Got a doubt regarding Caching Server Implementation

[Kevin Darcy]

Sanjib Das wrote:

>Hi
>I have setup a local domain my.domain. & it consists of two machines...
>I configured one of them as primary server for my domain & another one
>as caching server .For both these servers I'm using BIND-9.2.4 package
>whenever I send query (using 'dig' command).....
>from the second machine (machine where the caching server is running 
>locally) 
>first it looks into its own cache....if its available it sends from there 
>itself...
>otherwise sends it the primary server...now whenever it (caching 
>server)sends to
>primary server, it includes some OPT pseudo-RR in the additional section 
>of the request...
>even if I donot send any OPT RR in my query, which I send using dig from 
>caching server.
>I donno the exact reason...why it happens like this......
>
That's an EDNS0 "buffer size" option, which is generated by default in 
BIND 9. BIND 9 will switch to a non-EDNS0 query if it detects that the 
other nameserver doesn't understand EDNS0. In pathological cases, you 
can disable EDNS0 altogether, for specific nameservers; see the "edns" 
clause in the "server" statement.

                                                                         
                                                         - Kevin