BGP is digit of the most Byzantine topics you'll think when pursuing your CCNP, if not the most complex. I undergo from individualized undergo that when I was earning my CCNP, BGP is the matter that gave me the most pain at first. One abstract I ready reminding today's CCNP candidates about, though, is that no Cisco profession is impracticable to wager if you meet fortuity it downbound and wager the principle before you move disagreeable to wager the more Byzantine configurations.
BGP attributes are digit much topic. You've got well-known mandatory, well-known discretionary, transitive, and non-transitive. Then you've got apiece individualist BGP concept to remember, and the meet in which BGP considers attributes, and what attributes modify are... and a aggregation more! As with whatever another Cisco topic, we hit to achievement before we crapper run. Let's verify a countenance at what attributes are and what they do in BGP.
BGP attributes are much same what poetics are to OSPF, RIP, IGRP, and EIGRP. You won't wager them traded in a routing table, but attributes are what BGP considers when choosing the prizewinning line to a instruction when binary legal (loop-free) paths exist.
When BGP has to end between much paths, there is an meet in which BGP considers the line attributes. For success on the CCNP exams, you requirement to undergo this order. BGP looks at line attributes in this order:
Highest coefficient (Cisco-proprietary BGP value)
Highest topical alternative (LOCALPREF)
Prefer locally originated route.
Shortest ASPATH is preferred.
Choose line with minimal lineage code. Internal paths are desirable over outside paths, and outside paths are desirable over paths with an lineage of incomplete.
Lowest multi-exit someone (MED)
External BGP routes desirable over Internal BGP routes.
If no outside route, superior line with minimal IGP outlay to the next-hop router for iBGP.
Choose most past route.
Choose minimal BGP RID (Router ID).
If you don't undergo what these values are, or how they're configured, don't panic! The incoming individual parts of this BGP tutorial module vindicate it all. So pay whatever instance studying this order, and in conception II of this liberated BGP tutorial, we'll countenance at apiece of these values in detail. Keep studying!
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