The ramblings of a computer geek
Any router that uses BGP must establish a peering (neighbour) with its neighbour routers before it can exchange any routing information. To establish this peering, the BGP router on each side of the connection must go through a number of stages called (BGP States) before it can complete a transfer of routes. A key point … Read more
We’re now going to explore BGP Route Redistribution. BGP Route Distribution is where you can redistribute routes that the router has learnt via some other protocol, e.g. static, OSPF, EIGRP, RIP etc. into BGP, so in effect it becomes a BGP Route. A common example for this might be the redistributing a default static route into … Read more
Within this article we are going to explore BGP Filtering, which is a method used to selectivity identify routes that are advertised (transmitted) or received from neighbour routers (and Autonomous Systems) in order to manipulate traffic flows, reduce memory utilisation or to improve security. It is a very common practice to use route filtering (also … Read more
I was having the issue in mRemoteNG where some hosts were showing the error: “Couldn’t agree a host key algorithm (available rsa-sha2-256)” when attempting to SSH to them. And even when ensuring all the ciphers are enabled with the Default Settings (session) -> Connection -> SSH -> Cipher, the issue was still observed. Turns out … Read more
A BGP Confederation, is like Route Reflectors another technique to remove the need for the “full-mesh” requirement of iBGP, where such a requirement is prohibitive, due to the size of the network. Remember that with an iBGP AS network, each Router must have a BGP Neighbour (peering) with every other for the AS to operate correctly, sure this … Read more
We’re now going to investigate Route Reflectors and how and when they can be used. Route Reflectors are for use within iBGP only, they are never used for eBGP. A Route Reflector (RR) is: An iBGP router, that is specifically allowed to re-advertise iBGP-learned routes to other iBGP peers (within the AS), and is designed to remove the iBGP full-mesh requirement (amongst other things). If you … Read more
In this article, we’re going to examine another mechanism of BGP, BGP Communities. These like MED are used to change/influence/direct how traffic will flow between different AS. Its just another mechanism like MED you could use, but has some advantages when compared to MED, namely it can be much more dictatorial rather than influencial and … Read more
In the previous article we got our AS Blue 65001 operating as we want it, now we crank up the complexity with a more complex example which is more like you’d find or want to architect in real world scenario. Previously our AS Blue 65001 only had a single exit point to AS Green 65002, … Read more
In the previous article we discovered that iBGP requires a topology and usage that ensures that our exchange of routes between routers is not stopped by the iBGP rule: “A route learned via iBGP must not be advertised to another iBGP peer.” We came across this problem in the previous article where although in normal operational the routes were being … Read more
We’ll continue to explore Internal BGP (iBGP) in this next part of our deployment. We are going to be deploying another route in the AS Blue 65001. Remember that eBGP is used between AS and iBGP is used within an AS. Be aware however, that this lab topology is flawed in terms of its configuration, but it shows up … Read more