Time to Remove Filters for Previously Unallocated IPv4 /8s
draft-ietf-grow-no-more-unallocated-slash8s-00

Abstract

It has been common for network administrators to filter IP traffic coming from unallocated IPv4 address space. Now that there are no longer any unallocated IPv4 /8s, this practise is more complicated, fragile and expensive. Network administrators are advised to remove filters based on the registration status of the address space.

This document explains why any remaining filters for unallocated IPv4 /8s should now be removed on border routers and documents those IPv4 unicast prefixes that should not be routed across the public Internet.

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 September 15, 2011.

Copyright Notice

Copyright (c) 2011 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.

Table of Contents

• 1. Introduction
• 2. Terminology
• 3. Traffic Filtering Options
• 3.1. No Longer Filtering Based on Address Registration Status
• 3.2. Continuing to Filter Traffic from Unallocated IPv4 Space
• 4. Prefixes That Should Not be Routed Across the Internet
• 5. Security Considerations
• 6. IANA Considerations
• 7. References
• Appendix A. Acknowledgments
• Author's Address

1. Introduction

It has been common for network administrators to filter IP traffic coming from unallocated IPv4 address space. Now that there are no longer any unallocated IPv4 /8s, this practise is more complicated, fragile and expensive. Network administrators are advised to remove filters based on the registration status of the address space.

This document explains why any remaining filters for unallocated IPv4 /8s should now be removed on border routers and documents those IPv4 unicast prefixes that should not be routed across the public Internet.

2. Terminology

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 BCP 14, RFC 2119 [RFC2119].

3. Traffic Filtering Options

3.1. No Longer Filtering Based on Address Registration Status

Network administrators who implemented filters for unallocated IPv4 /8s did so in the knowledge that those /8s were not a legitimate source of traffic on the Internet and that there was a small number of filters to implement. Now that there are no longer any unallocated unicast IPv4 /8s, there will be legitimate Internet traffic coming from all unicast /8s that are not reserved for special purposes in an RFC.

Removing ingress filters based on the registration status of the IPv4 address is a simple approach that will avoid blocking legitimate Internet traffic.

3.2. Continuing to Filter Traffic from Unallocated IPv4 Space

Some network administrators might want to continue filtering unallocated IPv4 addresses managed by the Regional Internet Registries (RIRs). This requires significantly more granular ingress filters and the highly dynamic nature of the RIRs' address pools means that filters need to be updated on a daily basis to avoid blocking legitimate incoming traffic.

4. Prefixes That Should Not be Routed Across the Internet

Network operators who only wish to filter traffic originating from addresses that should never be routed across the Internet can deploy a set of ingress filters designed to block traffic from address blocks reserved for special purposes. These are:

• - 0.0.0.0/8 (Local identification) [RFC1122];
• - 10.0.0.0/8 (Private use) [RFC1918];
• - 127.0.0.0/8 (Loopback) [RFC1122];
• - 169.254.0.0/16 (Link local) [RFC3927];
• - 172.16.0.0/12 (Private use) [RFC1918];
• - 192.0.2.0/24 (TEST-NET-1) [RFC5737];
• - 192.168.0.0/16 (Private use) [RFC1918];
• - 198.18.0.0/15 (Benchmark testing) [RFC2544];
• - 198.51.100.0/24 (TEST-NET-2) [RFC5737];
• - 203.0.113.0/24 (TEST-NET-3) [RFC5737];
• - 224.0.0.0/4 (Multicast) [RFC5771]; and
• - 240.0.0.0/4 (Future use) [RFC1112].

A full set of special use IPv4 addresses can be found in [RFC5735]. It includes prefixes that are intended for Internet use.

5. Security Considerations

The cessation of filters based on unallocated IPv4 /8 allocations is an evolutionary step towards reasonable security filters. While these filters are no longer necessary, and in fact harmful, this does not obviate the need to continue other security solutions. These other solutions are as necessary today as they ever were.

6. IANA Considerations

This document makes no request of IANA.

7. References

Appendix A. Acknowledgments

Thanks are owed to Kim Davies, Terry Manderson, Dave Piscitello and Joe Abley for helpful advice on how to focus this document. Thanks also go to Andy Davidson, Philip Smith and Rob Thomas for early reviews and suggestions for improvements to the text and Carlos Pignataro for his support and comments.

Author's Address