3 posts tagged with "Labs"

Counting prefixes the same way my wife counts my mistakes​

Anyone who has accidentally advertised too many prefixes and watched their ISP BGP peerings collapse (I'm looking at you, BT) knows that prefix limits are a common safeguard in networking. While exploring anycast configurations in Azure, I carefully noted the official Route Server prefix limit of 1,000 routes. However, I recently discovered something far more interesting in the fine print about how Azure actually calculates this limit.

I went down the AWS Gateway Load Balancer rabbit hole recently and it's an interesting solution to some quite specific problems. There are use cases for it on ingress and egress where regulatory requirements, or more likely legacy skillsets, dictate that traffic passes through NVA based network security appliances. The problem with NVAs is often the difficulty scaling them in AWS. You need to distribute traffic and typically you need a loadbalancer but you can't use an ALB or a NLB because unlike Azure the load balancers in AWS do not allow for traffic routing so they cannot be targets for route tables in the same way Azure loadbalancers can be targets for UDRs.

There used to be a great little website for route summarisation and it did it far more intelligently than Cisco kit does it. It looks like the site has dropped off the internet which is a shame but there is a handy python library called netaddr with has the same capabilities.

I have written a little wrapper for it which will regex the prefixes out of a ‘show ip bgp’ and then list the summary routes. You pass the output of ‘show ip bgp’ as a text file, it’s the only argument the script expects.