Hi,

I am pulling my hair out configuring a 3900.

I current have a network running 4VLAN (Lans not WANs) into a 2862 and TP link managed switch. Everything runs beautifully.

I wanted to upgrade so acquired a 3900. I have manually configured the 3900 and just about everything in the configuration works EXCEPT the VLANs.

I start testing everything by plugging a laptop into port 1 on the 3900, it's untagged but I have allowed that in the Lan configuration. I get an IP address served exactly as I should and this is how I know that just about everything on the 3900 is working.

HOWEVER, when I switch from my Laptop to the TP link switch, I get nothing. A PC that is set up to attached using VLAN ID 10 (tagged at the switch), which is configured to LAN1 on the 3900 does not get served an IP address and just hangs as though it is not recognised.

Before you ask, yes I know it is being tagged correctly by the TP Link switch as the 2862 is set to not accept untagged traffic. Rebooting the PC does not improved the situation (not that I thought it would, but it was worth a try). And Yes, I have configured the LAN port to accept both tagged and untagged traffic.

I am sure I am missing something obvious, so can someone point me in the right direction please?

Well it's been a week and I am not surprised no one has been able to help.

After spending a lot of time trying to track this problem down I started noticing some inconsistencies...

The first thing I noticed was that Wi-Fi traffic entering the 3900 WAS connecting..

I then checked ALL the wired connections across all the Vlans and nothing connected. Now given that the Wi-Fi AP is also wired this was a real curiosity.

Checking the switch and there was nothing unusual about the AP, EXCEPT that it was passing VLAN Tagged traffic and the Vlans/SSid's are all managed by the AP itself.

The next odd thing I noticed was suddenly all the wired connections started working, however I then started having unrelated issued and figured I may have screwed the set up so decided to factory reset and start again.

But this with with a difference, I pulled the 3900 out of the rack and put it on the bench and plugged a laptop in to do the configuration. All seemed to progress the same was as the first time, but after I did the configuration, rather than put it on the rack, I decided to do an extra step. I plugged in a really old TP Link managed switch to test the VLAN configuration. It worked. My conclusion at this stage was, Oh, the configuration must have been corrupted, my bad, but it works now.

That was a little premature!

Put the 3900 back in the rack, plug everything in, back to square one, Wi-Fi connections work, but not wired connections.... Arrgh.

In frustration, I pulled the main switch and replaced it with the unit on the bench. EVERYTHING worked.

Now at this stage I would naturally conclude that the TP Link switch was at fault.... But it worked perfectly with the 2862's so I think that's a false conclusion.

A little more digging and I noticed while checking the DHCP table that the original TP link switch wasn't in the table, but the new one is..... Rebooting the original switch did not result in a DHCP entry.

This got me pondering, does the 3900 REQUIRE the allocation of a DHCP address before it fully recognises the Switch???

I confirmed the switch was set to acquire a DHCP IP and it is, so now I am thinking, does the switch only make a DHCP request at the end of it's existing lease?

This would explain why the original configuration suddenly started working and why the switch had retained it's original ip address....

Can anyone throw any other thoughts into the mix as it's a little drastic to replace a switch like this, particularly as the current switch is a lot older than the one that was having trouble connecting and both are made by TP-Link...My current plan is to wait until the end of the IP lease, plug it in and see what happens....

My final reply to this topic.

I am not surprised to report that this morning I plugged in the original switch to the 3900 and bam, it is now working properly.

My only conclusion is that DHCP was to blame in one way or another.

Was it the TP-Link switch or the 3900?

I really don't want to call it and suspect it may be a combination of both. As I started moving individual plugs back to the old switch I started noticing that some devices would not re-connect after they were moved back. Some, if I rebooted, would reconnect, others stubbornly refused.

I have stopped moving devices over now to see if these errant items re-appear tomorrow.

So if this happens to you, remember to wait long enough for the DHCP lease to expire and then re-attach and whatever device you are having problems with may and probably will re-appear.