![]() ![]() ![]() My test client WS18 (Windows 7) 192.168.111.18 is also hosted on LS7. I have checked the net.bridge* parameters in /etc/sysctl and they were all default to 0. Then when that didn't work I went with the rtl8139 virtual adapter on both the DNS server as well as the test client which made no difference. I assumed it was the VirtIO network driver so I upgraded to the newest provided by Fedora. I have looked at the Windows DNS event logs and everything seems ok. The CentOS 6.2 host servers logs don't reveal any errors or warnings worth mentioning. All other network connectivity seems ok, routing is working, ping responses are fast and file transfers are fine. The queries seem a little slow and sometimes work and other times the DNS servers completely fail to provide the client with a resolved IP. The DNS servers are Windows Server 2008 R2 guest servers running on two separate CentOS 6.2 servers. No visible errors except for the "DNS lookup failed" which can usually be fixed by one or two browser refresh attempts. Since the move I have started experiencing strange DNS query failures but not always. All the hosts have been configured with a bridge adapter. We'll do a separate blog on this when I have more test data.I have recently moved my Windows 2008 guest servers from OpenSuse 11.2 and Fedora 16 KVM host servers where they were working fine to a CentOS 6.2 KVM host. One last gotcha, if your server is set to automatically update the DNS server with its IP address then sometimes the DNS server will start giving the IP on the loopback adapter as your primary address! This is not good so disable automatic DNS entries on both the server and in the DNS management console. Solving the ARP problem for Linux or Windows How can you use DSR (Direct Server Return) in AWS?Īll the Load balancing methods starting with DSR. Just think if we didn't have Linux to push the boundaries - Microsoft may never have been able to copy the best features so well :-) References I've still got some more research to do on this but it looks like you can do all sorts of cool routing tricks in the new Windows TCP/IP stack. Or if you want look up the index number instead using the following command: netsh interface ipv4 show interface Obviously first you will need to rename the specific adapters from the default of "Local Area Network Connection 1" to either "net" or "loopback" respectively i.e. Netsh interface ipv4 set interface "loopback" weakhostsend=enabled Netsh interface ipv4 set interface "loopback" weakhostreceive=enabled You still need to disable the firewall (or enable traffic to and from the loopback)īut then you MUST use the following command line magic : netsh interface ipv4 set interface "net" weakhostreceive=enabled.You still need to configure the loopback adapter with the VIP (but you don't need to set the metric).The Next Generation TCP/IP stack in Windows Vista and Windows Server 2008+ supports strong host sends and receives for both IPv4 and IPv6 by default." "Windows XP and Windows Server® 2003 use the weak host model for sends and receives for all IPv4 interfaces and the strong host model for sends and receives for all IPv6 interfaces. Weak and strong host behavior in Windows: We have a whole new way of controlling networking, and I must admit it looks like Microsoft finally have a sensible way of controlling network interfaces. In Windows 2003 you also need to disable the firewall (or enable rules for the loopback adapter) In Windows 2008, Windows 2012 & Windows 2016 however: Up to and including Windows 2000 adding a loopback adapter works fine, just set the interface metric to 254 to stop dodgy routing issues. "THE SERVER MUST NEVER TELL THE NETWORK ABOUT THIS FAKE IP"! And how do you solve the ARP problem on Windows? Yes, it will drive your network mad if you start sending out ARP notifications from multiple machines on the same IP address. This then enables the real server can accept the packet. So, how do you solve the Direct Routing problem on Windows Server?īasically, we just need to add a loopback adapter with the VIP address. Then the real server will say, "Get lost, no I'm not!". The packet will say "Hello are you the VIP?" !( You can see the problem here can't you? Then the load balancer simply changes the destination MAC address of the packet (to one of the destination real servers in the pool) and flips it back to the switch which duefully delivers the packets to the selected real server: So, how does Direct Routing work?įirst, the incoming traffic from the client hits the Virtual IP (VIP) on the load balancer. ![]() And it is without doubt the fastest method possible. ![]()
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