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

• Interior Automatic discovery

Generally trust your IGP routers

Routes go to all IGP routers

• Exterior Specifically configured peers

Connecting with outside networks

Set administrative boundaries

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 0 ∞ ∞ ∞ ∞

1 0 -1 4 ∞ ∞

2 0 -1 2 1 1

4 0 -1 2 -2 1

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 100

AS 101B

A

Stub Network

• Point default towards the ISP

• ISP advertises the stub network

• Policy confined within ISP policy

BGP AS Types :Multi-Homed AS

AS 100

AS 200

AS 300

D

CB

A

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

BGP AS : TransitAS 100 AS 200

AS 400

AS 300

F

E

D

G

H

CB

A

Transit AS

• IBGP used to carry exterior routes

• IGP carries local information only

• Full IBGP mesh is required

• Mainly uses by service proviers

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

2) 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

Size of routing table in IPV6 world

Rouge routing table

• Solutions :

Aggregation Proxies

DNS like lookup System

Loc/ID separation Protocol (LISP) , CISCO