Configuring BGP to Block Denial-of-Service Attacks
RFC 3882

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Network Working Group                                            D. Turk
Request for Comments: 3882                                   Bell Canada
Category: Informational                                   September 2004

           Configuring BGP to Block Denial-of-Service Attacks

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2004).

Abstract

   This document describes an operational technique that uses BGP
   communities to remotely trigger black-holing of a particular
   destination network to block denial-of-service attacks.  Black-holing
   can be applied on a selection of routers rather than all BGP-speaking
   routers in the network.  The document also describes a sinkhole
   tunnel technique using BGP communities and tunnels to pull traffic
   into a sinkhole router for analysis.

Table of Contents

   1.  Existing BGP-Triggered Black holing Techniques . . . . . . . .  2
   2.  Enhanced BGP-Triggered Black holing Technique. . . . . . . . .  3
   3.  Sinkhole Tunnels . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  Security Considerations. . . . . . . . . . . . . . . . . . . .  7
   5.  Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . .  7
   6.  Informative References . . . . . . . . . . . . . . . . . . . .  7
   7.  Author's Addresses . . . . . . . . . . . . . . . . . . . . . .  7
   8.  Full Copyright Statement . . . . . . . . . . . . . . . . . . .  8

Turk                         Informational                      [Page 1]
RFC 3882          Configuring BGP to Block DoS Attacks    September 2004

1.  Existing BGP-Triggered Black-holing Techniques

   Current BGP-triggered black-holing techniques rely on altering the
   BGP next hop address of a network targeted by an attack throughout
   the iBGP network.  A customized iBGP advertisement is generated from
   a router participating in the destination/attacked AS where the next
   hop address for the targeted network or host is modified to point to
   an RFC 1918 [RFC1918] (private internet) address.  Most routers on
   the Internet, especially edge routers, have static routes pointing
   RFC 1918 addresses to the null interface.  Those static routes drive
   all traffic destined to the network under attack to the null
   interface.

   When an iBGP-speaking router inside the destination AS receives the
   iBGP update, the advertised prefix will be added to the routing table
   with a next hop of one of the networks listed in RFC 1918.  The
   router will then attempt to resolve the RFC 1918 next-hop in order to
   qualify the route and derive a forwarding interface.  This process
   will return a valid next hop as the null interface.  Assuming the
   router is properly configured to direct RFC 1918 destined traffic to
   a null interface, traffic destined to the attacked network gets
   dropped, making the attacked network unreachable to the attacker and
   everyone else.

   While this technique shields the internal infrastructure from the
   attack, protecting a large number of devices, it has the undesirable
   side effect of rendering the targeted/attacked network unreachable
   throughout the entire destination AS.  Even if a static route
   pointing an RFC 1918 address to a null interface is not configured on
   all routers within the destination AS, the modified next hop makes
   the traffic un-routable to its legitimate destination.

   Network operators usually use the BGP-triggered black holes for a
   short period of time.  The technique causes traffic drops on all
   ingress points of the AS for traffic destined to the attacked
   network.  By default, routers dropping traffic into a null interface
   should send an "ICMP unreachable" message to the source address
   belonging to the origin/attacking AS.

   Once the procedure reaches this point, one of the source addresses of
   the attack traffic is hijacked by introducing a device with the same
   source IP address into the BGP domain of the destination/attacked AS.
   The device hijacking the source address collects the ICMP unreachable
   packets.  The source addresses of these ICMP unreachable packets
   reveal which edge routers within the destination/attacked AS the
   attack is coming from.  The network operator may then opt to manually
   stop the traffic on the routers from which attack traffic is
   entering.

Turk                         Informational                      [Page 2]
RFC 3882          Configuring BGP to Block DoS Attacks    September 2004

2.  Enhanced BGP-Triggered Black-holing Technique

   This paper describes a technique developed to instruct a selected set
   of routers to alter the next hop address of a particular prefix by
   use of the BGP protocol.  The next hop can either be a null interface
   or, as discussed later on in this paper, a sinkhole tunnel interface.