[nsp] intra-domain anycast

[Michael Sinatra]

On Tue, 21 Oct 2003, Haesu wrote:

> Now my question is..

> For those who do anycast within your AS, do you use IGP such as OSPF to
> do it (this *seems* like the popular way), or do you just throw it on
> IBGP? I have tendancy to carry only infrastructure (router next-hop
> addresses) on IGP and carry everything else over ibgp (i.e. transit
> routes, etc. anything need not be announced to internet are tagged
> no-export and other measures)..

On Tue, 21 Oct 2003, Brian Apley wrote:

> Our DNS servers advertise /32s via RIP to their connected routers. The
> routers then redistribute this into our core IGP. The A.D. is manipulated so
> that RIP is preferred (otherwise, the connected routers will not
> redistribute because it will see a better route via the IGP instead of RIP).
> We're hoping to implement the IGP directly on the DNS platform in the
> future, as well as add some scripting so that if BIND fails-unlikely-the OS
> will cease to advertise the /32.

We have been doing intra-AS anycast for DNS for about 4 years.  Our DNS
servers advertise /32s directly into authenticated OSPF, which is our IGP.
(Each DNS server is in a separate area, directly connected to the backbone
area.)  Since we feed it into our main IGP, there's no need to mess with
admin distances and the like.  We use FreeBSD + BIND for the OS/DNS
platform, and we originally used gated as the routing engine, but have
since moved on to zebra (will probably move to Quagga eventually).

We use iBGP for certain special applications, like uRPF shunning and in
the core, where routers need to make forwarding decisions as to which
border routers to send packets to (e.g. Internet2 vs. commodity ISP).  We
don't use it for this anycast application.

Question: Does anyone use anycast for NTP?  It's not as interesting as for
DNS, since NTP can use hostnames rather than hardwired IP addresses, but
there is some benefit to providing a mechanism for the topologically
closest NTP server without the user having to figure it out for themselves
and come up with the resultant ntp.conf file.  This sort of thing is "way
back burner" for me, but I was wondering if anyone else did it.

michael