Internet is working very slow through ISA 2006 Srever

Hi,

We are using isa server 2006 for accessing internet service, but internet is working is very slow.

When we ping the public DNC its show the lot of delay time.

And in ISA alerts its display the following error messages:-

1."ISA Server is no longer experiencing a SYN attack".

2. The request was denied because the number of connections per second allowed for the [System] Allow DNS from ISA Server to selected servers rule was exceeded.

I am new for ISA 2006. SO, Plz provide required solution if anybody face such type of problem.

Thanks and regards ,

Ravi Singh