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• Flushing iptables broke my pipe, how can I save my instance?

  - by Niels

  I was setting up my iptables when I performed a iptables -F and my ssh pipe broke. This is the last output of my session: root@alfapaints:~# iptables -L Chain INPUT (policy DROP) target prot opt source destination ACCEPT all -- anywhere anywhere ACCEPT tcp -- anywhere anywhere state NEW,ESTABLISHED tcp dpt:2222 ACCEPT tcp -- li465-68.members.linode.com anywhere state NEW,ESTABLISHED tcp dpt:nrpe ACCEPT tcp -- anywhere anywhere tcp dpt:9200 state NEW,ESTABLISHED ACCEPT tcp -- anywhere anywhere tcp dpt:http state NEW,ESTABLISHED ACCEPT udp -- anywhere anywhere udp spt:domain Chain FORWARD (policy DROP) target prot opt source destination Chain OUTPUT (policy DROP) target prot opt source destination ACCEPT all -- anywhere anywhere ACCEPT tcp -- anywhere anywhere state ESTABLISHED tcp spt:2222 ACCEPT tcp -- anywhere anywhere state ESTABLISHED tcp spt:nrpe ACCEPT tcp -- anywhere anywhere tcp spt:9200 state ESTABLISHED ACCEPT tcp -- anywhere anywhere tcp spt:http state ESTABLISHED ACCEPT udp -- anywhere anywhere udp dpt:domain root@alfapaints:~# iptables -F Write failed: Broken pipe I tested my connection just before and I was able to connect with ssh. Now I did a nmap scan and not a single port is open anymore. I know my VPS is running on VMWare ESXi, could a reboot help? Or if not could I attach and mount the disk to another vm to save the data? Does anybody have some advise? And maybe an explanation what happend or what could have cause my pipe to break? ps: I didn't save my rules on the config directories of iptables. But used a file I stored in ~/rules.config to apply my rules like this: iptables-restore < rules.config So probably a reboot would help? Thanks a lot in advance.

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• iptables command

  - by neha soni

  how can i start/stop the iptables service on ubuntu?? i hav tried "service iptables stop" but it is giving "unrecognized service". why is it doing so??? is there any other method???

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• Is this iptables NAT exploitable from the external side?

  - by Karma Fusebox

  Could you please have a short look on this simple iptables/NAT-Setup, I believe it has a fairly serious security issue (due to being too simple). On this network there is one internet-connected machine (running Debian Squeeze/2.6.32-5 with iptables 1.4.8) acting as NAT/Gateway for the handful of clients in 192.168/24. The machine has two NICs: eth0: internet-faced eth1: LAN-faced, 192.168.0.1, the default GW for 192.168/24 Routing table is two-NICs-default without manual changes: Destination Gateway Genmask Flags Metric Ref Use Iface 192.168.0.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1 (externalNet) 0.0.0.0 255.255.252.0 U 0 0 0 eth0 0.0.0.0 (externalGW) 0.0.0.0 UG 0 0 0 eth0 The NAT is then enabled only and merely by these actions, there are no more iptables rules: echo 1 > /proc/sys/net/ipv4/ip_forward /sbin/iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE # (all iptables policies are ACCEPT) This does the job, but I miss several things here which I believe could be a security issue: there is no restriction about allowed source interfaces or source networks at all there is no firewalling part such as: (set policies to DROP) /sbin/iptables -A FORWARD -i eth0 -o eth1 -m state --state RELATED,ESTABLISHED -j ACCEPT /sbin/iptables -A FORWARD -i eth1 -o eth0 -j ACCEPT And thus, the questions of my sleepless nights are: Is this NAT-service available to anyone in the world who sets this machine as his default gateway? I'd say yes it is, because there is nothing indicating that an incoming external connection (via eth0) should be handled any different than an incoming internal connection (via eth1) as long as the output-interface is eth0 - and routing-wise that holds true for both external und internal clients that want to access the internet. So if I am right, anyone could use this machine as open proxy by having his packets NATted here. So please tell me if that's right or why it is not. As a "hotfix" I have added a "-s 192.168.0.0/24" option to the NAT-starting command. I would like to know if not using this option was indeed a security issue or just irrelevant thanks to some mechanism I am not aware of. As the policies are all ACCEPT, there is currently no restriction on forwarding eth1 to eth0 (internal to external). But what are the effective implications of currently NOT having the restriction that only RELATED and ESTABLISHED states are forwarded from eth0 to eth1 (external to internal)? In other words, should I rather change the policies to DROP and apply the two "firewalling" rules I mentioned above or is the lack of them not affecting security? Thanks for clarification!

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• iptables and jmx

  - by AboMajed

  how to make full control of iptables using java and jmx ?

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• iproute2 rules and iptables NAT... what is the difference?

  - by Jakobud

  We have 2 different ISP connections. Our previous "IT guy" setup our firewall like so: When /etc/rc.local was executed on startup, it did a bunch of ip rule add and ip route add commands in order to route certain internal hosts to use certain ISP connections. Then at the end of /etc/rc.local, he executed our iptables firewall rules that were generated by Firewall Builder. These iptables rules have both Policy and NAT rules setup in them. What I don't understand, is why did he use iproute2 to specify rules and routes but also specify NAT rules for iptables? Why didn't he just do it all in one or the other instead of using them both? Could he have got rid of the iproute2 rules and routes and just put all those same rules into the iptables NAT settings?

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• Can iptables allow Squid to process a request, then redirect the response packets to another port?

  - by Dan H

  I'm trying to test a fancy traffic analyzer app, which I have running on port 8890. My current plan is to let any HTTP request come into Squid, on port 3128, and let it process the request, and then just before it sends the response back, use iptables to redirect the response packets (leaving port 3128) to port 8890. I've researched this all night, and tried many iptables commands, but I'm missing something and my hair is falling out. I thought something like this would work: iptables -t nat -A OUTPUT -p tcp --sport 3128 -j REDIRECT --to-ports 8990 This rule gets created ok, but it never redirects anything. Is this even possible? If so, what iptables incantation could do it? If not, any idea what might work on a single host, given multiple remote browser clients?

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• Any non-custom way to manage iptables with fail2ban and libvirt+kvm?

  - by Peter Hansen

  I have an Ubuntu 9.04 server running libvirt/kvm and fail2ban (for SSH attacks). Both libvirt and fail2ban integrate with iptables in different ways. Libvirt uses (I think) some XML config and during startup (?) configures forwarding to the VM subnet. Fail2ban installs a custom chain (probably at init) and periodically modifies it to ban/unban probable attackers. I also need to install my own rules to forward various ports to servers running in VMs and on other machines, and set up rudimentary security (e.g. drop all INPUT traffic except the few ports I want open), and of course I'd like the ability to add/remove rules safely without restarting. It seems to me iptables is a powerful tool that's sorely lacking some sort of standardized way of juggling all this stuff. Every project, and every sysadmin, seems to do it differently! (And I think there's lots of "cargo cult" admin going on here, with people cloning crude approaches like "use iptables-save like so".) Short of figuring out the gory details of exactly how both of these (and potentially other) tools manipulate the netfilter tables, and developing my own scripts or just manually executing iptables commands, is there any way to safely work with iptables while not breaking the functionality of these other tools? Any nascent standards or projects defined to bring sanity to this area? Even a helpful web page I missed that might cover at least these two packages together?

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• iptables : how to correctly allow incoming and outgoing traffic for certain ports?

  - by Rubytastic

  Im trying to get incoming and outgoing traffic to be enabled on specific ports, because I block everything at the end of the iptables rules. INPUT and FORWARD reject. What would be the appropiate way to open certain ports for all traffic incoming and outgoing? From docs I found below but one has to really define both lines? iptables -A INPUT -i eth0 -p tcp --dport 22 -m state --state NEW,ESTABLISHED -j ACCEPT iptables -A OUTPUT -o eth0 -p tcp --sport 22 -m state --state ESTABLISHED -j ACCEPT I try to open ports for xmpp service and some other deamons running on server. Rules: *filter # Allow all loopback (lo0) traffic and drop all traffic to 127/8 that doesn't use lo0 -A INPUT -i lo -j ACCEPT -A INPUT -d 127.0.0.0/8 -j REJECT # Accept all established inbound connections -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT # Allow all outbound traffic - you can modify this to only allow certain traffic -A OUTPUT -j ACCEPT # Allow HTTP # Prevent DDOS attacks (http://blog.bodhizazen.net/linux/prevent-dos-with-iptables/) # Disallow HTTPS -A INPUT -p tcp --dport 80 -m state --state NEW -m limit --limit 50/minute --limit-burst 200 -j ACCEPT -A INPUT -m state --state RELATED,ESTABLISHED -m limit --limit 50/second --limit-burst 50 -j ACCEPT -A INPUT -p tcp --dport 443 -j DROP # Allow SSH connections # The -dport number should be the same port number you set in sshd_config -A INPUT -p tcp -s <myip> --dport ssh -j ACCEPT -A INPUT -p tcp -s <myip> --dport 5984 -j ACCEPT -A INPUT -p tcp --dport ssh -j REJECT # Attempt to block portscans # Anyone who tried to portscan us is locked out for an entire day. -A INPUT -m recent --name portscan --rcheck --seconds 86400 -j DROP -A FORWARD -m recent --name portscan --rcheck --seconds 86400 -j DROP # Once the day has passed, remove them from the portscan list -A INPUT -m recent --name portscan --remove -A FORWARD -m recent --name portscan --remove # These rules add scanners to the portscan list, and log the attempt. -A INPUT -p tcp -m tcp --dport 139 -m recent --name portscan --set -j LOG --log-prefix "Portscan:" -A INPUT -p tcp -m tcp --dport 139 -m recent --name portscan --set -j DROP -A FORWARD -p tcp -m tcp --dport 139 -m recent --name portscan --set -j LOG --log-prefix "Portscan:" -A FORWARD -p tcp -m tcp --dport 139 -m recent --name portscan --set -j DROP # Stop smurf attacks -A INPUT -p icmp -m icmp --icmp-type address-mask-request -j DROP -A INPUT -p icmp -m icmp --icmp-type timestamp-request -j DROP -A INPUT -p icmp -m icmp -j DROP # Drop excessive RST packets to avoid smurf attacks -A INPUT -p tcp -m tcp --tcp-flags RST RST -m limit --limit 2/second --limit-burst 2 -j ACCEPT # Don't allow pings through -A INPUT -p icmp -m icmp --icmp-type 8 -j DROP # Log iptables denied calls -A INPUT -m limit --limit 5/min -j LOG --log-prefix "iptables denied: " --log-level 7 # Reject all other inbound - default deny unless explicitly allowed policy -A INPUT -j REJECT -A FORWARD -j REJECT COMMIT

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• How to configure iptables to use apt-get in a server?

  - by segaco

  I'm starting using iptables (newbie) to protect a linux server (specifically Debian 5.0). Before I configure the iptables settings, I can use apt-get without a problem. But after I configure the iptables, the apt-get stop working. For example I use this script in iptables: #!/bin/sh IPT=/sbin/iptables ## FLUSH $IPT -F $IPT -X $IPT -t nat -F $IPT -t nat -X $IPT -t mangle -F $IPT -t mangle -X $IPT -P INPUT DROP $IPT -P OUTPUT DROP $IPT -P FORWARD DROP $IPT -A INPUT -i lo -j ACCEPT $IPT -A OUTPUT -o lo -j ACCEPT $IPT -A INPUT -p tcp --dport 22 -j ACCEPT $IPT -A OUTPUT -p tcp --sport 22 -j ACCEPT $IPT -A INPUT -p tcp --dport 80 -j ACCEPT $IPT -A OUTPUT -p tcp --sport 80 -j ACCEPT $IPT -A INPUT -p tcp --dport 443 -j ACCEPT $IPT -A OUTPUT -p tcp --sport 443 -j ACCEPT # Allow FTP connections @ port 21 $IPT -A INPUT -p tcp --sport 21 -m state --state ESTABLISHED -j ACCEPT $IPT -A OUTPUT -p tcp --dport 21 -m state --state NEW,ESTABLISHED -j ACCEPT # Allow Active FTP Connections $IPT -A INPUT -p tcp --sport 20 -m state --state ESTABLISHED,RELATED -j ACCEPT $IPT -A OUTPUT -p tcp --dport 20 -m state --state ESTABLISHED -j ACCEPT # Allow Passive FTP Connections $IPT -A INPUT -p tcp --sport 1024: --dport 1024: -m state --state ESTABLISHED -j ACCEPT $IPT -A OUTPUT -p tcp --sport 1024: --dport 1024: -m state --state ESTABLISHED,RELATED -j ACCEPT #DNS $IPT -A OUTPUT -p udp --dport 53 --sport 1024:65535 -j ACCEPT $IPT -A INPUT -p tcp --dport 1:1024 $IPT -A INPUT -p udp --dport 1:1024 $IPT -A INPUT -p tcp --dport 3306 -j DROP $IPT -A INPUT -p tcp --dport 10000 -j DROP $IPT -A INPUT -p udp --dport 10000 -j DROP then when I run apt-get I obtain: core:~# apt-get update 0% [Connecting to ftp.us.debian.org] [Connecting to security.debian.org] [Conne and it stalls. What rules I need to configure to make it works. Thanks

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• Is there a suitable chain for iptables when eth is in Promisc mode?

  - by user1495181

  I have a fron-end machine. Machine have2 eth cards. I want to use netfilter queue to do some checks on the packets. I set eth like this: ifconfig eth0 0.0.0.0 promisc up ifconfig eth1 0.0.0.0 promisc up I want to have an iptable rule like this(only example): iptables -A INPUT -i eth0 -j LOG --log-prefix " eth0 packet " but the packet is no passed through the iptables ,because it dosnt target to this MAC. Promisc mode didnt help. I saw that there is a way to add iptables chain for PROMISC, but need compilation... Is there any simplier way to have iptables rule when packet is not target to this eth. Currently i bypass this by creating a bridge between 2 eth and put rule on the FORWARD, but i done want to create bridge.

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• FTP not listing files behind firewall (setsockopt (ignored): Permission denied)

  - by KennyDs

  We are developing a Magento application that has a module that works with FTP. Today we deployed this on the testing environment which is setup in the following way: Gateway server which has the following iptables rules: # iptables -L -n -v Chain INPUT (policy ACCEPT 2 packets, 130 bytes) pkts bytes target prot opt in out source destination 0 0 ACCEPT all -- lo * 0.0.0.0/0 0.0.0.0/0 165 13720 ACCEPT all -- * * 0.0.0.0/0 0.0.0.0/0 state RELATED,ESTABLISHED Chain FORWARD (policy ACCEPT 7 packets, 606 bytes) pkts bytes target prot opt in out source destination 0 0 ACCEPT all -- eth1 eth0 0.0.0.0/0 0.0.0.0/0 state RELATED,ESTABLISHED 15 965 ACCEPT all -- eth0 eth1 0.0.0.0/0 0.0.0.0/0 0 0 REJECT all -- eth1 eth1 0.0.0.0/0 0.0.0.0/0 reject-with icmp-port-unreachable Chain OUTPUT (policy ACCEPT 126 packets, 31690 bytes) pkts bytes target prot opt in out source destination These are set at runtime via the following bash script: #!/bin/sh PATH=/usr/sbin:/sbin:/bin:/usr/bin # # delete all existing rules. # iptables -F iptables -t nat -F iptables -t mangle -F iptables -X # Always accept loopback traffic iptables -A INPUT -i lo -j ACCEPT # Allow established connections, and those not coming from the outside iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT iptables -A FORWARD -i eth1 -o eth0 -m state --state ESTABLISHED,RELATED -j ACCEPT # Allow outgoing connections from the LAN side. iptables -A FORWARD -i eth0 -o eth1 -j ACCEPT # Masquerade. iptables -t nat -A POSTROUTING -o eth1 -j MASQUERADE # Don't forward from the outside to the inside. iptables -A FORWARD -i eth1 -o eth1 -j REJECT # Enable routing. echo 1 > /proc/sys/net/ipv4/ip_forward The gateway server is connected to the WAN via eth1 and is connected to the internal network via eth0. One of the servers from eth1 has the following problem when trying to list files over ftp: $ ftp -vd myftpserver.com Connected to myftpserver.com 220 Welcome to MY FTP Server ftp: setsockopt: Bad file descriptor Name (myftpserver.com:magento): XXXXXXXX ---> USER XXXXXXXX 331 User XXXXXXXX, password please Password: ---> PASS XXXX 230 Password Ok, User logged in ---> SYST 215 UNIX Type: L8 Remote system type is UNIX. Using binary mode to transfer files. ftp> ls ftp: setsockopt (ignored): Permission denied ---> PORT 192,168,19,15,135,75 421 Service not available, remote server has closed connection When I try listing the files in passive mode, same result. When I run the same command on the gateway server, everything works fine so I believe that the issue is happening because of the iptables rules not forwarding properly. Does anyone have an idea which rule I need to add to make this work?

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• How long does a blocked connection from Iptables last? Is there a way to set the timeout?

  - by Josh

  iptables -A INPUT -m state --state NEW -m recent --set # If we receive more than 10 connections in 10 seconds block our friend. iptables -A INPUT -m state --state NEW -m recent --update --seconds 5 --hitcount 15 -j Log-N-Drop I have these two relevant rules from iptables. if more than 15 connections are made in 5 seconds it logs the attempt and blocks it. How long does iptables maintain the counter? Does it refresh if connections are attempted again?

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• iCloud stuff stops working while connected to OpenVPN

  - by Taco Bob

  I have a fairly simple OpenVPN setup on an OpenVZ VPS with Ubuntu 11.10. Client is the Viscosity client on Mac OS X 10.8.2, and after some testing, we can rule out the client as being part of the problem. Everything has been working fine except for Apple's iCloud stuff. Web surfing, email, FTP, NNTP, and Skype are all working as expected. It's ONLY the iCloud services that cease to function. If I connect to the VPN, iCloud stuff stops working. I no longer get anything in Messages, Calendar items don't get updated, and Notifications stop working. If I disconnect, the iCloud stuff all starts working. Connect again, iCloud stops working. Here's the server.conf: status openvpn-status.log log /var/log/openvpn.log verb 4 port 1194 proto udp dev tun ca /etc/openvpn/ca.crt cert /etc/openvpn/server.crt key /etc/openvpn/server.key dh /etc/openvpn/dh1024.pem server 10.9.8.0 255.255.255.0 ifconfig-pool-persist ipp.txt push "redirect-gateway def1" push “dhcp-option DNS 10.9.8.1? keepalive 10 120 duplicate-cn cipher BF-CBC comp-lzo user nobody group nogroup persist-key persist-tun tun-mtu 1500 mssfix 1400 I'm using iptables in a script, and it's also fairly simplistic. iptables -F iptables -t nat -F iptables -t mangle -F iptables -A FORWARD -i tun0 -o venet0 -j ACCEPT iptables -A FORWARD -i venet0 -o tun0 -j ACCEPT iptables -A INPUT -p tcp --dport 22 -j ACCEPT iptables -A INPUT -p tcp --dport 1194 -j ACCEPT iptables -A INPUT -p udp --dport 1194 -j ACCEPT iptables -t nat -A POSTROUTING -s 10.9.8.0/24 -j SNAT --to-source <server's public ip> echo 1 > /proc/sys/net/ipv4/ip_forward I tried forwarding ports as well, with no success. iptables -A FORWARD -p tcp -d 10.9.8.0/24 --dport 5222:5230 -j ACCEPT iptables -t nat -A PREROUTING -p tcp --dport 5222:5230 -j DNAT --to-destination 10.9.8.6 I am also sometimes behind a double-NAT situation that I have no control over. Client -> work VPN -> my OpenVPN box -> Internet. Client -> Airport Express -> ISP (which is doing NAT) -> my OpenVPN box -> Internet. Those two situations are just the fact of life where I am, and I cannot change them. I do have full control over my client and the OpenVPN server. I am completely out of ideas. I have posted a similar query at the OpenVPN forums, but it hasn't posted yet and seems to be in their moderation queue still. Tried on freenode irc channels, but nobody is awake, so here I am. I have Googled extensively for this, and can find nothing that is related. Help me get iCloud stuff working again! (I tried serverfault, it was closed as off-topic. I'm trying here and the Unix site as well. Here because it's a more general audience that might know more about OpenVPN based on the number of questions I see asked about it) EDIT: -I have also tried upgrading to Version: 2.3-beta1-debian0 - issue persists. -Removed all iptables rules except for the ones that flush -left this rule:iptables -t nat -A POSTROUTING -s 10.9.8.0/24 -j SNAT --to-source (server ip) -added iptables -A FORWARD -m state --state RELATED,ESTABLISHED -j ACCEPT still, nothing works. I can see traffic in tcpdump on the server if i watch the tunnel: 20:03:48.702835 IP nk11p01st-courier105-bz.push.apple.com.5223 10.9.8.6.60772: Flags [F.], seq 2635, ack 1218, win 76, options [nop,nop,TS val 914984811 ecr 745921298], length 0 20:03:48.911244 IP 10.9.8.6.60772 nk11p01st-courier105-bz.push.apple.com.5223: Flags [R], seq 3621143451, win 0, length 0 But still, no push messages/notifications are ever delivered. :/ EDIT: * Further testing indicates that it might actually be the client after all.

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• iCloud stuff stops working while connected to OpenVPN [closed]

  - by Taco Bob

  I have a fairly simple OpenVPN setup on an OpenVZ VPS with Ubuntu 11.10. Client is the Viscosity client on Mac OS X 10.8.2, and after some testing, we can rule out the client as being part of the problem. Everything has been working fine except for Apple's iCloud stuff. Web surfing, email, FTP, NNTP, and Skype are all working as expected. It's ONLY the iCloud services that cease to function. If I connect to the VPN, iCloud stuff stops working. I no longer get anything in Messages, Calendar items don't get updated, and Notifications stop working. If I disconnect, the iCloud stuff all starts working. Connect again, iCloud stops working. Here's the server.conf: status openvpn-status.log log /var/log/openvpn.log verb 4 port 1194 proto udp dev tun ca /etc/openvpn/ca.crt cert /etc/openvpn/server.crt key /etc/openvpn/server.key dh /etc/openvpn/dh1024.pem server 10.9.8.0 255.255.255.0 ifconfig-pool-persist ipp.txt push "redirect-gateway def1" push “dhcp-option DNS 10.9.8.1? keepalive 10 120 duplicate-cn cipher BF-CBC comp-lzo user nobody group nogroup persist-key persist-tun tun-mtu 1500 mssfix 1400 I'm using iptables in a script, and it's also fairly simplistic. iptables -F iptables -t nat -F iptables -t mangle -F iptables -A FORWARD -i tun0 -o venet0 -j ACCEPT iptables -A FORWARD -i venet0 -o tun0 -j ACCEPT iptables -A INPUT -p tcp --dport 22 -j ACCEPT iptables -A INPUT -p tcp --dport 1194 -j ACCEPT iptables -A INPUT -p udp --dport 1194 -j ACCEPT iptables -t nat -A POSTROUTING -s 10.9.8.0/24 -j SNAT --to-source <server's public ip> echo 1 > /proc/sys/net/ipv4/ip_forward I tried forwarding ports as well, with no success. iptables -A FORWARD -p tcp -d 10.9.8.0/24 --dport 5222:5230 -j ACCEPT iptables -t nat -A PREROUTING -p tcp --dport 5222:5230 -j DNAT --to-destination 10.9.8.6 I am also sometimes behind a double-NAT situation that I have no control over. Client -> work VPN -> my OpenVPN box -> Internet. Client -> Airport Express -> ISP (which is doing NAT) -> my OpenVPN box -> Internet. Those two situations are just the fact of life where I am, and I cannot change them. I do have full control over my client and the OpenVPN server. I am completely out of ideas. I have posted a similar query at the OpenVPN forums, but it hasn't posted yet and seems to be in their moderation queue still. Tried on freenode irc channels, but nobody is awake, so here I am. I have Googled extensively for this, and can find nothing that is related. Help me get iCloud stuff working again!

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• How to forward UDP Wake-on-Lan port to broadcast IP with IPTABLES?

  - by Nazgulled

  I'm trying to setup Wake-on-Lan for some of the LAN computers at home and it seems that I need to open a UDP port (7 or 9 being the most common) and forward all requests to the broadcast IP, which in my case is 192.168.1.255. The problem is that my router does not allow me to forward anything to the broadcast IP. I can connect to my router through telnet and it seems this router uses IPTABLES, but I don't know much about it or how to is. Can someone help me out with the proper iptables commands to do what I want? Also, in case it doesn't work, the commands to put everything back would be nice too. One last thing, rebooting the router will keep those manually added iptables entries or I would need to run them every time?

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• iptables secure squid proxy

  - by Lytithwyn

  I have a setup where my incoming internet connection feeds into a squid proxy/caching server, and from there into my local wireless router. On the wan side of the proxy server, I have eth0 with address 208.78.∗∗∗.∗∗∗ On the lan side of the proxy server, I have eth1 with address 192.168.2.1 Traffic from my lan gets forwarded through the proxy transparently to the internet via the following rules. Note that traffic from the squid server itself is also routed through the proxy/cache, and this is on purpose: # iptables forwarding iptables -A FORWARD -i eth1 -o eth0 -s 192.168.2.0/24 -m state --state NEW -j ACCEPT iptables -A FORWARD -m state --state ESTABLISHED,RELATED -j ACCEPT iptables -A POSTROUTING -t nat -j MASQUERADE # iptables for squid transparent proxy iptables -t nat -A PREROUTING -i eth1 -p tcp --dport 80 -j DNAT --to 192.168.2.1:3128 iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 80 -j REDIRECT --to-port 3128 How can I set up iptables to block any connections made to my server from the outside, while not blocking anything initiated from the inside? I have tried doing: iptables -A INPUT -i eth0 -s 192.168.2.0/24 -j ACCEPT iptables -A INPUT -i eth0 -j REJECT But this blocks everything. I have also tried reversing the order of those commands in case I got that part wrong, but that didn't help. I guess I don't fully understand everything about iptables. Any ideas?

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• How do I prevent libvirt from adding iptables rules for guest NAT networks?

  - by Jack Douglas

  Similar to this old request on BugZilla for Fedora 8, I'm hoping something has changed since then or someone knows another way. I want to manage the iptables rules by hand—the one-size-fits-all automatic rules don't suit me at all. These rules seem to be added and removed when a network is started and destroyed. Is there a way of either preventing these rules being added at all or hooking a script into the network start that restores the default rules afterwards. For now, I'm using a very crude method with cron, but I hope there is a better way: * * * * * root iptables-restore < /etc/sysconfig/iptables

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• Iptables: how do I LOG what's not being ACCEPTED and limit what gets logged?

  - by Kris

  How do I log what's not being accepted by the following rule: iptables -A OUTPUT -p icmp --icmp-type 3 -m -limit --limit 10/minute -j ACCEPT And how do I limit what's being logged because I don't want to log 1000s of pings? My first thought was: iptables -A OUTPUT -p icmp --icmp-type 3 -m -limit --limit 50/day -j LOG iptables -A OUTPUT -p icmp --icmp-type 3 -m -limit --limit 10/minute -j ACCEPT But that doesn't seem right to me. I think this limits the logging to 50/day but not necessarily what is not being accepted, or am I wrong?

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• Redirect packages directed to port 5000 to another port

  - by tdc

  I'm trying to use eboard to connect to the FICS servers (http://www.freechess.org), but it fails because port 5000 is blocked (company firewall). However, I can connect to the server through the telnet port (23): telnet freechess.org 23 (succeeds) telnet freechess.org 5000 (fails) Unfortunately the port number is hardcoded (see here: http://ubuntuforums.org/archive/index.php/t-1613075.html). I'd rather not have to hack the source code as the author of that thread ended up doing. Can I just forward the port on my local machine using iptables? I tried: sudo iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 5000 -j REDIRECT --to-port 23 and sudo iptables -t nat -I OUTPUT --src 0/0 -p tcp --dport 5000 -j REDIRECT --to-ports 23 but these didn't work... Note that: $ sudo iptables -t nat -L Chain PREROUTING (policy ACCEPT) target prot opt source destination REDIRECT tcp -- anywhere anywhere tcp dpt:5000 redir ports 23 Chain INPUT (policy ACCEPT) target prot opt source destination Chain OUTPUT (policy ACCEPT) target prot opt source destination REDIRECT tcp -- anywhere anywhere tcp dpt:5000 redir ports 23 Chain POSTROUTING (policy ACCEPT) target prot opt source destination

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• Trouble setting up openVPN/VPN

  - by kkiller23

  I'm having trouble setting up a VPN on my VPS that's running Ubuntu 11.04. I'm been following this guide http://tipupdate.com/how-to-install-openvpn-on-ubuntu-vps/ I'm able to start the VPN, but the command it tell's me to do after I start the VPN doesn't work for me. I've tried it about 5 different way's and i'll show you what i get now. :~# iptables -A FORWARD -m state --state RELATED,ESTABLISHED -j ACCEPT iptables: No chain/target/match by that name. :~# iptables -A FORWARD state --state RELATED,ESTABLISHED -j ACCEPT Bad argument `state' Try `iptables -h' or 'iptables --help' for more information. I just can't get that to work and the VPN doesn't seem to be workign with out it. Can someone help me fix this?

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• Use IPtables or null route for blacklisting about 1 million IP addresses?

  - by tylerl

  I've come across a situation where a client needs to blacklist a set of just under 1 million individual IP addresses (no subnets), and network performance is a concern. While I would conjecture that IPTables rules would have less of a performance impact than routes, that's just conjecture. Does anyone have any solid evidence or other justification for favoring either IPTables or null routing as solution for blacklisting long lists of IP addresses? In this case everything is automated, so ease-of-use isn't really a concern.

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• Is there a decent diagram of packet flow for a modern era (2.6+) iptables setup?

  - by stsquad

  I'm currently trying to debug a particularly hairy set of DNAT based iptables rules (the UDP reply never makes it back to the original requester) and I'm struggling to visualise the packet flow through all the numerous tables involved. So far Google'ing has shown me old 2.4 based ipchains ones. The netfilter site has some good text docs but is short on diagrams and a number of the external links are now dead. So is there a canonical diagram for iptables packet flow, preferably showing how NAT/Masqueraded packets are also dealt with?

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• make local only daemon listening on different interface (using iptables port forwarding)?

  - by UniIsland

  i have a daemon program which listens on 127.0.0.1:8000. i need to access it when i connect to my box with vpn. so i want it to listen on the ppp0 interface too. i've tried the "ssh -L" method. it works, but i don't think it's the right way to do that, having an extra ssh process running in the background. i tried the "netcat" method. it exits when the connection is closed. so not a valid way for "listening". i also tried several iptables rules. none of them worked. i'm not listing here all the rules i've used. iptables -A FORWARD -j ACCEPT iptables -t nat -A PREROUTING -i ppp+ -p tcp --dport 8000 -j DNAT --to-destination 127.0.0.1:8000 the above ruleset doesn't work. i have net.ipv4.ip_forward set to 1. anyone knows how to redirect traffic from ppp interface to lo? say, listen on "192.168.45.1:8000 (ppp0)" as well as "127.0.0.1:8000 (lo)" there's no need to alter the port. thanx

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• Why is this iptables rule that does port forwarding not working?

  - by videoguy

  I have a server bound to localhost:7060. It is using ipv6 socket instead of ipv4. Below is netstat outout. # netstat -an Proto Recv-Q Send-Q Local Address Foreign Address State tcp 0 0 10.200.32.98:1720 0.0.0.0:* LISTEN tcp 0 0 0.0.0.0:4122 0.0.0.0:* LISTEN tcp 0 0 0.0.0.0:4123 0.0.0.0:* LISTEN tcp 0 0 127.0.0.1:4123 127.0.0.1:43051 ESTABLISHED tcp 0 0 10.200.32.98:5555 10.200.32.44:53162 ESTABLISHED tcp6 0 0 :::5060 :::* LISTEN tcp6 0 0 ::ffff:127.0.0.1:7060 :::* LISTEN tcp6 0 0 :::23 :::* LISTEN tcp6 0 0 ::ffff:10.200.32.98:23 ::ffff:10.200.32.142:43505 ESTABLISHED tcp6 0 0 ::ffff:127.0.0.1:43051 ::ffff:127.0.0.1:4123 ESTABLISHED tcp6 0 0 ::ffff:10.200.32.98:23 ::ffff:10.200.32.44:53195 ESTABLISHED udp6 0 0 :::5060 :::* CLOSE # I want to setup a port forwarding rule that accepts connections on port 24 (on all interfaces loopback as well as eth0) and forward the data to localhost:7060. This is how I am setting up the iptables rule: iptables -t nat -A PREROUTING -p tcp --dport 24 -j DNAT --to 127.0.0.1:7060** It is not working. When I telnet from different box, I see the following $telnet 10.200.32.98 24 Trying 10.200.32.98... If I change the server to bind to *:7060 and set the following rule, it seems to work fine. iptables -t nat -A PREROUTING -p tcp --dport 24 -j REDIRECT --to-port 7060 But that will make my server available on WAN interface which I don't like. I feel it had something to do with ipv6 socket (tcp6 line in netstat output). This whole thing is done on an Android device with custom built Android platform image. How do I get this working?

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• iptables: How to combine DNAT and SNAT to use a secondary IP address?

  - by Que_273

  There are lots of questions on here about iptables DNAT/SNAT setups but I haven't found one that solves my current problem. I have services bound to the IP address of eth0 (e.g. 192.168.0.20) and I also have a IP address on eth0:0 (192.168.0.40) which is shared with another server. Only one server is active, so this alias interface comes and goes depending on which server is active. In order to get traffic accepted by the service a DNAT rule is used to change the destination IP. iptables -t nat -A PREROUTING -d 192.168.0.40 -p udp --dport 7100 -j DNAT --to-destination 192.168.0.20 I also wish all outbound traffic from this service to appear to come from the shared IP, so that return responses will work in the event of a active-standby failover. iptables -t nat -A POSTROUTING -p udp --sport 7100 -j SNAT --to-source 192.168.0.40 My problem is that the SNAT rule is not always run. Inbound traffic causes a connection tracking entry like this. [root]# conntrack -L -p udp udp 17 170 src=192.168.0.185 dst=192.168.0.40 sport=7100 dport=7100 src=192.168.0.20 dst=192.168.0.185 sport=7100 dport=7100 [ASSURED] mark=0 secmark=0 use=2 which means the POSTROUTING chain is not run and outbound traffic leaves with the real IP address as the source. I am thinking I can set up a NOTRACK rule in the raw table to prevent conntracking for this port number, but is there a better or more efficient way to make this work? Edit - Alternative question: Is there a way (in CentOS/Linux) to have an interface that can be bound to but not used, such that it can be attached to the network or detached when a shared IP address is swapped between servers?

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