ICNRG M. Mosko
Internet-Draft I. Solis
Intended status: Experimental PARC, Inc.
Expires: December 31, 2015 June 29, 2015
CCNx Semantics
draft-irtf-icnrg-ccnxsemantics-00
Abstract
This document describes the core concepts of the CCNx architecture
and presents a minimum network protocol based on two messages:
Interest and Content Object. It specifies the set of mandatory and
optional fields within those messages and describes their behavior
and interpretation. This architecture and protocol specification is
independent of a specific wire encoding.
The protocol also uses a Control message called an InterestReturn,
whereby one system can return an Interest message to the previous hop
due to an error condition. It indicates to the previous hop that the
current system will not respond to the Interest.
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 December 31, 2015.
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
Mosko & Solis Expires December 31, 2015 [Page 1]
Internet-Draft CCNx TLV June 2015
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
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 5
2. Named Payload . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4. Interests . . . . . . . . . . . . . . . . . . . . . . . . . . 9
5. Content Objects . . . . . . . . . . . . . . . . . . . . . . . 11
6. Link . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
7. Validation . . . . . . . . . . . . . . . . . . . . . . . . . . 13
7.1. Validation Algorithm . . . . . . . . . . . . . . . . . . . 13
8. Interest to Content Object matching . . . . . . . . . . . . . 14
9. Request/Response Protocol . . . . . . . . . . . . . . . . . . 15
10. Interest Return . . . . . . . . . . . . . . . . . . . . . . . 16
10.1. Message Format . . . . . . . . . . . . . . . . . . . . . . 16
10.2. ReturnCode Types . . . . . . . . . . . . . . . . . . . . . 17
10.3. Interest Return Protocol . . . . . . . . . . . . . . . . . 17
10.3.1. No Route . . . . . . . . . . . . . . . . . . . . . . 18
10.3.2. HopLimit Exceeded . . . . . . . . . . . . . . . . . . 19
10.3.3. Interest MTU Too Large . . . . . . . . . . . . . . . 19
10.3.4. No Resources . . . . . . . . . . . . . . . . . . . . 19
10.3.5. Path Error . . . . . . . . . . . . . . . . . . . . . 19
10.3.6. Prohibited . . . . . . . . . . . . . . . . . . . . . 19
10.3.7. Congestion . . . . . . . . . . . . . . . . . . . . . 19
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 20
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
13. Security Considerations . . . . . . . . . . . . . . . . . . . 22
14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
14.1. Normative References . . . . . . . . . . . . . . . . . . . 23
14.2. Informative References . . . . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 24
Mosko & Solis Expires December 31, 2015 [Page 2]
Internet-Draft CCNx TLV June 2015
1. Introduction
This document describes the principles of the CCNx architecture. It
describes the network protocol based on two message types: Interests
and Content Objects. The description is not dependent on a specific
wire format or particular encodings.
CCNx uses subjective names to identify bytes of payload. The Name
combines a routable prefix with an arbitrary suffix assigned by the
publisher to a piece of content. The result is a "named payload".
This is different from other systems that use only self-certifying
names, where the payload name is intrinsically derivable from the
payload or its realization in a network object (e.g. a SHA-256 hash
of the payload or network object).
The key concept of CCNx is that a subjective name is bound to a fixed
payload via cryptographic operations. This implies that the fact
that a given publisher bound a certain subjective name to a certain
payload can be verified via cryptographic means. For example, a
publisher could use a cryptographic hash over the name and payload,
sign the hash, and deliver the tuple {Name, Payload, Validation}.
Additional information would be included as needed by different
validation mechanisms are used. A typical named payload is thus
{Name, Payload, ValidationAlgorithm}.
CCNx specifies a network protocol around Interests (request messages)
and Content Objects (response messages) to move named payloads. An
Interest includes the Name, the desired payload, and two optional
restrictions to limit responses to a specific publisher or a specific
Content Object. The Content Object response carries a matching Name
and the specified payload. Matching a Content Object to an Interest
is an exact match on the Name. The CCNx network protocol of
Interests and Content Objects imposes a restriction on Names: each
Name should be hierarchical and is used to route towards an
authoritative source. The CCNx Name looks like a URI absolute path
and we use URI terminology to describe CCN Names as made up of name
segments. In practice it has a binary encoding, not a text string.
The hierarchy of a CCNx Name is used for routing via the longest
matching prefix in a Forwarder. The longest matching prefix is
computed name segment by name segment in the hierarchical path name,
where each name segment must be exactly equal to match. There is no
requirement that the prefix be globally routable. Within a
deployment any local routing may be used, even one that only uses a
single flat (non-hierarchical) name segment. Some Forwarders may use
more advanced matching rules that allow both longest matching prefix
and shorter prefixes.
Mosko & Solis Expires December 31, 2015 [Page 3]
Internet-Draft CCNx TLV June 2015
Another central concept of CCNx is that there should be flow balance
between Interest messages and Content Object messages. At the
network level, an Interest traveling along a single path should
elicit no more than one Content Object response. If some node sends
the Interest along more than one path, that node should consolidate
the responses such that only one Content Object flows upstream from
it to the requester.
There are additional optional attributes in an Interest message that
can be used to select between multiple Content Objects with matching
Names (it is possible that multiple publishers could issue Content
Objects with the same Name). An Interest may carry an optional
KeyIdRestriction and / or an optional ContentObjectHashRestriction.
If either or both of these are present, a Forwarder must ensure that
they exactly match the corresponding KeyId and computed
ContentObjectHash in the Content Object.
As an Interest travels the forward path following the Forwarding
Information Base (FIB), it leaves behind state at each Forwarder.
This state is stored in the Pending Interest Table (PIT), which
tracks the ingress and egress ports as well as the Name,
KeyIdRestriction (if one exists), and ContentObjectHashRestriction
(if one exists) of each Interest. When a Content Object arrives at
the node, it is exactly matched against that tuple to see if it
satisfies any Interests in the PIT. If it does, it is returned along
the matching Interest's reverse path. If it does not, the Content
Object is dropped.
If multiple Interests with the same tuple {Name, KeyIdRestriction,
ContentObjectHashRestriction} arrive at a node before a Content
Object matching the first Interest comes back, they are grouped in
the same PIT entry and their reverse paths aggregated. Thus, one
Content Object might satisfy multiple pending Interests.
In CCNx, higher-layer protocols often become so-called "name-based
protocols" because they operate on the CCNx Name. For example, a
versioning protocol might append additional name segments to convey
state about the version of payload. A content discovery protocol
might append certain protocol-specific name segments to a prefix to
discover content under that prefix. Many such protocols may exist
and apply their own rules to Names. They may be layered with each
protocol encapsulating (to the left) a higher layer's Name prefix.
This document also describes a control message called an
InterestReturn. A network element may return an Interest message to
a previous hop if there is an error processing the Interest. The
returned Interest may be further processed at the previous hop or
returned towards the Interest origin. When a node returns an
Mosko & Solis Expires December 31, 2015 [Page 4]
Internet-Draft CCNx TLV June 2015
Interest it indicates that the previous hop should not expect a
response from that node for the Interest -- i.e. there is no PIT
entry left at the returning node for a Content Object to follow.
There are multiple ways to describe larger objects in CCNx. Some
options may use the namespace while others may use a structure such
as a Manifest. This document does not address these options at this
time.
The remainder of this document describes a named payload, and the
Interest/Content Object network protocol behavior in detail.
TODO -- we have not adopted the Requirements Language yet.
1.1. 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].
Mosko & Solis Expires December 31, 2015 [Page 5]
Internet-Draft CCNx TLV June 2015
2. Named Payload
CCNx supports several cryptographic means to bind a Name to a
payload. Interest and Content Object messages include a section
called the ValidationAlgorithm, which specifies the algorithm to use
to verify the binding. Several validation algorithms are supported
including specific Message Integrity Checks (MICs), Message
Authentication Codes (MACs), and Signature types. These are over
specific wire format encodings. Additional schemes could be added in
the future. Interest and Content Object messages also include a
section called the ValidationPayload which contains the validation
output.
The KeyId is an optional field in the ValidationAlgorithm. It is an
octet string that identifies the key used to sign the Content Object.
It uniquely identifies the publisher. It is similar to a Subject Key
Identifier from X509 [RFC 3280, Section 4.2.1.2]. It should be
derived from the key used to sign, for example SHA-256 hash of the
key. It applies to both public/private key systems and to symmetric
key systems using HMAC.
A PublicKeyLocator is an optional field in the ValidationAlgorithm.
It may be one of (a) the signer's public key, (b) the signer's
certificate, or (c) a KeyName that points to the location of the
signer's key or certificate.
A Key inside a PublicKeyLocator is a public key corresponding to the
signer's private key. Examples would be PEM or DER encodings. The
exact encoding is up to the wire format.
A Certificate is an X.509 certificate of the signer's public key.
Examples would be PEM or DER encodings of the certificate. The exact
encoding is up to the wire format.
A KeyName is a CCNx Name and optional signer's KeyId of that name's
publisher. The CCNx Name points to a Key or Certificate. The
KeyName signer KeyId is of the signer of the target name's Content
Object, not of the target key or certificate.
A SignatureTime is an optional field in the ValidationAlgorithm. It
may be used as part of the signature validation check to ensure the
signature was generatred around the expected time. In particular, if
the public key is conveyed in a certificate with a validity period,
the verifying system may enforce that the signature came from a
corresponding period. Some verifiers might determine a signature
without a SignatureTime to be invalid.
Mosko & Solis Expires December 31, 2015 [Page 6]
Internet-Draft CCNx TLV June 2015
3. Names
A CCNx name is a composition of name segments. Each name segment
carries a label identifying the purpose of the name segment, and a
value. For example, some name segments are general names and some
serve specific purposes, such as carrying version information or the
sequencing of many chunks of a large object into smaller, signed
Content Objects.
The name segment labels specified in this document are given in the
table below. Name Segment is a general name segment, typically
occurring in the routable prefix and user-specified content name.
Other segment types are for functional name components that imply a
specific purpose.
A forwarding table entry may contain name segments of any type.
Routing protocol policy and local system policy may limit what goes
into forwarding entries, but there is no restriction at the core
level. An Interest routing protocol, for example, may only allow
binary name segments. A load balancer or compute cluster may route
through additional component types, depending on their services.
+-------------+-----------------------------------------------------+
| Name | Description |
+-------------+-----------------------------------------------------+
| Name | A generic name segment that includes arbitrary |
| Segment | octets. |
| | |
| Interest | An octet string that identifies the payload carried |
| Payload ID | in an Interest. As an example, the Payload ID |
| | might be a hash of the Interest Payload. This |
| | provides a way to differentiate between Interests |
| | based on the Payload solely through a Name Segment |
| | without having to include all the extra bytes of |
| | the payload itself. |
| | |
| Application | An application-specific payload in a name segment. |
| Components | An application may apply its own semantics to these |
| | components. A good practice is to identify the |
| | application in a Name segment prior to the |
| | application component segments. |
+-------------+-----------------------------------------------------+
Table 1: CCNx Name Segment Types
At the lowest level, a Forwarder does not need to understand the
semantics of name segments; it need only identify name segment
boundaries and be able to compare two name segments (both label and
Mosko & Solis Expires December 31, 2015 [Page 7]
Internet-Draft CCNx TLV June 2015
value) for equality. The Forwarder matches paths segment-by-segment
against its forwarding table to determine a next hop.
Mosko & Solis Expires December 31, 2015 [Page 8]
Internet-Draft CCNx TLV June 2015
4. Interests
An Interest is composed of the tuple {Name, Metadata, Payload,
Validator}. These fields are defined below. Only the Name is
mandatory. Other fields, if missing, should be interpreted as "do
not care".
Name is a hierarchical path that identifies the resource. It is
matched as described above.
An Interest may also have a Payload which carries state about the
Interest but is not used to match a Content Object. If an Interest
contains a payload, the Interest name should contain an Interest
Payload ID (IPID). The IPID allows a PIT table entry to correctly
multiplex Content Objects in response to a specific Interest with a
specific payload ID. The IPID could be derived from a hash of the
payload or could be a GUID or a nonce. An optional Metadata field
defines the IPID field so other systems could verify the IPID, such
as when it is derived from a hash of the payload. No system is
required to verify the IPID.
An Interest may contain Validation fields including a
ValidationAlgorithm section describing the type of validator to use
and the ValidationPayload fields containig the output of the
validation. Typically this would only be a MIC - a crc, checksum, or
digest.
An Interest contains additional fields with information about the
query. Two fields - the KeyIdRestriction and
ContentObjectHashRestriction - serve as selectors to help identify
the specific Content Object that should be returned.
The Interest Lifetime element specifies the maximum number of
milliseconds a Forwarder should retain the Interest in its PIT. A
lifetime of "0" means the requester does not expect a response from
the Interest - it serves as a type of notification. The lifetime is
only a guideline for a Forwarder, which may keep an Interest for a
shorter or longer time, based on local conditions and system policy.
It may change hop to hop if the Interest is delayed for any
signifiant amount of time. It is measured in millisecond resolution,
so in fast switching it normally would not need to change. This
field does not affect the matching of Content Objects.
The Interest HopLimit element is a counter that is decremented with
each hop. It limits the distance an Interest may travel. The node
originating the Interest may put in any value - up to the maximum -
in network byte order. Each node that receives an Interest with a
HopLimit decrements the value upon reception. If the value is 0
Mosko & Solis Expires December 31, 2015 [Page 9]
Internet-Draft CCNx TLV June 2015
after the decrement, the Interest cannot be forwarded off the node.
The PIT entry should also track the maximum HopLimit forwarded. If
an Interest with a longer HopLimit arrives, it should be forwarded
even if it is identical to a previously forwarded Interest.
Other implementations may define additional optional headers, for
example Nonces for loop detection, headers for Differentiated
Services Code Points (DSCP), or Flow Labels.
Mosko & Solis Expires December 31, 2015 [Page 10]
Internet-Draft CCNx TLV June 2015
5. Content Objects
A Content Object is composed of the same tuple as an Interest: {Name,
Metadata, Payload, Validator}.
The Name is a mandatory field that identifies the contents.
The Payload of a Content Object holds the upper layer payload. It
may be encrypted, based on outside information or a protocol
information header.
The optional Metadata PayloadType field identifies the type of
Content Object: "DATA" implies an opaque payload; "LINK" is a Content
Object with an encoded Link as a payload. "DATA" is the default.
The optional field ExpiryTime is a millisecond timestamp containing
the number of milliseconds since the epoch in UTC of when the
contents will expire. If it is not present, there is no expiration
on the Content Object. The ExpiryTime should be part of the signed
information covered by the Validator, if present.
A publisher or upstream node may include a Recommended Cache Time for
Content Objects. It is represented as the number of milliseconds
since the epoch in UTC as the desired minimum time to keep the
content object in cache. This recommendation is a guideline as to
the useful lifetime of a Content Object, but may be ignored. The
RecommendedCacheTime should not be covered by the Validator, if
present, as nodes may change the value based on their caching. The
ExpiryTime takes precedence over the RecommendedCacheTime, if both
exist.
Other protocols, such as versioning or chunking, could place other
kinds of metadata in the Content Object.
Mosko & Solis Expires December 31, 2015 [Page 11]
Internet-Draft CCNx TLV June 2015
6. Link
A Link is the tuple {Name, KeyId, ContentObjectHash}. The
information in a Link comprises the fields the fields of an Interest
which would retrieve the Link target. A Content Object with
PayloadType = "Link" is an object whose payload is a Link. This
tuple may be used as a KeyName to identify a specific object with the
certificate wrapped key.
Mosko & Solis Expires December 31, 2015 [Page 12]
Internet-Draft CCNx TLV June 2015
7. Validation
7.1. Validation Algorithm
The Validator consists of a ValidationAlgorithm that specifies how to
verify the message and a ValidationPayload containing the validation
output. The ValidationAlgorithm section defines the type of
algorithm to use and includes any necessary additional information.
The validation is calculated from the beginning of the CCNx Message
through the end of the ValidationAlgorithm section. The
ValidationPayload is the actual cryptographic bytes, such as a CRC
value or an HMAC value or a signature value.
Some Validators contain a KeyId, identifying the publisher
authenticating the Content Object. If an Interest carries a
KeyIdRestriction, then that KeyIdRestriction MUST exactly match the
Content Object's KeyId.
Validation Algorithms fall into three categories: MICs, MACs, and
Signatures. Validators using MIC algorithms do not need to provide
any additional information; they may be computed and verified based
only on the algoritm (e.g. CRC32C). MAC validators require the use
of a KeyId identifying the secret key used by the authenticator.
Because MACs are usually used between two parties that have already
exchanged secret keys via a key exchange protocol, the KeyId may be
any agreed-upon value to identify which key is used. Signature
validators use public key cryptography such as RSA, DSA, or
Elliptical Curve (EC). The KeyId field in the ValidationAlgorithm
identifies the public key used to verify the signature. A signature
may optionally include a KeyLocator, as described above, to bundle a
Key or Certificate or KeyName. MAC and Signature validators may also
include a SignatureTime, as described above.
A PublicKeyLocator KeyName points to a Content Object with an X509
certificate in the payload. In this case, the target KeyId must
equal the first object's KeyId. The target KeyLocator must include
the public key corresponding to the KeyId. That key must validate
the target Signature. The payload is an X.509 certificate whose
public key must match the target KeyLocator's key. It must be issued
by a trusted authority, preferably specifying the valid namespace of
the key in the distinguished name.
Mosko & Solis Expires December 31, 2015 [Page 13]
Internet-Draft CCNx TLV June 2015
8. Interest to Content Object matching
A Content Object satisfies an Interest if and only if (a) the Content
Object name exactly matches the Interest name, and (b) the
ValidationAlgorithm KeyId of the Content Object exactly equals the
Interest KeyIdRestriction, if given, and (c) the computed
ContentObjectHash exactly equals the Interest
ContentObjectHashRestriction, if given. A Content Object does not
carry the ContentObjectHash as an expressed field, it must be
calculated in network to match against. It is sufficient within an
autonomous system to calculate a ContentObjectHash at a border router
and carry it via trusted means within the autonomous system. If a
Content Object ValidationAlgorithm does not have a KeyId then the
Content Object cannot match an Interest with a KeyIdRestriction.
Mosko & Solis Expires December 31, 2015 [Page 14]
Internet-Draft CCNx TLV June 2015
9. Request/Response Protocol
As an Interest moves through the network following the FIB table
based on longest matching prefix, it leaves state at each forwarding
node. The state is represented in a notional Pending Interest Table
(PIT). The PIT tracks the Name, KeyIdRestriction, and
ContentObjectHashRestriction to be matched by a Content Object. If a
second Interest arrives with the same Name and selector values, it
may be aggregated with the existing pending Interest. If the second
Interest extends the Lifetime of the pending Interest, it should be
forwarded to extend the life of downstream Interests.
When a Content Object arrives at a Forwarder, it is matched against
the Interests in the PIT. For each matching Interest, the Content
Object is forwarded along the reverse path of that PIT entry and the
PIT entry is removed.
A Content Object that does not match any Interest in the PIT is
dropped.
A Forwarder may implement a Content Object cache called a Content
Store. At the core protocol level, the Content Store must obey
similar rules as the Forwarder. If an Interest specifies a
ContentObjectHashRestriction, the Content Store SHOULD NOT respond
unless it has verified the hash of the Content Object. If the
Interest carries a KeyIdRestriction then the Content Store MUST
cryptographically verify the signature or not respond.
TODO: Specify what to do in case of failure.
Mosko & Solis Expires December 31, 2015 [Page 15]
Internet-Draft CCNx TLV June 2015
10. Interest Return
This section describes the process whereby a network element may
return an Interest message to a previous hop if there is an error
processing the Interest. The returned Interest may be further
processed at the previous hop or returned towards the Interest
origin. When a node returns an Interest it indicates that the
previous hop should not expect a response from that node for the
Interest -- i.e. there is no PIT entry left at the returning node.
The returned message maintains compatibility with the existing TLV
packet format (a fixed header, optional hop-by-hop headers, and the
CCNx message body). The returned Interest packet is modified in only
two ways:
o The PacketType is set to InterestReturn to indicate a Feedback
message.
o The ReturnCode is set to the appropriate value to signal the
reason for the return
The specific encodings of the Interest Return are specified in
[CCNMessages].
A Forwarder is not required to send any Interest Return messages.
A Forwarder is not required to process any received Interest Return
message. If a Forwarder does not process Interest Return messages,
it should silently drop them.
The Interest Return message does not apply to a Content Object or any
other message type.
An Interest Return message is a 1-hop message between peers. It is
not propagated multiple hops via the FIB. An intermedate node that
receives an InterestReturn may take corrective actions or may
propagage its own InterestReturn to previous hops as indicated in the
reverse path of a PIT entry.
10.1. Message Format
The Interest Return message looks exactly like the original Interest
message with the exception of the two modifications mentioned above.
The PacketType is set to indicate the message is an InterestReturn
and the reserved byte in the Interest header is used as a Return
Code. The numeric values for the PacketType and ReturnCodes are in
[CCNMessages].
Mosko & Solis Expires December 31, 2015 [Page 16]
Internet-Draft CCNx TLV June 2015
10.2. ReturnCode Types
This section defines the InterestReturn ReturnCode introduced in this
RFC. The numeric values used in the packet are defined in
[CCNMessages].
+---------------------+---------------------------------------------+
| Name | Description |
+---------------------+---------------------------------------------+
| No Route | The returning Forwarder has no route to the |
| (Section 10.3.1) | Interest name. |
| | |
| HopLimit Exceeded | The HopLimit has decremented to 0 and need |
| (Section 10.3.2) | to forward the packet. |
| | |
| Interest MTU too | The Interest's MTU does not conform to the |
| large | required minimum and would require |
| (Section 10.3.3) | fragmentation. |
| | |
| No Resources | The node does not have the resources to |
| (Section 10.3.4) | process the Interest. |
| | |
| Path error | There was a transmission error when |
| (Section 10.3.5) | forwarding the Interest along a route (a |
| | transient error). |
| | |
| Prohibited | An administrative setting prohibits |
| (Section 10.3.6) | processing this Interest. |
| | |
| Congestion | The Interest was dropped due to congestion |
| (Section 10.3.7) | (a transient error). |
+---------------------+---------------------------------------------+
Table 2: Interest Return Reason Codes
10.3. Interest Return Protocol
This section describes the Forwarder behavior for the various Reason
codes for Interest Return. A Forwarder is not required to generate
any of the codes, but if it does, it must conform to this
specification.
If a Forwarder receives an Interest Return, it SHOULD take these
standard corrective actions. A forwarder is allowed to ignore
Interest Return messages, in which case its PIT entry would go
through normal timeout processes.
Mosko & Solis Expires December 31, 2015 [Page 17]
Internet-Draft CCNx TLV June 2015
o Verify that the Interest Return came from a next-hop to which it
actually sent the Interest.
o If a PIT entry for the corresponding Interest does not exist, the
Forwarder should ignore the Interest Return.
o If a PIT entry for the corresponding Interest does exist, the
Forwarder MAY do one of the following:
* Try a different forwarding path, if one exists, and discard the
Interest Return, or
* Clear the PIT state and send an Interest Return along the
reverse path.
If a forwarder tries alternate routes, it MUST ensure that it does
not use same same path multiple times. For example, it could keep
track of which next hops it has tried and not re-use them.
If a forwarder tries an alternate route, it may receive a second
InterestReturn, possibly of a different type than the first
InterestReturn. For example, node A sends an Interest to node B,
which sends a No Route return. Node A then tries node C, which sends
a Prohibited. Node A should choose what it thinks is the appropriate
code to send back to its previous hop
If a forwarder tries an alternate route, it should decrement the
Interest Lifetime to account for the time spent thus far processing
the Interest.
10.3.1. No Route
If a Forwarder receives an Interest for which it has no route, or for
which the only route is back towards the system that sent the
Interest, the Forwarder SHOULD generate a "No Route" Interest Return
message.
How a forwarder manages the FIB table when it receives a No Route
message is implementation dependent. In general, receiving a No
Route Interest Return should not cause a forwarder to remove a route.
The dynamic routing protocol that installed the route should correct
the route or the administrator who created a static route should
correct the configuration. A forwarder could suppress using that
next hop for some period of time.
Mosko & Solis Expires December 31, 2015 [Page 18]
Internet-Draft CCNx TLV June 2015
10.3.2. HopLimit Exceeded
A Forwarder MAY choose to send HopLimit Exceeded messages when it
receives an Interest that must be forwarded off system and the
HopLimit is 0.
10.3.3. Interest MTU Too Large
If a Forwarder receives an Interest whose MTU exceeds the prescribed
minimum, it MAY send an "Interest MTU Too Large" message, or it may
silently discard the Interest.
If a Forwarder receives an "Interest MTU Too Large" is SHOULD NOT try
alternate paths. It SHOULD propagate the Interest Return to its
previous hops.
10.3.4. No Resources
If a Forwarder receives an Interest and it cannot process the
Interest due to lack of resources, it MAY send an InterestReturn. A
lack of resources could be the PIT table is too large, or some other
capacity limit.
10.3.5. Path Error
If a forwarder detects an error forwarding an Interest, such as over
a reliable link, it MAY send a Path Error Interest Return indicating
that it was not able to send or repair a forwarding error.
10.3.6. Prohibited
A forwarder may have administrative policies, such as access control
lists, that prohibit receiving or forwarding an Interest. If a
forwarder discards an Interest due to a policy, it MAY send a
Prohibited InterestReturn to the previous hop. For example, if there
is an ACL that says /parc/private can only come from interface e0,
but the Forwarder receives one from e1, teh Forwarder must have a way
to return the Interet with an explanation.
10.3.7. Congestion
If a forwarder discards an Interest due to congestion, it MAY send a
Congestion InterestReturn to the previous hop.
Mosko & Solis Expires December 31, 2015 [Page 19]
Internet-Draft CCNx TLV June 2015
11. Acknowledgements
Mosko & Solis Expires December 31, 2015 [Page 20]
Internet-Draft CCNx TLV June 2015
12. IANA Considerations
This memo includes no request to IANA.
All drafts are required to have an IANA considerations section (see
Guidelines for Writing an IANA Considerations Section in RFCs
[RFC5226] for a guide). If the draft does not require IANA to do
anything, the section contains an explicit statement that this is the
case (as above). If there are no requirements for IANA, the section
will be removed during conversion into an RFC by the RFC Editor.
Mosko & Solis Expires December 31, 2015 [Page 21]
Internet-Draft CCNx TLV June 2015
13. Security Considerations
The Interest Return message has no authenticator from the previous
hop. Therefore, the payload of the Interest Return should only be
used locally to match an Interest. A node should never forward that
Interest payload as an Interest. It should also verify that it send
the Interest in the Interest Return to that node and not allow anyone
to negate Interest messages.
If two peers require authenticated messaging, they must use an
external mechanism.
Mosko & Solis Expires December 31, 2015 [Page 22]
Internet-Draft CCNx TLV June 2015
14. References
14.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
14.2. Informative References
[CCN] PARC, Inc., "CCNx Open Source", 2007,
<http://www.CCNx.org>.
[CCNMessages]
Mosko, M., Solis, I., and M. Stapp, "CCNx Messages in TLV
Format (Internet draft)", 2015, <http://tools.ietf.org/
html/draft-mosko-icnrg-ccnxmessages-00>.
[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552,
July 2003.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
Mosko & Solis Expires December 31, 2015 [Page 23]
Internet-Draft CCNx TLV June 2015
Authors' Addresses
Marc Mosko
PARC, Inc.
Palo Alto, California 94304
USA
Phone: +01 650-812-4405
Email: marc.mosko@parc.com
Ignacio Solis
PARC, Inc.
Palo Alto, California 94304
USA
Phone: +01 650-812-4405
Email: marc.mosko@parc.com
Mosko & Solis Expires December 31, 2015 [Page 24]
