Boarder Gateway Protocol (BGP) Presented By Jasim Alam jasim21@ymail.com

Overview Terminologies BGP Main Characteristics Algorithm overview Message Overview AS Types ASN , Compatibility Future Q &A

What is Protocol ? Set of rules Common language Internet Engineering Task Force (IETF) ,1986, 1993 Request for Comment (RFC) -> Internet Standard (STD)

Autonomous System (AS) Automatic, Self-Directed Collection of IP routing prefixes Centralized control ( can be multiple) Single or multiple routing protocol

IGP Interior Gateway Protocol Within an Autonomous System Carries information about internal prefixes Examples—OSPF, EIGRP , IGRP, RIP

Interior vs. Exterior Routing Protocols Specifically configured peers Connecting with outside networks Set administrative boundaries Interior Automatic discovery Generally trust your IGP routers Routes go to all IGP routers 10

EGP Exterior Gateway Protocol (EGP), RFC 827, 1982 BGP, RFC 1105, 1985. Current BGP 4 , 1997 AS, Scalability

BGP :Main Attributes Only EGP Unlike EIGRP/OSPF runs over TCP ( port 179) EIGRP/OSPF use one-to-one window, transmission after acknowledgement. More than 120,000 internet routers 16 bit TCP windows allow up to 65535 bytes to send without acknowledgement. 1000 bytes -> 65 bytes allowed Metric “ BGP attributes” . Massive, most tunable. Consider 18 different factors to break tie.

Main Attributes (Contd.) Slowest to converge . BGP table size more than 100 MB. Thousands updates in every seconds. Uses distance vector routing. Without tuning act like RIP

Algorithm Overview Based on Distance – Vector routing (Bellman Ford Algorithm). Also known as “ Vector Path Selection” Can detect negative edges but can’t work on negative cycle. Less smarter in IGP than Link State (Dijkstra Algorithm) Works on relaxation of edges O (V,E) Protocols : RIP, EIGRP, BGP

Algorithm Overview (contd.) Seconds A B C D E  0  ∞ 1 -1 4 2 -2

BGP Message :Header Marker : Detect loss in synchronization, authentication when enabled Length : Indicate length of marker Type : Indicate message type

BGP Message :Type 1) Open : Hello message 2) Update : Incremental 3) Notification : Notify errors 4) Keep Alive : Only sends 19 byte message header. 1 second <, default : 60 seconds, 1/3 hold time

BGP Message : Open Message Version : BGP version My Autonomous Number : ASN Hold time : session time. Default 180 seconds. At least 3 seconds. BGP Identifier : Origin router info ( IP and others)

BGP Routing Table show ip bgp BGP table version is 111849680, local router ID is 203.62.248.4 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal Origin codes: i - IGP, e - EGP, ? - incomplete Network Next Hop Metric LocPrf Weight Path . . . *>i192.35.25.0 134.159.0.1 50 0 16779 1 701 703 i *>i192.35.29.0 166.49.251.25 50 0 5727 7018 14541 i *>i192.35.35.0 134.159.0.1 50 0 16779 1 701 1744 i *>i192.35.37.0 134.159.0.1 50 0 16779 1 3561 i *>i192.35.39.0 134.159.0.3 50 0 16779 1 701 80 i *>i192.35.44.0 166.49.251.25 50 0 5727 7018 1785 i *>i192.35.48.0 203.62.248.34 55 0 16779 209 7843 225 225 225 225 225 i *>i192.35.49.0 203.62.248.34 55 0 16779 209 7843 225 225 225 225 225 i *>i192.35.50.0 203.62.248.34 55 0 16779 3549 714 714 714 i *>i192.35.51.0/25 203.62.248.34 55 0 16779 3549 14744 14744 14744 14744 14744 14744 14744 14744 i

BGP AS Types : Stub AS 101 B A AS 100 40

Stub Network Point default towards the ISP ISP advertises the stub network Policy confined within ISP policy 41

BGP AS Types :Multi-Homed AS C B A 42

Multihomed AS Internal BGP used with IGP IBGP only between border gateways Only border gateways speak BGP Exterior routes must be redistributed into IGP or use defaults 7

BGP AS : Transit AS 100 AS 200 A H B C AS 300 D F E G AS 400 49

Transit AS IBGP used to carry exterior routes IGP carries local information only Full IBGP mesh is required Mainly uses by service proviers 7

Autonomous System Numbering (ASN) Provided by Internet Assigned Number Authority (IANA), distributed by Regional Internet Registers (RIRs) - 6 16 bit ( 0- 65535) RFC 4893, 32 bit, 429 core, 2007 Up to mid 2014 distributed 49150. Only 23.8% available Helps – Path selection ( As_path) , detect loops, resolve routing aggregation,

2 byte & 4 byte Comp ability 1) Asplain -= Plain Decimal Asdot + Break 65000 -> 0.65000 655356 -> 1.0 655357 -> 1.1 327700 -> 5.20 ( 5* 65536 +20)

2 byte & 4 byte Comp ability 3) Asdot : Mixture of Asplain and Asdot 65532 -> 65532 65536 -> 1.0

Neighbor , Path & Community Compatibility BGP capability Advertisement ( 4 bytes ) AS-Trans ( reserved 2 byte ASN 23456) Old AS may see multiple AS-Trans in path. May create loop 4 bytes ( EXT_COMM) community

Looking Future Problems Solutions : Size of routing table in IPV6 world Rouge routing table Solutions : Aggregation Proxies DNS like lookup System Loc/ID separation Protocol (LISP) , CISCO