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why all vlans have same Mac address but different IP address

this is output of sh int command

sh int

Vlan3 is up, line protocol is up

Hardware is Cat6k RP Virtual Ethernet, address is 000f.35e0.7bfc (bia 000f.35e0.7bfc)

Description:

Internet address is 10.163.40.225/28

MTU 1500 bytes, BW 1000000 Kbit, DLY Encapsulation ARPA, loopback not set

Vlan4 is up, line protocol is up

Hardware is Cat6k RP Virtual Ethernet, address is 000f.35e0.7bfc (bia 000f.35e0.7bfc)

Description:

Vlan7 is up, line protocol is up

Hardware is Cat6k RP Virtual Ethernet, address is 000f.35e0.7bfc (bia 000f.35e0.7bfc)

Description:

Internet address is 10.180.0.1/30

Vlan9 is up, line protocol is up

Hardware is Cat6k RP Virtual Ethernet, address is 000f.35e0.7bfc (bia 000f.35e0.7bfc)

Description:

Internet address is 10.180.0.6/30

MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec,

output hang never

Last clearing of "show interface" counters never

Vlan12 is up, line protocol is up

Hardware is Cat6k RP Virtual Ethernet, address is 000f.35e0.7bfc (bia 000f.35e0.7bfc)

Description: BTRadianz - London Stock Exchange Feed

Internet address is 10.180.0.9/29

buffers swapped out

Vlan17 is up, line protocol is up

Hardware is Cat6k RP Virtual Ethernet, address is 000f.35e0.7bfc (bia 000f.35e0.7bfc)

Description: S2E - CFT Axway

Internet address is 10.180.0.18/30

ARP type: ARPA, ARP Timeout 04:00:00

Vlan100 is administratively down, line protocol is down

Hardware is Cat6k RP Virtual Ethernet, address is 000f.35e0.7bfc (bia 000f.35e0.7bfc)

Description: Swift/Crest backup

Vlan101 is up, line protocol is up

Hardware is Cat6k RP Virtual Ethernet, address is 000f.35e0.7bfc (bia 000f.35e0.7bfc)

Description: Swift Crest SAG VPN

Internet address is 192.168.0.174/29

Input queue: 0/75/4/2 (size/max/drops/flushes); Total output drops: 0

Queueing strategy: fifo

Output queue :0/40 (size/max)

5 minute input rate 2000 bits/sec, 2 packets/sec

5 minute output rate 2000 bits/sec, 2 packets/sec

182518373 packets input, 2626452751 bytes, 0 no buffer

Received 23918852 broadcasts, 0 runts, 0 giants, 0 throttles

0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored

167599924 packets output, 2621003072 bytes, 0 underruns

0 output errors, 2 interface resets

0 output buffer failures, 0 output buffers swapped out

Loopback0 is up, line protocol is up

Hardware is Loopback

Internet address is 10.163.40.14/32

MTU 1514 bytes, BW 8000000 Kbit, DLY 5000 usec,

reliability 255/255, txload 1/255, rxload 1/255

Encapsulation LOOPBACK, loopback not set

Last input 43w6d, output never, output hang never

Last clearing of "show interface" counters never

Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0

Queueing strategy: fifo

Output queue :0/0 (size/max)

5 minute input rate 0 bits/sec, 0 packets/sec

5 minute output rate 0 bits/sec, 0 packets/sec

0 packets input, 0 bytes, 0 no buffer

Received 0 broadcasts, 0 runts, 0 giants, 0 throttles

0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort

4 packets output, 2416 bytes, 0 underruns

0 output errors, 0 collisions, 0 interface resets

0 output buffer failures, 0 output buffers swapped out

My question is w ehave different IP address for vlans but why we have same Mac-address for all vlans?

If someone can explain we this ?

1 ACCEPTED SOLUTION

Accepted Solutions

Re: why all vlans have same Mac address but different IP address

by design, your physical interfaces on your switch will have a unique L2 mac address assigned to it. Your Logical Vlan interfaces (SVI) will share the same mac address assigned by the hardware by design.

Franco.

17 REPLIES
Silver

Re: why all vlans have same Mac address but different IP address

VLAN's are vitual interfaces that must have a seperate IP address.

The only way to keep them seperate is by IP addresses, like any other inerface you would use, you cannot have the same network assigned to different interfaces on the same device. In this case your VLAN, just as the name implies is virtual. It must be assigned with some type of layer 2 address so the rest of the layer devices know where it is at.

Is this what you were looking for?

Community Member

Re: why all vlans have same Mac address but different IP address

when i do this command

sh vlans

No Virtual LANs configured.

it shows no virtual vlans config

why it says no virtual vlans config

Silver

Re: why all vlans have same Mac address but different IP address

VLAN = Virtual Local Area Network

Re: why all vlans have same Mac address but different IP address

Hi Engagerocks,

A simple explaination would be A VLAN do not have a mac address as it's virtual and not physical, this is why it will use the mac address of the interface it will use to transport the vlan.

HTH, Please rate

Regards,

Justin

Community Member

Re: why all vlans have same Mac address but different IP address

Hi justin,

thanks for your answer

for e.g vlan 9 has one physical port

and vlan 12 has 3 physical ports so it will

use mac address of these switch ports to pass

the traffic

Silver

Re: why all vlans have same Mac address but different IP address

That is exactly what was said.

See previous post.

Re: why all vlans have same Mac address but different IP address

Community Member

Re: why all vlans have same Mac address but different IP address

hi thanks for you reply.

so now we have this

vlan7 with mac address 000f.35e0.7bfc (bia 000f.35e0.7bfc)

port 3/3 is in vlan7.

i did

sh port mac-address 3/3

Port Mac address

----- -----------------

3/3 00-0f-f7-16-99-52

so this mac address is of switch port 3/3 right?

then i did

sh cam dynamic 3/3

* = Static Entry. + = Permanent Entry. # = System Entry. R = Router Entry.

X = Port Security Entry $ = Dot1x Security Entry

VLAN Dest MAC/Route Des [CoS] Destination Ports or VCs / [Protocol Type]

---- ------------------ ----- -------------------------------------------

7 00-0b-fc-c4-b4-08 3/3 [ALL]

Total Matching CAM Entries Displayed =1

so now this mac address is learned dynamically from switch port 3/3 right????????

Silver

Re: why all vlans have same Mac address but different IP address

It has been a while since working with catOS

I believe the sh cam dynam is showing the MAC of the attached device to that port.

Re: why all vlans have same Mac address but different IP address

by design, your physical interfaces on your switch will have a unique L2 mac address assigned to it. Your Logical Vlan interfaces (SVI) will share the same mac address assigned by the hardware by design.

Franco.

Re: why all vlans have same Mac address but different IP address

so port 3/3 will have it own unique mac address. any frame going out of that port 3/3 will originate from that mac address. for example if that port is trunk to anther switch.

while your vlans SVI will share same mac address assigned by the switch

Community Member

Re: why all vlans have same Mac address but different IP address

thanks Francisco.

So how it is decided which Mac address is assinged to SVI interfaces.

From where that Mac address comes????

Re: why all vlans have same Mac address but different IP address

the switch decides that. the switch got built in mac addresses which it uses.

for example on a catalyst 6500 switch the "sh catalyst6000 chassis-mac-addresses" will give you the output below which shows that the cat 6500 got 1024 mac addresses to use for maybe STP (Spanning-tree), Vlan SVI etc.

chassis MAC addresses: 1024 addresses from 001a.e314.b000 to 001a.e314.b3ff

what is your switch model?

Franco.

Community Member

Re: why all vlans have same Mac address but different IP address

Hi Francisco

thanks for reply

my switch model is WS-C6509 Software, Version NmpSW: 7.6(6)

Community Member

Re: why all vlans have same Mac address but different IP address

Hi Francisco

model is

Cisco 6509 SUP II MSFC II

Re: why all vlans have same Mac address but different IP address

not sure the command to use on catos similar to "sh catalyst6000 chassis-mac-addresses" on ios to look at mac address. but the design are the same, the way the switches uses mac address.

did i answered your question above? is there anything you need help with?

Franco.

Community Member

Re: why all vlans have same Mac address but different IP address

Hi francisco,

also it has Cat OS

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