Re: TFTP over anycast

[Javier Gutierrez <GutierrezJ () westmancom com>]

Thanks to you all for your answers, it has helped me a lot already.

My design is very simplistic, I have 2 sets of firewalls that I will have advertising a /32 unicast to the network at 
each location and it will have a TFTP server behind each firewall.

I have no intention to have this be part of the internet as it will be used to serve internal customers devices that 
require TFTP
For the setup where you are running Anycast on a datacenter, are you running it inside the datacenter only or across 
multiple datacenters? other than having to replicate IPs and file services between datacenters have you seen any other 
issues?


Kind regards,



Javier Gutierrez,

Network Architect – AS19016
https://www.peeringdb.com/net/4073

Westman Communications Group

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________________________________
From: NANOG <nanog-bounces+gutierrezj=westmancom.com () nanog org> on behalf of Bill Woodcock <woody () pch net>
Sent: Saturday, February 24, 2024 1:09 AM
To: Ask Bjørn Hansen <ask () develooper com>
Cc: nanog () nanog org <nanog () nanog org>
Subject: Re: TFTP over anycast


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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