Why Linux can't visit public net?

[jludwig]

On Thu, 2004-09-02 at 06:05, Edward King wrote:
> My computer's OS is Red Hat Linux7.3,I can ping this Linux computer
> from other computers,but in this Linux computer,I ping publish net,I
> fount I can't ping it,and I can't visit public net in Red Hat
> Linux7.3,for example:
> [root at www root]# ping www.sina.com
> ping: unknown host www.sina.com
>  
> Then I try ping gateway,I got follow result:
> [root at www root]# ping 210.xx.xx.xx
> PING 210.xx.xx.xx (210.xx.xx.xx) from 210.xx.xx.xx : 56(84) bytes of
> data.
> From 210.xx.xx.xx icmp_seq=1 Packet filtered
> From 210.xx.xx.x x icmp_seq=2 Packet filtered
> From 210.xx.xx.xx icmp_seq=3 Packet filtered
> From 210.xx.xx.xx icmp_seq=4 Packet filtered
> From 210.xx.xx.xx icmp_seq=5 Packet filtered
>  
> --- 210.xx.xx.xx ping statistics ---
> 5 packets transmitted, 0 received, +5 errors, 100% loss, time 4012ms
>  
> Then I try to ping DNS Server,I found I can't ping it!
> [root at www root]# ping 210.x.x.x
> connect: Network is unreachable
>  
> Then I use Windows OS,I configure IP address,gateway and DNS as same
> as Red Hat Linux7.3,I found I can ping public net and visit public
> net,like follows:
> C:\Documents and Settings\Administrator>ping www.sina.com
>  
> Pinging us.sina.com.cn [66.77.9.79] with 32 bytes of data:
>  
> Reply from 66.77.9.79: bytes=32 time=190ms TTL=237
> Reply from 66.77.9.79: bytes=32 time=181ms TTL=237
> Reply from 66.77.9.79: bytes=32 time=190ms TTL=237
> Reply from 66.77.9.79: bytes=32 time=181ms TTL=237
>  
> Ping statistics for 66.77.9.79:
>     Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
> Approximate round trip times in milli-seconds:
>     Minimum = 181ms, Maximum =  190ms, Average =  185ms
>  
> Why can't I  ping and visit public net under Red Hat Linux7.3? I am a
> beginer in Linux,please give me detail command.
> Thanks in advance!
>  
> Best regards,
> Edward
> 
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Many ISP's and network servers "turn off" or limit the ping replies
since this can be used for denial of service attacks.
-- 
jludwig <wralphie at comcast.net>