The ramblings of a computer geek
In previous articles, we have mentioned the use of BFD – Bidirectional Forwarding Detection. RFC 5880. Essentially BGP failure detection is slow by design and for good reason when you are dealing with truly massive networks. BFD exists to make it fast, but also while being safe too. As was discussed in previous articles BGP … Read more
A BGP peer group is: A way to apply the same configuration and policy to multiple BGP neighbours as a single unit. Kinda like Active Directory Group Policy but for BGP Neighbour (peers). If you have specific configuration such as the timers, route policies, BFD and so forth, having to repeat that for multiple peer Router’s … Read more
An Autonomous System (AS) is: A collection of IP networks and routers under a single administrative domain that presents a common routing policy to the Internet. These might be an ISP, a cloud provider, a large enterprise that is running external BGP, a content provider (such as Google or Meta), to identify each of these an Autonomous System Number … Read more
It’s key to understand BGP Timers to understand how and when certain actions will be taken by BGP. BGP timers help the protocol answer these four fundamental questions: Everything else is a refinement of those. Topology and Configuration We’re making some additional changes to the topology, we are adding two new routers, Router K and … Read more
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