BGP, from theory to practice - THE BOOK
[#]BGP process model explained in detail.
"The best paths determined by the BGP selection process are not necessarily installed in the #IP routing table (#RIB, Routing Information Base) and then transferred to the #FIB (Forwarding Information Base) to be used in traffic forwarding. Indeed, if the same prefix is announced to the #router via BGP and also in other ways (dynamic routing protocol, static routing, directly connected prefix), the router chooses which advertisement to install in the RIB, based on a level of preference assigned by the router to each routing protocol. Please be aware that the level of preference (known in #Cisco documents as administrative distance, or in #Juniper documents as preference value), is a number assigned locally by the router to each routing protocol, and expressing a level of preference for the protocol. For instance, let’s assume that a prefix Pfx is announced to the router both by BGP and by #OSPF. Which of the two protocols does the router consider more reliable? In other words, what information <Pfx, Next-Hop> will be installed in the RIB, the one announced by OSPF or the one announced by BGP? The rule used by all manufacturers is preferring the advertisement of the protocol with the lowest preference level. Note that preference level values are assigned by manufacturers according to different logics, and so it is common to see completely different numbers, which can be varied through a configuration, if needed."
The book will be available in the next weeks; I'll give a heads-up when ready.
Meanwhile, download the Table of contents and the first chapter here:
https://book.reissromoli.com/product/bgp-from-theory-to-practice/
my co-authors:
Tiziano Tofoni
Flavio Luciani
Many thanks to Simone Morandini for his precious help!
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