Thursday, February 21, 2013

Default Gateway

Over the last few years we've had several instances of Windows 7 computers having a default gateway of assigned. In all cases, the computers were obtaining an IP address from DHCP.

This is a fairly well know issue with several products the use the Bonjour service for some networking services. References I've seen to Bonjour include iTunes and Adobe CS3. However, there are likely to be others.

The basic problem is the timing of service startup. If the Bonjour service starts before the networking is initialized, the Bonjour service adds a default gateway of which overrides the default gateway that you eventually get from DHCP.

There are several ways to fix this:
  1. Update your product. I've found several references online that indicate that the latest versions of the Bonjour service don't have this issue.
  2. Disable the Bonjour service. The only downside to this is that it may impact some functionality in the product.
  3. Manually remove the default gateway (route delete and the release and renew the IP address.
In my case, the Bonjour service was not installed. However, I did see references to the Bonjour service being an mDNS provider. This is multicast DNS and used to resolve names on a local network when DNS may not be properly configured. This is primarily for peer to peer name resolution. I believe iTunes uses this for local networking with devices such as Apple TV.

Our client did have a National Instruments mDNS Responder Service and disabling this service did resolve the issue. To further optimize this and keep any functionality in that service that might be required, I changed the startup type of service to Delayed. This allowed the networking services to configure before the service started and worked fine.

So, the final option for resolving this appears to be setting the offending mDNS service to a statup type of Delayed.

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