Routing Loops

Routing loops are created when a request to origin from Instart is redirected to an Instart IP address. In this case the request becomes looped on the Instart network. The request receives a HTTP 508 Status code as its response, meaning that the request is stuck in a loop.

As a general rule: Do not map your origin domain to a Instart IP address.

Debugging Routing Loops

If you notice HTTP 508 responses, please verify that the origin domain is not resolving to a Instart IP address.

Example:

Say that my-origin.customer.com is the origin domain for www.customer.com and it is responding with HTTP 508 responses.

You can use command line tools (host, dig, nslookup) to verify that the origin domain is not resolving to an Instart IP address. Using the host command, for example:

sh #: host my-origin.customer.com

my-origin.customer.com is an alias for origin1.customer.com

origin1.customer.com has address <xx.xx.xx.xx>

Take the IP address returned and do a reverse lookup for it:

sh #: host <xx.xx.xx.xx>

The result should not include any insw.net, inscname.net, or instart.com domains.

If you see a Instart domain on the reverse lookup, please verify the origin DNS setup. The routing loop could be because of an error in this setup.

Instart's loop detection

The X-Instart-Via header

To detect and avoid routing loops, the Instart service appends a X-Instart-Via header in the request when forwarding a request to the origin. The syntax of this header is

<http version> <proxy name>

A typical X-Instart-Via header looks like:

X-Instart-Via: 1.1 SJC01-ACCEL09

Loop detection

In order to detect a request which has come back to the proxy due to the existence of a loop, the proxy checks incoming request for an X-Instart-Via header containing an Instart proxy name. If the proxy finds itself in the list of proxy names in the header, it rejects the request, returning a 508: Loop Detected message; otherwise it serves the request normally.

If everything appears normal on the origin setup and you still see a 508 response, or if you need any further help, please contact Support.