This article provides a behavior matrix for Cisco desk phones (SPA303, SPA504G, SPA525G2) in different LAN environments.

Network Condition Phone Visual Changes Phone Behavior Changes
Power up with no layer 1 connectivity Mute light turns red and stays lit.  Display says "Initializing Network". Phone stays in this condition forever until something changes. No phone functionality in this condition.
Power up and register, but then lose layer 1 connectivity Mute light turns red and stays lit.  Line buttons turn from green to yellow. No incoming or outgoing calls.
Power up with no layer 3 connectivity Display says “Checking DNS”. Phone stays in this condition forever until something changes. No phone functionality in this condition.
Power up with, but then lose, layer 3 connectivity Line buttons light turns amber, phone icon next to the button is split. No incoming or outgoing calls.
Power up with layer 3 connectivity but no internet access Display says “Checking DNS”. Phone stays in this condition forever until something changes. No phone functionality in this condition.
Power up with layer 3 connectivity, register, then lose internet access Line buttons light turns amber, phone icon next to the button is split. No incoming or outgoing calls.
Power up with no DNS server available Display says “Checking DNS”. Phone stays in this condition forever until something changes. No phone functionality in this condition.
Power up and register, but then lose connection to DNS server No changes until cached DNS entries expire. After this line buttons light turns amber, phone icon next to the button is split. No incoming or outgoing calls after DNS cache expires.
Power up with no DHCP server available Mute light turns red and stays lit.  Display says "Initializing Network". Phone stays in this condition forever until something changes. No incoming or outgoing calls.
Power up and register, then lose connection DHCP server No changes until lease time is over. After this line buttons light turns amber, phone icon next to the button is split. No incoming or outgoing calls after DHCP lease expires.
Power up with no layer 2 connectivity Mute light turns red and stays lit.  Display says "Initializing Network".  Phone stays in this condition forever until something changes. No phone functionality in this condition.
Power up with, but then lose, layer 2 connectivity Line buttons light turns amber, phone icon next to the button is split. No incoming or outgoing calls.
DNS proxying enabled in DHCP options for DNS settings No changes No changes
DHCP race condition or an IP conflict Line buttons light turns amber, phone icon next to the button is split. No incoming or outgoing calls.
Network loop / broadcast storms No changes

Device hangs completely and doesn’t respond to any action. No phone functionality in this condition.

Photos

Checking DNS:

Initializing Network: