So, I seem to be having some issues with PPPoE on my Mimosa driven wireless network.
I would like some input on this as I have been researching what MTU’s are supported on Mimosa AP gear and seem to be having a hard time.
- All my CPE clients connect via a VLAN enabled SSID.
- All my CPE C5x’s have a management VLAN assigned via radius, and my AP’s are on another VLAN for management.
- All my clients use PPPoE on their mikrotik routers to connect with a static IP (private) assigned to them via PPPoE (Radius), PPPoE servers do rate limiting dynamically.
- All my Switches (Netonix) Routers, (Mikrotik) have support for larger MTU values to support: VPLS, MPLS and VLANs.
Here is where I am kinda stuck / may be missing something that perhaps someone has the answer to:
When I try to set my PPPoE clients to true full 1500 MTU they will connect - but I seem to have issues uploading and other strange packet / VOIP issues etc.
If I lower the MTU to say 1470 then all seems to work - but the default PPPoE MTU of 1492 does not seem to work as well. ( I think that is industry standard)
If I do some math ( and I may be doing it wrong - so please speak up if you see something) and compute the packet size I should have with a 1470 MTU the following:
1470 = data + IP = 20 + VLAN = 4 + PPPoE = 8
Total = 1502 flowing from CPE router through CPE Radio to AP to switch.
So by this logic the C5x’s only push 1500 MTU through them and I am over - it should not work at 1470 - but it does.
If I ping with “Do not fragment” from one of my client devices to the PPPoE server - I get stopped up about 1497 - 1496 does work.
That feels like the VLAN (4 bytes) being added / passing through the Mimosa gear.
I will admit there are gaps in my knowledge - but the rest of my network is able to handle everything else - just the CPE routers seem to have this problem.
For reference I have at each point in my network a L2 MTU of 1580 and an MTU of 1550.
As I see it this should be the max packet size anywhere in the network:
Data = 1480 + IP =20 + MPLS = 4 + VLAN = 4 + Eth = 14 + PPPoE = 8
Total = 1530
I guess what I really need to know here - is if you are setting up your AP’s with VLANS for customers are you adding 4 bytes to each packet giving you only 1496 over the Mimosa CPE and AP?
Or are you still at 1500 MTU to be able to pass through each CPE / AP.
If 1496 then you have to add PPPoE on that in my case ( So 1488 should be max?)
Now, I do see that the Mimosa AP’s have the ability to use Jumbo frames - but I do not see any mention in the CPE’s of MTU.
So, I need to know:
- What max MTU do the Mimosa C5x’s (CPE radios) support? Is it changeable?
- Does the Mimosa A5(x) (C in this case) include VLAN’s in the 1500 MTU by default - or do you have to subtract 4 for that?
2.5 Oh - and do management VLANS work into all of this as well for the C5X and the A5c’s?
Thanks - and I hope the answers we come up with here will help others in the future.