Single nic multiple subnets colocation
I have a web server (Windows 2008) colocated at a data center. I requested additional IP's and they assigned new IP's with a different subnet mask and default gateway. I added the new IP's but not the new default gateway which I understand could cause problems. Nor did I add static routes. I tested pinging out with the source option set to the new IPs, pinging in to a new IP and accessing into the ftp server and they all worked. Could this work well? Or how else should I test or configure this? How is it that the new IPs seem to work with the default gateway of the other IP block? Should I add a static route?
June 27th, 2011 7:26pm

Hi, Thank you for your post. Your server can have multiple IP addresses—even if the computers only have a single network adapter card. When you're installing an intranet server, you may also want the server to provide Web, FTP, and SMTP services. You can use a different IP address for each service, and you can use different IP addresses for the intranet and the FTP services. If your network is divided into multiple logical IP networks (subnets) and the computer needs access to these subnets to route information or provide other internetworking services, you may want a single network adapter card to have multiple IP addresses. For example, the address 192.168.1.10 could be used for workstations accessing a server from the 192.168.1.0 subnet and the address 192.168.11.10 could be used for workstations accessing a server from the 192.168.11.0 subnet. Meanwhile, the default gateway is a global configuration for the server, not a setting that must be set for each network adapter or each IP address. The default gateway is used only for traffic that needs to go to a network for which the server has no route. For more information about Default Gateway Configuration for Multihomed Computers: http://support.microsoft.com/kb/157025 For your scenario, I think there are two instances where you might need to manually edit the local route table for your server: 1.The computer is multihomed, and has no access to a default gateway. The computer in this case must provide the routing information to send IP packets from one network to the next, because no router is provided to perform this task. 2. The required routing information is not provided by any default gateway, or a different route is wanted. Best Regards, James Zou In this example it seems I would know the destination addresses and for an intranet server. My server is a web server with public IPs The destination can be any public IP address so I cannot setup a route based on the destination. Is it possible to set a route based on the source IP address? In the case of a datacenter, will it usually work to use a gateway corresponding to a different subnet?
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June 28th, 2011 2:37pm

That is why I expected. But why does ping -S x.x.x.x yahoo.com work with x.x.x.x=the new IP?
July 1st, 2011 4:15pm

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