Multiple Default Gateways Can Cause Connectivity Problems
For more information on dead gateway detection and registry parameterTcpMaxDataRetransmissions, please see the following Microsoft KnowledgeBase articles:
TITLE : Dead Gateway Detection in TCP/IP for Windows NT
TITLE : How to Optimize Windows NT to Run Over Slow WAN Links w/TCP/IP
If the switched gateway is unreachable or inactive on the network, it losesconnectivity to all remote sites. At this point, a ping to this computerfrom a remote network will fail to get a positive response. Similarly, anyoutgoing ping to a remote host from this computer will give a Request timedout error. This behavior is by design and conforms to TCP/IPspecifications.
The following illustrations describe situations where multiple gateways areused.
Consider a computer with two network cards, Netcard1 and Netcard2, and thefollowing IP addresses and default gateways:
Netcard1: IP Address: 18.104.22.168 Mask: 255.255.0.0 Default Gateway: 22.214.171.124 126.96.36.199Netcard2: IP Address: 188.8.131.52 Mask: 255.255.0.0 Default Gateway: 184.108.40.206
If you want to Telnet to a workstation with an IP address of 220.127.116.11,the IP datagrams will be routed through the 18.104.22.168 gateway. If22.214.171.124 is detected as unavailable, IP switches to the second gateway126.96.36.199. When this gateway fails, then use 188.8.131.52, and so on. Thisapplies only to TCP traffic and switching gateways occurs based on themechanism described earlier. Telnet, FTP, and NetBIOS Session servicenetwork traffic use TCP for network communications.
Also consider where the two networks connected to Netcard1 andNetcard2 are disjointed (that is, not connected to each other through anyother router). If there is a network (say 22.101.x.x) that is accessibleonly through Netcard2, the IP datagrams for this network will still berouted through 184.108.40.206 because it is the primary default gateway. Toroute IP datagrams destined to network 22.101.x.x through 220.127.116.11, astatic route needs to be added to the routing table through the ROUTEutility. To add the route, type the following command:
route add 18.104.22.168 MASK 255.255.0.0 22.214.171.124
Another possible solution for the above scenario is to run multiprotocolrouting on the multihomed Windows NT computer so it can exchange routinginformation with other routers on the network running Routing InformationProtocol. Multiprotocol routing is available in Windows NT 3.51 ServicePack 2 or later.
For further information, please reference the following Microsoft KnowledgeBase article:
TITLE : TCP/IP Dead Gateway Detection Algorithm Updated for Windows NT
Αναγνωριστικό άρθρου: 159168 - Τελευταία αναθεώρηση: 02/21/2009 00:19:13 - Αναθεώρηση: 3.0
- kbnetwork KB159168