one network interface with 2 ip addresses

[omar_elmohri]

I have heared about configuring an NIC on a computer with a two ip addresses using something called "ip alias" or alike, i don't understand how it can be set while we have only one MAC address.. and how we can do it?

[vladrac-ccna]

Hello Omar,

I dont know how to set it either on a pc, as I'm not very good in workstations configuration.

But, there's no problem having more than 1 IP using the same MAC.

If someone needs to communicate with your machine, it will send the packet to your IP, and the last hop router will ARP for this IP, your machine will respond with it's only MAC for every IP it has.

So you're gateway will have an 2 ARP entries:

IP1 MAC

IP2 MAC

No problem here, you can still be unique, even with 1 mac.

Actually when you have a Multi-layer switch, you'll see the IPs you have configured on the interface vlan (SVI) all associated with a single MAC (unless you configure a MAC in each interface vlan of course)

check this "live example" for instance:

switch-layer3>sh arp | i 0101.207a.1a7f

Internet 10.12.221.195 - 0101.207a.1a7f ARPA Vlan606

Internet 10.12.192.145 - 0101.207a.1a7f ARPA GigabitEthernet1/1

Internet 10.12.163.195 - 0101.207a.1a7f ARPA Vlan706

Internet 10.12.166.3 - 0101.207a.1a7f ARPA Vlan166

Internet 10.12.164.3 - 0101.207a.1a7f ARPA Vlan164

Internet 10.12.165.3 - 0101.207a.1a7f ARPA Vlan165

Internet 10.12.170.3 - 0101.207a.1a7f ARPA Vlan170

Internet 10.12.171.3 - 0101.207a.1a7f ARPA Vlan171

Internet 10.12.168.3 - 0101.207a.1a7f ARPA Vlan168

Internet 10.12.169.3 - 0101.207a.1a7f ARPA Vlan169

Internet 10.12.174.3 - 0101.207a.1a7f ARPA Vlan174

Internet 10.12.172.3 - 0101.207a.1a7f ARPA Vlan172

Internet 10.12.173.3 - 0101.207a.1a7f ARPA Vlan173

HTH,

if it does, I'd appreciate if you rated this post.

Vlad

[omar_elmohri]

It's ok,

but i still need to know how to configure it on a host.. i knew how to do it in a router inferface but not on a host NIC

[vladrac-ccna]

What is the OS? windows? linux? aix? mac?

Vlad

[vladrac-ccna]

Anyway, sorry I dont know much about workstations.

But, for your first question, I thought that the doubt was about 1 IP - 1 MAC only possibility.

Please rate that post, if it was helpfull in any means.

Vlad

[omar_elmohri]

the OS is Windows 2003 what I need to configure

[vladrac-ccna · Accepted solution]

Hello Omar,

go to network properties, TCP/IP settings -> static IP, advanced options, and there you'll be able to add as many IP that you want.

this forum is not intended for workstations issues, but I hope this helps.

and do be cheat on the votes! kidding!

Vlad