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DHCP problems Cisco 4500 and VOIP Siemens phones.


L3 - 4503 and L2 - access 2960

Siemens Optioint 420 series

I have a voice vlan with a /16 mask. I have almost 500 IP phones on this subnet.

Here are some configs:

voice vlan

ip dhcp pool telefon-pool



   lease 7

data vlan

ip dhcp pool OU_APSUP




   option 43 hex 010a.5369.656d.656e.7300.0000.0204.0000.0064.0000.0000.00ff

   lease 7

I have to use the 43 option for the Siemens phones to work correctly.

I had to disable the ip conflict logging because the router had few resets.

Now I have an issue that some phones cannot get an IP from the DHCP, and some of those that get the address loose the connection after some time.

I am not using and dhcp database and all configs are storred in the NVRAM so it is normal that the router confused itself after the reset.

For some telephones that I could not get the IP from the dhcp I have cleared some IP dhcp bindings that had the different MAC address associated and after that the telehone got the IP address.

Here is some output from the dhcp debug, everything seems ok to me, but there is a lot of debug information and this is happening throgh complete work hours, the telephones are asking for the IP address, this debug could be running 24 hours and still giving some output:

16:48:22: DHCPD: DHCPREQUEST received from client 0100.01e3.2e62.89.

16:48:22: DHCPD: Sending DHCPACK to client 0100.01e3.2e62.89 (

16:48:22: DHCPD: broadcasting BOOTREPLY to client 0001.e32e.6289.

16:48:22: DHCPD: DHCPDISCOVER received from client 0100.01e3.2e62.0e on interface Vlan100.

16:48:22: DHCPD: Sending DHCPOFFER to client 0100.01e3.2e62.0e (

16:48:22: DHCPD: broadcasting BOOTREPLY to client 0001.e32e.620e.

16:48:23: DHCPD: DHCPDISCOVER received from client 0100.01e3.2e62.f3 on interface Vlan100.

16:48:23: DHCPD: Sending DHCPOFFER to client 0100.01e3.2e62.f3 (

16:48:23: DHCPD: broadcasting BOOTREPLY to client 0001.e32e.62f3.

any ideas ?

thanks in advance.

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