1. Boarder Gateway Protocol (BGP)
Presented By
Jasim Alam

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

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

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

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

6. 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

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

8. 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 bytes to send without acknowledgement.
1000 bytes -> 65 bytes allowed
Metric “ BGP attributes” . Massive, most tunable. Consider 18 different factors to break tie.

9. 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

10. 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

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

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

13. 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

14. 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)

15. BGP Routing Table show ip bgp
BGP table version is , local router ID is
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
. . .
*>i i
*>i i
*>i i
*>i i
*>i i
*>i i
*>i i
*>i i
*>i i
*>i / i

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

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

18. BGP AS Types :Multi-Homed ASC B A 42

19. 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

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

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

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

23. 2 byte & 4 byte Comp ability
1) Asplain -= Plain Decimal
Asdot + Break
>
> 1.0
> 1.1
> ( 5* )

24. 2 byte & 4 byte Comp ability
3) Asdot : Mixture of Asplain and Asdot > > 1.0

25. 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

26. 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