Network Working Group R. Bush
Internet-Draft Internet Initiative Japan, Inc.
Intended status: Standards Track March 3, 2009
Expires: September 4, 2009
The RPKI/Router Protocol
draft-ymbk-rpki-rtr-protocol-00
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Abstract
In order to formally validate the origin ASes of BGP announcements,
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routers need a simple but reliable mechanism to receive RPKI
[I-D.ietf-sidr-arch] or analogous prefix origin data from a trusted
cache. This document describes a protocol to deliver validated
prefix origin data to routers over ssh.
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].
Table of Contents
1. Items that Need Work . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Deployment Structure . . . . . . . . . . . . . . . . . . . . . 3
4. Operational Overview . . . . . . . . . . . . . . . . . . . . . 4
5. Protocol Data Units (PDUs) . . . . . . . . . . . . . . . . . . 4
5.1. Serial Notify . . . . . . . . . . . . . . . . . . . . . . 4
5.2. Serial Query . . . . . . . . . . . . . . . . . . . . . . . 5
5.3. Reset Query . . . . . . . . . . . . . . . . . . . . . . . 5
5.4. Cache Response . . . . . . . . . . . . . . . . . . . . . . 5
5.5. IPv4 Prefix . . . . . . . . . . . . . . . . . . . . . . . 6
5.6. IPv6 Prefix . . . . . . . . . . . . . . . . . . . . . . . 6
5.7. End of Data . . . . . . . . . . . . . . . . . . . . . . . 7
5.8. Cache Reset . . . . . . . . . . . . . . . . . . . . . . . 7
5.9. Fields of a PDU . . . . . . . . . . . . . . . . . . . . . 7
6. Protocol Sequences . . . . . . . . . . . . . . . . . . . . . . 8
6.1. Start or Restart . . . . . . . . . . . . . . . . . . . . . 8
6.2. Typical Exchange . . . . . . . . . . . . . . . . . . . . . 9
6.3. Cache has Reset . . . . . . . . . . . . . . . . . . . . . 9
7. SSH Transport . . . . . . . . . . . . . . . . . . . . . . . . 10
8. Router-Cache Setup . . . . . . . . . . . . . . . . . . . . . . 10
9. Deployment Scenarios . . . . . . . . . . . . . . . . . . . . . 11
10. Security Considerations . . . . . . . . . . . . . . . . . . . 12
11. Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13
14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
14.1. Normative References . . . . . . . . . . . . . . . . . . . 14
14.2. Informative References . . . . . . . . . . . . . . . . . . 14
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 14
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1. Items that Need Work
Errors - Need to figure out what kinds of errors there might be and
then how to report and handle them.
2. Introduction
In order to formally validate the origin ASes of BGP announcements,
routers need a simple but reliable mechanism to receive RPKI
[I-D.ietf-sidr-arch] or analogous formally validated prefix origin
data from a trusted cache. This document describes a protocol to
deliver validated prefix origin data to routers over ssh.
Section 3 describes the deployment structure and Section 4 then
presents an operational overview. The binary payloads of the
protocol are formally described in Section 5, and the expected PDU
sequences are described in Section 6. And the transport protocol is
described in Section 7. Section 8 details how routers and caches are
configured to connect and authenticate. Section 9 describes likely
deployment scenarios. The traditional security and IANA
considerations end the document.
3. Deployment Structure
Deployment of the RPKI to reach routers has a three level structure
as follows:
Global RPKI: The authoritative data of the RPKI are published in a
distributed set of servers, RPKI publication repositories, e.g.
the IANA, RIRs, NIRs, and ISPs, see [I-D.ietf-sidr-repos-struct].
Local Caches: A local set of one or more collected and verified non-
authoritative caches. A relying party, e.g. router or other
client, MUST have a formally authenticated trust relationship
with, and a secure transport channel to, any non-authoritative
cache(s) it uses.
Routers: A router fetches data from a local cache using the protocol
described in this document. It is said to be a client of the
cache. There are mechanisms for the router to assure itself of
the authenticity of the cache and to authenticate itself to the
cache.
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4. Operational Overview
A router establishes and keeps open an authenticated connection to a
cache with which it has an client/server relationship. It is
configured with a semi-ordered list of caches, and establishes a
connection to the highest preference cache that accepts one.
Periodically, the router sends to the cache the serial number of the
highest numbered data record it has received from that cache, i.e.
the router's current serial number. When a router establishes a new
connection to a cache, or wishes to reset a current relationship, it
sends a Reset Query.
The Cache responds with all data records which have serial numbers
greater than that in the router's query. This may be the null set,
in which case the End of Data PDU is still sent. Note that 'greater'
must take wrap-around into account, see [RFC1982].
When the router has received all data records from the cache, it sets
its current serial number to that of the serial number in the End of
Data PDU.
5. Protocol Data Units (PDUs)
The exchanges between the cache and the router are sequences of
exchanges of the following PDUs according to the rules described in
Section 6.
5.1. Serial Notify
The cache notifies the router that the cache has new data.
0 8 16 24 31
.-------------------------------------------.
| Protocol | PDU | |
| Version | Type | reserved = zero |
| 0 | 0 | |
+-------------------------------------------+
| |
| Serial Number |
| |
`-------------------------------------------'
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5.2. Serial Query
Serial Query: The router sends Serial Query to ask the cache for all
payload PDUs which have serial numbers higher than the serial number
in the Serial Query.
0 8 16 24 31
.-------------------------------------------.
| Protocol | PDU | |
| Version | Type | reserved = zero |
| 0 | 1 | |
+-------------------------------------------+
| |
| Serial Number |
| |
`-------------------------------------------'
5.3. Reset Query
Reset Query: The router tells the cache that it wants to receive the
total active, current, non-withdrawn, database.
0 8 16 24 31
.-------------------------------------------.
| Protocol | PDU | |
| Version | Type | reserved = zero |
| 0 | 2 | |
`-------------------------------------------'
5.4. Cache Response
The cache responds with zero or more payload PDUs, the set of all
data records it has with serial numbers greater than that sent by the
client router, or all data records if the cache received a Reset
Query.
0 8 16 24 31
.-------------------------------------------.
| Protocol | PDU | |
| Version | Type | reserved = zero |
| 0 | 3 | |
`-------------------------------------------'
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5.5. IPv4 Prefix
0 8 16 24 31
.-------------------------------------------.
| Protocol | PDU | |
| Version | Type | Color |
| 0 | 4 | |
+-------------------------------------------+
| Announce | Prefix | Max | Data |
| Withdraw | Length | Length | Source |
| 0/1 | 0..32 | 0..32 | RPKI/IRR |
+-------------------------------------------+
| |
| IPv4 prefix |
| |
+-------------------------------------------+
| |
| Autonomous System Number |
| |
`-------------------------------------------'
5.6. IPv6 Prefix
0 8 16 24 31
.-------------------------------------------.
| Protocol | PDU | |
| Version | Type | Color |
| 0 | 6 | |
+-------------------------------------------+
| Announce | Prefix | Max | Data |
| Withdraw | Length | Length | Source |
| 0/1 | 0..128 | 0..128 | RPKI/IRR |
+-------------------------------------------+
| |
+--- ---+
| |
+--- IPv6 prefix ---+
| |
+--- ---+
| |
+-------------------------------------------+
| |
| Autonomous System Number |
| |
`-------------------------------------------'
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5.7. End of Data
End of Data: Cache tells router it has no more data for the request.
0 8 16 24 31
.-------------------------------------------.
| Protocol | PDU | |
| Version | Type | reserved = zero |
| 0 | 9 | |
+-------------------------------------------+
| |
| Serial Number |
| |
`-------------------------------------------'
5.8. Cache Reset
The cache may respond to a Serial Query informing the router that the
cache's serial number is no longer commensurate with that of the
router.
0 8 16 24 31
.-------------------------------------------.
| Protocol | PDU | |
| Version | Type | reserved = zero |
| 0 | 10 | |
`-------------------------------------------'
5.9. Fields of a PDU
PDUs contain the following data elements:
Protocol Version: A cardinal, currently 0, denoting the version of
this protocol.
Serial Number: The serial number of the RPKI Cache when this ROA was
received from the cache's up-stream cache server or gathered from
the global RPKI. A cache increments its serial number when
completing an rcynic from a parent cache. See [RFC1982] on DNS
Serial Number Arithmetic for too much detail on serial number
arithmetic.
Color: An arbitrary 16 bit field that might be used in some way.
Announce/Withdraw: Whether this PDU announces a new right to
announce the prefix or withdraws a previously announced right.
The allowed values are 0 for withdraw and 1 for announce. A
withdraw effectively deletes all previously announced IPvX Prefix
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PDUs with the exact same Prefix, Length, Max-Len, ASN, Data
Source, and Color.
Prefix Length: A cardinal denoting the shortest prefix allowed for
the prefix.
Max Length: A cardinal denoting the longest prefix allowed by the
prefix. This MUST NOT be less than the Prefix Length element.
Data Source: A cardinal denoting the source of the data, e.g. for
RPKI data, it is 0, for IRR data it is 1.
Prefix: The IPv4 or IPv6 prefix of the ROA.
Autonomous System Number: ASN allowed to announce this prefix, a 32
bit cardinal.
6. Protocol Sequences
The sequences of PDU transmissions fall into three conversations as
follows:
6.1. Start or Restart
Cache Router
~ ~
| <----- Reset Query -------- | R requests data
| |
| ----- Cache Response -----> | C tells R C's serial
| ------- IPvX Prefix ------> | C sends zero or more
| ------- IPvX Prefix ------> | IPv4 and IPv6 Prefix
| ------- IPvX Prefix ------> | Payload PDUs
| ------ End of Data ------> | C sends End of Data
~ ~
When a transport session is first established, the router sends a
Reset Query and the cache responds with a data sequence of all data
it contains.
This Reset Query sequence is also used in response to the cache
sending a Cache Reset, the router choosing a new cache, or the router
fearing it has otherwise lost its way.
To limit the length of time a cache must keep withdraws, a router
MUST send either a Serial Query or a Reset Query no less frequently
than once an hour. This also acts as a keep alive at the application
layer.
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6.2. Typical Exchange
Cache Router
~ ~
| -------- Notify ----------> | (optional)
| |
| <----- Serial Query ------- | R requests data
| |
| ----- Cache Response -----> | C tells R C's serial
| ------- IPvX Prefix ------> | C sends zero or more
| ------- IPvX Prefix ------> | IPv4 and IPv6 Prefix
| ------- IPvX Prefix ------> | Payload PDUs
| ------ End of Data ------> | C sends End of Data
The cache server SHOULD send a notify PDU with its current serial
number when the cache's serial changes, with the expectation that the
router MAY then issue a serial query earlier than it otherwise might.
This is analogous to DNS NOTIFY in [RFC1996]. The cache SHOULD rate
limit Serial Notifies to no more frequently than one per minute.
When the transport layer is up and either a timer has gone off in the
router, or the cache has sent a Notify, the router queries for new
data by sending a Serial Query, and the router sends all data newer
than the serial in the Serial Query.
To limit the length of time a cache must keep old withdraws, a router
MUST send either a Serial Query or a Reset Query no less frequently
than once an hour.
6.3. Cache has Reset
Cache Router
~ ~
| <----- Serial Query ------ | R requests data
| ------- Cache Reset ------> | C has lost serial
| |
| <------ Reset Query ------- | R requests new data
| |
| ----- Cache Response -----> | C tells R C's serial
| ------- IPvX Prefix ------> | C sends zero or more
| ------- IPvX Prefix ------> | IPv4 and IPv6 Prefix
| ------- IPvX Prefix ------> | Payload PDUs
| ------ End of Data ------> | C sends End of Data
~ ~
The cache may respond to a Serial Query informing the router that the
cache's serial number is no longer commensurate with that of the
router. The most likely cause is that the cache was completely
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restarted when or since the transport session to the router was down.
When a router receives this, the router SHOULD attempt to connect to
any more preferred caches in its cache list. If there are no more
preferred caches it MUST issue a Reset Query and get an entire new
load from the cache
7. SSH Transport
The transport layer session between a router and a cache carries the
binary Protocol Data Units (PDUs) in a persistent SSH session.
To run over SSH, the client router first establishes an SSH transport
connection using the SSH transport protocol, and the client and
server exchange keys for message integrity and encryption. The
client then invokes the "ssh-userauth" service to authenticate the
application, as described in the SSH authentication protocol RFC 4252
[RFC4252]. Once the application has been successfully authenticated,
the client invokes the "ssh-connection" service, also known as the
SSH connection protocol.
After the ssh-connection service is established, the client opens a
channel of type "session", which results in an SSH session.
Once the SSH session has been established, the application invokes
the application transport as an SSH subsystem called "rpki-rtr".
Subsystem support is a feature of SSH version 2 (SSHv2) and is not
included in SSHv1. Running this protocol as an SSH subsystem avoids
the need for the application to recognize shell prompts or skip over
extraneous information, such as a system message that is sent at
shell start-up.
It is assumed that the router and cache have exchanged keys out of
band by some reasonably secured means.
8. Router-Cache Setup
A cache has the public authentication data for each router it is
configured to support.
When a router or cache peers with multiple serving caches, it must
have the name of each server and authentication data for each. In
addition, the list has a non-unique preference value for each server
in order of preference. The client router or cache attempts to
establish a session with each potential serving cache in priority
order, and then starts to load data from the highest preference cache
to which it can connect and authenticate. The router's list of
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caches has the following elements:
Preference: A cardinal denoting the router's preference to use that
cache, the lower the value the more preferred.
Name: The IP Address or fully qualified domain name of the cache.
Key: The public ssh key of the cache.
MyKey: The private ssh key of this client.
As caches can not be rigorously synchronous, a client which changes
servers can not combine data from different parent caches.
Therefore, when a lower preference cache becomes available, if
resources allow, it would be prudent for the client to start a new
buffer for that cache's data, and only switch to those data when that
buffer is fully up to date.
9. Deployment Scenarios
For illustration, we present three likely deployment scenarios.
Small End Site: The small multi-homed end site may wish to outsource
the RPKI cache to one or more of their upstream ISPs. They would
exchange authentication material with the ISP using some out of
band mechanism, and their router(s) would connect to one or more
up-streams' caches. The ISPs would likely deploy caches intended
for customer use separately from the caches with which their own
BGP speakers peer.
Large End Site: A larger multi-homed end site might run one or more
caches, arranging them in a hierarchy of client caches, each
fetching from a serving cache which is closer to the global RPKI.
They might configure fall-back peerings to up-stream ISP caches.
ISP Backbone: A large ISP would likely have one or more redundant
caches in each major PoP, and these caches would fetch from each
other in an ISP-dependent topology so as not to place undue load
on the global RPKI publication infrastructure.
Experience with large DNS cache deployments has shown that complex
topologies are ill-advised as it is easy to make errors in the graph,
e.g. not maintaining a loop-free condition.
Of course, these are illustrations and there are other possible
deployment strategies. It is expected that minimizing load on the
global RPKI servers will be a major consideration.
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To keep load on global RPKI services from unnecessary peaks, it is
recommended that primary caches which load from the distributed
global RPKI not do so all at the same times, e.g. on the hour.
Choose a random time, perhaps the ISP's AS number modulo 60 and
jitter the inter-fetch timing.
10. Security Considerations
As this document describes a security protocol, many aspects of
security interest are described in the relevant sections. This
section points out issues which may not be obvious in other sections.
Cache Validation: In order for a collection of caches as described
in Section 9 to guarantee a consistent view, they need to be given
consistent trust anchors to use in their internal validation
process. Distribution of a consistent trust anchor is assumed to
be out of band.
Cache Peer Identification: As the router initiates an ssh transport
session to a cache which it identifies by either IP address or
fully qualified domain name, a DNS or address spoofing attack
could make the correct cache unreachable. No session would be
established, as the authorization keys would not match.
Transport Security: The RPKI relies on object, not server or
transport, trust. I.e. the IANA root trust anchor is distributed
to all caches through some out of band means, and can then be used
by each cache to validate certificates and ROAs all the way down
the tree. The inter-cache relationships are based on this object
security model, hence the inter-cache transport can be lightly
protected.
But this protocol document assumes that the routers can not do the
validation cryptography. Hence the last link, from cache to
router, is secured by server authentication and transport level
security. This is dangerous, as server authentication and
transport have very different threat models than object security.
So the strength of the trust relationship and the transport
between the router(s) and the cache(s) are critical. You're
betting your routing on this.
While we can not say the cache must be on the same LAN, if only
due to the issue of an enterprise wanting to off-load the cache
task to their upstream ISP(s), locality, trust, and control are
very critical issues here. The cache(s) really SHOULD be as
close, in the sense of controlled and protected (against DDoS,
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MITM) transport, to the router(s) as possible. It also SHOULD be
topologically close so that a minimum of validated routing data
are needed to bootstrap a router's access to a cache.
11. Glossary
The following terms are used with special meaning:
Global RPKI: The authoritative data of the RPKI are published in a
distributed set of servers at the IANA, RIRs, NIRs, and ISPs, see
[I-D.ietf-sidr-repos-struct].
Non-authorative Cache: A coalesced copy of the RPKI which is
periodically fetched/refreshed directly or indirectly from the
global RPKI using the [rcynic] protocol/tools
Cache: The rcynic system is used to gather the distributed data of
the RPKI into a validated cache. Trusting this cache further is a
matter between the provider of the cache and a relying party.
Serial Number: A 32-bit monotonically increasing, cardinal which
wraps from 2^32-1 to 0. It denotes the logical version of a
cache. A cache increments the value by one when it successfully
updates its data from a parent cache or from primary RPKI data.
As a cache is rcynicing, new incoming data, and implicit deletes,
are marked with the new serial but MUST not be sent until the
fetch is complete. A serial number is not commensurate between
caches, nor need it be maintained across resets of the cache
server. See [RFC1982] on DNS Serial Number Arithmetic for too
much detail on serial number arithmetic.
12. IANA Considerations
This document request the IANA to create a registry for PDU types.
In addition, a registry for Version Numbers would be needed if new
Version Number is defined in a new RFC.
Note to RFC Editor: this section may be replaced on publication as an
RFC.
13. Acknowledgments
The author wishes to thank Rob Austein, Steve Bellovin, Rex Fernando,
Russ Housley, Pradosh Mohapatra. Megumi Ninomiya, Robert Raszuk,
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John Scudder, Ruediger Volk, David Ward, and Bert Wijnen.
14. References
14.1. Normative References
[RFC1982] Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982,
August 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4252] Ylonen, T. and C. Lonvick, "The Secure Shell (SSH)
Authentication Protocol", RFC 4252, January 2006.
[rcynic] Austein, R., "rcynic protocol",
<https://subvert-rpki.hactrn.net/rcynic/>.
14.2. Informative References
[I-D.ietf-sidr-arch]
Lepinski, M. and S. Kent, "An Infrastructure to Support
Secure Internet Routing", draft-ietf-sidr-arch-04 (work in
progress), November 2008.
[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-01 (work in progress),
October 2008.
[RFC1996] Vixie, P., "A Mechanism for Prompt Notification of Zone
Changes (DNS NOTIFY)", RFC 1996, August 1996.
Author's Address
Randy Bush
Internet Initiative Japan, Inc.
5147 Crystal Springs
Bainbridge Island, Washington 98110
US
Phone: +1 206 780 0431 x1
Email: randy@psg.com
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