Fwd: [CentOS] HOW to enable traceroute with IPTABLES

[Robert Spangler]

On Sat February 17 2007 03:11, Indunil Jayasooriya wrote:

>  > I am setting up a firewall on CENTOS 4.4.
>  >
>  >
>  > I have enabled ICMP to www.google.com
>  >
>  > iptables -A OUTPUT -p icmp -d 64.233.189.104 -j ACCEPT
>  > iptables -A INPUT -p icmp -s 64.233.189.104 -j ACCEPT
>
>  traceroute uses by default UDP with port 33434.

While this is true for a starting point, this is not the whole story.

Traceroute starts on this port but every time it sends out a packet the port 
number is increased automatically.  Why?  Simple, the TTL is exceeded so 
traceroute sends out on the next port in numerical order.  Thus traceroute 
needs more then 33434 open there should be a range of ports open.  Traceroute 
does not always start on this port either I have found out.  Sometimes it 
starts on a hight port but only by a few hopes.

>  I wrote below 2 rules
>
>  iptables -A OUTPUT -p udp -d 64.233.189.104 --dport 33434 -j ACCEPT
>  iptables -A INPUT -p udp -s 64.233.189.104 --sport 33434 -j ACCEPT

I have the following ( I do not restrict traceroute destination);

-A OUTPUT -o eth0 -p udp --dport 33200:33500 -m state --state NEW -j ACCEPT

Also you don't need the INPUT statement if you have ESTABLISHED,RELATED at the 
top of your INPUT chain.

>  Then I tried as below

[snip]

>  But Still the same.
>
>  WHY?

I placing my money on the port settings

>  IF my rules are wrong can you rectify it ?

See above.


-- 

Regards
Robert

Smile... it increases your face value!