Lab Course “RouterLab” BGP - Border Gateway Protocol (RFC 4271) Some of the slides come from: http://www.ietf.org/proceedings/07dec/slides/IDRTut-0.pdf 1
Miscellaneous • Anything that needs discussion? BGP 2
Miscellaneous • Anything that needs discussion? SUBMIT YOUR CONFIG FILES, TRACES, COMMAND DUMP!!! BGP 2
Internet Routing • There is no single.... - Routing Protocol - Routing Configuration - Routing State, - Routing Management • ....... for the entire Internet! • Routing System is a collection of many components hopefully operating in a consistent manner BGP 3
Internet Routing • Distance Vector • Link State - I tell you all my “best” - I announce to everyone routes for all about my links and the destinations that I addresses I originate on know and you tell me each link and listen to yours. everyone ʼ s announcement. - Build simplified - Build full topology topology from local perspective - E.g. OSPF - E.g. RIP BGP 4
Internet Routing • The Routing Architecture uses a 2-level hierarchy, based on the concept of a routing domain ( Autonomous System - AS) • An AS is an interconnected network with a single exposed topology, a coherent routing policy, and a consistent metric framework • Within an AS: Interior Gateway Protocols - IGP • Among ASes: Exterior Gateway Protocols - EGP BGP 5
IGPs and EGPs • IGPs - Distance Vector: RIP, IGRP, EIGRP - Link State: OSPF, IS-IS • EGPs - Distance Vector: (EGP, BGPv3) BGPv4 BGP 6
RIP/OSPF RIP/OSPF RIP/OSPF What the Internet looks like! AS1 AS666 IS-IS/OSPF RIP/OSPF AS3 OSPF AS2 OSPF AS7 IS-IS EGP RIP AS69 IGP BGP 7
Why BGP? ! Simple protocol to implement and operate ! Very simple distance metric ! Occludes local policies from external inspection ! Limited inter-SP coordination required ! Mature deployment Source: http://www.ietf.org/proceedings/07dec/slides/IDRTut-0.pdf BGP 8
Why BGP? ! Simple protocol to implement and So simple that to have full knowledge you should read 15 RFCs (~400 Pages!) operate ■ RFC 4271, A Border Gateway Protocol 4 (BGP-4) ■ ! Very simple distance metric RFC 4456, BGP Route Reflection - An Alternative to Full Mesh Internal BGP (IBGP) ■ RFC 4278, Standards Maturity Variance ! Occludes local policies from external Regarding the TCP MD5 Signature Option (RFC 2385) and the BGP-4 Specification inspection ■ RFC 4277, Experience with the BGP-4 Protocol ! Limited inter-SP coordination required ■ RFC 4276, BGP-4 Implementation Report ■ RFC 4275, BGP-4 MIB Implementation Survey ■ ! Mature deployment RFC 4274, BGP-4 Protocol Analysis ■ RFC 4273, Definitions of Managed Objects for BGP-4 ■ RFC 4272, BGP Security Vulnerabilities Analysis ■ RFC 3392, Capabilities Advertisement with BGP-4 ■ RFC 5065, Autonomous System Confederations for BGP ■ RFC 2918, Route Refresh Capability for BGP-4 ■ RFC 1772, Application of the Border Gateway Protocol in the Internet Protocol (BGP-4) using SMIv2 ■ RFC 4893, BGP Support for Four-octet AS Number Space Source: http://www.ietf.org/proceedings/07dec/slides/IDRTut-0.pdf BGP 8
Why BGP? ! Simple protocol to implement and operate AS-Path, which is a variation of the ! Very simple distance metric Distance-Vector Algorithm. ! Occludes local policies from external Guess what: it still doesn’t scale!!! inspection ! Limited inter-SP coordination required ! Mature deployment Source: http://www.ietf.org/proceedings/07dec/slides/IDRTut-0.pdf BGP 8
Why BGP? ! Simple protocol to implement and operate ! Very simple distance metric ! Occludes local policies from external Consequence of the Distance-Vector Algorithm. inspection ! Limited inter-SP coordination required ! Mature deployment Source: http://www.ietf.org/proceedings/07dec/slides/IDRTut-0.pdf BGP 8
Why BGP? ! Simple protocol to implement and operate ! Very simple distance metric ! Occludes local policies from external inspection ! Limited inter-SP coordination required BGP sessions are statically set up and manually managed, is this “limited inter- SP” coordination? ! Mature deployment Well.... they can do dirty things in the route selection process without the need to talk to each other! (You will do it in the worksheet) Source: http://www.ietf.org/proceedings/07dec/slides/IDRTut-0.pdf BGP 8
Why BGP? ! Simple protocol to implement and operate ! Very simple distance metric ! Occludes local policies from external inspection ! Limited inter-SP coordination required On this they are right! It is the “De ! Mature deployment Facto” Standard. Source: http://www.ietf.org/proceedings/07dec/slides/IDRTut-0.pdf BGP 8
BGP Basics • BGP obtains route to prefixes from neighboring ASes • BGP Propagate “best” routes to other neighbors - “best” depends on policies that depend on neighbors business relationship (customer-provider model, peering) • Each BGP routing object is a Prefix and a set of attributes: - <AS Path vector, Origin, Next Hop, Local Pref, …> ‣ AS Path Vector is a vector of AS identifiers that form a viable path - Used for loop prevention and best-path selection BGP 9
RIP/OSPF RIP/OSPF RIP/OSPF Prefix Announcements AS1 AS666 AS3 AS2 AS7 10.0.0.0/8 AS69 BGP 10
RIP/OSPF RIP/OSPF RIP/OSPF Prefix Announcements AS1 AS666 AS3 AS2 10.0.0.0/8 AS7 AS7 10.0.0.0/8 10.0.0.0/8 AS69 AS7 BGP 10
RIP/OSPF RIP/OSPF RIP/OSPF Prefix Announcements 10.0.0.0/8 AS2 AS7 AS1 AS666 10.0.0.0/8 AS2 AS7 10.0.0.0/8 AS3 AS7 AS3 AS2 10.0.0.0/8 AS7 AS7 10.0.0.0/8 10.0.0.0/8 AS69 AS7 BGP 10
RIP/OSPF RIP/OSPF RIP/OSPF Prefix Announcements 10.0.0.0/8 10.0.0.0/8 AS1 AS2 AS7 AS2 AS7 AS1 AS666 10.0.0.0/8 AS2 AS7 10.0.0.0/8 AS3 AS7 AS3 AS2 10.0.0.0/8 AS7 AS7 10.0.0.0/8 10.0.0.0/8 AS69 AS7 BGP 10
RIP/OSPF RIP/OSPF RIP/OSPF Prefix Announcements 10.0.0.0/8 10.0.0.0/8 AS1 AS2 AS7 AS2 AS7 AS1 AS666 Prefix AS Path * 10.0.0.0/8 AS3 AS7 10.0.0.0/8 AS1 AS2 AS7 10.0.0.0/8 AS2 AS7 10.0.0.0/8 AS3 AS7 AS3 AS2 10.0.0.0/8 AS7 AS7 10.0.0.0/8 10.0.0.0/8 AS69 AS7 BGP 10
BGP = DV Protocol • Maintains a collection of local best paths for all advertised prefixes • Passes changes to all neighbors containing: - One single best-path for each prefix - Only incremental updates never a full dump (unless opening the session or other specific events) • Changes reflect only events in the local database: - New reachability information to a prefix (update) - Reachability information lost for a prefix (withdraw) BGP 11
BGP Messages • Peers exchange messages over TCP sessions - Port:179 - Can span several physical links • OPEN - Open TCP Connection - Authenticate peers • UPDATE - Advertises new paths - Withdraw old paths - Carry all the attributes of the path BGP 12
BGP Messages • KEEPALIVE - Keeps connection alive in the absence of updates - Otherwise connection is reset due to inactivity • NOTIFICATION - Reports errors in previous messages - Used to close a session • ROUTE_REFRESH - Request for full routing information without breaking TCP connection - There are BGP sessions that have lasted years! BGP 13
BGP Messages over TCP • BGP is not a byte stream protocol like TCP • The byte stream is divided into messages using BGP-defined markers • Each message is a standalone protocol element • Maximum message size: 4096 bytes BGP 14
Path Attributes (I) • Origin - How this route was injected into BGP in the first place • Next_hop - Exit border router • Multi-Exit-Discriminator - Preference between 2 or more sessions among the same AS pair • Local-Pref - Local preference setting BGP 15
Path Attributes (II) • Atomic Aggregate - The path is the result of aggregation • Aggregator - ID of proxy aggregator • Community - Locally defined information field • Destination-Pref - Preference setting for remote AS BGP 16
RIP/OSPF RIP/OSPF RIP/OSPF Local_Pref AS1 AS666 Prefix AS Path * 10.0.0.0/8 AS3 AS7 10.0.0.0/8 AS1 AS2 AS7 AS3 AS2 AS7 10.0.0.0/8 AS69 BGP 17
RIP/OSPF RIP/OSPF RIP/OSPF Local_Pref AS1 AS666 Prefix AS Path LP Prefix AS Path 10.0.0.0/8 AS3 AS7 10 * 10.0.0.0/8 AS3 AS7 * 10.0.0.0/8 AS1 AS2 AS7 20 10.0.0.0/8 AS1 AS2 AS7 AS3 AS2 AS7 10.0.0.0/8 AS69 BGP 17
RIP/OSPF RIP/OSPF RIP/OSPF Peering & C-P Relationship AS1 $$ AS666 = $$ $$ Prefix AS Path LP 10.0.0.0/8 AS3 AS7 10 * 10.0.0.0/8 AS1 AS2 AS7 20 AS3 AS2 $$ $$ AS7 10.0.0.0/8 AS69 $$ Customer- Provider = Peering BGP 18
RIP/OSPF RIP/OSPF RIP/OSPF MED Example 10.0.0.0/8 MED 10 11.0.0.0/8 MED 20 10.0.0.0/8 AS2 AS1 AS666 11.0.0.0/8 10.0.0.0/8 MED 20 11.0.0.0/8 MED 10 AS2 Text AS3 AS2 AS7 AS69 BGP 19
eBGP and iBGP • eBGP is used across AS boundaries • To synchronize all eBGP speakers of an AS iBGP is used • iBGP sessions are manually configured • iBGP needs a full mesh (or at least a flooding hierarchy - Route Reflectors) • iBGP does not detect loops • iBGP does not prepend AS number BGP 20
iBGP eBGP iBGP BGP 21
iBGP eBGP iBGP BGP 21
iBGP + RR Route-Reflector eBGP iBGP BGP 22
Anything Missing? BGP 23
Recommend
More recommend
