BLACKHOLEIXP BGP Community for Blackholing at IXPs
draft-ymbk-grow-blackholing-00

Abstract

This document describes the use of a well-known Border Gateway Protocol (BGP) community for blackholing at Internet Exchange Points (IXP). This well-known advisory transitive BGP community, namely BLACKHOLEIXP, allows an origin AS to specify through the route server that IXPs should blackhole a specific route.

Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as described in [RFC2119] only when they appear in all upper case. They may also appear in lower or mixed case as English words, without normative meaning.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on November 29, 2015.

Copyright Notice

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Table of Contents

• 1. Introduction
• 2. BLACKHOLEIXP Attribute
• 3. Operational Recommendations
• 3.1. Peering at Route Servers
• 3.2. Accepting Blackholed IP Prefixes
• 4. IANA Considerations
• 5. Security Considerations
• 6. Normative References
• Authors' Addresses

1. Introduction

Massive DDoS attacks targeting Internet Exchange Point (IXP) members may cause a congestion of their peering port(s). In order to limit the impact of such a scenario on legitimate traffic, IXPs adopted a feature called blackholing. A member may trigger blackholing via BGP through the route server [I-D.ietf-idr-ix-bgp-route-server]. All traffic destined to the such announced prefixes is discarded on the switching fabric of the IXP. This resolves the port congestion caused by the DDoS attack.

The concept of blackholing at IXPs is similar to blackholing in iBGP scenarios [RFC3882] and the expansion RTBH filtering [RFC5635].

Different operators of IXPs specified various mechanisms for their members to trigger blackholing. This includes but is not limited to BGP communities from the private community space or specific next hop IP addresses.

Having several different mechanisms to trigger blackholing at different IXPs makes it an unnecessary complex, error-prone and cumbersome task for IXPs members. A well-known and commonly agreed BGP community for blackholing at IXPs allows members to easily utilize this feature for all their IXP peerings.

Having such a well-known and commonly agreed BGP community for blackholing also supports IXPs as

• implementing and monitoring blackholing gets easier if implementation and operational guides do not cover many options to trigger blackholing
• the amount of support requests from members about how to trigger blackholing at a particular IXP will be reduced as the mechanism is unified for all IXPs

Making it considerably easier for operators and members of IXP to utilize blackholing will reduce the impact of massive DDoS attacks and thus make the Internet more reliable.

2. BLACKHOLEIXP Attribute

This document defines the use a new well-known BGP transitive community, BLACKHOLEIXP.

The semantics of this attribute is to allow an IXP to interpret the presence of this community as an advisory qualification to drop any traffic being sent towards this prefix.

3. Operational Recommendations

3.1. Peering at Route Servers

If a member of an IXP experiences a massive DDoS attack, blackholing can be leveraged to limit the arising collateral damage. Therefore, the member must tag the BGP announcements of their prefix with the BLACKHOLEIXP BGP community. However, if only a sub-prefix is affected by the attack a more specific announcement SHOULD be used.

Many IXPs provide the so-called policy control feature as part of their route servers (see e.g. the LINX website). Policy control allows to specify by using BGP communities which ASNs connected to the IXP receives a particular BGP announcement.

Combined usage of the BGP communities for blackholing and policy control allows a fine-grained control of a blackhole. Traffic from certain ASes can be blackholed exclusively.

In many implementations of blackholing at IXPs, the route server after receiving a BGP announcement carrying the BLACKHOLEIXP BGP community rewrites the next hop IP address to the pre-defined Blackholing IP address before redistruting the announcement.

3.2. Accepting Blackholed IP Prefixes

In order to limit the space required to store the routing table on a router, IP prefixes larger than /24 for IPv4 and /48 for IPv6 are usually not accepted (see section 6.1.3 [RFC7454]). However, blackholes in the IP space should be as small as possible in order to limit the impact of blackholing for IP space that is not experiencing a massive DDoS attack.

Routers SHOULD accept BGP announcements carrying the BLACKHOLEIXP BGP community up to /32 for IPv4 and /128 for IPv6.

4. IANA Considerations

The IANA is requested to register BLACKHOLEIXP as a well-known community with global significance:

• BLACKHOLEIXP (= 0xFFFF029A)

The value 0xFFFF029A is preferable as it can also be written as 65535:666 following the ASN:ASN (16-bit) notation. 65535 is from the reserved ASN space and 666 is often used to signal blackholing in iBGP and eBGP transit provider networks scenarios.

5. Security Considerations

BGP contains no specific mechanism to prevent the unauthorized modification of information by the forwarding agent. This allows routing information to be modified, removed, or false information to be added by forwarding agents. Recipients of routing information are not able to detect this modification. Also, RKPI [RFC6810] and BGPSec [I-D.ietf-sidr-bgpsec-overview] do not fully resolve this situation. For instance, BGP communities can still be added or altered by a forwarding agent even if RPKI and BGPSec are in place.

The BLACKHOLEIXP BGP community does not alter this situation.

A new additional attack vector is introduced into BGP by using the BLACKHOLEIXP BGP community: denial of service attacks for IP prefixes.

Unauthorized addition of the BLACKHOLEIXP BGP community to an IP prefix by a forwarding agent may cause a denial of service attack based on denial of reachability. The denial of service will happen if an IXP offering blackholing is traversed. However, denial of service attack vectors to BGP are not new as the injection of false routing information is already possible.

In order to further limit the impact of unauthorized BGP announcements carrying the BLACKHOLEIXP BGP community the receiving router or route server SHOULD verify by applying strict filtering (see section 6.2.1.1.2. [RFC7454]) that the peer announcing the prefix is authorized to do so. If not, the BGP announcement should be filtered out.

6. Normative References

Authors' Addresses