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 <a...@develooper.com> wrote:
>
>
>
>>> On Feb 23, 2024, at 20:32, William Herrin <b...@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
