While getting together some command prompt syntax from my lab, I got a jolt of nostalgia from labbing ROUTE, and decided to instead configure the lab Topology shown above as I started configuring my switches for Layer 3 routing and before I knew it I was troubleshooting OSPF and EIGRP Ajdacencies! I will try to … Continue reading TSHOOT – Redistribution Part 1 – Configuring an OSPF / EIGRP / iBGP Lab to completion, ready for Redistribution!
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!
Full-Mesh vs No Full-Mesh iBGP AS The only time iBGP Speakers will advertise routes is if it meets one of the following criteria: If the route was created on the local router and added via the network command If you configure static route or IGP route redistribution If the route is a directly connected route … Continue reading iBGP: Full Mesh vs Non-Full Mesh, Synchronization / Transit Rule, BGP Split horizon and other important details!
I'd like to start off with a quick example of the output from when I was adjusting routers from the previous lab for this lab, by doing "no router bgp 123" on it and creating AS 15 on it, with a neigbor statement point at 184.108.40.206 and went to R5 to do the same: *Apr … Continue reading BGP Route Aggregation / Summarization explained, configured, and some important details for exam day!
Same Topology, only this time I added a second logical network between R3 and R4 by creating 2 loopback interfaces in the same subnet 220.127.116.11 /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 18.104.22.168 … 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!!!
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!
So my initial thought was to make R2 the iBGP Peer to R1 in AS 100, however I may want to use R4 also running on 15.x code to get into the mix here as we progess, so on R3 it goes! And a quick tidbit of knowledge to start things off: You cannot make … Continue reading BGP RID manual configuration, iBGP Peering with R3, a much briefer “show” command for verification, and important BGP behavior info for exam day!