Secure Border Gateway Protocol (S-BGP): Real World Performance - - PowerPoint PPT Presentation

Secure Border Gateway Protocol (S-BGP): Real World Performance & Deployment Issues

Stephen Kent, Charles Lynn, Joanne Mikkelson, and Karen Seo

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Outline

 BGP Model  BGP security concerns & requirements  S-BGP design  S-BGP performance & scaling  Conclusions

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Basic BGP Model

DSP-A ISP-2 DSP-B Org-X Org-Z ISP-3 ISP-4 ISP-1 Org-Y DSP-C

non-BGP Router BGP Router

• path vector inter-domain routing protocol
• UPDATEs generated in response to loss of

connectivity or receipt of an UPDATE from a peer router, that results in a LOCRIB change

NAP

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The BGP Security Problem

 BGP is the critical infrastructure for Internet,

inter-domain routing

 Benign configuration errors have wreaked havoc

for portions of the Internet address space

 The current system is highly vulnerable to human

errors, as well as a wide range of attacks

 At best, BGP uses point-to-point keyed MAC, with

no automated key management

 Most published BGP security proposals have

been pedagogic, not detailed, not deployable

 Solutions must take into account Internet

topology, size, update rates, ...

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Attack Model

 BGP can be attacked in various ways

• active or passive wiretapping of communications links

between routers

• tampering with BGP speaker software
• tampering with router management data en route
• tampering with router management workstations/servers

(the last three can result in Byzantine failures)

 Addition of the proposed countermeasures

introduces a new concern

• compromise of secret/private keying material in the routers or

in the management infrastructure

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BGP Security Requirements

 Verification of address space “ownership”  Authentication of Autonomous Systems (AS)  Router authentication and authorization

(relative to an AS)

 Route and address advertisement authorization  Route withdrawal authorization  Integrity and authenticity of all BGP traffic on

the wire

 Timeliness of BGP traffic

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S-BGP Design Overview

 IPsec: authenticity and integrity of peer-to-peer

communication, automated key management

 Public Key Infrastructures (PKIs): secure

identification of BGP speakers and of owners of AS’s and of address blocks

 Attestations --> authorization of the subject (by

the issuer) to advertise specified address blocks

 Validation of UPDATEs based on a new path

attribute, using certificates and attestations

 Distribution of countermeasure data: certificates,

CRLs, attestations

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S-BGP Residual Vulnerabilities

 Failure to advertise route withdrawal  Premature re-advertisement of withdrawn routes  Erroneous application of local policy  Erroneous traffic forwarding, bogus traffic

generation, etc. (not really a BGP issue)

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Internet Address Space Ownership

DSP-A ORG-X ORG-Z ISP-2 DSP-D DSP-B ORG-XX ISP-1 DSP-C ORG-YY ICANN/IANA ARIN/RIPE/APNIC ORG-Y ORG-ZZ

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Simplified PKI for Address Blocks

ICANN All Addr blocks APNIC Addr blocks ARIN Addr blocks GTE-I Addr block(s) RIPE Addr blocks AT&T Addr block(s) DSP 1 Addr block(s) ISP 2 Addr block(s) MCI Addr block(s) DSP 3 Addr block(s) Subscriber A Addr block(s) Subscriber B Addr block(s) ISP 4 Addr block(s) Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ ҐҐ ҐҐ Ґ ҐҐҐ Ґ Ґ Ґ ICANN All Addr blocks APNIC Addr blocks ARIN Addr blocks GTE-I Addr block(s) RIPE Addr blocks AT&T Addr block(s) DSP 1 Addr block(s) ISP 2 Addr block(s) MCI Addr block(s) DSP 3 Addr block(s) Subscriber A Addr block(s) Subscriber B Addr block(s) ISP 4 Addr block(s) Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ Ґ ҐҐ Ґ ҐҐ ҐҐ Ґ ҐҐ Ґ ҐҐҐ ҐҐҐ Ґ Ґ Ґ Ґ Ґ Ґ

• Only networks that execute BGP need certificates
• All ISPs are BGP users, but only about ~10% of DSPs,

maybe 5% of subscribers, are BGP users

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PKI for Speaker ID & AS Assignment

ICANN All AS Numbers APNIC AS Numbers ARIN AS Numbers GTE-I AS Numbers RIPE AS Numbers AT&T AS Numbers DSP 1 AS# W ISP 2 AS Numbers MCI AS Numbers AS# X DSP 3 AS# Y Routers in AS# X AS# X, Router BGP ID ISP 4 AS# Z

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AS# Y Routers in AS# Y AS# Y, Router BGP ID AS# Z Routers in AS# Z AS# Z, Router BGP ID

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ICANN All AS Numbers APNIC AS Numbers ARIN AS Numbers GTE-I AS Numbers RIPE AS Numbers AT&T AS Numbers DSP 1 AS# W ISP 2 AS Numbers MCI AS Numbers AS# X DSP 3 AS# Y Routers in AS# X AS# X, Router BGP I ISP 4 AS# Z

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AS# Y Routers in AS# Y AS# Y, Router BGP I AS# Z Routers in AS# Z AS# Z, Router BGP I

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Securing UPDATE messages

 A secure UPDATE consists of an UPDATE

message with a new, optional, transitive path attribute for route authorization

 This attribute consists of a signed sequence of

route attestations, nominally terminating in an address space attestation

 This attribute is structured to support both route

aggregation and AS sets

 Validation of the attribute verifies that the route

was authorized by each AS along the path and by the ultimate address space owner

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An UPDATE with Attestations

BGP Header Addr Blks of Rtes Being Withdrawn BGP Path Attributes Dest Addr Blks (NLRI) Attribute Header Route Attestations Attestation Header Issuer Certificate ID Algorithm ID & Signature Signed Info Validity Dates Subject AS Path Info Other Protected Path Attributes NLRI Info Signed Information Route Attestation Path Attribute for Attestations UPDATE Message

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Simplified Attribute Format

AA: Owning Org, NLRI, first Hop AS, SIG RA: Issuer, Cert ID, Validity, Subject, Path, NLRI, SIG BGP Hdr: Withdrawn NLRI, Path Attributes, Dest. NLRI RA: Issuer, Cert ID, Validity, Subject, Path, NLRI, SIG RA: Issuer, Cert ID, Validity, Subject, Path, NLRI, SIG (usually omitted)

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Distributing Certificates, CRLs, & AAs

 Putting certificates & CRLs in UPDATEs would

be redundant and make UPDATEs too big

 Same is true for address attestations  Solution: use servers for these data items

• replicate for redundancy & scalability
• locate at NAPs for direct (non-routed) access
• download options:

– whole certificate/AA/CRL databases – queries for specific certificates/AAs/CRLs

 To minimize processing & storage overhead,

NOCs should validate certificates & AAs, and send processed extracts to routers

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Distributing Route Attestations

 Distributed with BGP UPDATEs as path attributes  RAs have implicit encoding option to reduce size,

avoid exceeding UPDATE size limit (4096b)

 Cache with associated routes in ADJ-RIBs to

reduce validation overhead

 Expiration date present, but no revocation

mechanism chosen yet

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BGP Statistics

 ~ 1,800 organizations own AS numbers  ~ 44,000 own address prefixes (NLRI)  ~ 7,500 BGP speakers  ~ 75,000 routes in an ISP BGP database  Few AS sets (~100), little address aggregation  Average path length (NAP perspective) is 2.6

hops; 50% of routes ≤ 2 hops, 96% ≤4 hops

 ~ 43,000 UPDATEs received each day at a BGP

speaker at a NAP (30 peers)

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S-BGP Storage Statistics

 ~ 58,000 certificates in database (~550b each)  Certificate & CRL database ~35Mb  Address attestation database ~4 Mbytes  Extracted certificate & AA database (with data

structure overhead in GateD) ~ 42Mb

 Route attestations occupy ~16 Mb per ADJ-RIB:

about 64 Mb (4 peers) to 480 Mb (at NAP)

 ADJ-RIB caching for received UPDATEs

increases storage requirements by about 50%, and yields about 58% validation savings

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Route Attestation Overhead

 Transmission

• RAs add ~450 bytes to a typical (3.6 ASes in path) UPDATE
• f 63 bytes, 700% overhead!
• But UPDATEs represent a very small portion of all traffic, so

steady state bandwidth for RA transmission is only ~ 1.4Kb/s

 Processing

• Average of 3.6 signature validations per received UPDATE

and 1 generation per emitted UPDATE

• Peak rates ~ 18/s validation and ~5/s generation w/o caching

(peak estimated as ten times average)

• UPDATE caching reduces validation rate by ~50%
• Start up transient would overwhelm a speaker, thus some

form of NV storage or heuristic is required

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Conclusions

 The transmission and processing costs of S-BGP

are not significant

 The proposed distribution mechanisms for

certificates, CRLs, and AAs is viable

 Storage overhead exceeds the capacity of existing

routers, but adding adequate storage is feasible, especially for ISP BGP speakers

 Testing and deployment issues

• Cisco handling of optional, transitive path attributes
• Intra-domain distribution of S-BGP attribute

 But deployment poses a chicken and egg problem!