MTU in the internal chain of routers starting with PPPoE
Posted on 2013-01-17
I understand that the MTU for PPPoE is usually 1492.
What I don't understand is how that affects everything inside my network.
I sorta reckon that if packets are limited to 1492 then a device with MTU set at 1500 should have no trouble. But, I'm not sure.
I've seen some very poor performance when the numbers aren't right but I can't remember the details as this happened years ago.
So, it's time to get things straight as I'm dealing with a throughput problem right now.
I have a fiber link from an ISP that is connected with a router via PPPoE. Let's say the MTU on that router is set to 1492.
1492 is the number I get using the typical ping test from a computer at the end of the chain. I don't care much about my workstation computer because there are LOTS of computers that will possibly be affected. I'm going to have to assume that their settings are OK for now.
Between the modem-like router with 1492, there is a firewall.
The firewall defaults to MTU=1500 but I can set it manually.
What should I do with the firewall re: MTU?
What should I do with the modem-like PPPoE router re: MTU?
I don't understand the interim device setting requirements.
Most of the stuff I find addresses single computer tweaking.
Is there a good, clear discussion of these things?