Phones do not retain DHCP IP address after rebooting

Unanswered Question
Jun 23rd, 2010
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I have a 3750-48PS switch acting as a layer 2 with a few ports configured for voice and data. This layer 2 switch is connected to another 3750-24PS switch acting as a layer 3 switch and having the Vlan interface configured with the IP helper addresses for DHCP.

We tried to configured the switch as a switch trunk and encountered the following problem:

The phone and data work at the same time, but if the phone is rebooted it will not get an IP address.

interface FastEthernet2/0/2

switchport trunk encapsulation dot1q

switchport trunk native vlan 240

switchport trunk allowed vlan 220,240

switchport mode trunk

priority-queue out

mls qos trust dscp

spanning-tree portfast

spanning-tree bpduguard enable

Any help is greatly appreciated.



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Jerry Ye Wed, 06/23/2010 - 11:58
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  • Cisco Employee,

What kind of phone? Cisco? Avaya?



gsanin Wed, 06/23/2010 - 12:23
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Hi Jerry,

We are using Avaya IP phones.



Jerry Ye Wed, 06/23/2010 - 12:37
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  • Cisco Employee,

Typical Avaya IP phone problem. Have you check your option 176 in your DHCP scope for both voice and data VLAN? Also, how much utilization is your DHCP range for both data and voice?

At my previous job, we always had this issue due to the reason that Avaya IP phone needs 2 DHCP assignment before it is operational. First, it askes the data VLAN first for IP, and the option 176 will tell it to change to voice VLAN. Then it will get the 2nd DHCP assignment from the voice VLAN. The problem is when the data VLAN scope about 75% when all the PC's are on, and you have the same amount of phone asking for DHCP from the data VLAN, some phones are not getting IP addresses. I will suggest you to check that also.




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