So far I was able to redirect TCP connections with a specific destination address or port to my own program with this iptables rule:
iptables -t nat -A OUTPUT -p tcp -d <address> --dport <port> -j REDIRECT --to <local_port>
This works well until I create a connection to this destination from my proxy because it recursively connects to itself.
Is there a way for iptables to know what the original connection is and only redirect it?
Or is there a better approach?
You can try using owner module and skip the redirection for the traffic coming from the proxy. Check for --uid-owner or --pid-owner, you should be able to differentiate the traffic based on either of these.
Something like this,
iptables -t nat -I OUTPUT -m owner -p tcp -d <address> --dport <port> --uid-owner <proxy-owner> -j ACCEPT
Related
I have a server running Linux : server A
I want the traffic on server A to be redirected to remote server b
Actually do the same as the forward port
I used the following command for the forward port.
sysctl net.ipv4.ip_forward = 1
iptables -A INPUT -i lo -j ACCEPT
iptables -A OUTPUT -o lo -j ACCEPT
iptables -t nat -A PREROUTING -p tcp --dport 150 -j DNAT - to-destination des_ip:dest_port
iptables -t nat -A POSTROUTING -j MASQUERADE
The forward port did well and i could connect to server B through server B.
Now I want to know how much traffic is used on port 150 on server A?
If Server A is not a router, I can easily set a limit with the following commands and calculate the traffic consumed on Server A.
sudo iptables -A INPUT -p tcp --dport 150 -j DROP
sudo iptables -A INPUT -p tcp --dport 150 -m quota --quota 100000000 -j ACCEPT
But because server A is a router, these commands do not work
Is there any other command line that I can use to calculate the consumed traffic of port 150 on server A(server A is a router)?
I want to collect the usage data of each port using Python and store it in the database.
In this question, I wanted to redirect port 150, which is the source port, to the destination port.
After research about PREROUTING and INPUT chain in iptables, this is what I realized:
INPUT chain is after PREROUTING chain. According to this schematic.
Ports are translated to the destination port, in PREROUTING chain by NAT, therefore In INPUT chain there is no traffic with the source port and all traffic translated to destination port.
I can see network usage on destination port in INPUT chain, but I can not see the network usage on source port in INPUT chain.
Because all packet headers translated to destination port.
So it's true that quota for source port does not start count in any of the chains.
Even if I create the following rules in FORWARD chain:
sudo iptables -A FORWARD -p tcp --dport 150 -j DROP
sudo iptables -A FORWARD -p tcp --dport 150 -m quota --quota 100000000 -j ACCEPT
Again, we will not see any change in quota
Because the FORWARD chain is after the PREROUTING chain.
I have a server (openvpn) which is not multithreaded and hence does not take advantage of the multiple cores in the box. I'm trying to solve the problem by running multiple servers, each on a different port, e.g. 127.0.0.1:8000, 127.0.0.1:8001, ... then load balancing the exterior 1194 port based on the source IP -- openvpn uses UDP but all packets for a client must arrive at the same server.
Issue I'm running into is how to load balance. I tried IPVS, but it seems like it doesn't work with servers on the same host. Then tried nginx's new udp feature, but again no dice. Any ideas on how to achieve this?
I discovered that plain old iptables can create such a load balancer, using the HMARK target extension (see man 8 iptables-extensions).
Essentially the HMARK target can mark a packet based on a hash of specific IP tuple parameters, source IP and source port in my case, as these will be unique per client, even behind a NAT. Then I can route the packets to the appropriate localhost server based on the mark:
iptables -A PREROUTING -t mangle -p udp --dport 1194 -j HMARK \
--hmark-tuple src,sport --hmark-mod 2 \
--hmark-rnd 0xcafeface --hmark-offset 0x8000
iptables -A PREROUTING -t nat -p udp -m mark --mark 0x8000 \
-j DNAT --to-destination 127.0.0.1:8000
iptables -A PREROUTING -t nat -p udp -m mark --mark 0x8001 \
-j DNAT --to-destination 127.0.0.1:8001
Remember to enable routing packets to localhost:
sysctl -w net.ipv4.conf.eth0.route_localnet=1
So I have a home server and i'd like to keep my IP masked to prevent DoS attacks and other security issues.
I'm using a VPS running Ubuntu to transfer traffic like this: Client -> VPS -> Home Server
But there's a problem. Everything works fine except everyone that connects to the home server has the same IP address as the VPS. I'd like each client to retain their own IP so they can be uniquely identified. How would I go about doing this? Currently using the following commands:
$ iptables -t nat -A PREROUTING -p tcp --dport 80 -j DNAT --to-destination myIP:80
$ iptables -t nat -A POSTROUTING -j MASQUERADE
Theres probably a million other questions on this, but I don't know what to search to find them.
Here is a little picture
Asterisk eth1 10.254.254.2/28------------- Many Good Guys
eth1:1 192.168.83.5/32----------- 192.168.59.3 Bad Guy Peer
I have an Asterisk which is connected with several peers. Some of them are connected through
eth1 and one the badest through alias eth1:1.
Then my asterisk send invite to peers it goes with the eth1 source. So for the bad guy I need to change my source ip to 192.168.83.5 As far as I know it can be done with iptables.
So I tried the rule
iptables -t nat -A POSTROUTING -s 10.254.254.2 -d 192.168.59.3 -j SNAT
--to 192.168.83.5
nothing happens.
When I log I can see send packets in INPUT and OUTPUT chains with :
iptables -t filter -A OUTPUT -o eth1 -s 10.254.254.2 -d 192.168.59.3
-j LOG --log-level 7 --log-prefix "OUTPUT"
iptables -t filter -A INPUT-i eth1 -s 192.168.59.3 -d 192.168.83.5 -j
LOG --log-level 7 --log-prefix "OUTPUT"
but I don’t see any in POSTROUTING chain with:
iptables -t nat -A POSTROUTING -s 10.254.254.2 -d 192.168.59.3 -j LOG
--log-level 7 --log-prefix "POSTROUTING"
That is I have nothing to SNAT(((
At the same time the traffic from other peers is visible in POSTROUTING log. What can it be?
Any thoughts, wishes, kicks would be very appreciated!
The solution has been found!!
I didn' t find a way to make my iptables work. But know i know how to do it without iptables at all.
So generally speaking my task was to modify|mask|replace my source ip of eth1 with eth1:1 ip.
By the way i use CentOS 5.8
And there is a command:
ip route add
which gives you ability to point scr address unlike the route command.
so
ip route add 192.168.59.3/32 via 10.254.254.1 dev eth1 src
192.168.83.5
is doing just what i need.
Thank you for attention!
That will not work. Reason is simple, asterisk will set in packet source addres=address of eth1.
You can start enother asterisk same host(with other config dir). I am sorry, i not know other simple variants.
I already know that the answer with be something simple that I have messed up with! But any idea what's going wrong with these rules?
sudo iptables -I INPUT -p tcp -m state --state NEW,ESTABLISHED,RELATED -m multiport --dports http,https -j ACCEPT
sudo iptables -I OUTPUT -p tcp -m state --state NEW,ESTABLISHED,RELATED -m multiport --sports http,https -j ACCEPT
I have the DNS set up and every packet for this is arriving to my server so this isn't the problem.
Thanks in advance,
Luke
Think about a NATted outbound connection to a remote web server. The first packet in the flow between the NAT and the remote web server will be an outbound packet with a destination port of 80. You have no rule that packet would match.