Re: TFTP over anycast

[Bill Woodcock <woody () pch net>]

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 () develooper com> wrote:
>
> 
>
> > > On Feb 23, 2024, at 20:32, William Herrin <bill () 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