I have several links running over all mt devices where vlan’s are transporting the traffic from A to Z (With B,C etc. in between)
All interfaces have mtu set at 1500 and all wireless links are nv2 802.11n
I have only one link where one radio link is made by two ubnt nanostation-loco’s. (Yeah well, they still work fine so why replace them)
No I put a vlan over this link too I suddenly cannot browse over this link any longer nor open a winbox session to a cpe (all MT)
I tried everything without success. Than I changed the mtu on the cpe to 1496 and suddenly it works again!
Weird, because I can reach the AP’s over the nanostation bridge without altering their mtu. But on the CPE’s I need to alter the mtu fm 1500 to 1495???
Anybody can explain this to me?
Its L2 and L3 MTU mess on part of UBNT.
UBNT uses 1300 L3 MTU (1314 L2 MTU), even if the link supports 1514 L2 MTU.
Mikrotik uses 1500 L3 MTU, which is 1514 L2 MTU.
Problem is the UBNT link only supports exact 1514 L2 MTU (this was a problem on older units with older firmware), so when you added a VLAN over the link (4bytes added to header), you can not use full 1500 L3 MTU (1514 L2 MTU) any longer.
Max MTU you can use now is 1496 L3 MTU (1514 L2 MTU with the vlan tag).
I have seen this exact problem multiple times when doing network updates for our clients. Up the MTU on the UBNT devices.
If you cant see it in the web-GUI, update the UBNT fw, or change that link if its already on newest FW.
Some older UBNT devices have a HW limitation of 1514 L2MTU.
hmm, very helpfull.
So, I have one client that has a MT wifi router, and he has no problems to pass his traffic over the link.
But other clients, all behind TP-link wifi routers, can’t browse.
I, from my end (central) can reach each of the MT devices without problem now after setting mtu on the MT’s to 1496.
I thought it had to be to do with the ubn stuff, because I did the same transfer (adding vlans over existing network) to several fully MT links without any of this problem… %&$-ubnt stuff, again… (These are the last resemblences of their stuff in my network. I think they are on their last legs…)
… hmm, just got a call that the clients are now back working again… after I increased the MTU on the nanostations to 1504…
I’m gonna set back some MT router to the full 1500 again, see if they still are reachable after that…
[sarcasm] MTU issues are always fun arent they… [/sarcasm]
UBNT is a total mess with MTUs, the first time I ran into this it took me half a day of googling, reading UBNT doc’s and testing untill I figured it out.
There is NO doc’s whatsoever from UBNT on how they handle L2 and L3 MTUs, so yeah, in the end, I figured it out by massive testing and experimenting.
You should be fine now with 1500 L3 MTU on everything after you increased the MTU on the UBNT link.
Yes, I just extended the life of these last to ubnt remantents in my network. And only because I don’t want to change these two into two SXT’s in a hurry.
I increased the mtu on the nanostation-loco’s and the clients inmediately could browse back again.
I also set one of the mt-cpe’s back to 1500 (I lowered the wlan’s to 1496) and I could still reach it by winbox. So I can now set the other 40 units back to 1500 (I want all my cpe’s to be the same. Otherwise in the future I’m wondering why these settings are done…)
So yeah, many thanks for your reply. It saved me probably a day or two searching with some 40 clients nagging me about the lack of internet!
thanks.