Hello,
we have Cisco 9200 switch in the distribution working as the DHCP server. Cisco SG350X switch is connected directly to the 9200 switch. From time to time phones connected to the SG350X are unable to receive the IP address from the DHCP server (Yalink T31 and T21 E2 phones), but if at the same time some small unmanaged switch is inserted between the phone and the SG350X switch, the phones are receiving IP addresses. We have auto voice vlan enabled on SG350X switchports and lldp is disabled. This kind of issues happen to some phones, they work without the problems for some time and after the reboot they are unable to receive the IP address (if they are connected directly to the switch without intermediate switch), but if the switch is added between the phone and SG350X switch, or another phone is connected directly to the same port of the SG350X, the IP address is received.
Any ideas what could be the reasons for this issue?
