rfc:rfc8367
Independent Submission T. Mizrahi Request for Comments: 8367 Marvell Category: Informational J. Yallouz ISSN: 2070-1721 Intel
1 April 2018
Wrongful Termination of Internet Protocol (IP) Packets
Abstract
Routers and middleboxes terminate packets for various reasons. In some cases, these packets are wrongfully terminated. This memo describes some of the most common scenarios of wrongful termination of Internet Protocol (IP) packets and presents recommendations for mitigating them.
Status of This Memo
This document is not an Internet Standards Track specification; it is published for informational purposes.
This is a contribution to the RFC Series, independently of any other RFC stream. The RFC Editor has chosen to publish this document at its discretion and makes no statement about its value for implementation or deployment. Documents approved for publication by the RFC Editor are not candidates for any level of Internet Standard; see Section 2 of RFC 7841.
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at https://www.rfc-editor.org/info/rfc8367.
Copyright Notice
Copyright (c) 2018 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 (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.
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Table of Contents
1. Introduction ................................................... 2
2. Abbreviations .................................................. 2
3. Wrongful Termination Scenarios ................................. 3
3.1. Color-Based Termination ................................... 3
3.2. Age-Based Termination ..................................... 3
3.3. Origin-Based Termination .................................. 4
3.4. Length-Based Termination .................................. 4
3.5. IP-Version-Based Termination .............................. 5
3.6. Flag-Based Termination .................................... 5
4. Security Considerations ........................................ 5
5. IANA Considerations ............................................ 5
6. Conclusion ..................................................... 6
7. References ..................................................... 6
7.1. Normative References ...................................... 6
7.2. Informative References .................................... 6
Authors' Addresses ................................................ 6
1. Introduction
IP packets are often terminated by network devices. In some cases, control-plane packets are terminated and processed by the local device, while in other cases packets are terminated (discarded) due to a packet filtering mechanism. Packet filtering is widely employed in network devices for sanity checking, policy enforcement, and security. IP routers and middleboxes, such as firewalls, often terminate packets that do not comply with a predefined policy. Unfortunately, some filtering policies cause false positive or unnecessary packet termination. Moreover, these wrongful terminations are sometimes biased and discriminate against packets based on their color, age, origin, length, or IP version.
This memo discusses some of the most common scenarios of wrongful termination of IP packets and presents recommendations for preventing such discrimination.
2. Abbreviations
IP Internet Protocol
TTL Time To Live
OAM Operations, Administration, and Maintenance
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3. Wrongful Termination Scenarios
3.1. Color-Based Termination
Synopsis
IP packets are terminated due to their color.
Description
Routers often employ metering mechanisms [RFC4115]. These
mechanisms often support a color-aware mode, in which the packet's
color (green, yellow, or red) is used as a criterion in the
metering algorithm. This mode has been known to prefer green
packets over red and yellow packets.
Recommendation
Use of color-blind metering is recommended, as it allows equal
opportunity for packets of different colors.
3.2. Age-Based Termination
Synopsis
IP packets are terminated based on their TTL.
Description
The IPv4 TTL field [RFC791] and the IPv6 Hop Limit field [RFC8200]
are used for loop prevention. These fields essentially represent
the packet's age. A router that receives an IP packet with a TTL
value of 0 or 1 typically terminates the packet. In this
document, packets with a TTL or Hop Limit of 0 or 1 are referred
to as 'senior packets'.
Recommendation
When possible, the practice of reverse discrimination is
recommended. Notably, senior packets have been known to be highly
effective for OAM tasks, such as Hello [RFC2328] and Traceroute
[RFC2151]. Therefore, senior packets should not be easily
dismissed; to the extent possible, senior packets should be used
in control-plane protocols.
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3.3. Origin-Based Termination
Synopsis
IP packets are terminated based on their origin (source IP address
prefix).
Description
Routers and middleboxes often perform IP address filtering.
Packets are often discarded based on the prefix of their source IP
address. In this memo, prefix-based source address filtering is
referred to as origin-based filtering. While source IP address
filtering is an acceptable technique for preventing security
attacks performed by known attackers, filtering an entire prefix
may lead to unnecessary termination of legitimate traffic.
Recommendation
Origin-based filtering should be limited, to the extent possible,
so as not to punish an entire autonomous system for the crime of a
single host. Individual address-based filtering should be
preferred in cases where the address of the potential threat is
well known.
3.4. Length-Based Termination
Synopsis
Short IP packets are wrongfully terminated due to their length.
Description
The minimum permissible size of an IPv4 [RFC791] packet is 20
octets, and the minimum size of an IPv6 [RFC8200] packet is 40
octets. However, due to the size limits of Ethernet, it is often
the case that IP packets that are shorter than 46 octets are
discarded. This is because the minimal Ethernet frame size is 64
octets, the minimal Ethernet header size is 14 octets, and the
Ethernet Frame Check Sequence is 4 octets long (i.e., 64 - 14 - 4
= 46). In the context of this memo, legitimate IP packets that are
less than 46 octets long are referred to as 'short IP packets'.
Recommendation
Short IP packets should not be discarded. The Ethernet frame
length should be enforced at the Ethernet layer, while the IP
layer should avoid discrimination of short IP packets.
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3.5. IP-Version-Based Termination
Synopsis
IPv6 packets are terminated due to their version.
Description
Many routers and middleboxes are configured to process only IPv4
[RFC791] packets and to reject IPv6 [RFC8200] packets.
Recommendation
It is quite unsettling that there are still networks in which IPv6
packets are deemed unwanted in the second decade of the 21st
century. Indeed, IPv6 packets have a slightly shorter payload
than IPv4 packets. However, they are essential to the future
growth of the Internet. It is time for operators to finally give
IPv6 its well-deserved opportunity.
3.6. Flag-Based Termination
Synopsis
IPv4 packets are terminated because their More Fragments (MF) flag
is set.
Description
Many routers and middleboxes are configured to discard fragmented
packets.
Recommendation
A packet should not be discarded on the grounds of a flag it
supports. All flags should be respected, as well as the features
they represent.
4. Security Considerations
This memo proposes to practice liberality with respect to IP packet filtering in routers and middleboxes. Arguably, such a liberal approach may compromise security in some cases. Not only must security be done; it must also be seen to be done.
5. IANA Considerations
This document has no IANA actions.
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6. Conclusion
This memo recommends that every router and middlebox be an Equal Opportunity Device, which does not discriminate on the basis of actual or perceived rate, color, age, origin, length, IP version, fragmentation characteristics, higher-layer protocols, or any other IP characteristic.
7. References
7.1. Normative References
[RFC791] Postel, J., "Internet Protocol", STD 5, RFC 791,
DOI 10.17487/RFC0791, September 1981,
<https://www.rfc-editor.org/info/rfc791>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
7.2. Informative References
[RFC2151] Kessler, G. and S. Shepard, "A Primer On Internet and
TCP/IP Tools and Utilities", FYI 30, RFC 2151,
DOI 10.17487/RFC2151, June 1997,
<https://www.rfc-editor.org/info/rfc2151>.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
DOI 10.17487/RFC2328, April 1998,
<https://www.rfc-editor.org/info/rfc2328>.
[RFC4115] Aboul-Magd, O. and S. Rabie, "A Differentiated Service
Two-Rate, Three-Color Marker with Efficient Handling of
in-Profile Traffic", RFC 4115, DOI 10.17487/RFC4115,
July 2005, <https://www.rfc-editor.org/info/rfc4115>.
Authors' Addresses
Tal Mizrahi Marvell Email: talmi@marvell.com
Jose Yallouz Intel Email: jose@alumni.technion.ac.il
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