UC500 and Linksys SRW248G4P: 524sg Phones getting vlan 1 DHCP from separate server.

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May 1st, 2009
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The UC500 is connected via the Expansion port to a Linksys PoE switch (SRW248G4P).  The UC500 is the DHCP server for voice VLAN 100, and a separate Windows server is the DHCP server for the VLAN 1 (native data).   Here is the Expansion Port configuration:

interface FastEthernet0/1/8

switchport mode trunk

spanning-tree portfast

This port is connected to port 48 on the Linksys switch which is configured as a Trunk as well. 

Ports 1-47 are configured as: (all 524sg phones are plugged into these ports)


VLAN 1: Untagged

VLAN 100: Tagged


The 524sg phones are getting their IP configuration from the Windows DHCP server on VLAN 1, so when a computer is connected to the PC port on the phone, the PC does not get an IP address and cannot access the data network.

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Steven Smith Fri, 05/01/2009 - 09:44
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I don't that switch supports CDP, which is how the phone finds its voice vlan.  If it doesn't get that, it will default to VLAN 1.  Look at changing the admin vlan on the phone to 100 and see if that helps.  You might need to select the box for enable VLAN as well.

brandon.kallas Fri, 05/01/2009 - 09:48
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Why does this seem to work when the UC500 is providing the DHCP for both VLANs?

Steven Smith Fri, 05/01/2009 - 09:53
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CDP doesn't make it past the switch.  The phone determines what VLAN is will try to get an IP address from the CDP info.  The phone is choosing VLAN 1.  If the it handed out an IP address on VLAN 100, the phone wouldn't have IP connectivity.  If the switch supported CDP, it wouldn't have this problem.

When plugging directly into the UC500, you shouldn't have this problem either.

brandon.kallas Fri, 05/01/2009 - 10:13
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I'll just have to set the phones manually to VLAN 100 then for now.   Thank you!


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