The ramblings of a computer geek
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
If you want to do a reminder for something, its quote straightforward, you type the following: Or for every weekday: To see what reminders you have on a channel, you can run:
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
A quick command to determine where a mailbox has been moved during its lifetime. It is common for a mailbox to have been moved from database to database, and therefore at different points in time been backed up to different databases. When it comes to a need to restore a database, then you’ll need to … 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
Internal BGP (iBGP) is the next part of our deployment. We are going to be deploying two routers within one of the AS, Blue 65001. Remember that eBGP is used between AS and iBGP is used within an AS. So in this case our second router, Router B, will be linked to Router A via a single link, these … Read more
You can submit commands into an EC2 instance via SSM (Secure Systems Manager), rather than having to open SSH to the machine. From within an authenticated session using AWS CLI on your workstation machine, you can remotely send commands to be run within the instance itself. The commands will typically be run as “root” within … Read more
Here’s an interesting one I came across today, there exists a problem whereby replacing a certificate on a Microsoft Exchange 2016 or 2019 won’t work if the Issuer and Subject of the new certificate happen to be the same as the old certificate (you are trying to replace). You’d expect most likely that when you … Read more