ip phone mac address

Answered Question
Dec 28th, 2008
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Hi every body!

My book describe cisco ip phone as a switch with three ports. One port is for PC connection, one port to connect to upstream switch, the last port that internally connect to voip data stream.

My question is if I use the show mac on upstream switch , it will show me the mac addresses of the hosts and ports via these hosts can be reached.

If a switch is connected to ip phone via trunk on f0/1,and I use the command show mac, what address will be listed there for ip phone? one thing I think it can not be the mac address of ip phone port connected to switch's f0/1 because it should be address of host not of the port connected to switch's f0/1.

thanks a lot!



Correct Answer by Edison Ortiz about 8 years 2 months ago

I read that ip pone has its mac address listed on its back.


Correct.


Is that mac address, we find in mac table of the switch for ip phone?


Correct again.


This mac address could not be same as the mac address of the IP phone's port, connected to switch?.


Huh?


The switchport will displayed the Mac-address of the phone (the one printed on the back of the phone). If you have a PC connected to the back of the phone, the switch will also list the PC Mac-address coming from the same port. Thus, the switch sees 2 devices coming from a single port /just like a hub connection to the switch/.


__


Edison.





Correct Answer by Giuseppe Larosa about 8 years 2 months ago

Hello Sarah,


let's use an example:


SW-RM-SXR000-A-C-1#sh mac-address-table int gi2/10

Unicast Entries

vlan mac address type protocols port

-------+---------------+--------+---------------------+--------------------

10 001e.4af3.4916 dynamic ip GigabitEthernet2/10


Multicast Entries

vlan mac address type ports

-------+---------------+-------+--------------------------------------------

4 ffff.ffff.ffff system Gi2/10,Gi2/19,Gi3/23,Te1/1

10 ffff.ffff.ffff system Gi2/1,Gi2/3,Gi2/4,Gi2/5,Gi2/9,Gi2/10,Gi2/11

Gi2/13,Gi2/14,Gi2/15,Gi2/16,Gi2/17,Gi2/19

Gi2/20,Gi2/21,Gi2/22,Gi2/23,Te1/1


SW-RM-SXR000-A-C-1#sh cdp n g2/10

Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge

S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone


Device ID Local Intrfce Holdtme Capability Platform Port ID

SEP001E4AF34916 Gig 2/10 148 H P IP Phone Port 1

SW-RM-SXR000-A-C-1#


the phone name is made of SEP+MAC address without the dots.

Actually the phone exposes only one MAC, it hasn't a MAC address for each of the 3 ports of the built-in bridge


Hope to help

Giuseppe


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Edison Ortiz Sun, 12/28/2008 - 19:49
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The switchport will show multiple mac-addresses, the phone and the workstation connected behind it.


That's the main aspect to consider when deploying port-security on switchports, you need to account for the VoIP phone and the host device.


HTH,


__


Edison.

sarahr202 Mon, 12/29/2008 - 20:03
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Thanks a lot Edison!

I am only concerned about the mac address of the ip phone. I read that ip pone has its mac address listed on its back. Is that mac address, we find in mac table of the switch for ip phone? This mac address could not be same as the mac address of the IP phone's port, connected to switch?.

Thanks a lot and happy new year!

Correct Answer
Giuseppe Larosa Tue, 12/30/2008 - 00:45
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Hello Sarah,


let's use an example:


SW-RM-SXR000-A-C-1#sh mac-address-table int gi2/10

Unicast Entries

vlan mac address type protocols port

-------+---------------+--------+---------------------+--------------------

10 001e.4af3.4916 dynamic ip GigabitEthernet2/10


Multicast Entries

vlan mac address type ports

-------+---------------+-------+--------------------------------------------

4 ffff.ffff.ffff system Gi2/10,Gi2/19,Gi3/23,Te1/1

10 ffff.ffff.ffff system Gi2/1,Gi2/3,Gi2/4,Gi2/5,Gi2/9,Gi2/10,Gi2/11

Gi2/13,Gi2/14,Gi2/15,Gi2/16,Gi2/17,Gi2/19

Gi2/20,Gi2/21,Gi2/22,Gi2/23,Te1/1


SW-RM-SXR000-A-C-1#sh cdp n g2/10

Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge

S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone


Device ID Local Intrfce Holdtme Capability Platform Port ID

SEP001E4AF34916 Gig 2/10 148 H P IP Phone Port 1

SW-RM-SXR000-A-C-1#


the phone name is made of SEP+MAC address without the dots.

Actually the phone exposes only one MAC, it hasn't a MAC address for each of the 3 ports of the built-in bridge


Hope to help

Giuseppe


sarahr202 Tue, 12/30/2008 - 12:55
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Thanks a lot Giuseppe!

Correct Answer
Edison Ortiz Tue, 12/30/2008 - 07:27
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I read that ip pone has its mac address listed on its back.


Correct.


Is that mac address, we find in mac table of the switch for ip phone?


Correct again.


This mac address could not be same as the mac address of the IP phone's port, connected to switch?.


Huh?


The switchport will displayed the Mac-address of the phone (the one printed on the back of the phone). If you have a PC connected to the back of the phone, the switch will also list the PC Mac-address coming from the same port. Thus, the switch sees 2 devices coming from a single port /just like a hub connection to the switch/.


__


Edison.





sarahr202 Tue, 12/30/2008 - 12:52
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Thanks a lot Edison!

I am still a novice and will remain so for long time.

I just want to reassure myself that I have correct understanding. thanks a lot for taking time to answer my weird , stupid questions

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