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I am migrating nearly 20 websites from a win 2003 server to a win 2012 server. Both are VMware VM's, on different boxes, but in the same server room, and attached to the same switch.

The 2003 server has one NIC and an IP address per site. IIS is mapped one site per IP.

When I have migrated and tested each site, I remove the IP from the old server and set it up on the new server's NIC settings, and in IIS.

This works fine, but for between 10 and 120 minutes (ish) the new server is unreachable. I assume due to moving the IP to an interface with a new MAC address the routing ARP tables are wrong for some time on the network switch(es)? There is no change to DNS.

Is there anything I can do to speed this up?(sorry i cant give any more in-depth network architecture info as i dont have it, and do not have access to the switches)

Digital Lightcraft
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In order to get the switch(es) routing table to update, the server needs to send out via its new IP, so that the new MAC can be known.

To do this I simply restarted the server - It seems on boot the NIC must send out some sort of data from all of its configured IP addresses.

Digital Lightcraft
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ipconfig /flushdns on the client should do the trick. If it's the router that's the issue, flushing the ARP cache would work.

Correction, I realized this was when changing DNS records, not moving IPs. Please disregard.

Jim G.
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  • I gave that a go, it didnt actually do anything, but thanks. – Digital Lightcraft Apr 23 '15 at 15:28
  • Both of those statements are wrong. DNS doesn't have anything to do with ARP. The website names and ip address aren't changing. Local traffic doesn't transit the router so flushing the ARP cache on the router would be pointless. Moreover, ARP resolves ip addresses to MAC addresses, which could be a problem on the client side, but not on the switch side. On the switch you would need to clear the MAC address table, which isn't related to ARP. – joeqwerty Apr 23 '15 at 15:28
  • I thought it was a bit hopeful @joeqwerty - it is not a client side issue. I have just tried restarting the server after an IP swap, this seems to have done the trick (this time) - will try the same again next time. Does the server send out some sort of "hello" broadcast from all configured IPs on startup? – Digital Lightcraft Apr 23 '15 at 15:32
  • The switch needs to know what switch port the MAC address of the server NIC is associated with and that only happens upon the server communicating. The MAC address learning process on a switch occurs from the `source` traffic, not the `destination` traffic. So while the server doesn't `broadcast` any information regarding the websites, it appears that it is communicating on the network during a reboot, allowing the switch to map it's MAC address to the port in the MAC address table. Switches generally have a MAC address table aging time of 5 minutes. – joeqwerty Apr 23 '15 at 15:37
  • Yes i know that joe! I was really asking if there was a way to make that process happen, as opposed to waiting for it to happen at some random point. – Digital Lightcraft Apr 23 '15 at 15:49