`man iptables` and the iptables programmers think that icmp-port-unreachable is 
an acceptable response.  You can set your own.

quoth `man iptables`:
 > which return  the  appropriate  ICMP  error message
 > (port-unreachable is the default).

As for which ICMPs to block, I took this from:

http://www.gentoo.org/doc/en/gentoo-security.xml#doc_chap12

Troy

Chris K Ellsworth wrote:
> So then are these the good ICMP's that should be allowed and all others be
> killed for "good" firewall admin practices?
> 
> ----- Original Message ----- 
> From: "Frank Gruellich" <frank@...>
> To: <gentoo-security@g.o>
> Sent: Thursday, January 08, 2004 8:55 AM
> Subject: Re: [gentoo-security] firewall suggestions?
> 
> 
> 
>>* Troy Farrell <troy@...>  8. Jan 04
>>
>>># iptables -L allow-icmp-traffic
>>
>>[output fixed]
>>
>>
>>>Chain allow-icmp-traffic (2 references)
>>>target     prot opt source               destination
>>>ACCEPT     icmp --  anywhere             anywhere           icmp
> 
> time-exceeded limit: avg 10/sec burst 5
> 
>>>ACCEPT     icmp --  anywhere             anywhere           icmp
> 
> destination-unreachable limit: avg 10/sec burst 5
> 
>>>ACCEPT     icmp --  anywhere             anywhere           icmp
> 
> source-quench limit: avg 10/sec burst 5
> 
>>>ACCEPT     icmp --  anywhere             anywhere           icmp
> 
> echo-request limit: avg 5/sec burst 5
> 
>>>ACCEPT     icmp --  anywhere             anywhere           icmp
> 
> echo-reply limit: avg 5/sec burst 5
> 
>>>LOG        icmp --  anywhere             anywhere           LOG level
> 
> warning prefix `Bad ICMP traffic:'
> 
>>>REJECT     icmp --  anywhere             anywhere
>>
>>The default answer of REJECT ist port unreachable.  I always wondered,
>>if this is a good way to answer to a question in a protocol with no
>>ports.  Shouldn't you answer with ICMP protocol unreachable maybe?
>>
>> Regards, Frank.
>>-- 
>>Sigmentation fault
>>
>>--
>>gentoo-security@g.o mailing list
>>
>>
>>
> 
> 
> 
> --
> gentoo-security@g.o mailing list
> 


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