Cisco phone connecting to 3750 switch

[BT1]

Hello,

So have a weird issue trying to get an IP phone to work on a 3750 switch. I have two 3750 switches uplinked to a 3650 switch. If I connect a phone on any port on 3750's it keeps trying to register. It gets the correct IP and TFTP addresses but doesn't finish the registering process. Now, while that phone is connected to 3750 if I take another phone and connect it into a port on the 3650 switch the one on 3750 will finish registering and will work fine. So the phones on 3750 only work as long as there is a phone connected to a 3650 as well. Any help is appreciated. 

This is the config on all the ports:

switchport access vlan 20
switchport trunk encapsulation dot1q
switchport voice vlan 41
spanning-tree portfast

[Meheretab Mengistu]

You might need to disable "SIP Fixup" if you are using SIP. Many SIP ALGs (aka SIP Fixup in Cisco) have bugs which cause call flow and registration failures.
To disable SIP Fixup:
no ip nat service sip udp port 5060

HTH,
Meheretab

[Leo Laohoo]

When the phone is constantly in "Registering", does it get an IP address? 

Post the complete output to the 3750 command "sh interface trunk".

[BT1]

Yes, the phone does get an ip address. On CUCM it shows the phone has an IP but shows unregistered.

Here's the output to "show interfaces trunk"

# show interfaces trunk

Port Mode Encapsulation Status Native vlan
Gi1/0/49 on 802.1q trunking 1

Port Vlans allowed on trunk
Gi1/0/49 1-4094

Port Vlans allowed and active in management domain
Gi1/0/49 1,4,11,18-20,22,24,26,28,30,36,40-47,96-99

Port Vlans in spanning tree forwarding state and not pruned
Gi1/0/49 1,20

[Meheretab Mengistu]

Port Vlans in spanning tree forwarding state and not pruned
Gi1/0/49 1,20
1. Are the phones getting IP addresses from the correct DHCP pool (vlan 41)?
2. Could you check "show spanning-tree summary" for vlan 41?
3. Vlan 41 may be not allowed on the other side of the trunk.

HTH,
Meheretab

[BT1]

Yes, the phones are getting the correct IP address. 

Here's the output to "show spannng-tree summary"

show spanning-tree summary
Switch is in pvst mode
Root bridge for: none
Extended system ID is enabled
Portfast Default is disabled
PortFast BPDU Guard Default is disabled
Portfast BPDU Filter Default is disabled
Loopguard Default is disabled
EtherChannel misconfig guard is enabled
UplinkFast is disabled
BackboneFast is disabled
Configured Pathcost method used is short

Name Blocking Listening Learning Forwarding STP Active
---------------------- -------- --------- -------- ---------- ----------
VLAN0001 0 0 0 1 1
VLAN0004 0 0 0 1 1
VLAN0011 0 0 0 1 1
VLAN0018 0 0 0 1 1
VLAN0019 0 0 0 1 1
VLAN0020 0 0 0 2 2
VLAN0022 0 0 0 1 1
VLAN0024 0 0 0 1 1

Name Blocking Listening Learning Forwarding STP Active
---------------------- -------- --------- -------- ---------- ----------
VLAN0026 0 0 0 1 1
VLAN0028 0 0 0 1 1
VLAN0030 0 0 0 1 1
VLAN0036 0 0 0 1 1
VLAN0040 0 0 0 1 1
VLAN0041 0 0 0 2 2
VLAN0042 0 0 0 1 1
VLAN0043 0 0 0 1 1
VLAN0044 0 0 0 1 1
VLAN0045 0 0 0 1 1
VLAN0046 0 0 0 1 1
VLAN0047 0 0 0 1 1
VLAN0096 0 0 0 1 1
VLAN0097 0 0 0 1 1
VLAN0098 0 0 0 1 1
VLAN0099 0 0 0 1 1
---------------------- -------- --------- -------- ---------- ----------
24 vlans 0 0 0 26 26

I have the same config in other vlans with multiple 3650 switches and it's working fine. Just these 3750's are not working for some reason. 

[Leo Laohoo]

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@BT1 wrote:

Yes, the phone does get an ip address.

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Ok, so the phone gets an IP address.  Is DHCP Option 150 configured correctly? 

If the phone gets an IP address, put the IP address into a web browser and go to the Networks Setup page.  What is stated in the line CUCM Server 1?