Mac address table cannot specified which vlan port number the client is connected

john.medalla · ‎02-26-2018

Hi Everyone,

Good Day!

I have a problem regarding showing the mac add table on C2960X. Please see below result.

When you check the ports Gi1/0/47 all mac add is pass through on this port wherein this is the trunking port. I don't why it show on the that port it must be on the specific port wherein the configuration is access mode.

Hoping for your positive response.

Thank you.

Vlan Mac Address Type Ports
13 0001.296b.59a9 DYNAMIC Gi1/0/47
13 0001.fc21.84fa DYNAMIC Gi1/0/47
13 0010.dbff.20d0 DYNAMIC Gi1/0/47
13 0019.99e2.3efa DYNAMIC Gi1/0/47
13 0019.99e2.3f26 DYNAMIC Gi1/0/47
13 001b.a9d5.1738 DYNAMIC Gi1/0/31
13 001b.a9de.32cc DYNAMIC Gi1/0/47
13 0080.7755.3db3 DYNAMIC Gi1/0/47
13 0080.7755.3e0d DYNAMIC Gi1/0/47
13 245e.be1a.06ae DYNAMIC Gi1/0/47
13 3005.5c0a.a805 DYNAMIC Gi1/0/31
13 3005.5c11.bc66 DYNAMIC Gi1/0/47
13 3005.5c11.be37 DYNAMIC Gi1/0/47
13 3005.5c11.be3f DYNAMIC Gi1/0/31
13 3005.5c11.be54 DYNAMIC Gi1/0/47
13 3005.5c11.bf4b DYNAMIC Gi1/0/47
13 3005.5c11.bf92 DYNAMIC Gi1/0/31
13 3005.5c11.bfa4 DYNAMIC Gi1/0/31
13 3005.5c11.bfba DYNAMIC Gi1/0/47
13 3005.5c11.bfbc DYNAMIC Gi1/0/47
13 3005.5c32.1137 DYNAMIC Gi1/0/47
13 3005.5c32.1139 DYNAMIC Gi1/0/31
13 3005.5c32.119a DYNAMIC Gi1/0/47
13 3005.5c32.11bf DYNAMIC Gi1/0/31
13 3005.5c32.11ce DYNAMIC Gi1/0/31
13 3005.5c32.1269 DYNAMIC Gi1/0/31
13 3005.5c32.1a2b DYNAMIC Gi1/0/47
13 3005.5c32.1a31 DYNAMIC Gi1/0/47
13 3005.5cf3.4373 DYNAMIC Gi1/0/47
13 3417.ebda.6752 DYNAMIC Gi1/0/47
13 3417.ebda.6baf DYNAMIC Gi1/0/47
13 3417.ebda.71f2 DYNAMIC Gi1/0/47
13 3417.ebda.7232 DYNAMIC Gi1/0/47
13 3417.ebda.727c DYNAMIC Gi1/0/47
13 3c2a.f40f.8d33 DYNAMIC Gi1/0/47
13 3c2a.f41b.485d DYNAMIC Gi1/0/47

brselzer · ‎02-26-2018

Hello,

If I understand correctly, Gi1/0/47 is a trunk port and you want to know why you are seeing the mac addresses learned there even though the devices are not directly connected to that port, is that correct?

Each switch in your topology will learn mac addresses from the source mac of a frame that comes in that port regardless of what type of port it is. Take the following topology.

PC_1 <--access--> [Port 1] Switch_1 [Port 2] <--Trunk--> [Port 1] Switch_2 [Port 2] <--Trunk--> [Port 1] Switch_3 [Port 2] <--access--> PC_2

This is three switches back to back with a PC on the ends. When a frame is sent from PC_1 to PC_2, the mac address of PC_1 will be learned on Switch_1 on Port 1 then on Switch_2 on Port 1, then on Switch_3 on Port 1 as the frame moves from switch to switch.

This is probably expected behavior unless you are learning the mac on the uplink for a PC that is directly connected to the same switch. That would be a problem and could indicate a loop of some sort.

Hope that helps!

-Bradley Selzer
CCIE# 60833

john.medalla · ‎02-26-2018

Hi Bradley,

If I understand correctly, Gi1/0/47 is a trunk port and you want to know why you are seeing the mac addresses learned there even though the devices are not directly connected to that port, is that correct?

-Yes, you are correct on this. But why are some client can pass through on specific port directly without recording the mac address on Gi1/0/47?

Please take a look the result in BOLD. The port is already on the access mode.

In my Topology.

Core Switch port 1 trunk mode<-->port 1 Distribution trunk mode port 2<--> port 2 access switch acess mode port 3<-->PC 1

13 0001.296b.59a9 DYNAMIC Gi1/0/47
13 0001.fc21.84fa DYNAMIC Gi1/0/47
13 0010.dbff.20d0 DYNAMIC Gi1/0/47
13 0019.99e2.3efa DYNAMIC Gi1/0/47
13 0019.99e2.3f26 DYNAMIC Gi1/0/47
13 001b.a9d5.1738 DYNAMIC Gi1/0/31
13 001b.a9de.32cc DYNAMIC Gi1/0/47
13 0080.7755.3db3 DYNAMIC Gi1/0/47
13 0080.7755.3e0d DYNAMIC Gi1/0/47
13 245e.be1a.06ae DYNAMIC Gi1/0/47
13 3005.5c0a.a805 DYNAMIC Gi1/0/31
13 3005.5c11.bc66 DYNAMIC Gi1/0/47
13 3005.5c11.be37 DYNAMIC Gi1/0/47
13 3005.5c11.be3f DYNAMIC Gi1/0/31
13 3005.5c11.be54 DYNAMIC Gi1/0/47
13 3005.5c11.bf4b DYNAMIC Gi1/0/47
13 3005.5c11.bf92 DYNAMIC Gi1/0/31
13 3005.5c11.bfa4 DYNAMIC Gi1/0/31
13 3005.5c11.bfba DYNAMIC Gi1/0/47
13 3005.5c11.bfbc DYNAMIC Gi1/0/47
13 3005.5c32.1137 DYNAMIC Gi1/0/47
13 3005.5c32.1139 DYNAMIC Gi1/0/31
13 3005.5c32.119a DYNAMIC Gi1/0/47
13 3005.5c32.11bf DYNAMIC Gi1/0/31
13 3005.5c32.11ce DYNAMIC Gi1/0/31

Thank you.

Regards,

John

brselzer · ‎02-28-2018

Hello,

I am still not very clear what you mean. I am not sure I understand what you mean by pass through. The mac addresses in bold should not be learned on port 1/0/31? Let's take an example mac address and show me the topology of where that device lives. This might help determine where that mac should be learned.

Thanks!

-Bradley Selzer
CCIE# 60833

john.medalla · ‎03-06-2018

Hi Bradley,

Sorry for the late response.

Please take look below the topology example.

For Switch 1- Distribution Switch

C2960X-2F3A-1#show mac address-table vlan 13
Mac Address Table
-------------------------------------------

Vlan Mac Address Type Ports
---- ----------- -------- -----
All 0100.0ccc.cccc STATIC CPU
All 0100.0ccc.cccd STATIC CPU
All 0180.c200.0000 STATIC CPU
All 0180.c200.0001 STATIC CPU
All 0180.c200.0002 STATIC CPU
All 0180.c200.0003 STATIC CPU
All 0180.c200.0004 STATIC CPU
All 0180.c200.0005 STATIC CPU
All 0180.c200.0006 STATIC CPU
All 0180.c200.0007 STATIC CPU
All 0180.c200.0008 STATIC CPU
All 0180.c200.0009 STATIC CPU
All 0180.c200.000a STATIC CPU
All 0180.c200.000b STATIC CPU
All 0180.c200.000c STATIC CPU
All 0180.c200.000d STATIC CPU
All 0180.c200.000e STATIC CPU
All 0180.c200.000f STATIC CPU
All 0180.c200.0010 STATIC CPU
All ffff.ffff.ffff STATIC CPU
13 0001.296b.59a9 DYNAMIC Gi1/0/25
13 0010.dbff.20d0 DYNAMIC Gi1/0/25
13 0019.99e2.3efa DYNAMIC Gi1/0/25
13 0019.99e2.3f26 DYNAMIC Gi1/0/25
13 001b.a9af.600d DYNAMIC Gi1/0/19
13 001b.a9d5.1700 DYNAMIC Gi1/0/15
13 001b.a9d5.1738 DYNAMIC Gi1/0/9
13 001b.a9de.32cc DYNAMIC Gi1/0/19
13 0080.7755.3db3 DYNAMIC Gi1/0/25
13 0080.7755.3e0d DYNAMIC Gi1/0/25
13 245e.be1a.06ae DYNAMIC Gi1/0/25
13 2c5a.0f7e.1ef5 DYNAMIC Gi1/0/25
13 3005.5c0a.2c97 DYNAMIC Gi1/0/15
13 3005.5c0a.a805 DYNAMIC Gi1/0/9
13 3005.5c0d.7767 DYNAMIC Gi1/0/19
13 3005.5c11.bc66 DYNAMIC Gi1/0/19
13 3005.5c11.be37 DYNAMIC Gi1/0/19
13 3005.5c11.be3f DYNAMIC Gi1/0/9
13 3005.5c11.bf4b DYNAMIC Gi1/0/19
13 3005.5c11.bf92 DYNAMIC Gi1/0/9
13 3005.5c11.bfa0 DYNAMIC Gi1/0/15
13 3005.5c11.bfa4 DYNAMIC Gi1/0/9
13 3005.5c12.5ebf DYNAMIC Gi1/0/15
13 3005.5c32.1139 DYNAMIC Gi1/0/9
13 3005.5c32.119a DYNAMIC Gi1/0/19
13 3005.5c32.119f DYNAMIC Gi1/0/15
13 3005.5c32.11a4 DYNAMIC Gi1/0/15
13 3005.5c32.11c6 DYNAMIC Gi1/0/15

For Switch 2- Access Switch

C2960X-2F3A-2#show mac address-table vlan 13
Mac Address Table
-------------------------------------------

Vlan Mac Address Type Ports
---- ----------- -------- -----
All 0100.0ccc.cccc STATIC CPU
All 0100.0ccc.cccd STATIC CPU
All 0180.c200.0000 STATIC CPU
All 0180.c200.0001 STATIC CPU
All 0180.c200.0002 STATIC CPU
All 0180.c200.0003 STATIC CPU
All 0180.c200.0004 STATIC CPU
All 0180.c200.0005 STATIC CPU
All 0180.c200.0006 STATIC CPU
All 0180.c200.0007 STATIC CPU
All 0180.c200.0008 STATIC CPU
All 0180.c200.0009 STATIC CPU
All 0180.c200.000a STATIC CPU
All 0180.c200.000b STATIC CPU
All 0180.c200.000c STATIC CPU
All 0180.c200.000d STATIC CPU
All 0180.c200.000e STATIC CPU
All 0180.c200.000f STATIC CPU
All 0180.c200.0010 STATIC CPU
All ffff.ffff.ffff STATIC CPU
13 0001.296b.59a9 DYNAMIC Gi1/0/47
13 0010.dbff.20d0 DYNAMIC Gi1/0/47
13 0019.99e2.3efa DYNAMIC Gi1/0/47
13 0019.99e2.3f26 DYNAMIC Gi1/0/47
13 001b.a9de.32cc DYNAMIC Gi1/0/47
13 0080.7755.3db3 DYNAMIC Gi1/0/47
13 0080.7755.3e0d DYNAMIC Gi1/0/47
13 245e.be1a.06ae DYNAMIC Gi1/0/47
13 3005.5c0d.7767 DYNAMIC Gi1/0/47
13 3005.5c11.bf4b DYNAMIC Gi1/0/47
13 3417.ebda.6baf DYNAMIC Gi1/0/47
13 3417.ebda.71f2 DYNAMIC Gi1/0/47
13 3417.ebda.7232 DYNAMIC Gi1/0/47
13 3417.ebda.727c DYNAMIC Gi1/0/47
13 3c2a.f40f.8d35 DYNAMIC Gi1/0/47
13 3c2a.f40f.8d3c DYNAMIC Gi1/0/47
13 3c2a.f40f.8e79 DYNAMIC Gi1/0/47
13 3c2a.f41b.4721 DYNAMIC Gi1/0/47
13 3c2a.f432.97e7 DYNAMIC Gi1/0/47
13 40f2.e90d.8175 DYNAMIC Gi1/0/47
13 40f2.e92b.2444 DYNAMIC Gi1/0/47
13 40f2.e993.efba DYNAMIC Gi1/0/47
13 40f2.e993.efbe DYNAMIC Gi1/0/47
13 40f2.e99b.b70a DYNAMIC Gi1/0/47
13 40f2.e99b.b70e DYNAMIC Gi1/0/47
13 4437.e6e3.7182 DYNAMIC Gi1/0/38
13 4437.e6e3.f6e6 DYNAMIC Gi1/0/47
13 4437.e6e3.f7b1 DYNAMIC Gi1/0/47
13 4437.e6e3.f954 DYNAMIC Gi1/0/47
13 4437.e6e3.fbea DYNAMIC Gi1/0/47
13 4437.e6e3.fc49 DYNAMIC Gi1/0/47
13 4437.e6e3.fc5b DYNAMIC Gi1/0/47
13 4437.e6e3.fc68 DYNAMIC Gi1/0/47

For another access switch

C2960X-2F3A-3#show mac address-table vlan 13
Mac Address Table
-------------------------------------------

Vlan Mac Address Type Ports
---- ----------- -------- -----
All 0100.0ccc.cccc STATIC CPU
All 0100.0ccc.cccd STATIC CPU
All 0180.c200.0000 STATIC CPU
All 0180.c200.0001 STATIC CPU
All 0180.c200.0002 STATIC CPU
All 0180.c200.0003 STATIC CPU
All 0180.c200.0004 STATIC CPU
All 0180.c200.0005 STATIC CPU
All 0180.c200.0006 STATIC CPU
All 0180.c200.0007 STATIC CPU
All 0180.c200.0008 STATIC CPU
All 0180.c200.0009 STATIC CPU
All 0180.c200.000a STATIC CPU
All 0180.c200.000b STATIC CPU
All 0180.c200.000c STATIC CPU
All 0180.c200.000d STATIC CPU
All 0180.c200.000e STATIC CPU
All 0180.c200.000f STATIC CPU
All 0180.c200.0010 STATIC CPU
All ffff.ffff.ffff STATIC CPU
13 0001.296b.59a9 DYNAMIC Gi1/0/47
13 0010.dbff.20d0 DYNAMIC Gi1/0/47
13 0019.99e2.3efa DYNAMIC Gi1/0/47
13 0019.99e2.3f26 DYNAMIC Gi1/0/47
13 001b.a9af.600d DYNAMIC Gi1/0/47
13 001b.a9d5.1738 DYNAMIC Gi1/0/31
13 001b.a9de.32cc DYNAMIC Gi1/0/47
13 0080.7755.3db3 DYNAMIC Gi1/0/47
13 0080.7755.3e0d DYNAMIC Gi1/0/47
13 245e.be1a.06ae DYNAMIC Gi1/0/47
13 3005.5c0a.a805 DYNAMIC Gi1/0/31
13 3005.5c0d.7767 DYNAMIC Gi1/0/47
13 3005.5c11.be3f DYNAMIC Gi1/0/31
13 3005.5c11.bf4b DYNAMIC Gi1/0/47
13 3005.5c11.bf92 DYNAMIC Gi1/0/31
13 3005.5c11.bfa4 DYNAMIC Gi1/0/31
13 3005.5c32.1139 DYNAMIC Gi1/0/31
13 3005.5c32.119a DYNAMIC Gi1/0/47
13 3005.5c32.11ce DYNAMIC Gi1/0/31
13 3005.5c32.1263 DYNAMIC Gi1/0/47
13 3005.5c32.1269 DYNAMIC Gi1/0/31
13 3005.5c32.1a2d DYNAMIC Gi1/0/31
13 3417.ebda.6baf DYNAMIC Gi1/0/47
13 3417.ebda.71f2 DYNAMIC Gi1/0/47
13 3417.ebda.7232 DYNAMIC Gi1/0/47
13 3417.ebda.727c DYNAMIC Gi1/0/47
13 3c2a.f40f.8d35 DYNAMIC Gi1/0/47
13 3c2a.f40f.8d3c DYNAMIC Gi1/0/47
13 3c2a.f40f.8e79 DYNAMIC Gi1/0/47
13 3c2a.f41b.4721 DYNAMIC Gi1/0/47
13 3c2a.f432.97e7 DYNAMIC Gi1/0/47
13 40f2.e90d.8175 DYNAMIC Gi1/0/47
13 40f2.e92b.2444 DYNAMIC Gi1/0/47
13 40f2.e993.efba DYNAMIC Gi1/0/47
13 40f2.e993.efbe DYNAMIC Gi1/0/47
13 40f2.e99b.b70a DYNAMIC Gi1/0/47
13 40f2.e99b.b70e DYNAMIC Gi1/0/47
13 4437.e6e3.7182 DYNAMIC Gi1/0/47

You can see on BOLD same mac address is learned. Why the trunk port is show in mac address of access switc. It should be the access port right? I already try this in packet tracer. I will attached screen shot for my packet tracer

Regards,

John

brselzer · ‎03-06-2018

Hello John,

What port is 0001.296b.59a9 actually connected to and what device is it? The packet tracer picture looks correct, you see each mac learned on the access port on the access switch but the mac addresses are learned on the trunk of the distribution switch.

From the outputs you gave me, both mac address of the access switches are learned on their uplinks (I assume gig1/0/47 is the uplink). On the distribution switch, it is learned on Gig1/0/25. What is connected to Gig1/0/25? Can you post the output of show cdp ne gig1/0/25 from C2960X-2F3A-1?

Thanks!

-Bradley Selzer
CCIE# 60833

john.medalla · ‎03-06-2018

Hi Bradley,

What port is 0001.296b.59a9 actually connected to and what device is it? The packet tracer picture looks correct, you see each mac learned on the access port on the access switch but the mac addresses are learned on the trunk of the distribution switch.

-Client PC is connected to that port but I don't know which port in the access switch the mac address is connected. It should be view in the mac address table of access switch but it view the wrong port.

From the outputs you gave me, both mac address of the access switches are learned on their uplinks (I assume gig1/0/47 is the uplink). On the distribution switch, it is learned on Gig1/0/25. What is connected to Gig1/0/25? Can you post the output of show cdp ne gig1/0/25 from C2960X-2F3A-1?

-Yes, you are correct the port gig1/0/47 is the uplink. On the distribution switch the port gi1/0/25 is the uplink going to our core switch.

I attached again screenshot.

Thank you.

Regards,

John

brselzer · ‎03-06-2018

Hello,

It sounds like whatever device owns 0001.296b.59a9 is connected somewhere on the other side of the core switch. If you go to the core switch and run "show mac add | inc 0001.296b.59a9" what port is it learned on? Do a show cdp ne for that port. If it is another switch, log into that switch and repeat the process. Eventually you will find the port where the device is connected. Does that make sense?

Hope that helps!

-Bradley Selzer
CCIE# 60833