BGP Prefix lists are important for their high flexibility, support for incremental updates, and that writing BGP Prefix lists are much more efficient than writing ACL's that filter BGP updates as BGP tables can have much more content (thousands of entries) in them as compared to IGP's route tables. They have some similarities to ACL's … Continue reading Prefix-Lists and BGP, fundamentals and configuration explained, important behaviors and more to know for exam day!
A router configure to be a BGP Route Reflector can take a route learned from one iBGP Peer and advertise it to another iBGP Peer, which basically is the equivalent of "no ip split-horizon" only BGP style! iBGP Peers that send routes to the route reflector are called "clients", and when the Reflector receives routes … Continue reading BGP Route Reflector configuration, explanation / need for them, and important behaviors / verification commands!
Same Topology, only this time I added a second logical network between R3 and R4 by creating 2 loopback interfaces in the same subnet 126.96.36.199 /24, and removed the previous "All or none" configuration for Local Preference. So first I want to review R2 and R1 to see if their ip bgp tables look correct: … Continue reading Local Preference Part 2: Configuring the “Some but not all” local preference attribute, behaviors, and explanations!
So as can be seen, once again we've ditched the NBMA as this Topology of a shared Ethernet segment will better illustrate Local Preference explanation, behaviors, etc. ***For labbing example purposes I want to point out there is another link in the above Topology, R3-R4 is connected by the Fa0/1 link on the network 188.8.131.52 … Continue reading The Local Preference attribute explained, and the ‘All or nothing’ way of configuring it and behaviors explained!
So as can be seen we have no NBMA in this topology, only Serial Links and an Ethernet segment, which almost makes feel naked without a Frame-Switch in there somewhere. So to begin, my last post included on the tail end a "sh ip bgp" to demonstrate something with a bunch of loopbacks being advertied … Continue reading BGP – The Multi-Exit Discriminator (MED) / Metric explained, configured, and we see some old friends ACL’s and Route-Maps to help accomplish the goal!
We are back with this Topology I believe once more before we switch gears and leave Path and Attribute discussion alone for a bit. One quick real world note, I fired up my lab and I was missing R4's loopback network / Peering across all routers, and I started troubleshooting when I stopped and saw … Continue reading BGP Best-Path selection process examined given its criteria for selection, IMPORTANT behaviors of iBGP vs eBGP, Next-Hop examined in detail, and more!
^ I created this mid-session, but put it here as well as I like to illustrate the struggle at the beginning of the post 🙂 There are 3 well-known and mandatory attributes a BGP Speaker includes in updates to other BGP Speakers, that they must know how to speak (or they aren't speaking BGP) which … Continue reading BGP Well-Known Mandatory attributes explained, Best-Path explained, configured, and VERY important details!
In my first post with BGP, when I said the key to success with BGP is knowing the "Attributes" of it, specifically which are well-known and which are optional. This is VERY important information to get a foundation understanding of BGP attributes. These are the 4 types of Attributes, the attributes themselves, and explanation below: … Continue reading BGP Attribute Intro – Foundational information that you MUST KNOW before getting into BGP attributes!!!
So lets get this party started with the dry stuff we all love, theory and concepts. BGP uses the "network" command in router configuration, which is basically the same as a network statement for OSPF or EIGRP, except for a couple differences you will see during configuration. The real differences however are in how IGP's … Continue reading eBGP Route Advertisement explained, troubleshooting BGP RIB Failure, and good to know eBGP behaviors for exams and real life!
As you can see from Topology, the NBMA routers are all running iBGP, while our outlying router are running eBGP - It just got real! Now I know what you are thinking, "What if the physical interface connected to the Remote BGP peer goes down? What then smart guy? Just lose the Adjacency of that … Continue reading eBGP: Creating Neighbors using loopback interfaces, configuration examples, and explanation of BGP behaviors / concepts when it comes to loopbacks!
From the BGP Intro, here are the points relevant to this post: BGP Peers in the same AS are iBGP (Internal) Peers BGP Peers NOT in the same AS are eBGP (External) Peers The underlying connection that forms BGP Peerings is connection oriented The connection runs on TCP port 179 BGP Adjacencies = BGP "Peerings" … Continue reading eBGP Peering basics reviewed, configuration example, BGP states explained from beginning to Established!