Purpose of adding Second IP address for the same Network Adapter

jskfan
jskfan used Ask the Experts™
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I have seen cases where a second IP address is added to the same Network Adapter. However I am not sure in what scenario this will be helpful.

Any idea ?

Thank you
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Configuring multiple IP addresses on one network card is called multi-homing.. it can answer for multiple IP addresses with a single MAC address.. This is mostly done in linux or in server virtualization.. This can be used to expose a server in two network ranges or to increase the reliability of an IP network..
Patrick BogersDatacenter platform engineer Lindows
Commented:
Hi

A purpose can be that you host 2 websites on 1 server which have seperate DNS entries. In this case you can have the webserver respond to specific ip adressess.
Dave BaldwinFixer of Problems
Most Valuable Expert 2014
Commented:
I have second IP addresses on several computers to access second web servers.  On some of my Linux machines, I have 6 or more IP addresses to directly access the 6 or more websites that are hosted there.
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Author

Commented:
I found a scenario here : https://www.youtube.com/watch?v=eumOs9LhBIo
on the same Network Adapter, the administrator added a second IP address on the same subnet as the main IP, and he added the subnet mask..that's all, no default gateway no DNS ip address.
He called it management ip address, I am not sure why..
and he disabled:
"Register this connection's addresses in DNS"
"Disable Netbios over TCP/IP"
Patrick BogersDatacenter platform engineer Lindows
Commented:
Clear, not registring to DNS simply means he does not want this ip address to be found through DNS.
Because is he naming it Management can mean he wants to remotely manage this machine for which he knows the ip address.
"Batchelor", Developer and EE Topic Advisor
Top Expert 2015
Commented:
That's the correct way if you have more than one IP on the same network. If the other IP would be registered in DNS, it would be used for every second request (round-robin, a default behaviour of DNS), and that is unwanted in most cases.
The same applies to NetBIOS, which registers and solicits NetBIOS services with name and IP.

In short, the DNS name, IP and MAC addresses should be unique.

Re purpose, you can build logical subnets that way. E.g. 192.168.20.0/24 and 192.168.21.0/24. Those subnets cannot talk on IP level with each other unless you allow for routing explicit. But both can reach that server if it has IP addresses in both networks.
However, IMHO a management address on the same NIC doesn't make sense to me. You usually have a management address on a separate NIC, if at all, to allow for out-of-band management (e.g. iLO and the like - being able to get to the BIOS and other non-OS featuers remotely).
Qlemo"Batchelor", Developer and EE Topic Advisor
Top Expert 2015
Commented:
On another note, I have seen NICs having IPs in the same subnet - that is nonsense in a LAN, but might be useful in a virtual server/service scenario as mentioned above (multi-homed).
Will SzymkowskiSenior Solution Architect
Most Valuable Expert 2015
Top Expert 2015
Commented:
The best scenario I could give you (as I had to perform this exact operation) is an Active Directory Domain upgrade.

I was working on a vary large migration 30,000+ User account alone and there was a very short timeline to get the new DC's up and running and decommissioning the old Domain controllers (which are acting as DNS servers as well).

Being in a large environment where we have hundreds of printers/servers etc it would have been impossible to complete this project ontime having to go around and change all of the DNS static pointers.

What I did instead was as I decommissioned the old DC's I added it's IP address to the corresponding DC that was replacing it as a secondary IP. This made for a smooth transition as they wanted to use New IP addresses (dont as me why), but having that many devices was the most seamless approach.

I then made this project phase 2 to cleanup all of the old DNS entries on printers/servers etc and then remove the secondary IP addresses from the new DC's.

Will.
Maidine FouadEngineer
Commented:
A simple scenario would be a a user served by more than one Internet service provider^^, so you have redunduncy set up if one link fails you...

A Complex scenario using  multihomed host would be backups ,Since you do not want these backups to cause congestion for example on a production network , so it can stay clear and go to the dedicated backup network even if I am working during the scheduled backups...
Qlemo"Batchelor", Developer and EE Topic Advisor
Top Expert 2015

Commented:
Fouad - we are talking about a single NIC here.

Author

Commented:
Thank you Guys!
I do this all the time when configuring and setting up consumer devices. For example if I want to change an IP Camera, SIP phone, or Router from 192.168/24 to 10.10/16 I bind both to my NIC and don't have to keep changing my IP.

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