Internet DRAFT - draft-blanchet-tvr-forwarding
draft-blanchet-tvr-forwarding
Internet Engineering Task Force M. Blanchet
Internet-Draft Viagenie
Intended status: Informational 13 March 2023
Expires: 14 September 2023
Forwarding in the context of Time-Variant Routing(TVR)
draft-blanchet-tvr-forwarding-00
Abstract
Some networks, such as in space, have links that are up and down
based on a known schedule. In this context, IP Packets or Bundle
Protocol Bundles should then be saved locally until the destination
becomes reachable again. This document describes forwarding node
policies regarding how to manage the local store as well as
forwarding decisions. This specification applies to both IP packets
or Bundle Protocol bundles.
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 14 September 2023.
Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://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
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Forwarding . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Policies . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Drop Policy . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Forwarding Preference Policy . . . . . . . . . . . . . . 5
4. TODO and Comments . . . . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Normative References . . . . . . . . . . . . . . . . . . 6
7.2. Informative References . . . . . . . . . . . . . . . . . 6
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
Some networks, such as in space, have links that are up and down
based on a known schedule. In this context, IP Packets or Bundle
Protocol Bundles should then be saved locally until the destination
becomes reachable again. This document describes forwarding node
policies regarding how to manage the local store as well as
forwarding decisions. This specification applies to both IP packets
or Bundle Protocol [RFC9171] bundles.
For easier reading, this document will use the word "packet" to
encompass both IP packets and Bundle Protocol bundles.
In typical IP forwarding engines, if the route for a destination does
not exist, a forwarding engine would drop the packet and then return
an ICMP Unreachable Error Message to the source of the packet. This
specification describes an atypical behavior of IP forwarding
engines.
Bundles of the Bundle Protocol are defined for the purpose of store
and forward, therefore it is a normal behavior to store the bundles
until reachability is possible.
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This document was written mostly based on Bundle Protocol
implementations that are targetted for space networks. It was then
generalized for IP. The IP behavior may be underspecified or
inadequately specified for the first versions of this document.
1.1. Requirements Language
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 BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. Forwarding
If the destination is unreachable, the packet is not discarded and
therefore saved in memory. Whether volatile or non-volatile is an
implementation decision. The packet should be saved with a timestamp
to be used by policies described in this document.
When a new route is installed, or in general when the forwarding
table has changed, then saved packets are parsed, and those that can
be sent are sent, in order of the preference policy discussed below.
How saved packets are parsed is implementation decision. For
example, an implementation may index saved packets based on
destination prefixes, so that the lookup is fast.
Policies are needed to guide the forwarding engine when the following
events happen.
* Packet memory store is full and a new packet is incoming.
* A destination becomes reachable by a new route entry in the
forwarding table. Which stored packets should be forwarded first.
* A packet has expired. BP Bundles have lifetimes. IP packets have
TTL (IPv4) or Hop Limit (IPv6). However, this specification does
not change the behavior of IP packets when TTL or Hop Limit has a
value of zero.
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* The capability of storing packets for a forwarding node may be
resource demanding, especially in scenarios where node resources
are very limited, such as in space. Therefore, the forwarding
node owner may want to have preference on which types of packets
are stored or not. For example, the forwarding node may prefer by
policy to store packets based on the source address, destination
address, both addresses or various fields, such as Flow Label,
Diffserv or else. Bundles also have various fields that may be
used for such policies.
* When a packet needs to be dropped, an error should be sent back to
the source. Both IP and BP has those error messages. However, in
a constraint environment, error messages may be too costly to send
back to source. Another case is when the packet is just "too" old
to make an error message relevant to be sent. A policy may tell
the forwarding node to not send error messages back to source when
dropping packets.
3. Policies
This section describes some policies that may be configured on the
forwarding node.
3.1. Drop Policy
When the packet memory store is full and space is needed such as a
new packet is incoming, the drop policy comes into effect. It may
also happen by other reasons, such as an asynchronous "garbage
collection" process. The drop policy may be one (TBD: or many? with
weights?) of the following.
* Drop oldest: The oldest packets are dropped. Error messages are
sent to the source.
* Drop last from these sources. Keep the packets from these sources
as long as possible: e.g. drop them after dropping all others,
Sources are specified as a list of prefixes. Order in the list is
relevant: first one in the list is the last one to drop.
* Drop last for these destinations. Keep the packets to this
destination as long as possible: e.g. drop them after dropping all
others. Destinations are specified as a list of prefixes. Order
in the list is relevant: first one in the list is the last one to
drop.
* Drop last if a field is set to a value. Keep the packets with the
specified field having the specified value as long as possible:
e.g. drop them after dropping all others
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An additional characteristic of the drop policy is related to the
error messages when dropping a packet. The following list the
possible error messages policies that may be added to any of the
above drop policies. If no error message policy is added, then the
default error message behavior from the respective stacks (IP or BP)
are used.
* do not send error message: If packets are dropped, error messages
are not sent to the source.
* send error message only if newer than x min/hour/day: If packets
are dropped, error messages are sent to the source only if the
timestamp of the packet is newer than the specified period from
now.
3.2. Forwarding Preference Policy
When a destination becomes reachable by a new route in the forwarding
table, the forwarding node may need to prefer starting sending some
packets instead of others, for various reasons. For example, in a
"short" time window of reachability, some packets or destinations may
be preferred over others. In bandwidth limited links, control plane
packets may be preferred to be sent first over data or telemetry or
large media. The forwarding preference policy may be one of the
following.
* Forward first from these sources: Start forwarding packets of this
list of sources before forwarding others. Sources are specified
as a list of prefixes. Order in the list is relevant: first one
in the list is the first one to forward.
* Forward first for these destinations: Start forwarding packets of
this list of destinations before forwarding others. Destinations
are specified as a list of prefixes. Order in the list is
relevant: first one in the list is the first one to forward.
* Forward first if a field is set to a value: Start forwarding
packets with the specified field having the specified value.
4. TODO and Comments
* Information model in Yang to describe policies?
* Default route "policy": avoid sending packets back to Earth?
* weighted multiple concurrent policies?
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5. IANA Considerations
This memo includes no request to IANA.
6. Security Considerations
TBD
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
7.2. Informative References
[RFC9171] Burleigh, S., Fall, K., and E. Birrane, III, "Bundle
Protocol Version 7", RFC 9171, DOI 10.17487/RFC9171,
January 2022, <https://www.rfc-editor.org/info/rfc9171>.
Acknowledgements
The following people have provided comments to improve this document:
Author's Address
Marc Blanchet
Viagenie
Email: marc.blanchet@viagenie.ca
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