Network Working Group H. Chen
Internet-Draft China Telecom
Intended status: Best Current Practice D. Ma
Expires: October 4, 2019 ZDNS
Y. Gu
S. Zhuang
H. Wang
Huawei
April 2, 2019
Enhanced AS-Loop Detection for BGP
draft-chen-grow-enhanced-as-loop-detection-01
Abstract
This document proposes to enhance AS-Loop Detection for BGP Inbound/
Outbound Route Processing. This could empower networks to quickly
and accurately figure out they're being victimized.
Requirements Language
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 RFC 2119 [RFC2119].
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
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This Internet-Draft will expire on October 4, 2019.
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Enhanced AS-Loop Detection for BGP Inbound Route Processing . 5
4. Enhanced AS-Loop Detection for BGP Outbound Route Processing 7
5. Benefits . . . . . . . . . . . . . . . . . . . . . . . . . . 8
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
8. Security Considerations . . . . . . . . . . . . . . . . . . . 9
9. Normative References . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
The Border Gateway Protocol (BGP) [RFC4271], as an inter-Autonomous
(AS) routing protocol, is used to exchange network reachability
information between BGP systems. BGP is widely used by Internet
Service Providers (ISPs) and large organizations.
BGP is used to exchange reachable inter-AS routes, establish inter-AS
paths, avoid routing loops, and apply routing policies between ASs.
BGP loop detection mechanism is defined in section 9.1.2. of RFC4271:
...
If the AS_PATH attribute of a BGP route contains an AS loop, the
BGP route should be excluded from the Phase 2 decision function.
AS loop detection is done by scanning the full AS path (as
specified in the AS_PATH attribute), and checking that the
autonomous system number of the local system does not appear in
the AS path. Operations of a BGP speaker that is configured to
accept routes with its own autonomous system number in the AS path
are outside the scope of this document.
...
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In ordinary BGP, every AS announces its route information with
different prefixes. However, its neighboring ASes cannot validate
this route information, but rather directly propagate it across the
Internet or simply discard AS-Loop routes directly. Obviously, this
weak trust model allows forged route announcement propagations and
rarely been found, which is a fundamental security weakness of BGP.
Forged routes, which can be generated by configuration errors or
malicious attacks, can cause large-scale network connectivity
problems.
Some cases can be worse, hackers exploit this property of BGP to
achieve their ulterior motives. They can add some providers' AS
number into the forged AS-Path and attempt to make it look like the
route had passed through these ASNs, or perhaps they are there to
prevent those providers from carrying the route.
For example, the cases shown in Figure 1.
o Forged Case 1: One upstream ISP of AS64596 forged a route with the
ASN 64596 as the origin ASN in the AS-Path.
o Forged Case 2: One upstream ISP of AS64596 forged a route with the
ASN 64596 as the transit ASN in the AS-Path.
After receiving the above routes, AS64596 treats them as normal loop
routes during the loop detecting phase and discards them directly.
In most NOSes (Netwok Operation Systems), such rejected routes are
not logged and only visable by puuting the router into debugging
mode. If the AS64596 is slightly enhanced, it can find that someone
has faked himself, which may cause unnecessary trouble for himself.
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AS-Loop-Detecting at this point
Discard AS-Loop Routes directly that contains AS64596
|
|
v x.y.z.0/24 Origin AS 64600
AS64595---AS64596---AS64597---AS64598---AS64599----AS64600
Normal Case:
<-- x.y.z.0/24, AS-Path: 64597 64598 64599 64600
Forged Case 1:
<-- x.y.z.0/24, AS-Path: 64597 64596
(Or: 64597 64598 64596 etc.)
Forged Case 2:
<-- x.y.z.0/24, AS-Path: 64597 64596 64600
(Or: 64597 64596 64599 64600 etc.)
Figure 1: BGP Inbound Route Processing
Split-Horizon for EBGP is an optional function that a BGP sender will
not advertise any routes that were previously received from that same
AS. In some current implementation, the BGP outbound route
processing step will simply discard the route if AS-Loop being
detected.
For example, the cases shown in Figure 1.
o Forged Case 1: One upstream ISP of AS64597 forged a route with the
ASN 64596 as the origin ASN in the AS-Path.
o Forged Case 2: One upstream ISP of AS64597 forged a route with the
ASN 64596 as the transit ASN in the AS-Path.
When sending the above routes, AS64597 treats them as normal loop
routes and discards them directly. If AS64597 is slightly enhanced,
it can find that someone has faked AS64596, which may cause large-
scale network connectivity problems.
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Split-Horizon Enable & AS-Loop-Detecting at this point
Discard AS-Loop Routes directly if sending AS-Path contains AS64596
|
|
v x.y.z.0/24 Origin AS 64600
AS64595---AS64596---AS64597---AS64598---AS64599----AS64600
Normal Case:
<-- x.y.z.0/24, AS-Path: 64597 64598 64599 64600
Forged Case 1:
<-- x.y.z.0/24, AS-Path: 64597 64596
(Or: 64597 64598 64596 etc.)
Forged Case 2:
<-- x.y.z.0/24, AS-Path: 64597 64596 64600
(Or: 64597 64596 64599 64600 etc.)
Figure 2: BGP Outbound Route Processing
Above cases are also being known As-Path Poisoning Attacks.
This document proposes to enhance AS-Loop Detection for BGP Inbound/
Outbound Route Processing. This could empower networks to quickly
and accurately figure out they're being victimized.
2. Terminology
The following terminology is used in this document.
AS: Autonomous System
BGP: Border Gateway Protocol
BGP hijacking : is the illegitimate takeover of groups of IP
addresses by corrupting Internet routing tables maintained using the
Border Gateway Protocol (BGP). (Sometimes referred to as prefix
hijacking, route hijacking or IP hijacking)
EBGP: External BGP
ISP: Internet Service Provider
3. Enhanced AS-Loop Detection for BGP Inbound Route Processing
This section proposes to enhance AS Loop Detection for BGP Inbound
Route Processing.
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As shown in Figure 3, when receiving the routes from AS64597, AS64596
should check whether its AS number is already in the AS-Path, If yes,
it further analyzes the location of the AS64596 in the received
AS_Path:
Case 1: AS 64596 is listed as Origin AS in the AS-Path
Lookup the local resource database (Such as ROA Cache) and determine
whether the route is originated from the AS 64596.
o Result 1: AS 64596 has no corresponding prefix; it is identified
as a purely forged AS_Path prefix hijacking event, which is
recorded as incident type 1.
o Result 2: The corresponding prefix is a sub-prefix of a certain
prefix of the AS 64596 and the AS 64596 has not advertise it. For
example, the prefix being hold by the AS 64596 is 10.10.128.0/17,
and the receiving route prefix is 10.10.192.0/24, the latter is a
sub-prefix of the former, which indicates that this is a forged
AS_Path sub-prefix hijacking event, which is recorded as incident
type 2.
o Result 3: The corresponding prefix is a sub-prefix of a certain
prefix of the AS 64596 and the AS 64596 has only advertised to
some special ASNs, and only wants it to be used internally by
those ASNs. The AS 64596 recognizes that At least one special AS
violates the route policy. Which is recorded as incident type 3.
o Result 4: The corresponding prefix is originated by the AS 64596,
this is the normal case.
Case 2: AS 64596 is listed as transit AS in the AS-Path
For example, AS-Path looks like the following form AS64596's
perspective:
(possible other AS), left AS, local AS(64596), right AS, (possible
other AS)
At this point, AS 64596 can lookup the local resource database and
check whether there is a real AS relationship between the local AS
and the left AS and the right AS. (From the perspective of the local
AS, it can manage/hold the AS-relationship database between the local
AS and each of its neighboring ASs (such as C2P, P2P, P2C, etc.).)
o Result 1: At least one of the AS ( the left AS or the right AS)
has no actual AS relationship with the local AS (i.e. A never
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before seen AS-AS adjacency). It is a purely forged AS_Path
prefix hijacking event. Which is recorded as incident type 4.
o Result 2: The AS relationships between the local AS and the left
AS and the right AS are correct, but the local AS has not
previously process this prefix , so it can be recognized that this
is a forged route. We classify this incident type as type 5.
o Result 3: The AS relationships between the AS and the left AS and
the right AS are correct, and the local AS 64596 has previously
processed the prefix, this is the normal case.
Enhanced AS-Loop-Detecting at this point
To identify the attack/forged information
|
|
v x.y.z.0/24 Origin AS 64600
AS64595---AS64596---AS64597---AS64598---AS64599----AS64600
Normal Case:
<-- x.y.z.0/24, AS-Path: 64597 64598 64599 64600
Forged Case 1:
<-- x.y.z.0/24, AS-Path: 64596 64595
(Or: 64597 64598 64596 etc.)
Forged Case 2:
<-- x.y.z.0/24, AS-Path: 64597 64596 64600
(Or: 64597 64596 64599 64600 etc.)
Figure 3: Enhance for BGP Inbound Route Processing
The local AS 64596 inputs the detected result to the route hijacking
management module, or/and records the log or/and the alarm
information, and the maintenance team of the local AS 64596 can
notify the maintenance team of the relevant AS to correct the error
in their networks .
After the above steps are added, the stability and security of the
network can be improved.
4. Enhanced AS-Loop Detection for BGP Outbound Route Processing
This section proposes to enhance AS Loop Detection for BGP Outbound
Route Processing.
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If Split-Horizon Enable, Enhanced AS-Loop-Detecting at this point
To identify the attack/forged information
|
|
v x.y.z.0/24 Origin AS 64600
AS64595---AS64596---AS64597---AS64598---AS64599----AS64600
Normal Case:
<-- x.y.z.0/24, AS-Path: 300 64598 64599 64600
Forged Case 1:
<-- x.y.z.0/24, AS-Path: 64597 64596
(Or: 64597 64598 64596 etc.)
Forged Case 2:
<-- x.y.z.0/24, AS-Path: 64597 64596 64600
(Or: 64597 64596 64599 64600 etc.)
Figure 4: Enhance for BGP Outbound Route Processing
As shown in Figure 4, when sending the routes from AS64597 to
AS64596, AS64597 will check whether the AS number 64596 is already in
the AS-Path, If yes, it can further analyzes the location of the
AS64596 in the received AS_Path:
The remaining processing steps are the same as the previous section.
5. Benefits
After the enhancements of the AS Loop Detection for BGP Inbound/
Outbound Route Processing are added, the stability and security of
the network can be improved.
6. Acknowledgements
The authors would like to acknowledge the review and inputs from Gang
Yan, Zhenbin Li, Aijun Wang, Jeff Haas, Robert Razsuk, Alexander
Asimov and the working group.
.
7. IANA Considerations
TBD.
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8. Security Considerations
TBD.
9. 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>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<https://www.rfc-editor.org/info/rfc4271>.
[RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
"Multiprotocol Extensions for BGP-4", RFC 4760,
DOI 10.17487/RFC4760, January 2007,
<https://www.rfc-editor.org/info/rfc4760>.
[RFC7854] Scudder, J., Ed., Fernando, R., and S. Stuart, "BGP
Monitoring Protocol (BMP)", RFC 7854,
DOI 10.17487/RFC7854, June 2016,
<https://www.rfc-editor.org/info/rfc7854>.
Authors' Addresses
Huanan Chen
China Telecom
109, West Zhongshan Road, Tianhe District
Guangzhou 510000
China
Email: chenhn8.gd@chinatelecom.cn
Di Ma
ZDNS
4 South 4th St. Zhongguancun
Beijing, Haidian
China
Email: madi@zdns.cn
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Yunan Gu
Huawei
Huawei Bld., No.156 Beiqing Rd.
Beijing 100095
China
Email: guyunan@huawei.com
Shunwan Zhuang
Huawei
Huawei Bld., No.156 Beiqing Rd.
Beijing 100095
China
Email: zhuangshunwan@huawei.com
Haibo Wang
Huawei
Huawei Bld., No.156 Beiqing Rd.
Beijing 100095
China
Email: rainsword.wang@huawei.com
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