5 "Advanced" networking questions
toni at soth.at
Mon Jul 7 08:33:17 PDT 2003
On Mon, Jul 07 2003 (01:22:05 +0200), Socketd wrote:
> 1. Reading "man blackhole" I found that net.inet.udp.blackhole=1 will
> prevent traceroute. Is this only if the host is the end target? or will
> it simply disable sending an ICMP packet when it get's a packet with
Look in sys/netinet/udp_usrreq.c. This flag operates on the UDP layer and
doesn't interfere with TTLs.
> 2. Does net.inet.icmp.drop_redirect drop all redirects?
> Redirect datagrams for the Network.
> Redirect datagrams for the Host.
> Redirect datagrams for the Type of Service and Network.
> Redirect datagrams for the Type of Service and Host.
Look in sys/netinet/ip_icmp.c, it checks for icp->icmp_type, not icp->icmp_code,
so all incoming ICMP packets with a type of ICMP_REDIRECT would be dropped.
> 3. What is the difference between net.inet.ip.redirect and the above?
Look in sys/netinet/ip_input.c. This is different from incoming redirects.
> 4. There is a net.inet.icmp.maskrepl, but can you also disable
> timestamp, echo request and information request messages the same way or
> do I need a firewall for that?
Look in sys/netinet/ip_icmp.c. You need to block these packets separately.
> 5. In order to drop SYN-FIN packets, do I need to compile the kernel
> with "options TCP_DROP_SYNFIN" or can I just use "tcp_drop_synfin="YES"" in
> /etc/rc.conf? Is there a net.inet.tcp.?? I can use instead of the above
Look in netinet/tcp_input.c. You need the kernel option "TCP_DROP_SYNFIN" in
addition to tcp_drop_synfin="YES".
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