http://www.ipadev.org/
http://www.verycd.com/topics/2863494/
Tuesday, November 23, 2010
Network Know how memo 201011
In an Ethernet switching environment (all providers have this), it's necessary to record a table of MAC addresses on the Ethernet ports of the switches. The MAC address is unique to each Ethernet device on the network; your servers each have globally unique MAC addresses. If the switch is Layer 2, it only records the port number and the MAC. If it's Layer 3 (like a router), it records the MAC, the port, and the IP in something we call the "arp table" (arp == Address Resolution Protocol, it's the method by which an IP-speaking Ethernet device resolves the map from IP to MAC).
When you added the IP .242 to the new server, the switch was still caching the old MAC in the arp table. It needed to be either cleared manually in the router, or the router would need to learn the new MAC-to-IP mapping by receiving a packet initiated from .242, or it would be cleared automatically at the end of the normal arp expiration time in the router (currently 4 hours). I would have cleared the arp table manually in this instance, but you wrote back and said it's working just a few minutes before I could get to a PC to do this.
This problem you had is unique only to customers who are in a private VLAN and can change their machine's IP themselves; perhaps in the future we can provide a way for customers to clear their own arp table within our router. But if you ever get into that situation again, you can resolve it within seconds by generating a packet toward the Internet with the source address of the IP you want to override in the arp table. Unfortunately "ping" does not allow you to do this (at least the Server 2003 version I'm looking at), because the -S flag (source address) only applies to ipv6. However you may be able to find a utility on the Internet that lets you bind to a certain IP. mIRC is one that immediately comes to mind.
When you added the IP .242 to the new server, the switch was still caching the old MAC in the arp table. It needed to be either cleared manually in the router, or the router would need to learn the new MAC-to-IP mapping by receiving a packet initiated from .242, or it would be cleared automatically at the end of the normal arp expiration time in the router (currently 4 hours). I would have cleared the arp table manually in this instance, but you wrote back and said it's working just a few minutes before I could get to a PC to do this.
This problem you had is unique only to customers who are in a private VLAN and can change their machine's IP themselves; perhaps in the future we can provide a way for customers to clear their own arp table within our router. But if you ever get into that situation again, you can resolve it within seconds by generating a packet toward the Internet with the source address of the IP you want to override in the arp table. Unfortunately "ping" does not allow you to do this (at least the Server 2003 version I'm looking at), because the -S flag (source address) only applies to ipv6. However you may be able to find a utility on the Internet that lets you bind to a certain IP. mIRC is one that immediately comes to mind.
VPN step by step and other resource link
http://technet.microsoft.com/en-us/network/bb545442.aspx
Remote Access Step-by-Step Guide: Deploying Remote Access with VPN Reconnect
http://www.microsoft.com/downloads/en/details.aspx?FamilyID=7E973087-3D2D-4CAC-ABDF-CC7BDE298847&%3Bdisplaylang=en
Remote Access Step-by-Step Guide: Deploying Remote Access with VPN Reconnect
http://www.microsoft.com/downloads/en/details.aspx?FamilyID=7E973087-3D2D-4CAC-ABDF-CC7BDE298847&%3Bdisplaylang=en
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