I have an issue where DHCP just stops working on Access Points, or any device that isn't directly plugged into one of the SG300 ports. Such as plugging in an Unmanaged switch, then some computers, or VOIP phones into that unmanaged switch. DHCP will work when the unmanaged switch first starts up, but stops working after a few moments.
Example, existing devices are plugged into unmanaged switch (which uplinks to an SG300) such as a VOIP phone, and a computer. on power up, the Phone will get its DHCP from the VLAN 100 it is setup for, and the computer will get its DHCP from VLAN 1, the regular network. Let's say 10 minutes later I plug in a new computer, or a new phone. These devices will no longer receive an IP address. If I power cycle the unmanaged switch, the two existing devices will keep their address, and 50/50 change the new third device will get an IP address from DHCP
I should note, this issue happens with unamanaged, AND MANAGED switches, that are after the SG300. It seems that these SG300 switches, if the client device isn't directly plugged into it, DHCP doesn't seem to reliably pass through. I've had this issue happen identically on different access points that are plugged into an SG300 directly as well. DHCP just stops working after a while, for no solid reason, or clients connections just "stop working" (see below for more details)
The issue that we are having is one that has become increasingly worse, and has not been consistent since day 1.
Also, to clarify the topology:
Router – Which serves DHCP on a regular lan and 1 VLAN Connects to 4 SG300-52 Port switches. From SG300-52, we have an access point directly plugged into. On this access point, there are DHCP issues on the regular LAN (no VLAN) where devices do not ever get a DHCP, or if they do, their connection just “stops working” that is the Wireless connection does not drop from the AP, but the client is no longer able to ping the router, switch in between, etc. This issue is random, and has happened across different brands of routers and access points. The only thing ever unchanged in our setup is the Cisco Switches and the problem has been intermittent, random. Additionally your comment about VLAN support on unmanaged switches. We have had unmanaged switches AFTER the Cisco switches for quite some time, and our VLAN/LAN devices still worked when plugged into these unmanaged switches, as they supported carrying VLAN tags. It is again here the issue happens that after some random amount of time, DHCP from the LAN, and VLAN, stop working after the unmanaged switch. It is hard to explain why it would work for some time, then stop working, and then at times work again, after power cycling the unmanaged switch. I can further elaborate on this particular issue on the phone, because what happens is that DHCP works on the unmanaged switch for the first few minutes after a power cycle (power cycle of the unmanaged switch only) but will not work after that for any new devices that plug in, or request a DHCP lease later on. Think new computer plugged in later in the day, or new WiFi client attempting to get an address via DHCP from an AP that is connected to an unmanaged switch.
Also, Static IPs.
I have several devices that have Static IP addresses. If there is a power loss to the client device, or even the unmanaged switch, the device with a Static IP is unable to communicate to the rest of the network, past that unmanaged switch, which has nothing to do with DHCP. My guess is here that the Cisco Switches has an issue with devices beyond any native port (access point, uplinked unmanaged switch, etc) and stops seeing device MAC address, or something.
