The ramblings of a computer geek
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
You can setup Putty to just log everything by adding logging to your Default Settings, that way whenever you connect, you’ll always be logging what the outputs are to your chosen location, e.g. your local machine. Although be aware of any sensitive on-screen information that would also be logged to these files. Your path may … Read more
In the previous article we talked about BGP Attributes and then how we can use MED (and Local Preference) to influence and control how traffic ingresses and egresses an Autonomous System (AS). But MED and Local Preference are just a couple of a few different techniques, in this article we’re going to explore how AS … Read more
Border Gateway Protocol (BGP) path selection works out the best path when BGP has routes that it could choose from. There are a number of BGP Attributes which are evaluated (top to bottom) so that the path with the best attribute is selected for the path. BGP Attributes There are 11 BGP Attributes, these are … Read more
We had an interesting issue where our EXIM configuration was flattening a subdomain’s “From” address, i.e. it was re-writing an email’s From (HFrom) and MailFrom (return-path/envelope-from) headers to @domain.com addresses, i.e. to catch emails such as root@mymachine.domain.comand re-write the From (HFrom) and MailFrom (return-path/envelope-from) to root@domain.com instead. Problem was, this configuration wasn’t documented, so needed a bit of investigation; but is also a good learning point … Read more