Nugget 19
BGP Routing - Foundation Concepts and Planning

NOTES:
The BGP series - CCIP/CCIE focuses on the cloud in BGP
whereas this series CCNP focuses on us, the customer/corporate SME/SMB

usually when running routing protocols people focus on the routes and traffic
outbound! but with BGP the main concern/focus is inbound

email/web servers , not to worried about peeps surfing web/vpn etc

organisations want redundancy so that people accessing the incoming corporate
infrastructure


How it works
You get a public block
advertise route out to both isps, then that is flooded to rest of community
if isp is unavailble then other isp has peer with with another isp


2 uses
BGP = typical aim is to make ur company redutant
BGP = shortest paths to destinations (even though bandwidth the same, maybe less hops)

Equals multihoming

NOTES ABOUT THE FACTS
Most routing protocols we have looked at so far, OSPF, EIGRP they are their own layer 4 protocol and have own reliability mechanisms ....

BGP runs on top of TCP (port 179) ... TCP already has its own reliability (ACks) so BGP uses these when sending updates, if not recieved, BGP will resend the update ..typical TCP behaviour)

METRIC - compound metric very tuneable - BGP attributes (10 or so) it goes through these attributes looking for something to break the tie.


SLOWEST PROTOCOL to converge (u can but dont!!!... well, you can use iBGP)
why use it, think of how many networks/routers a second go down on the internet ... loads and all the time! this would swarm us in chaos with updates!!!


STYLES of BGP


DEFAULT ROUTE ONLY BGP implementation

PARTIAL routing table BGP implementation

FULL routing table BGP implementation
You need a router beefy enough to hold the full routing table of the internet TWICE! if multihoming with x2 isps (like 100 odd MB each or 300MB if x3 ISPS ... etc)

although only x1 route will go into the routing table, the router still maintains the other routes in the BGP table

This is the most flexible approach and you can really shape your network to how you want it, BUT it is the most resource consuming too!