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How do you block new incoming tcp connections on X port?
The Next CEO of Stack OverflowUsing iptables to redirect incoming requests from port 2525 to port 25?how limit the number of open TCP streams from same IP to a local port?iptables rule to block incoming/outgoing traffic to a Xen containerConnection timed out after plenty of new TCP connections through Juniper firewallBlock incoming connections but outgoing UDP is also blocked?UFW/IPTables: how to securely allow authenticated git access with githubiptables - Block incoming on Eth1 and Allow All from eth0iptables error: unknown option --dportHow to apply port forwarding with iptables on existing connections?Disconnecting connections to TCP server by external means
How do you block new incoming tcp connections on X port? Needs to be done with iptables. I actually have a working iptables command but we always reach ip_conntrack_max even when ip_conntrack_max isset at very high. There a way to do it without keeping track?
networking firewall iptables
asked Feb 2 '10 at 19:17
user30199user30199
7416
add a comment |
How do you block new incoming tcp connections on X port? Needs to be done with iptables. I actually have a working iptables command but we always reach ip_conntrack_max even when ip_conntrack_max isset at very high. There a way to do it without keeping track?
networking firewall iptables
asked Feb 2 '10 at 19:17
user30199user30199
7416
add a comment |
How do you block new incoming tcp connections on X port? Needs to be done with iptables. I actually have a working iptables command but we always reach ip_conntrack_max even when ip_conntrack_max isset at very high. There a way to do it without keeping track?
networking firewall iptables
asked Feb 2 '10 at 19:17
user30199user30199
7416
How do you block new incoming tcp connections on X port? Needs to be done with iptables. I actually have a working iptables command but we always reach ip_conntrack_max even when ip_conntrack_max isset at very high. There a way to do it without keeping track?
networking firewall iptables
networking firewall iptables
asked Feb 2 '10 at 19:17
user30199user30199
7416
asked Feb 2 '10 at 19:17
user30199user30199
7416
asked Feb 2 '10 at 19:17
user30199user30199
7416
asked Feb 2 '10 at 19:17
user30199user30199
7416
asked Feb 2 '10 at 19:17
user30199user30199
7416
7416
add a comment |
add a comment |
4 Answers
4
active
oldest
votes
If you want to block attempts to establish new sessions to a given port, but still allow packets to established sessions through, you'd need to do something like:
iptables -A INPUT -j DROP -p tcp --syn --destination-port dport
This should allow any connection initiated from the local machine, that happens to use dport as its local port number.
answered Feb 3 '10 at 8:30
VatineVatine
4,8801622
add a comment |
this should block the traffic without involving conn_track:
iptables -A INPUT -j DROP -p tcp --destination-port <your port>
connection tracking should only do its job when you specify -m state or --state in your rules.
answered Feb 3 '10 at 7:17
ChristianChristian
4,15211826
1
The question was for blocking incoming TCP connections - that should have been a huge clue to filter on SYN
– PP.
Mar 10 '10 at 14:23
as i understand it: when you drop syn packets, there will be no connections, so you can drop every connection to the port.
– Christian
Mar 10 '10 at 14:50
If, for some reason, you have attempted to initiate a connection using that port number as the local port, dropping everything would drop the returning SYNACK, dropping SYN-only packets just stops non-locally-initiated packets. Admittedly, less of a problem when you have a specified destination port, but in the general case...
– Vatine
Mar 16 '10 at 11:29
add a comment |
Dropping --syn will stop new connections and there shouldn't be any half-open connections to track. In general filtering "without keeping track" is possible at the -t raw -I PREROUTING stage.
answered Dec 11 '14 at 21:19
Cedric KnightCedric Knight
939519
add a comment |
You could accept everything other than SYN packets. One way to do it would be:
iptables -A INPUT -p tcp '!' --syn --destination-port <your-port> -j ACCEPT
answered yesterday
Arindam MukherjeeArindam Mukherjee
1011
New contributor
Arindam Mukherjee is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
add a comment |
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4 Answers
4
active
oldest
votes
4 Answers
4
active
oldest
votes
active
oldest
votes
active
oldest
votes
If you want to block attempts to establish new sessions to a given port, but still allow packets to established sessions through, you'd need to do something like:
iptables -A INPUT -j DROP -p tcp --syn --destination-port dport
This should allow any connection initiated from the local machine, that happens to use dport as its local port number.
answered Feb 3 '10 at 8:30
VatineVatine
4,8801622
add a comment |
If you want to block attempts to establish new sessions to a given port, but still allow packets to established sessions through, you'd need to do something like:
iptables -A INPUT -j DROP -p tcp --syn --destination-port dport
This should allow any connection initiated from the local machine, that happens to use dport as its local port number.
answered Feb 3 '10 at 8:30
VatineVatine
4,8801622
add a comment |
If you want to block attempts to establish new sessions to a given port, but still allow packets to established sessions through, you'd need to do something like:
iptables -A INPUT -j DROP -p tcp --syn --destination-port dport
This should allow any connection initiated from the local machine, that happens to use dport as its local port number.
answered Feb 3 '10 at 8:30
VatineVatine
4,8801622
If you want to block attempts to establish new sessions to a given port, but still allow packets to established sessions through, you'd need to do something like:
iptables -A INPUT -j DROP -p tcp --syn --destination-port dport
This should allow any connection initiated from the local machine, that happens to use dport as its local port number.
answered Feb 3 '10 at 8:30
VatineVatine
4,8801622
answered Feb 3 '10 at 8:30
VatineVatine
4,8801622
answered Feb 3 '10 at 8:30
VatineVatine
4,8801622
answered Feb 3 '10 at 8:30
VatineVatine
4,8801622
4,8801622
add a comment |
add a comment |
this should block the traffic without involving conn_track:
iptables -A INPUT -j DROP -p tcp --destination-port <your port>
connection tracking should only do its job when you specify -m state or --state in your rules.
answered Feb 3 '10 at 7:17
ChristianChristian
4,15211826
1
The question was for blocking incoming TCP connections - that should have been a huge clue to filter on SYN
– PP.
Mar 10 '10 at 14:23
as i understand it: when you drop syn packets, there will be no connections, so you can drop every connection to the port.
– Christian
Mar 10 '10 at 14:50
If, for some reason, you have attempted to initiate a connection using that port number as the local port, dropping everything would drop the returning SYNACK, dropping SYN-only packets just stops non-locally-initiated packets. Admittedly, less of a problem when you have a specified destination port, but in the general case...
– Vatine
Mar 16 '10 at 11:29
add a comment |
this should block the traffic without involving conn_track:
iptables -A INPUT -j DROP -p tcp --destination-port <your port>
connection tracking should only do its job when you specify -m state or --state in your rules.
answered Feb 3 '10 at 7:17
ChristianChristian
4,15211826
1
The question was for blocking incoming TCP connections - that should have been a huge clue to filter on SYN
– PP.
Mar 10 '10 at 14:23
as i understand it: when you drop syn packets, there will be no connections, so you can drop every connection to the port.
– Christian
Mar 10 '10 at 14:50
If, for some reason, you have attempted to initiate a connection using that port number as the local port, dropping everything would drop the returning SYNACK, dropping SYN-only packets just stops non-locally-initiated packets. Admittedly, less of a problem when you have a specified destination port, but in the general case...
– Vatine
Mar 16 '10 at 11:29
add a comment |
this should block the traffic without involving conn_track:
iptables -A INPUT -j DROP -p tcp --destination-port <your port>
connection tracking should only do its job when you specify -m state or --state in your rules.
answered Feb 3 '10 at 7:17
ChristianChristian
4,15211826
this should block the traffic without involving conn_track:
iptables -A INPUT -j DROP -p tcp --destination-port <your port>
connection tracking should only do its job when you specify -m state or --state in your rules.
answered Feb 3 '10 at 7:17
ChristianChristian
4,15211826
answered Feb 3 '10 at 7:17
ChristianChristian
4,15211826
answered Feb 3 '10 at 7:17
ChristianChristian
4,15211826
answered Feb 3 '10 at 7:17
ChristianChristian
4,15211826
4,15211826
1
The question was for blocking incoming TCP connections - that should have been a huge clue to filter on SYN
– PP.
Mar 10 '10 at 14:23
as i understand it: when you drop syn packets, there will be no connections, so you can drop every connection to the port.
– Christian
Mar 10 '10 at 14:50
If, for some reason, you have attempted to initiate a connection using that port number as the local port, dropping everything would drop the returning SYNACK, dropping SYN-only packets just stops non-locally-initiated packets. Admittedly, less of a problem when you have a specified destination port, but in the general case...
– Vatine
Mar 16 '10 at 11:29
add a comment |
1
The question was for blocking incoming TCP connections - that should have been a huge clue to filter on SYN
– PP.
Mar 10 '10 at 14:23
as i understand it: when you drop syn packets, there will be no connections, so you can drop every connection to the port.
– Christian
Mar 10 '10 at 14:50
If, for some reason, you have attempted to initiate a connection using that port number as the local port, dropping everything would drop the returning SYNACK, dropping SYN-only packets just stops non-locally-initiated packets. Admittedly, less of a problem when you have a specified destination port, but in the general case...
– Vatine
Mar 16 '10 at 11:29
1
1
The question was for blocking incoming TCP connections - that should have been a huge clue to filter on SYN
– PP.
Mar 10 '10 at 14:23
The question was for blocking incoming TCP connections - that should have been a huge clue to filter on SYN
– PP.
Mar 10 '10 at 14:23
as i understand it: when you drop syn packets, there will be no connections, so you can drop every connection to the port.
– Christian
Mar 10 '10 at 14:50
as i understand it: when you drop syn packets, there will be no connections, so you can drop every connection to the port.
– Christian
Mar 10 '10 at 14:50
If, for some reason, you have attempted to initiate a connection using that port number as the local port, dropping everything would drop the returning SYNACK, dropping SYN-only packets just stops non-locally-initiated packets. Admittedly, less of a problem when you have a specified destination port, but in the general case...
– Vatine
Mar 16 '10 at 11:29
If, for some reason, you have attempted to initiate a connection using that port number as the local port, dropping everything would drop the returning SYNACK, dropping SYN-only packets just stops non-locally-initiated packets. Admittedly, less of a problem when you have a specified destination port, but in the general case...
– Vatine
Mar 16 '10 at 11:29
add a comment |
Dropping --syn will stop new connections and there shouldn't be any half-open connections to track. In general filtering "without keeping track" is possible at the -t raw -I PREROUTING stage.
answered Dec 11 '14 at 21:19
Cedric KnightCedric Knight
939519
add a comment |
Dropping --syn will stop new connections and there shouldn't be any half-open connections to track. In general filtering "without keeping track" is possible at the -t raw -I PREROUTING stage.
answered Dec 11 '14 at 21:19
Cedric KnightCedric Knight
939519
add a comment |
Dropping --syn will stop new connections and there shouldn't be any half-open connections to track. In general filtering "without keeping track" is possible at the -t raw -I PREROUTING stage.
answered Dec 11 '14 at 21:19
Cedric KnightCedric Knight
939519
Dropping --syn will stop new connections and there shouldn't be any half-open connections to track. In general filtering "without keeping track" is possible at the -t raw -I PREROUTING stage.
answered Dec 11 '14 at 21:19
Cedric KnightCedric Knight
939519
answered Dec 11 '14 at 21:19
Cedric KnightCedric Knight
939519
answered Dec 11 '14 at 21:19
Cedric KnightCedric Knight
939519
answered Dec 11 '14 at 21:19
Cedric KnightCedric Knight
939519
939519
add a comment |
add a comment |
You could accept everything other than SYN packets. One way to do it would be:
iptables -A INPUT -p tcp '!' --syn --destination-port <your-port> -j ACCEPT
answered yesterday
Arindam MukherjeeArindam Mukherjee
1011
New contributor
Arindam Mukherjee is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
add a comment |
You could accept everything other than SYN packets. One way to do it would be:
iptables -A INPUT -p tcp '!' --syn --destination-port <your-port> -j ACCEPT
answered yesterday
Arindam MukherjeeArindam Mukherjee
1011
New contributor
Arindam Mukherjee is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
add a comment |
You could accept everything other than SYN packets. One way to do it would be:
iptables -A INPUT -p tcp '!' --syn --destination-port <your-port> -j ACCEPT
answered yesterday
Arindam MukherjeeArindam Mukherjee
1011
New contributor
Arindam Mukherjee is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
You could accept everything other than SYN packets. One way to do it would be:
iptables -A INPUT -p tcp '!' --syn --destination-port <your-port> -j ACCEPT
answered yesterday
Arindam MukherjeeArindam Mukherjee
1011
New contributor
Arindam Mukherjee is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
answered yesterday
Arindam MukherjeeArindam Mukherjee
1011
New contributor
Arindam Mukherjee is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
answered yesterday
Arindam MukherjeeArindam Mukherjee
1011
answered yesterday
Arindam MukherjeeArindam Mukherjee
1011
1011
New contributor
Arindam Mukherjee is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
Arindam Mukherjee is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Arindam Mukherjee is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
add a comment |
add a comment |
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