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[SYN] [SYN-ACK] [ACK]General Network Error! Check your network documentation. is dedicated to dispelling the myth that the network is usually the source of unknown and errant behavior in applications. This is rarely the case in a well-designed network.  The difference of application to network errors is usually orders of magnitude, and geometrically increases with load. 

We will explore various networking topics from real-world experiences, ranging from L2-L3 configuration and troubleshooting to L5/L7 load-balancing to the infamous general network error.  Although many possibilities exist to accomplish a given task, tried and true methods will be presented, but these should only be taken under consideration for use in your own network after proper vetting for fit and function.

Please check out one of the most recent blog entries. You may find what you’re seeking quicker by using the Search box or jumping into the Blog posts or Forums.

Cisco ‘ip helper-address’ and Windows DHCP Servers

All ip helper-address lines configured in your VLAN take the DHCP broadcast from the client, add the router’s (gateway) address into the UDP packet, then unicasts to the DHCP servers.  [I’m sure the packet rewrite is only done once, then a copy sent to each DHCP server.]  All the listed servers configured receive the DHCPDiscover packet by the router relay.

The redundancy of your DHCP servers not only depends on your OS, but the specific version!  For Windows, your options range from a true split-scope in Windows 2008 R2 to active-failover redundancy in Windows 2012.  For not-so-robust DHCP servers (i.e., Windows 2003), you can manually configure a split-scope.  Common recommendation is the 80/20 rule with 80% of the leases configured on what you (and you alone) consider your primary DHCP server and 20% and the secondary. Exclusions get added to each DHCP server as they have overlapping scopes. 

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