with a validity period.
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To reduce vulnerability to a lost beacon announcement, a router
SHOULD beacon at a rate somewhat greater than half the signature
validity period it uses.
As beaconing places a load on the entire global routing system,
careful thought MUST be given to any need to beacon frequently. This
would be based on a conservative estimation of the vulnerability to a
replay attack.
Beacon timing and signature validity periods SHOULD be as follows:
The Exemplary Citizen: Prefix originators who are not overly
concerned about replay attacks might announce with a signature
validity of multiple weeks and beacon one third of the validity
period.
Normal Prefix: Most prefixes SHOULD announce with a signature
validity of a week and beacon every three days.
Critical Prefix: Of course, we all think what we do is critical.
But prefixes of top level DNS servers, and RPKI publication points
are actually critical to large swaths of the Internet and are
therefore tempting targets for replay attacks. It is suggested
that the beaconing of these prefixes SHOULD be two to four hours,
with a signature validity of six to twelve hours.
Note that this may incur route flap damping (RFD) with current
default but deprecated RFD parameters, see [I-D.ymbk-rfd-usable].
8. Routing Policy
Unlike origin validation based on the RPKI, BGPsec marks a received
announcement as Valid or Invalid, there is no NotFound state. How
this is used in routing is up to the operator's local policy. See
[I-D.ietf-sidr-pfx-validate].
As BGPsec will be rolled out over years and does not allow for
intermediate non-signing edge routers, coverage will be spotty for a
long time. Hence a normal operator's policy SHOULD NOT be overly
strict, perhaps preferring valid announcements and giving very low
preference, but still using, invalid announcements.
A BGPsec speaker validates signed paths at the eBGP edge.
Local policy on the eBGP edge MAY convey the validation state of a
BGP signed path through normal local policy mechanisms, e.g. setting
a BGP community, or modifying a metric value such as local-preference
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or MED. Some MAY choose to use the large Local-Pref hammer. Others
MAY choose to let AS-Path rule and set their internal metric, which
comes after AS-Path in the BGP decision process.
Because of possible RPKI version skew, an AS Path which does not
validate at router R0 might validate at R1. Therefore, signed paths
that are invalid and yet propagated SHOULD have their signatures kept
intact and should be signed if sent to external BGPsec speakers.
This implies that updates which a speaker judges to be invalid MAY be
propagated to iBGP peers. Therefore, unless local policy ensures
otherwise, a signed path learned via iBGP MAY be invalid. If needed,
the validation state SHOULD be signaled by normal local policy
mechanisms such as communities or metrics.
On the other hand, local policy on the eBGP edge might preclude iBGP
or eBGP announcement of signed AS Paths which are invalid.
If a BGPsec speaker receives an unsigned path, it SHOULD perform
origin validation per [I-D.ietf-sidr-pfx-validate].
If it is known that a BGPsec neighbor is not a transparent route
server, and the router provides a knob to disallow a received pCount
(prepend count, zero for transparent route servers) of zero, that
knob SHOULD be applied.
9. Notes
Like the DNS, the global RPKI presents only a loosely consistent
view, depending on timing, updating, fetching, etc. Thus, one cache
or router may have different data about a particular prefix than
another cache or router. There is no 'fix' for this, it is the
nature of distributed data with distributed caches.
Operators who manage certificates SHOULD have RPKI Ghostbuster
Records (see [I-D.ietf-sidr-ghostbusters]), signed indirectly by End
Entity certificates, for those certificates on which others' routing
depends for certificate and/or ROA validation.
As a router must evaluate certificates and ROAs which are time
dependent, routers' clocks MUST be correct to a tolerance of
approximately an hour.
If a router has reason to believe its clock is seriouly incorrect,
e.g. it has a time earlier than 2011, it SHOULD NOT attempt to
validate incoming updates. It SHOULD defer validation until it
believes it is within reasonable time tolerance.
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Servers should provide time service, such as NTP [RFC5905], to client
routers.
10. Security Considerations
BGPsec is all about security, routing security. The major security
considerations for the protocol are described in
[I-D.ietf-sidr-bgpsec-protocol].
11. IANA Considerations
This document has no IANA Considerations.
12. Acknowledgments
The author wishes to thank the BGPsec design team.
13. References
13.1. Normative References
[I-D.ietf-sidr-bgpsec-protocol]
Lepinski, M., "BGPSEC Protocol Specification",
draft-ietf-sidr-bgpsec-protocol-00 (work in progress),
June 2011.
[I-D.ietf-sidr-ghostbusters]
Bush, R., "The RPKI Ghostbusters Record",
draft-ietf-sidr-ghostbusters-15 (work in progress),
October 2011.
[I-D.ietf-sidr-roa-format]
Lepinski, M., Kent, S., and D. Kong, "A Profile for Route
Origin Authorizations (ROAs)",
draft-ietf-sidr-roa-format-12 (work in progress),
May 2011.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
13.2. Informative References
[I-D.ietf-sidr-arch]
Lepinski, M. and S. Kent, "An Infrastructure to Support
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Secure Internet Routing", draft-ietf-sidr-arch-13 (work in
progress), May 2011.
[I-D.ietf-sidr-ltamgmt]
Reynolds, M. and S. Kent, "Local Trust Anchor Management
for the Resource Public Key Infrastructure",
draft-ietf-sidr-ltamgmt-02 (work in progress), June 2011.
[I-D.ietf-sidr-pfx-validate]
Mohapatra, P., Scudder, J., Ward, D., Bush, R., and R.
Austein, "BGP Prefix Origin Validation",
draft-ietf-sidr-pfx-validate-02 (work in progress),
July 2011.
[I-D.ietf-sidr-repos-struct]
Huston, G., Loomans, R., and G. Michaelson, "A Profile for
Resource Certificate Repository Structure",
draft-ietf-sidr-repos-struct-09 (work in progress),
July 2011.
[I-D.lepinski-bgpsec-overview]
Lepinski, M. and S. Turner, "An Overview of BGPSEC",
draft-lepinski-bgpsec-overview-00 (work in progress),
March 2011.
[I-D.ymbk-rfd-usable]
Pelsser, C., Bush, R., Patel, K., Mohapatra, P., and O.
Maennel, "Making Route Flap Damping Usable",
draft-ymbk-rfd-usable-01 (work in progress), June 2011.
[RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
Protocol 4 (BGP-4)", RFC 4271, January 2006.
[RFC5905] Mills, D., Martin, J., Burbank, J., and W. Kasch, "Network
Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, June 2010.
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Author's Address
Randy Bush
Internet Initiative Japan
5147 Crystal Springs
Bainbridge Island, Washington 98110
US
Phone: +1 206 780 0431 x1
Email: randy@psg.com
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