Need to map static mac to multiple ports

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Apr 8th, 2010
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I want to map a mac-address to 2 different ports on the same switch.  However, it appears that I am only able to map one mac-address to one port.  here is the command I entered:

(config)#mac-address-table static 0001.0243.e6ce vlan 45 int gig1/27 gig1/28 (when entering the second interface it is no longer a valid command)

Switch: WS-C4948

IOS:  12.2.53(SG2)

Any ideas?

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Federico Coto F... Thu, 04/08/2010 - 13:15
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The switch will only allow you to define a MAC address via a single port (as far as I know).

If the switch learns about a MAC address via more than one port it generates an error.

Why do you want to map the same MAC address via 2 different ports on the switch?


d3mb0y555 Thu, 04/08/2010 - 13:33
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It can be done. I am able to do this on other 4948 switches on my network. I need to do this for a MS NLB that load balances between two servers.

Federico Coto F... Thu, 04/08/2010 - 13:54
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What if you try it like this:

mac-address-table static 0001.0243.e6ce vlan 45 int gig1/27

mac-address-table static 0001.0243.e6ce vlan 45 int gig1/28


d3mb0y555 Thu, 04/08/2010 - 15:15
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I tried that also. It only overwrites the previous entry

Federico Coto F... Thu, 04/08/2010 - 15:17
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Can you post the valid command from one of your 4948s?


d3mb0y555 Thu, 04/08/2010 - 15:45
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This is what a valid command looks like on the switch

mac-address-table static 03bf.8fd6.0c59 vlan 12 interface Gi1/17 Gi1/43 

adfsdafs adsfafds Mon, 02/15/2016 - 23:01
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Switch(config)#$-table static 1111.1111.1111 vlan 2 in gi 0/0 gi 0/1 gi 0/2

Switch(config)#$-table static 1111.1111.1111 vlan 3 in gi 0/0 gi 0/1 gi 0/2

Switch#show mac address-table static
Mac Address Table

Vlan Mac Address Type Ports
---- ----------- -------- -----
2 1111.1111.1111 STATIC Gi0/0 Gi0/1 Gi0/2
3 1111.1111.1111 STATIC Gi0/0 Gi0/1 Gi0/2
Total Mac Addresses for this criterion: 2

I managed to add a static mac address to multiple interfaces without ip multicast-routing.

vios_l2-ADVENTERPRISEK9-M), Version 15.2(4.0.55)E

adfsdafs adsfafds Mon, 02/15/2016 - 23:05
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How well has this kind of load balancer worked for you? If I am understand correctly, you have 2 servers with identical mac address and and you try to have them each receive a copy of the inbound traffic. Both server have other NICs, correct (so this pair of NICs with the same MAC is dedicated for load balancing the application and nothing else, not sure if this is even possible on Windows)? If not I can imagine so many things go horribly wrong.

paolo bevilacqua Thu, 04/08/2010 - 16:05
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You cannot have the same mac address mapped to more than one port.

Rule from "bridging basics"

Federico Coto F... Thu, 04/08/2010 - 16:09
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That's what I said!

But how come you have those commands on your others 4948s?

On the mac-address table of those 4948s, do you see those MAC addresses on both ports?


d3mb0y555 Thu, 04/08/2010 - 16:38
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Of course you can. The switch will treat it as a multicast address and switch information to the ports assigned to it.

"Rule from bridging basics"

d3mb0y555 Thu, 04/08/2010 - 16:39
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Yes, the entry is in the mac table as a static multicast entry with the designated ports assigned to it.

Federico Coto F... Thu, 04/08/2010 - 16:43
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Not any MAC address is a multicast MAC address (just as not any IP address is a multicast IP address)

How does a router or a switch relate a multicast IP address with a MAC address? Normally, network interface cards (NICs) on a LAN segment only receive packets destined for their burned-in MAC address. However, there is no Address Resolution Protocol (ARP) equivalent for multicast address mapping.

Instead, IANA has set aside the vendor code portion of the reserved Organizationally Unique Identifier (OUI) value to identify multicast MAC addresses. Multicast MAC addresses always begin with the low-order bit (0x01) in the first octet. Specifically, the 0x01005e prefix (plus the next lower bit, which is zero) has been reserved for mapping Layer 3 IP multicast addresses into Layer 2 MAC addresses. The complete multicast MAC address range is from 0100.5e00.0000 through 0100.5e7f.ffff


aburnworth Wed, 10/09/2013 - 16:32
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So I know this is WAAAAY old, but just wanted to document this: ip multicast-routing needs to be enabled (not configured in depth, just the single command) before it will allow you to map MACs to multiple destination interfaces.


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