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New Member

Need to map static mac to multiple ports

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?

15 REPLIES

Re: Need to map static mac to multiple ports

Hi,

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?

Federico.

New Member

Re: Need to map static mac to multiple ports

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.

Re: Need to map static mac to multiple ports

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

Federico.

New Member

Re: Need to map static mac to multiple ports

I tried that also. It only overwrites the previous entry

Re: Need to map static mac to multiple ports

Can you post the valid command from one of your 4948s?

Federico.

New Member

Re: Need to map static mac to multiple ports

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 

New Member

Switch(config)#$-table static

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

New Member

How well has this kind of

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.

Hall of Fame Super Gold

Re: Need to map static mac to multiple ports

You cannot have the same mac address mapped to more than one port.

Rule from "bridging basics"

Re: Need to map static mac to multiple ports

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?

Federico.

New Member

Re: Need to map static mac to multiple ports

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"

New Member

Re: Need to map static mac to multiple ports

Yes, the entry is in the mac table as a static multicast entry with the designated ports assigned to it.

Re: Need to map static mac to multiple ports

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

Federico.

New Member

Need to map static mac to multiple ports

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.

Cisco Employee

Re: Need to map static mac to multiple ports

Hi all

 

It's been really some time since this thread was brought but I have some usefull information: I believe mapping of a single MAC to multiple ports is possible, but it depends of the MAC type.

 

-for unicast MACs this kind of configuration ishould not not possible;

 

-for multicast MACs this is allowed. Multicast MACs have their 8th bit set to 1, and this is something that explains why  d3mb0y555 managed to map 03bf.8fd6.0c59 to multiple ports (03 =  00000011)

 

Information from Federico Coto Fajardo is almost complete: what I want to add is that is that Multicast MAC doesn't necessarily must start with "0100.5e": this range is for automatic IP to MAC map. Just by by having the 8th bit set to 1 is enough for it to be a multicast MAC

 
Regards

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