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Users are not assigned IP address through DHCP when switching VLANs or even switchports.

Alisson-CR
Occasional Visitor

Users are not assigned IP address through DHCP when switching VLANs or even switchports.

Hello All,

 

I've got a HP 7503 with DHCP enabled on several VLANs.

 

There's a strange issue going on.

 

We have some users that are wired to their desks.

Eventually, they move to any of our meeting rooms and plug their laptops on the wired connection avaliable.

When they get back to their desks, they got no network connectivity.

They do get DHCP address settings, but they're unable to ping their gateway.

 

I need to do the his procedure.

- Log on the access switch CLI and clear that mac-address from the mac-address table.

- Also, i have to logon to my L3 switch and clear the mac-address from the mac-address table and remove the arp entry from my mac-address.

 

So, i'm wondering if this is a spoofing protection or a bug.

If it's not a bug, how do I turn it off?

This is causing a lot of problems to the users.

 

Any advice is much appreciated.

Best regards.

3 REPLIES
paulgear
Esteemed Contributor

Re: Users are not assigned IP address through DHCP when switching VLANs or even switchports.

Hi Alisson-CR,

That sounds very strange indeed. If you post your configuration and any log messages relating to those ports it might help get to the bottom of things.
Regards,
Paul
Alisson-CR
Occasional Visitor

Re: Users are not assigned IP address through DHCP when switching VLANs or even switchports.

Hello Paul,

 

Thanks for your reply.

 

Apparently it's an issue with one of our Cisco phones (7492).

 

The phone is not releasing the Mac-address from it's table after the users disconnects from the PC port.

 

<CWB_N01_R06_P01>dis mac-address b888-e3e0-aa3b
MAC ADDR       VLAN ID  STATE          PORT INDEX               AGING TIME(s)
b888-e3e0-aa3b 152      Learned        GigabitEthernet2/0/6     AGING
b888-e3e0-aa3b 152      Learned        GigabitEthernet4/0/17    AGING

 

When this happens, users have no L2 connectivity until I unplug the phone from the network or clear the mac-address entries for this mac.

 

We also have other Cisco phone models, but they are working fine.

Cisco 6921, for example, correctly "migrates" the mac-address after disconnecting from one phone and reconnecting to other phone.

 

[CWB_N01_R06_P01]dis mac-address b888-e3e0-aa3b
MAC ADDR       VLAN ID  STATE          PORT INDEX               AGING TIME(s)
b888-e3e0-aa3b 152      Learned        GigabitEthernet2/0/3     AGING

  ---  1 mac address(es) found  ---

 

*** Disconnected and reconnected on other switchport - The mac has moved correctly ***

 

[CWB_N01_R06_P01]dis mac-address b888-e3e0-aa3b
MAC ADDR       VLAN ID  STATE          PORT INDEX               AGING TIME(s)
b888-e3e0-aa3b 152      Learned        GigabitEthernet2/0/6     AGING

  ---  1 mac address(es) found  ---

 

 

We'll try to upgrade the phone firmware.

if that does not work, I'll probably have to decrease the Mac-address aging time to 30s.

 

Thanks and regards.

paulgear
Esteemed Contributor

Re: Users are not assigned IP address through DHCP when switching VLANs or even switchports.

Hi Alisson-CR,

I'm not convinced this is the right track to be pursuing with this problem.

When a switch learns a MAC through two different ports, it should send packets for that MAC out *both* ports, so until the old port has aged, everything should continue to work. Even if the switch has an extra port for that MAC, it should still behave correctly.

If it is a MAC aging issue, then if you leave the device on the new port for a while and wait for the old MAC table entry to expire, it should start working. Does this happen? If not, then i think it has nothing to do with MAC tables. What concerns me more is that you have to also remove the ARP entry to make it work, especially since the ARP entry shouldn't change if they're on the same VLAN.
Regards,
Paul