# Same MAC address in multiple VLANs
**URL:** https://forum.networklessons.com/t/same-mac-address-in-multiple-vlans/1595
**Category:** Switching
**Created:** [March 21, 2017, 4:18am UTC](https://forum.networklessons.com/t/same-mac-address-in-multiple-vlans/1595 "2017-03-21T04:18:37Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@rushabhajaydoshi](https://forum.networklessons.com/u/rushabhajaydoshi)
#### Post date: [March 21, 2017, 4:18am UTC](https://forum.networklessons.com/t/same-mac-address-in-multiple-vlans/1595/1 "2017-03-21T04:18:37Z")
Hello Team,
Can you please help me out with this:
```
interface Ethernet46
description CUST-COPROSYS-DIRECT
load-interval 5
switchport trunk native vlan 50
switchport trunk allowed vlan 50,705,1373
switchport mode trunk
ip access-group acl_l3_peering_vlan_in in
ipv6 access-group acl_v6_l3_peering_vlan_in in
no lldp transmit
no lldp receive
switchport port-security maximum 3
switchport port-security violation protect
spanning-tree bpduguard enable
!
show mac address-table int et46
Vlan Mac Address Type
---- ----------- ---- ----- ----- ---------
50 0018.194a.afd0 DYNAMIC
50 001b.0de6.ab80 DYNAMIC
705 001b.0de6.ab80 DYNAMIC
1373 001b.0de6.ab80 DYNAMIC
```
Here we can see that the address 001b.0de6.ab80 was learnt over multiple VLANs. Does that indicate the presence of duplicate NICs or something else?
Warm regards.
---
### Author:  [@baskar.961](https://forum.networklessons.com/u/baskar.961)
#### Post date: [March 24, 2017, 4:13pm UTC](https://forum.networklessons.com/t/same-mac-address-in-multiple-vlans/1595/2 "2017-03-24T16:13:27Z")
In switch supports independent vlan learning, same mac-address can be learnt on different vlans. while mac lookup is based on vlan-id + dst-mac. In case of shared vlan learning this is not supported. Normally most asics today support IVL tables
---
### Author:  [@lagapidis](https://forum.networklessons.com/u/lagapidis)
#### Post date: [March 26, 2017, 7:40pm UTC](https://forum.networklessons.com/t/same-mac-address-in-multiple-vlans/1595/3 "2017-03-26T19:40:00Z")
Hello Rushabh
This is normal behaviour. Notice that the Ethernet46 interface is a TRUNK interface configured with three VLANs. That means that this trunk connects to THREE separate VLANs. This port however has only one MAC address. So it is expected that this one interface MAC address will be assocated with all of the VLANs included in the trunk.
I hope this has been helpful!
Laz
---
### Author:  [@A1A1](https://forum.networklessons.com/u/A1A1)
#### Post date: [March 5, 2023, 12:32pm UTC](https://forum.networklessons.com/t/same-mac-address-in-multiple-vlans/1595/4 "2023-03-05T12:32:15Z")
Why is there one MAC addresses for multiple VLANs? If there are multiple clients in different VLANs, shouldn’t we see different MAC addresses, too?
Does this mean it is some kind of inter-switch communication by seeing only one MAC for different VLANs?
---
### Author:  [@lagapidis](https://forum.networklessons.com/u/lagapidis)
#### Post date: [March 13, 2023, 6:22am UTC](https://forum.networklessons.com/t/same-mac-address-in-multiple-vlans/1595/5 "2023-03-13T06:22:10Z")
Hello Quirik
Indeed this post requires a deeper explanation. I went in to lab this up to get a deeper understanding of how these MAC addresses populate the MAC address table. You will see such duplication of MAC addresses whenever you have a trunk between two switches.
I created a topology where there were seven VLANs created on two switches (SW2, and SW3), and all of those VLANs are sent over a trunk connection between the two switches. The trunk connection goes across the Gi0/1 interface on both switches. Take a look at the MAC address table of SW3:
```auto
SW3#show mac address-table
Mac Address Table
-------------------------------------------
Vlan Mac Address Type Ports
---- ----------- -------- -----
1 5254.000b.225e DYNAMIC Gi0/0
1 5254.0010.949f DYNAMIC Gi0/1
1 5254.0010.defe DYNAMIC Gi0/1
1 5254.0011.337a DYNAMIC Gi0/1
1 5254.0012.4282 DYNAMIC Gi0/1
10 5254.0011.337a DYNAMIC Gi0/1
20 5254.0011.337a DYNAMIC Gi0/1
30 5254.0011.337a DYNAMIC Gi0/1
40 5254.0011.337a DYNAMIC Gi0/1
50 5254.0011.337a DYNAMIC Gi0/1
60 5254.0011.337a DYNAMIC Gi0/1
Total Mac Addresses for this criterion: 11
SW3#
```
Notice that we have the same MAC address of `5254.0011.337a` for every VLAN. What is this MAC address? Well, it’s the MAC address of the Gi0/1 interface of SW2. Note the following:
```auto
SW2#show inter gi 0/1
GigabitEthernet0/1 is up, line protocol is up (connected)
Hardware is iGbE, address is 5254.0011.337a (bia 5254.0011.337a)
MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
```
So, although in general it is considered a **hard and fast rule** that you **cannot have multiple entries of MAC addresses within a MAC address table** of a switch, the only exception to this rule is when you consider the MAC address of the port on the switch connected to your trunk. These entries are typically installed due to various control plane communications that take place using several different protocols, including CDP, STP, VTP and DTP to name a few.
> [@A1A1](#):
>
> Why is there one MAC addresses for multiple VLANs? If there are multiple clients in different VLANs, shouldn’t we see different MAC addresses, too?
The MAC address table will be populated only when there is traffic. Even if you have hosts in various VLANs, if there is no traffic to and from these devices, no additional entries will appear.
I hope this has been helpful!
Laz