TFTP over anycast

Sat Feb 24 07:09:15 UTC 2024

The system Ask is describing is the traditional method of using anycast to geographically load-balance long-lived flows.  The first time I did that was with FTP servers in Berkeley and Santa Cruz, in 1989. 

I did a bigger system, also load balancing FTP servers for Oracle, their public-facing documentation stores, with servers in San Jose and Washington DC, a couple of years later.   A couple of years further on and the World Wide Web was a thing, and everybody was doing it. 

                -Bill

> On Feb 24, 2024, at 7:38 AM, Ask Bjørn Hansen <ask at develooper.com> wrote:
> 
> 
> 
>>> On Feb 23, 2024, at 20:32, William Herrin <bill at herrin.us> wrote:
>>> 
>>> The relay server `dhcplb` could, maybe, help in that scenario
>>> (dhcplb runs on the anycast IP, the “real” DHCP servers on
>>> unicast IPs behind dhcplb).
>> 
>> Although they used the word "anycast", they're just load balancing.
> 
> The idea is to run the relays on an anycasted IP (so the load balancer / relay IP is anycasted).
> 
>> [….] Relying on ECMP for anycasted DHCP would be a disaster
>> during any sort of failure. Add or remove a single route from an ECMP
>> set and the hashed path selection changes for most of the connections.
> 
> 
> Consistent hashing (which I thought was widely supported now in ECMP implementations) and a bit of automation in how announcements are added can greatly mitigate this.
> 
> 
> 
> Ask
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