On Thu, 10 Mar 2016 08:23:30 +0200 Tassos Chatzithomaoglou <achatz@forthnet.gr> wrote:
Niels Bakker wrote on 10/3/16 02:44:
* nanog@nanog.org (Kurt Kraut via NANOG) [Thu 10 Mar 2016, 00:59 CET]:
I'm pretty confident there is no need for a specific MTU consensus and not all IXP participants are obligated to raise their interface MTU if the IXP starts allowing jumbo frames.
You're wrong here. The IXP switch platform cannot send ICMP Packet Too Big messages. That's why everybody must agree on one MTU.
Isn't that the case for IXP's current/default MTU? If an IXP currently uses 1500, what effect will it have to its customers if it's increased to 9200 but not announced to them?
None. Until someone actually tries to make use of the higher MTU. Then things start breaking. Let's say I'm a customer at this IXP. I have 100 peers. I have one peer that likes large MTUs, so I set my L3 MTU to 9000 (or whatever I agree with this peer). Now I have broken connectivity towards my 99 other peers who are all still at 1500. So today you need a separate VLAN for Jumbo's, which some IXPs have. On this VLAN you will only find the peers that actually care about Jumboframes. The majority of IXP participants don't bother to connect to this VLAN for varying reasons. If the number of interested parties is too low, IXPs may well decide it is not worth the investment of time and resources to set this up, implement monitoring for it, deal with customers messing up their configs, etc. In order for Jumboframes to be successful on IXPs _on a large scale_ the technology has to change. There needs to be a mechanism to negotiate MTU for each L2 neighbor individually. Something like draft-van-beijnum-multi-mtu-03, which was mentioned before in this thread. With this in place individual sets of peers could safely use different MTUs on the same VLAN, and IXPs would have a migration path towards supporting larger framesizes. -- Kind regards, Martin Pels Network Engineer LeaseWeb Technologies B.V. T: +31 20 316 0232 M: E: m.pels@tech.leaseweb.com W: http://www.leaseweb.com Luttenbergweg 8, 1101 EC Amsterdam, Netherlands