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draft-wood-icnrg-ccnxdiscovery.txt
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ICNRG Working Group I. Solis
Internet-Draft C. Wood
Intended status: Informational PARC
Expires: April 16, 2016 October 14, 2015
CCNx End-host Forwarder Discovery
draft-wood-icnrg-ccnxdiscovery
Abstract
This document describes how an end host forwarder discovers its
first-hop CCNx forwarder over UDP.
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
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 16, 2016.
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.
Solis & Wood Expires April 16, 2016 [Page 1]
Internet-Draft CCNx-discovery October 2015
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions and Terminology . . . . . . . . . . . . . . . 2
2. Forwarder Discovery Requirements . . . . . . . . . . . . . . 2
3. Discovery Mechanisms . . . . . . . . . . . . . . . . . . . . 3
3.1. Zero configuration bootstrapping with DNS . . . . . . . . 4
3.1.1. Unicast DNS discovery . . . . . . . . . . . . . . . . 4
3.1.2. Multicast DNS discovery . . . . . . . . . . . . . . . 4
3.1.3. DNS Service Discovery (SD) . . . . . . . . . . . . . 5
3.2. Manual configuration bootstrapping . . . . . . . . . . . 5
3.2.1. Configuration file . . . . . . . . . . . . . . . . . 5
3.2.2. Fixed (IP,port) tuples . . . . . . . . . . . . . . . 6
4. Network Configuration Considerations . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
6. Normative References . . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
CCNx networks will run over IP as an overlay to enable
experimentation and interoperability. Virtual links between two
forwarders in this overlay network will be UDP [RFC0768] links.
Consequently, there needs to be a mechanism for an end host to
discover the IP address [RFC0791] and UDP port number of its first-
hop forwarder. There are several ways this can be done, including
DNS-based service discovery and manually configuring forwarder
addresses. There is no silver bullet; different network
configurations may call for or require different techniques. In this
document, we present two bootstrapping mechanisms for zero- and
manual-configuration discovery of the first-hop forwarder.
We assume forwarders are configured and connected to each other by
some other means. Such connectivity is outside the scope of this
document.
1.1. Conventions and Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in RFC
2119 [RFC2119].
2. Forwarder Discovery Requirements
A necessary step for bootstrapping a CCNx end host connection is to
discover the IP address and UDP port number of the appropriate first-
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Internet-Draft CCNx-discovery October 2015
hop forwarder. The resultant (IP address, UDP port) tuple is then
used to create a virtual link to this forwarder.
+---+ (Virtual link) +---+
| C +-------------------+ F |
+---+ +---+
Figure 1: A virtual link between a CCNx end host C and first-hop
forwarder F.
These links are general, or virtual, in the sense that they connect
any two CCNx-compliant endpoints over UDP. One endpoint of this link
is a forwarder that supports the CCNx routing protocol and the other
is the end host attempting to connect to the CCNx overlay network.
Virtual links may traverse multiple IP routers, switches, and hubs
between two endpoints (H1 and H2 in the example below, which are
connected over multiple IP-compliant network elements). Note that,
for the purposes of this document, we assume router connections and
links are already configured by some other means.
+----+ +----+
+---> N2 +----+ N3 +-+
| +----+ +----+ |
+----+ | | +----+
+-----+ | +-+ +-+ | +----+ +-----+
| C +----+ N1 | | N5 +----+ N6 +---+ F |
+-----+ | +---+ +-----+ | +----+ +-----+
+----+ | +----+ | +----+
+----+ N4 +----+
+----+
Figure 2: An example of the physical topology of a link between a end
host C and router F with multiple network nodes (routers, switches).
3. Discovery Mechanisms
Forwarder discovery may be done automatically, i.e., with zero
configuration, or manually. Zero-configuration is done via DNS-based
discovery, of which there are three varieties: managed DNS [RFC1034]
[RFC1035] [RFC2181], mDNS [RFC6762], and DNS-SD [RFC6763]. Manual
configuration is done via a stack or local configuration file, e.g.,
a hostname file. This section details these two flavors of
discovery.
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3.1. Zero configuration bootstrapping with DNS
3.1.1. Unicast DNS discovery
Standard managed (unicast) DNS is appropriate for discovery in
networks where administrators can install DNS records. In this case,
if a CCNx router R at a machine with the hostname ccnx.parc.com
(operating within PARC) is to expose a forwarding service on UDP port
9695, then a DNS service record (SRV) [RFC2782] can be created with
the following contents:
_ccnx._udp.linklocal. 86400 IN SRV 0 3 9596 ccnx.parc.com.
Figure 3: CCNx DNS SRV structure.
Assuming properly-scoped DNS SRV and CNAME records exist for a CCNx
forwarder, an end-host within the PARC network (using DHCP, with an
IP address already configured) will perform the following steps to
bootstrap a connection to said forwarder:
1. Use DNS [RFC6762] to query for the service with the name
_ccnx._udp.linklocal and retrieve the corresponding SRV record.
Specifically, issue a query with the query type (qtype) SRV and
use the result.
2. Use DNS to query for the IP address (CNAME record) associated
with the target name specified in the SRV record.
3.1.2. Multicast DNS discovery
In cases where unicast DNS servers cannot be directly managed,
multicast DNS (mDNS) may be used. Multicast DNS queries are the same
as unicast DNS queries (except that SRV records are not supported).
The record name must match the question type (qtype) unless the qtype
is "ANY" or the record type is "CNAME" (see section 6 of [RFC6762]).
mDNS queries for the CCNx forwarder are not continuous - they are
one-shot. A client will blindly issue DNS queries for the CCNx
forwarder to the address 224.0.0.251 at port 5353. The client will
use the first response it receives. It is not necessary to wait for
all responses (if there are more than one), since a client only needs
to discover a single forwarder.
Based on this information, the client discovery process using mDNS
is:
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1. The client issues mDNS queries of type A (address) or CNAME
(canonical name record) and uses the first result that is
returned.
2. The client uses the default forwarder port of 9596 to associate
with the resultant IP address. This is because neither of the
resultant records will contain port numbers.
3.1.3. DNS Service Discovery (SD)
DNS-based service discovery (DNS-SD) is an extension of mDNS that
supports SRV and TXT [RFC1035]. That is, DNS-SD can use unicast or
multicast DNS queries for SRV and TXT records. Both record types
will carry the same name for a given service. The SRV records will
be created as in Section Section 3.1.1. TXT records will be
constructed to provide additional information to accompany the
associated SRV record. These TXT records contain key-value pairs for
additional information. In our case, the TXT record will convey, at
a minimum, the UDP port number.
Clients use DNS-SD to discover the list of services offered in a
particular domain. This is done by issuing a query for a DNS PTR
[RFC1035] record with a name containing:
o service=ccnx
o domain=parc
The resultant record will contain a (possibly empty) list of names
that contain the SRV and TXT record names referred to above. The
client then issues SRV and TXT queries for these records using
unicast or multicast DNS. The resultant records contain the IP
address(es) and UDP port(s) necessary to bootstrap a forwarder
connection.
3.2. Manual configuration bootstrapping
3.2.1. Configuration file
An end host can maintain a hostname file that contains (IP,port)
tuples for several possible CCNx forwarders which can serve as
gateways to the overlay network. The end host forwarder can
sequentially parse this file and attempt to create a connection to
the provided addresses until one succeeds. This hostname file can be
configured and modified manually as users roam across different
networks.
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3.2.2. Fixed (IP,port) tuples
(IP,port) tuples of fixed CCNx forwarders which can be used as
gateways to a (the) CCNx overlay can be hard-coded into the end host
forwarder software. This option hinders configuration and is
difficult to maintain. It should be used as a default when automatic
discovery is not possible and a host configuration file is not found.
4. Network Configuration Considerations
Some of the aforementioned bootstrapping mechanisms may not be
appropriate for all networks. For example, not all networks may
allow custom DNS service records to be installed to enable mDNS-based
discovery. Below we outline several common network setting problems
and suggest the bootstrapping mechanisms that would be best suited to
these environments where these are a reality.
o Unable to install DNS service records: Use the manual discovery.
o The network is partitioned: Use manual discovery.
o Multicast messaging is disallowed or blocked: Use manual
discovery.
5. Security Considerations
DNS service records may be secured via DNSSEC. Manual configuration
settings are only as secure as their weakest form of OS-level
protection.
6. Normative References
[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
DOI 10.17487/RFC0768, August 1980,
<http://www.rfc-editor.org/info/rfc768>.
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
DOI 10.17487/RFC0791, September 1981,
<http://www.rfc-editor.org/info/rfc791>.
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<http://www.rfc-editor.org/info/rfc1034>.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <http://www.rfc-editor.org/info/rfc1035>.
Solis & Wood Expires April 16, 2016 [Page 6]
Internet-Draft CCNx-discovery October 2015
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS
Specification", RFC 2181, DOI 10.17487/RFC2181, July 1997,
<http://www.rfc-editor.org/info/rfc2181>.
[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
DOI 10.17487/RFC2782, February 2000,
<http://www.rfc-editor.org/info/rfc2782>.
[RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
DOI 10.17487/RFC6762, February 2013,
<http://www.rfc-editor.org/info/rfc6762>.
[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service
Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,
<http://www.rfc-editor.org/info/rfc6763>.
Authors' Addresses
Ignacio Solis
PARC
Email: [email protected]
Christopher A. Wood
PARC
Email: [email protected]
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