No Topology again, I know the lack of pictures is boring. A few things I wanted to note about configuring address-family's in BGP: You can either do it as a single IPv4 or IPv6 Peering, which would look something like: router bgp 100 neighbor 126.96.36.199 remote-as 500 neighbor 2005::5/64 remote-as 500 address-family ipv4 … Continue reading Important BGP Address-Family notes, IPv4 and IPv6 behaviors for exam day! Last post before my exam 5/26, see you on the other side!!
No topology for this particular post, just some quick notes on BGP filtering which probably won't be a huge topic on ROUTE as it's more a Service Provider So here we go. BGP Filtering can be done on any router, there are no limitations like in OSPF where filtering is done on specific router types … Continue reading BGP Filtering / Authentication / BGP Peer group notes for exam day!
Private AS Numbers: When you look at router bgp ? you see (1-65535), which the range of 64496-65535 are actually reserved or Private AS's, which should not be advertised Externally as Private IP's on your LAN should not be advertised to External networks. Also to note, you cannot use AS 0, and will get an … Continue reading BGP Private AS’s, RID, Redistribution, and some other quick but important information for success on exam day!
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 188.8.131.52 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 184.108.40.206 /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 220.127.116.11 … 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!