Nugget 20
BGP Routing - Implementing Basic BGP 1

An Autonomous System (AS) is the foundation of everything ,it represents the networks under
1 authority.


There are public AS's and private AS's

IBGP = a relationship between 2 BGP speakers in the  same AS
EBGP = is used when the two routers are different AS's (like the BGP relationship you would have if you were to peer with your ISP)

NEED to make mind change, as neighbours are now redefined .... as opposed to how we think of them with other routing protocols

Neighbours DONT have to be directly connected! they can form through routers! becuase BGP rides ONTOP of your existing network infastructure...say OSPF/EIGRP etc

USUALLY BGP does NOT REPLACE an internal routing protocol, it really is used to establish relationships with the outside world.

Thru this relationship the ISPs can exchange routes via you, so this means they end up using you as a path to reach each the other ISP (so you are a transit AS)

You can solve this by redistribution, but interior routing protocols are not designed to handle hundreds of megabyte's of routing tables, OSPF wont handle it etc ... so although this is not WISE, you can do this if you redistribute a small subset of networks

You could also bring up a WAN link between these two routers (IBGP) to directly connect them to solve this problem .... or you could run BGP on the other router ... but this needs to be able to support the hardware requirements etc ...

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!