how to flush director dns ttl

[Gao Yongwei]

The whole point of the DNS director and it's TTL settings is to have
> Varnish automatically update the backend definitions based on TTL. So the
> only option you have is AFAIK:
> 1) To lower the TTL so it won't become a problem (speed up your DNS)
> 2) To modify the DNS director and implement flushing through VCL
>

Thanks,perbu ,I can achieve  the first method ,  and could you please teach
me more about the second method , how does this vcl look like ?
many thanks , :-)
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