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Routed Subnets, rp_filter and arp_ignore

by Simon

Over the past couple of years, I’ve been quite accustomed to my ISP providing me with an IP block (typically a /29) instead of just a single static IP, but recently I’ve switched to Hyperoptic for their FTTP offering (Because, Gigabit!). Unfortunately, they seem to only offer single IPs for residential service and require you to be on their business package which costs £££ if you want more IPs.

To get around this I decided to try to tunnel some IPs home – My setup is rather complex but I’m going to skip over the specifics for most of it and focus on the issue I was facing – lets ignore how the IPs route around the rest of my network and ultimately end up at the router for now and just look at the rather simplified view below.

Slow DNS resolving using bind9 as caching resolver

I currently have 4 DNS servers across my estate and until recently these were all configured to forward all queries to Google DNS ( I ended up having an issue with Google caching an undesired record value so I opted to change my DNS servers so that they no longer forward queries elsewhere, but instead try to answer it themselves; Doing this gives me slightly more control over my DNS cache.

As I use named (bind9) this was a pretty trivial change – Simply remove the forwarders {; }; clause in my configuration and that should be that.

During my post-change testing though I’d noticed that resolution was taking significantly longer for un-cached queries than I’d expect ( is only used to illustrate my issue):