Clients connected through EX4400-48MP were unable to establish network connectivity. Despite the reported outage, Mist did not report any errors or anomalies on the associated switch ports, and switch logs showed no indications of network device faults.

• Clients connected to switch were unable to access network resources beyond the local subnet.
• Devices successfully obtained IP addresses from DHCP.
• Mist Wired Assurance reported no switch port errors.
• Switch logs and monitoring systems showed no hardware or software faults.
• Multiple user reports indicated loss of connectivity on the affected floor.
• Layer 2 connectivity remained operational, but Layer 3 communication failed.

Investigation confirmed that the switching infrastructure was functioning normally and that DHCP address assignment was successful.

The root cause was identified as a DHCP server configuration issue:

• DHCP Option 003 (Default Gateway) was not being provided to client devices.
• Without a default gateway, clients could only communicate within their local subnet and could not reach remote networks.

Verification Steps

1. Confirm clients are receiving IP addresses from the DHCP server.
2. Verify the DHCP lease information includes a valid default gateway.
3. Check the client network configuration.

Example client output:

IP Address: 10.x.x.x

Subnet Mask: 255.255.255.0

Default Gateway: Not Present

After correcting the DHCP configuration and restoring Option 003, client connectivity was fully restored.

The EX4400 switches and associated switch ports were operating normally. Mist reporting no errors was expected because the issue originated from the DHCP server configuration rather than the network switching infrastructure. When clients receive valid IP addresses but cannot reach resources outside their subnet, verify DHCP Option 003 (Default Gateway) before investigating switch hardware or software issues.