Re: [nznog] Transit Questions (IPv6, MTU, EDNS)

On 25/06/2014, at 11:32 pm, Roland Dobbins wrote:

On Jun 25, 2014, at 5:35 PM, Alexander Neilson wrote:

...

* How many transit providers provide MTU above 1500 Bytes?

1500 is pretty much the most prevalent MTU size on the Internet these days, as packets ingress at operator edges and then egress them on the 'far side'. So, an MTU larger than 1500 isn't going to help you on the public Internet. It's mainly useful within internal data centers, and WAN-type connections between same.

I guess I was expecting if blocking of needs fragmentation wasn’t too frequent then MTU sizes would start to grow through transit and then as people upgraded PMTUD would start to use larger MTU sizes end to end as links improved.

...

* How do others handle EDNS?

Fragmentation of large EDNS0 responses (or anything else) is pretty much automagic, from an operational perspective (except when folks have done silly things like block ICMP type-3/code-4 or ICMPv6 type-2). So, this isn't really a concern when looking at the MTU size your upstream transit provider offers.

I guess I was thinking people would have done those silly things more (as per the MTU size not growing on the internet) and therefore EDNS would have size issues. Is it more that fewer people have these silly config errors? or that DNS has a robust fallback position trying smaller EDNS sizes / alternatives to get a useful reply?

---------------------------------------------------------------------- Roland Dobbins // http://www.arbornetworks.com

Equo ne credite, Teucri.

-- Laocoön

_______________________________________________ NZNOG mailing list NZNOG(a)list.waikato.ac.nz http://list.waikato.ac.nz/mailman/listinfo/nznog