Bgp protocol
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BGP is the exterior gateway protocol that connects different autonomous systems on the internet. It allows for the exchange of routing and reachability information between these systems. BGP operates using a finite state machine to manage the states of connections between peers. It establishes TCP connections between routers to exchange routing updates and keep connections alive through regular keepalive messages. BGP version 4, defined in RFC 4271, is the current standard implementation which supports features like classless inter-domain routing and route aggregation.
Bgp protocol
- 2. Contents • Introduction • IGP • eGP • Current Version • Uses • Operation • Route map mechanisms • Extension negotiation • FSM • Problems and Mitigation
- 3. Introduction • BGP- Border Gateway Protocol. • It makes internet work. • Standardized exterior gateway protocol. • Designed to exchange routing and reach ability of info b/w autonomous systems. • Often classified as a path vector protocol. • BGP makes routing decisions based on paths , n/w policies or rule – sets configured by a n/w administrator & is involved in making core routing decisions.
- 4. Continued…. • BGP makes use of routing within an autonomous system(AS). • It is one the most complex and difficult to configure protocol but its emphasis on security and scalability makes its usage essential.
- 5. Interior Gateway Protocol • Used for exchanging info between gateways( routers) within an autonomous system. • This routing info can then be used to route network layer protocols like IP. • IGP can divided into 2 categories- link state routing protocols and distance vector routing protocol. • Examples of IGP – RIP, OSPF, IS-IS.
- 6. Exterior Gateway Protocol • Protocol for exchanging info between two neighbor gateway hosts in a network of autonomous systems. • Commonly used between hosts on the internet to exchange routing table information. • BGP is an example of EGP
- 8. Current Version • Present version of BGP is version 4(BGP4) codified in RFC 4271 since 2006. • Earlier versions of protocol considered obsolete & rarely supported. • RFC 4271 went through more than 20 drafts is based on RFC 1771 version 4.
- 9. Continued… • RFC 4271 corrected a no. of errors, clarified ambiguities & brought RFC closer to industrial practices. • Major improvement brought by version 4 is support for classless inter domain routing and use of route aggregation to reduce size of routing tables .
- 10. Uses • Most ISP must use BGP to establish routing b/w one another ( specially if multi homed). • Very large private IP n/w use BGP internally. • Another to use BGP is multi homing a n/w for better redundancy, either to multiple access points of a single ISP or to multiple ISP’s .
- 11. Operation • BGP’s neighbors called peers are established by manual configuration b/w routers to create a tcp session on port . • A bgp speaker sends 19byte keep alive messages after every 60 sec to maintain connection. • If BGP runs b/w two peers in the same autonomous system it is called internal bgp and when among different autonomous systems then called external bgp.
- 13. • RTA# • router bgp 100 neighbor 129.213.1.1 remote- as 200 • RTB# • router bgp 200 neighbor 129.213.1.2 remote- as 100 neighbor 175.220.1.2 remote-as 200 • RTC# • router bgp 200 neighbor 175.220.212.1 remote-as 200
- 14. • Border/Edge routers- routers on boundary of one AS exchanging info with another AS, typically connected directly while iBGP peers can be interconnected through other intermediate routers. • The main difference in iBGP and eBGP peering is way the routes received from peer is propagated to other peers.
- 17. Route map mechanisms • Helps in filtering routes from peers • Transformation of routes before redistribution to peers and plumbing them in routing tables. • These are basic rules which allow to apply certain actions to routes matching a certain criteria on ingress or egress path. • These rules specify whether to drop or modify a route.
- 18. Finite –State machines • To make decisions in its operations with peers, a bgp uses a simple FSM. • FSM has six states • Idle • Connect • Active • Open sent • Open confirm • Established
- 19. • For each peer-to-peer session, a BGP implementation maintains a state variable that tracks which of these six states the session is in. • The BGP defines the messages that each peer should exchange in order to change the session from one state to another. The first state is the "Idle" state. • In the "Idle" state, BGP initializes all resources, refuses all inbound BGP connection attempts and initiates a TCP connection to the peer. The second state is "Connect".
- 20. • In the "Connect" state, the router waits for the TCP connection to complete and transitions to the "Open Sent" state if successful. If unsuccessful, it starts the Connect Retry timer and transitions to the "Active" state upon expiration. • In the "Active" state, the router resets the Connect Retry timer to zero and returns to the "Connect" state. • In the "Open Sent" state, the router sends an Open message and waits for one in return in order to transition to the "Open Confirm" state. • Keep alive messages are exchanged and, upon successful receipt, the router is placed into the "Established" state. • In the "Established" state, the router can send/receive: Keep alive; Update; and Notification messages to/from its peer.
- 23. BGP Problems and mitigation • Internal BGP scalability- route reflectors and confederations are a solution. • Instability- caused by route flapping the solution is route flap damping • Routing Table Growth • Load balancing Problem • Security Issues
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