Cisco Catalyst 4224 Release Notes page 10

Important Notes
Design
The Catalyst 4224 hardware is designed to support many IGMP groups and VLAN interfaces, as long as
the multicast address count is <= 255 and/or IGMP snooping address count is <= 255.
When the table limit is exceeded, no friendly message is displayed.
Note
IP Phones Running SRST Fail to Get DHCP Reply
This section explains what happens when the lease time expires for IP phones running Survivable
Remote Site Telephony (SRST) that are assigned by the DHCP server in a central site.
IP Phones will try to renew the lease, but they will fail to get any DHCP replies due to the WAN failure.
Eventually IP phones will not only lose IP addresses but also lose phone services. Resetting or power
cycling the phones will not clear this situation. IP address and phone services cannot be restored until a
valid DHCP response is received by the IP Phone or the phone's IP address is manually configured
(DHCP is disabled).
When the IP address leased from the DHCP server is not infinite, the DHCP client will start sending
DHCP renew messages to extend the lease before the lease expires. When the lease time expires, IP
phones will start sending DHCP request messages and go to DHCP init state after a certain amount of
time without receiving DHCP replies from the server (this time is configurable). In the case when IP
phones already register with the SRST router in Cisco CallManager fall back mode, renewing the IP
address request will not be replied unless the SRST router itself is a DHCP server or there is a DHCP
server that can be reached. IP phones will lose their IP addresses assigned by the DHCP server in the
central site due to WAN failure, and hence lose the phone services, which cannot be recovered until a
valid DHCP response is received by the IP phone or the phone's IP address is manually configured, thus
disabling the DHCP service.
Note that loosing the lease is not the same as resetting. If the phone resets, it comes up in the
INIT-REBOOT state; this is the state where it has an IP address stored in flash. If it cannot contact the
DHCP server, it will use its stored address and continue to do DHCP Discovers in the background until
the server responds. In the case were the lease expires, the phone clears the IP address stored in flash
and goes to the INIT state. It cannot reinitialize until it gets a response from the DHCP server. This
behavior is as specified in the DHCP protocol RFC 2131.
IP Phones Running SRST Fail to Get DHCP Reply
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