cisco 3650 trunk ports

[Network Pro]

hi

we have a cisco 3560 and the config is

int fa0/1

switchport mode trunk

switchpo trunk encap dot1q

switchport voice vlan 100

switchport portfast

but when a laptop is connected, it does not get an ip address (switchport trunk encap native vlan1) command is given but it does not display on sh run - looks like its a default command - still the pc does not get an ip address when connected by itself - but works when connected daisy chaied with a phone

any ideas?

thanks

[Leo Laohoo]

switchport mode trunk

This turns your switchport into a dot1q trunk.  Remove this will turn your switch port into an access switch and is assigned to VLAN 1.

[Network Pro]

yes thats true but even if a port is in trunk mode with ths command switchport trunk native vlan 1 (the pc should get an ip address..shouidnt it ?

[Leo Laohoo]

yes thats true but even if a port is in trunk mode with ths command switchport trunk native vlan 1 (the pc should get an ip address..shouidnt it

Not always true.  If your PC's port is configured as a Trunk then yes.  It could potentially get a DHCP lease.  But if it's an ordinary port then it should connect to an access port.

Try it.  Remove the "switchport mode trunk" command and see if the PC gets a valid IP address.

[Network Pro]

yes removing gets an address...but i think this just happens on this switch cisco 3560..the config is set to trunk

switchport mode trunk

switchport trunk native vla 1

switchport trunk encap dot1q

switchport voce vlan100

but i thought this shd work even without the phones connected as the pc will send untagged frames through this trunk which in turn will get an dhcp address?

[Leo Laohoo]

but i think this just happens on this switch cisco 3560

No it doesn't.  It happens because you have "switchport mode trunk".

What are you trying to do?

[Network Pro]

right, we are using nortel ip phones daisy chaied to pc's...since nortel ip phones dont support cdp..we had to trunk ports ..but not all ports are used for phones daisy chaied with pc's. some ports are used for pc's but they seem to get an ipaddress with the same config

[Leo Laohoo]

Yup.  I remembered this.  Nortel phones running very old firmwares don't support CDP so, yes, we made each ports 802.1Q trunk.  However, we did something funky to the DHCP server and I don't remember how.  This was back in 2007.

[Network Pro]

so is the only way to get an ip is to change it to switch port voice vlan and remove trunk...so wont it get an ip with a trunk config even though native vlan is allowed ?

also with the same trunk port config..static add seems to work fine

[Network Pro]

actually the same config seems to work on a different port on the same switch - the pc has got an ip without a phone connected to it ? confusing

[cadet alain]

could  you post output of sh run int x where x are the port number for the one working and the failing one.

also same with show int xx switchport and sh int xx status command.

also post sh  run | be dhcp and sh ip dhcp binding as well as sh ip dhcp pool  outputs.

Regards.

Alain.

[stephenshaw]

Hi,

we use Nortel IP Phones with a PC connected to the phone and use the following config on a 3560:

interface FastEthernet0/1

switchport access vlan 20

switchport mode access

switchport voice vlan 30

spanning-tree portfast

By default, the DHCP request goes to the data VLAN first (great for the PC, not so great for the IP Phone), so the strings on the DHCP server need to point to the Voice VLAN as well so that both the PC and IP Phone receive the correct IP address in the correct VLAN. A different team handles the DHCP strings so I have no examples for you.

Years ago, someone had configured what you attempted and we simply removed the "old" config and replaced with this one.

HTH,

Steve

[Network Pro]

Hi Stephen shaw,

thanks for the reply..does the above config work as i thought nortel phones dont understand the command voice vlan..initially we tried this but i think pc and phone did pick the ip address inthe same range even though the strings were present...is it working for you ?

thanks