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how to avoid dns caching for a few urls with a CE 507 ?

how to avoid dns caching for a few urls with a CE 507 ?

2 REPLIES
Silver

Re: how to avoid dns caching for a few urls with a CE 507 ?

The following document explains how to filter urls on the cache engine. http://www.cisco.com/warp/public/117/cache_engine/url_filtering.html Use the bypass commands to set up a bypass for WCCP-redirected traffic.

Bronze

Re: how to avoid dns caching for a few urls with a CE 507 ?

Hello,

the question regarding DNS-Caching is quite intresting. Unfortunatly I could only find informations regarding URL-Filtering in the above link. DNS caching is intressting in another environment as one has the possibility to have multiple IP-Adresses per DNS-Name (e.g. www.foo.de will be resolved as 10.1.1.1 and the next request or in failure conditions it will be resolved as 10.1.1.2)

Lets think about the following:

The CE would cache the DNS-resolution of www.foo.de and would cache content of www.foo.de. A user requests www.foo.de. The CE will send a request towards 10.1.1.1 (the cached DNS-entry) to proove if the content is still valid or not. Now lets think of the possibility that 10.1.1.1 has a problem and is not responding. Now the CE does not know what to do as the server is not responding. In my opinion this would cause an error (Server not available). Now let's imagine that the DNS-Server knows about the problems of 10.1.1.1 and does only send the IP-adress 10.1.1.1 of www.foo.de if 10.1.1.1 is alive and if not 10.1.1.2. In this case a new DNS-resolution of www.foo.de for prooving if the content is still valid or not will have the result 10.1.1.2 and the prooving could take place and everything is fine. This problem will also occur if a new page on www.foo.de will be requested and the already (cached) DNS-Entry will be used to get this information and 10.1.1.1 is not present.

Now my question:

How does the CE behave: Will the CE cache the DNS-resolution of a server or not?

If yes is this caching duration configurable or not.

Regards,

Joerg

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