PC Port to Switch?

[copco_online]

I have a CP-8851 phone.

An ethernet cable goes from the wall jack to the Ethernet Port and a cable goes from the PC Port to my PC.  The PC is configured to have its IP address assigned via DHCP.  DHCP is enabled on the phone.

What I would like to do is to configure a second PC by adding an unmanaged switch.  I'm not sure if this is feasible.

When I put the switch between the wall and phone, the phone would not power-up.

When I put the switch off the PC port and connected my two computers to the switch.  The one obtaining the IP address automatically still worked.  The newly added PC would not obtain an IP.  If I configured it using a static IP both PCs work.

I'm wondering if I can use it the way I am and have both PCs obtain the address via DHCP, if the way it is currently working might be short-lived until a DHCP address renewal request is made, or if the only real way is to configure them both statically.

Thank you,

- Nick

[Kalai@Madison]

Hi Nick,

I have two of my PCs and a Cisco phone connected to one port that same way you have done the cabling. So cabling is correct.  You should see 4 mac address like this. 

sh mac address-table int g3/0/40
Mac Address Table
-------------------------------------------

Vlan Mac Address Type Ports
---- ----------- -------- -----
200 00f8.2c06.8827 DYNAMIC Gi3/0/40
200 509a.4c5a.5079 DYNAMIC Gi3/0/40
200 6400.6a5f.479a DYNAMIC Gi3/0/40
3000 00f8.2c06.8828 DYNAMIC Gi3/0/40
Total Mac Addresses for this criterion: 4

Also in the port configuration need to look like:

switchport access vlan 200
switchport mode access
switchport voice vlan 3000

did you try unplugging network cable from the computer that works with dhcp and used that cable into other computer? If that works, there is no issue with DHCP. 

[copco_online]

Hello,

Thank you for the response. Where would I see the Mac Address table and port configuration? Also, what is it telling me?

I have not tried swapping the cables.  That would indicate?

[wall] --- [phone]----[switch via uplink port 5]--[(C#1-dynamic IP assignment on Port 3)  & (C#2 static IP assignment on Port 4)]

I would be switching the cables on Port 3 and Port 4 to different computers.  Is that correct?

[Kalai@Madison]

Nick,

I assume you have CLI access to the cisco switch. As you mentioned cisco phone directly connect to the wall jack. This means it is directly connected to the cisco switch. Therefore the cisco switch will learn all the mac addresses on that port (phone + PCs). Say if that phone is connected to port G1/0/10 in cisco switch. You CLI into cisco switch and issue a #sh mac-addrress table int g1/0/10

[copco_online]

Oh. OK. So, is it possible that the Cisco switch just hasn't updated itself? How does the phone relay the MAC addresses of what's connected to it. Is it configured or transparent?
Thank you.

[Kalai@Madison]

The way cisco phone works is little interesting. Basically phone and the PC are in different vlans. But you don't need a trunk port. Here is a post that explain it:



https://supportforums.cisco.com/t5/ip-telephony/how-does-the-cisco-ip-phone-work/td-p/2892620



Best

Kalai

[Kalai@Madison]

Nick,

Cisco phone has an un-managed workgroup switch inside it with two ports. One port plugs into the data jack and other one plugs in to the PC. When you connect another unmanaged switch to the PC port it is like cascading workgroup switches. So the real managed Cisco switch will see all the mac address connected to that port. 

[copco_online]

The MAC address of the cascaded unmanaged switch into which the two PCs are connected?
I've switched the cables for the PCs to use different ports and the one obtaining an IP dynamically still seems to work. The one statically assigned also works.
I've also released and renewed the IP Configuration and it seems the dynamic IP assignment still works.
Perhaps relevant, the dynamically assigned PC is older. The other PC is new and supposedly the MAC address is important for configuration. I'm thinking that the issue is probably that the MAC address is not being found/recognized.
I wouldn't know how to test that.
Thanks.

[Kalai@Madison]

To test whether the mac address is recognized at the port level - you can plug the new PC into a different port and see you can find the mac address on that port. As I mentioned before use the #sh mac address table int g1/0/10 (use the correct port number here). I think mac address is not an issue here, because if the port can't recognize the mac address it will not recognize it when you have a static IP also. I believe your NIC has some issue. Try to reset the NIC: here is how to do it

https://iihelp.iinet.net.au/Resetting_Network_Adapter_%28Winsock_Reset%29

[Kalai@Madison]

did you get this resolved?

[copco_online]

No. While it is working with one PC getting its IP assigned dynamically and the other setup statically, I have not figured out why this is occurring and whether I can get both working via DHCP. Thank you.