So looks like this may be a reason not to use UBNT stuff for our backup links. Looks like the highest I can set the MTU is 1515 on a couple units and 1524 on another. Neither capable of 1528 or more.
I'll have to find some brand new hardware and see if it can go higher. How big of a performance hit are we talking here? Potentially requiring double the pps to move the same amount of large packets? I could that potentially being a pretty big problem. On Wed, Dec 10, 2014 at 4:49 PM, Shayne Lebrun via Af <[email protected]> wrote: > To my understanding, it works like this: > > > > Say you take an IP packet coming into ether1, and it’s full MTU; 1500 > bytes. > > > > Now, you want to bridge ether1 to an EoIP tunnel. EoI is GRE, and there’s > a 28 byte overhead for the GRE encapsulation. Now you have a 1528 byte > packet. > > > > Unless every device between that router and the EoIP endpoint has layer2 > MTUs of at least 1528 bytes, you’re going to transmit two packets to move > that one original packet. One packet will have something like 1472 bytes > of the original packet, plus GRE overhead for 1500, and one will have the > remaining 28 bytes of the original packet, plus 28 GRE overhead, so, > something like 56 bytes. > > > > This introduces the obvious slowdowns, as well as not so obvious ones, > like maybe you have a device in the middle that’s not so good at PPS. Or > that queues up small packets into one big air frame, and therefore you’re > waiting for reassembly on the far end. > > > > Now, if you’re going from a 1500 byte LAN across a 9000 byte fiber > connection, you’ll not notice this. If you’re going to a satellite office > behind DSL with PPPoE, or a cable modem, or whatever, you’re going to > notice. > > > > > > *From:* Af [mailto:[email protected]] *On Behalf Of *Kade Sullivan via > Af > *Sent:* Wednesday, December 10, 2014 5:17 PM > *To:* [email protected] > *Subject:* Re: [AFMUG] EoIP over fiber - high latency? > > > > Could you elaborate on this? We have a couple EOIP links across "other" > networks and have never adjusted the MTU anywhere. I just pulled up the > EOIP interfaces on each router and they are all set for 1500. Should we be > increasing this number as a best practice when building EOIP Tunnels? > > > > On Wed, Dec 10, 2014 at 3:52 PM, Shayne Lebrun via Af <[email protected]> > wrote: > > Bear in mind that unless you’ve increased your MTU from end to end, or > dropped the MTU on your two devices that the EoIP are bridging, you’re > going to get packet fragmentation. > > > > Otherwise, what RouterOS version? > > > > *From:* Af [mailto:[email protected]] *On Behalf Of *Erich Kaiser via > Af > *Sent:* Wednesday, December 10, 2014 4:25 PM > *To:* [email protected] > *Subject:* [AFMUG] EoIP over fiber - high latency? > > > > So I have an EoIP tunnel setup over two fiber connections for a customer, > I am seeing high latency over the tunnel any idea? MTU Issue? Using > RB1100AHx2 on both ends. > > >
