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• DHCP reply packets do not make it into KVM instance in OpenStack

  - by Lorin Hochstein

  I'm running a KVM instance inside of OpenStack, and it isn't getting an IP address from the DHCP server. Using tcpdump, I can see the request and reply packets on vnet0 of the compute host: # tcpdump -i vnet0 -n port 67 or port 68 tcpdump: WARNING: vnet0: no IPv4 address assigned tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on vnet0, link-type EN10MB (Ethernet), capture size 65535 bytes 19:44:56.176727 IP 0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP, Request from fa:16:3e:46:f6:11, length 300 19:44:56.176785 IP 0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP, Request from fa:16:3e:46:f6:11, length 300 19:44:56.177315 IP 10.40.0.1.67 > 10.40.0.3.68: BOOTP/DHCP, Reply, length 319 19:45:02.179834 IP 0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP, Request from fa:16:3e:46:f6:11, length 300 19:45:02.179904 IP 0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP, Request from fa:16:3e:46:f6:11, length 300 19:45:02.180375 IP 10.40.0.1.67 > 10.40.0.3.68: BOOTP/DHCP, Reply, length 319 However, if I do the same thing on eth0 inside the KVM instance, I only see the request packets, not the reply packets. What would prevent the packets from making it from vnet0 of the host to eth0 of the guest? My host is running Ubuntu 12.04 and my guest is running CentOS 6.3. Note that I have added this rule in my iptables, but it doesn't resolve the issue: -A POSTROUTING -p udp -m udp --dport 68 -j CHECKSUM --checksum-fill The instance corresponds to vnet0 and is connected via br100: # brctl show bridge name bridge id STP enabled interfaces br100 8000.54781a8605f2 no eth1 vnet0 vnet1 virbr0 8000.000000000000 yes Here's the full iptables-save: # Generated by iptables-save v1.4.12 on Tue Apr 2 19:47:27 2013 *nat :PREROUTING ACCEPT [8323:2553683] :INPUT ACCEPT [7993:2494942] :OUTPUT ACCEPT [6158:461050] :POSTROUTING ACCEPT [6455:511595] :nova-compute-OUTPUT - [0:0] :nova-compute-POSTROUTING - [0:0] :nova-compute-PREROUTING - [0:0] :nova-compute-float-snat - [0:0] :nova-compute-snat - [0:0] :nova-postrouting-bottom - [0:0] -A PREROUTING -j nova-compute-PREROUTING -A OUTPUT -j nova-compute-OUTPUT -A POSTROUTING -j nova-compute-POSTROUTING -A POSTROUTING -j nova-postrouting-bottom -A POSTROUTING -s 192.168.122.0/24 ! -d 192.168.122.0/24 -p tcp -j MASQUERADE --to-ports 1024-65535 -A POSTROUTING -s 192.168.122.0/24 ! -d 192.168.122.0/24 -p udp -j MASQUERADE --to-ports 1024-65535 -A POSTROUTING -s 192.168.122.0/24 ! -d 192.168.122.0/24 -j MASQUERADE -A nova-compute-snat -j nova-compute-float-snat -A nova-postrouting-bottom -j nova-compute-snat COMMIT # Completed on Tue Apr 2 19:47:27 2013 # Generated by iptables-save v1.4.12 on Tue Apr 2 19:47:27 2013 *mangle :PREROUTING ACCEPT [7969:5385812] :INPUT ACCEPT [7905:5363718] :FORWARD ACCEPT [158:48190] :OUTPUT ACCEPT [6877:8647975] :POSTROUTING ACCEPT [7035:8696165] -A POSTROUTING -o virbr0 -p udp -m udp --dport 68 -j CHECKSUM --checksum-fill -A POSTROUTING -p udp -m udp --dport 68 -j CHECKSUM --checksum-fill COMMIT # Completed on Tue Apr 2 19:47:27 2013 # Generated by iptables-save v1.4.12 on Tue Apr 2 19:47:27 2013 *filter :INPUT ACCEPT [2196774:15856921923] :FORWARD ACCEPT [0:0] :OUTPUT ACCEPT [2447201:1170227646] :nova-compute-FORWARD - [0:0] :nova-compute-INPUT - [0:0] :nova-compute-OUTPUT - [0:0] :nova-compute-inst-19 - [0:0] :nova-compute-inst-20 - [0:0] :nova-compute-local - [0:0] :nova-compute-provider - [0:0] :nova-compute-sg-fallback - [0:0] :nova-filter-top - [0:0] -A INPUT -j nova-compute-INPUT -A INPUT -i virbr0 -p udp -m udp --dport 53 -j ACCEPT -A INPUT -i virbr0 -p tcp -m tcp --dport 53 -j ACCEPT -A INPUT -i virbr0 -p udp -m udp --dport 67 -j ACCEPT -A INPUT -i virbr0 -p tcp -m tcp --dport 67 -j ACCEPT -A FORWARD -j nova-filter-top -A FORWARD -j nova-compute-FORWARD -A FORWARD -d 192.168.122.0/24 -o virbr0 -m state --state RELATED,ESTABLISHED -j ACCEPT -A FORWARD -s 192.168.122.0/24 -i virbr0 -j ACCEPT -A FORWARD -i virbr0 -o virbr0 -j ACCEPT -A FORWARD -o virbr0 -j REJECT --reject-with icmp-port-unreachable -A FORWARD -i virbr0 -j REJECT --reject-with icmp-port-unreachable -A OUTPUT -j nova-filter-top -A OUTPUT -j nova-compute-OUTPUT -A nova-compute-FORWARD -i br100 -j ACCEPT -A nova-compute-FORWARD -o br100 -j ACCEPT -A nova-compute-inst-19 -m state --state INVALID -j DROP -A nova-compute-inst-19 -m state --state RELATED,ESTABLISHED -j ACCEPT -A nova-compute-inst-19 -j nova-compute-provider -A nova-compute-inst-19 -s 10.40.0.1/32 -p udp -m udp --sport 67 --dport 68 -j ACCEPT -A nova-compute-inst-19 -s 10.40.0.0/16 -j ACCEPT -A nova-compute-inst-19 -p tcp -m tcp --dport 22 -j ACCEPT -A nova-compute-inst-19 -p icmp -j ACCEPT -A nova-compute-inst-19 -j nova-compute-sg-fallback -A nova-compute-inst-20 -m state --state INVALID -j DROP -A nova-compute-inst-20 -m state --state RELATED,ESTABLISHED -j ACCEPT -A nova-compute-inst-20 -j nova-compute-provider -A nova-compute-inst-20 -s 10.40.0.1/32 -p udp -m udp --sport 67 --dport 68 -j ACCEPT -A nova-compute-inst-20 -s 10.40.0.0/16 -j ACCEPT -A nova-compute-inst-20 -p tcp -m tcp --dport 22 -j ACCEPT -A nova-compute-inst-20 -p icmp -j ACCEPT -A nova-compute-inst-20 -j nova-compute-sg-fallback -A nova-compute-local -d 10.40.0.3/32 -j nova-compute-inst-19 -A nova-compute-local -d 10.40.0.4/32 -j nova-compute-inst-20 -A nova-compute-sg-fallback -j DROP -A nova-filter-top -j nova-compute-local COMMIT # Completed on Tue Apr 2 19:47:27 2013

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• KVM Guest with NAT + Bridged networking

  - by Daniel

  I currently have a few KVM Guests on a dedicated server with bridged networking (this works) and i can successfully ping the outside ips i assign via ifconfig (in the guest). However, due to the fact i only have 5 public ipv4 ip addresses, i would like to port forward services like so: hostip:port - kvm_guest:port UPDATE I found out KVM comes with a "default" NAT interface, so added the virtual NIC to the Guest virsh configuration then configured it in the Guest, it has the ip address: 192.168.122.112 I can successfully ping 192.168.122.112 and access all ports on 192.168.122.112 from the KVM Host, so i tried to port forward like so: iptables -t nat -I PREROUTING -p tcp --dport 5222 -j DNAT --to-destination 192.168.122.112:2521 iptables -I FORWARD -m state -d 192.168.122.0/24 --state NEW,RELATED,ESTABLISHED -j ACCEPT telnet KVM_HOST_IP 5222 just hangs on "trying" telnet 192.168.122.112 2521 works [root@node1 ~]# tcpdump port 5222 tcpdump: WARNING: eth0: no IPv4 address assigned tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes 23:43:47.216181 IP 1.152.245.247.51183 > null.xmpp-client: Flags [S], seq 1183303931, win 65535, options [mss 1400,nop,wscale 3,nop,nop,TS val 445777813 ecr 0,sackOK,eol], length 0 23:43:48.315747 IP 1.152.245.247.51183 > null.xmpp-client: Flags [S], seq 1183303931, win 65535, options [mss 1400,nop,wscale 3,nop,nop,TS val 445778912 ecr 0,sackOK,eol], length 0 23:43:49.415606 IP 1.152.245.247.51183 > null.xmpp-client: Flags [S], seq 1183303931, win 65535, options [mss 1400,nop,wscale 3,nop,nop,TS val 445780010 ecr 0,sackOK,eol], length 0 7 packets received by filter 0 packets dropped by kernel [root@node1 ~]# iptables -L Chain INPUT (policy ACCEPT) target prot opt source destination Chain FORWARD (policy ACCEPT) target prot opt source destination ACCEPT all -- anywhere 192.168.122.0/24 state NEW,RELATED,ESTABLISHED Chain OUTPUT (policy ACCEPT) target prot opt source destination All help is appreciated. Thanks.

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• fail2ban log parsing too slow on Raspberry Pi - options? [migrated]

  - by Gordon Morehouse

  I'm running fail2ban on a Raspberry Pi at 950MHz which I cannot overclock further. The Pi is occasionally subject to SYN floods on particular ports. I've set up iptables to throttle the rate of SYNs on the port of interest; when the throttle limits are exceeded, hosts which send SYNs are dropped into the REJECT chain and the particular SYN packet which exceeded the limit is logged. fail2ban then watches for these logged SYNs and, after seeing a few, temporarily bans the host for a short time (this is a transient issue in the app I'm working with). The problem is that the SYN floods can occasionally reach rates which are too fast for fail2ban to keep up with; I'll see 20-40 log messages per second, and eventually fail2ban falls behind and becomes ineffective. To add insult to injury, it continues consuming a LOT of CPU as it tries to catch up. I have verified that DROP chained packets from hosts already banned by fail2ban are not logged, and thus do not add to its load. What are my options here? I have a few ideas, but no clear path forward. Could I make the log-parse regex "easier" so it takes fewer cycles? Would using iptables --log-prefix to put a token near the start of the log message, and/or otherwise simplifying/altering the fail2ban regex help? Here is the current fail2ban config line containing a regex: failregex = kernel:.*?SRC=(?:::f{4,6}:)?(?P<host>[\w\-.^_]+) DST.*?SYN Is there a faster way for fail2ban to watch for the packets exceeding the limits than parsing kern.log? Could fail2ban be run under PyPy instead of CPython with minimal nonstandard wizardry (the OS is Raspbian 7, so, mostly Debian 7)? Is there something better than fail2ban that I could use to watch for the packets which exceed the SYN limits, and after N exceeds in X seconds, temporarily put the offending IP into the iptables DROP bucket, and take it out when the ban timer expires? Again, I'd vastly prefer a solution that uses as much software available in Debian as possible, though I can build Debian packages in a pinch.

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• Shared firewall or multiple client specific firewalls?

  - by Tauren

  I'm trying to determine if I can use a single firewall for my entire network, including customer servers, or if each customer should have their own firewall. I've found that many hosting companies require each client with a cluster of servers to have their own firewall. If you need a web node and a database node, you also have to get a firewall, and pay another monthly fee for it. I have colo space with several KVM virtualization servers hosting VPS services to many different customers. Each KVM host is running a software iptables firewall that only allows specific ports to be accessed on each VPS. I can control which ports any given VPS has open, allowing a web VPS to be accessed from anywhere on ports 80 and 443, but blocking a database VPS completely to the outside and only allowing a certain other VPS to access it. The configuration works well for my current needs. Note that there is not a hardware firewall protecting the virtualization hosts in place at this time. However, the KVM hosts only have port 22 open, are running nothing except KVM and SSH, and even port 22 cannot be accessed except for inside the netblock. I'm looking at possibly rethinking my network now that I have a client who needs to transition from a single VPS onto two dedicated servers (one web and one DB). A different customer already has a single dedicated server that is not behind any firewall except iptables running on the system. Should I require that each dedicated server customer have their own dedicated firewall? Or can I utilize a single network-wide firewall for multiple customer clusters? I'm familiar with iptables, and am currently thinking I'll use it for any firewalls/routers that I need. But I don't necessarily want to use up 1U of space in my rack for each firewall, nor the power consumption each firewall server will take. So I'm considering a hardware firewall. Any suggestions on what is a good approach?

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• Is iptable capable of this or should I go with mod_proxy?

  - by Jesper

  I'm trying to configure my network to receive an incoming connection on one device and then redirect it to another device on a specific port. Right now I'm on about port 80 and a device running apache. The problem I'm facing is that when the forwarding is done it also sets the source ip to the first device instead of the source ip the user that connects to the service has. Let me illustrate it: [Internet User] = 7.7.7.7 connects to [Device 1] = 1.1.1.1:80 [Device 1] forwards it to [Device 2] = 1.1.1.2:80 [Device 2] outputs response that [Internet User] sees So on [Device 2] I will naturally see [Device 1]s IP in the logs, but I wanna see if there is a way to connect the internet user through [Device 1] to [Device 2] while seeing the real source IP in the logs on [Device 2]. Is that possible? My rule-set looks like this at the moment: (on Device 1) iptables -P FORWARD ACCEPT iptables -t nat -I PREROUTING -j DNAT -p tcp --dport 80 --to-destination 1.1.1.2:80 iptables -t nat -I POSTROUTING -j SNAT -p tcp -d 1.1.1.2 --to-source 1.1.1.1 On [Device 2] it accepts all incoming on port 80 from [Device 1] as well as accepts all related and established connections. So, would there be any way to get the real source onto [Device 2]? Let me know if you need more information!

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• fail2ban block ports rules iptable

  - by J Spen

  I just installed Ubuntu Server 14.04 and don't have much experience with IPtables. I am trying to get a basic setup going where I only accept SSH connections on port 22 and 2222. I actually have that working with no problem using fail2ban ssh. Then I wanted to block all other ports except 423 and 4242 but either method of DROPing all connections that are not listed seems not to work and it blocks me out of everything. Below is the setup that works: -P INPUT ACCEPT -P FORWARD ACCEPT -P OUTPUT ACCEPT -N fail2ban-ssh -A INPUT -p tcp -m multiport --dports 22,2222 -j fail2ban-ssh -A fail2ban-ssh -j RETURN I tried to change it either to: -P INPUT DROP -P FORWARD ACCEPT -P OUTPUT ACCEPT -N fail2ban-ssh -A INPUT -p tcp -m multiport --dports 22,2222 -j fail2ban-ssh -A fail2ban-ssh -j RETURN or: -P INPUT ACCEPT -P FORWARD ACCEPT -P OUTPUT ACCEPT -N fail2ban-ssh -A INPUT -p tcp -m multiport --dports 22,2222 -j fail2ban-ssh -A INPUT -j DROP -A fail2ban-ssh -j RETURN I have noticed that the rules for fail2ban-ssh are automatically added to my iptables on boot because if I save them with iptables-persistant they are entered twice. How do I go about blocking everything accept those 2 ports using fail2ban? Is it a bad fail2ban configuration or do I need to add the fail2ban-ssh -j Return somewhere else in my code.

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• Enabling NAT forwarding using a second WAN interface and a second gateway on ubuntu

  - by nixnotwin

  I have 3 interfaces: eth0 192.168.0.50/24 eth1 10.0.0.200/24 eth2 225.228.123.211 The default gateway is 192.168.0.1 which I want to keep as it is in the changes I want to make. I want to masquerade eth1 10.0.0.200/24 and enable NAT forwarding to eth2. So I have done this: ip route add 225.228.123.208/29 dev eth2 src 225.228.123.211 table t1 ip route add default via 225.228.123.209 dev eth2 table t1 ip rule add from 225.228.123.211 table t1 ip rule add to 225.228.123.211 table t1 Now I can receive ping replies from any internet host if I did: ping -I eth2 8.8.8.8 To enable NAT forwarding I did this: sudo iptables -A FORWARD -o eth2 -i eth1 -s 10.0.0.0/24 -m conntrack --ctstate NEW -j ACCEPT sudo iptables -A FORWARD -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT sudo iptables -t nat -A POSTROUTING -o eth1 -j MASQUERADE But it isn't working. To test I used a client pc and put it on 10.0.0.0/24 network and gateway was set as 10.0.0.200. I want to have 192.168.0.1 as default gateway. And the traffic that comes in via eth1 10.0.0.200/24 should be forwarded to eth2 225.228.123.211. I have enabled forwarding on ubuntua also.

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• IPTABLE & IP-routed netwok solution for HOST net and VM's subnet

  - by Daniel

  I've got ProxmoxVE2.1 ruled KVM node on Debian and bunch of VM's guests machine. That is how my networking looks like: # network interface settings auto lo iface lo inet loopback # device: eth0 auto eth0 iface eth0 inet static address 175.219.59.209 gateway 175.219.59.193 netmask 255.255.255.224 post-up echo 1 > /proc/sys/net/ipv4/conf/eth0/proxy_arp And I've got two working subnet solution auto vmbr0 iface vmbr0 inet static address 10.10.0.1 netmask 255.255.0.0 bridge_ports none bridge_stp off bridge_fd 0 post-up ip route add 10.10.0.1/24 dev vmbr0 This way I can reach internet, to resolve outside hosts, update and download everything I need but can't reach one guest VM out of any other VM's inside my network. The second solution allows me to communicate between VM's: auto vmbr1 iface vmbr1 inet static address 10.10.0.1 netmask 255.255.255.0 bridge_ports none bridge_stp off bridge_fd 0 post-up echo 1 > /proc/sys/net/ipv4/ip_forward post-up iptables -t nat -A POSTROUTING -s '10.10.0.0/24' -o vmbr1 -j MASQUERADE post-down iptables -t nat -D POSTROUTING -s '10.10.0.0/24' -o vmbr1 -j MASQUERADE I can even NAT internal addresses: -t nat -I PREROUTING -p tcp --dport 789 -j DNAT --to-destination 10.10.0.220:345 My inexperienced mind is ready to double VM's net adapters: one for the first solution and another - for second (with slightly different adresses) but I'm pretty sure that it's a dumb way to resolve the problem and everything can be resolved via iptables/ip route rules that I can't create. I've tried a dozen of "wizard manuals" and "howto's" to mix both solution but without success. Looking for an advice (and good reading links for networking begginers).

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• fail2ban iptable rule wont block

  - by Termiux

  So I set up fail2ban on my Debian 7 server, still I've been getting hit a lot and I dont know why is not blocking properly. The regex works, it recognizes the attempts but it seems the iptables rules it insert wont work, this is how it look iptables ouput looks after fail2ban tries to block. Chain INPUT (policy ACCEPT) num target prot opt source destination 1 fail2ban-courierauth tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:25 2 fail2ban-couriersmtp tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:25 3 sshguard all -- 0.0.0.0/0 0.0.0.0/0 Chain FORWARD (policy ACCEPT) num target prot opt source destination Chain OUTPUT (policy ACCEPT) num target prot opt source destination Chain fail2ban-courierauth (1 references) num target prot opt source destination 1 DROP all -- 216.x.y.z 0.0.0.0/0 2 RETURN all -- 0.0.0.0/0 0.0.0.0/0 Chain fail2ban-courierimap (0 references) num target prot opt source destination 1 RETURN all -- 0.0.0.0/0 0.0.0.0/0 Chain fail2ban-courierpop3 (0 references) num target prot opt source destination 1 RETURN all -- 0.0.0.0/0 0.0.0.0/0 Chain fail2ban-couriersmtp (1 references) num target prot opt source destination 1 RETURN all -- 0.0.0.0/0 0.0.0.0/0 Chain fail2ban-postfix (0 references) num target prot opt source destination 1 RETURN all -- 0.0.0.0/0 0.0.0.0/0 Chain fail2ban-sasl (0 references) num target prot opt source destination 1 RETURN all -- 0.0.0.0/0 0.0.0.0/0 In the iptables above you can see the "Chain fail2ban-courierauth" rule that added the drop rule for the ip but Im still able to connect!! I can still connect to the server, why isn't it blocking?

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• Preventing endless forwarding with two routers

  - by jarmund

  The network in quesiton looks basically like this: /----Inet1 / H1---[111.0/24]---GW1---[99.0/24] \----GW2-----Inet2 Device explaination H1: Host with IP 192.168.111.47 GW1: Linux box with IPs 192.168.111.1 and 192.168.99.2, as well as its own route to the internet. GW2: Generic wireless router with IP 192.168.99.1 and its own route to the internet. Inet1 & Inet2: Two possible routes to the internet In short: H has more than one possible route to the internet. H is supposed to only access the internet via GW2 when that link is up, so GW1 has some policy based routing special just for H1: ip rule add from 192.168.111.47 table 991 ip route add default via 192.168.99.1 table 991 While this works as long as GW2 has a direct link to the internet, the problem occurs when that link is down. What then happens is that GW2 forwards the packet back to GW1, which again forwards back to GW2, creating an endless loop of TCP-pingpong. The preferred result would be that the packet was just dropped. Is there something that can be done with iptables on GW1 to prevent this? Basically, an iptables-friendly version of "If packet comes from GW2, but originated from H1, drop it" Note1: It is preferable not to change anything on GW2. Note2: H1 needs to be able to talk to both GW1 and GW2, and vice versa, but only GW2 should lead to the internet TLDR; H1 should only be allowed internet access via GW2, but still needs to be able to talk to both GW1 and GW2. EDIT: The interfaces for GW1 are br0.105 for the '99' network, and br0.111 for the '111' network. The sollution may or may not be obnoxiously simple, but i have not been able to produce the proper iptables syntax myself, so help would be most appreciated. PS: This is a follow-up question from this question

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• [openVPN] server & client on same machine . And multiple VPN servers

  - by HiWorld

  Hello everyone, im stucked configuring openvpn to build a multi vpn connection. like this: CLIENT - VPN1 - VPN2 - INTERNET Well, i already have and know how to done a normal sigle vpn but want to use a chain of vpns, so i explain what i have done and how i did it. ON VPN1. i have 1 openvpn instance running as server( where client connect to) and another as client connecting to VPN2 running as server. { Here comes the problem } when i connect VPN1 as client of VPN2 i cant connect to VPN1 from CLIENT, my question is HOW TO procced with this... Also have another third instance working as server to use VPN1 without chains. ON VPN2. 1 openvpn instance as server where VPN1 will connect and then forward to the NET. Im using TUN interface on configs. And iptables are on this way: VPN1 - openvpn ip server1 : 192.168.6.0 / ip as client of VPN2: 192.168.5.70 iptables -t nat -A POSTROUTING -s 192.168.6.0 -j SNAT --to-source 192.168.5.70 VPN2 - openvpn ip server2 : 192.168.5.0 iptables -t nat -A POSTROUTING -s 192.168.5.0/24 -j SNAT --to-source EXTERNAL_IP_TO_INTERNET Hope someone help me with this. thanks in advance

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• OpenVPN + iptables / NAT routing

  - by Mikeage

  Hi, I'm trying to set up an OpenVPN VPN, which will carry some (but not all) traffic from the clients to the internet via the OpenVPN server. My OpenVPN server has a public IP on eth0, and is using tap0 to create a local network, 192.168.2.x. I have a client which connects from local IP 192.168.1.101 and gets VPN IP 192.168.2.3. On the server, I ran: iptables -A INPUT -i tap+ -j ACCEPT iptables -A FORWARD -i tap+ -j ACCEPT iptables -t nat -A POSTROUTING -s 192.168.2.0/24 -o eth0 -j MASQUERADE On the client, the default remains to route via 192.168.1.1. In order to point it to 192.168.2.1 for HTTP, I ran ip rule add fwmark 0x50 table 200 ip route add table 200 default via 192.168.2.1 iptables -t mangle -A OUTPUT -j MARK -p tcp --dport 80 --set-mark 80 Now, if I try accessing a website on the client (say, wget google.com), it just hangs there. On the server, I can see $ sudo tcpdump -n -i tap0 tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on tap0, link-type EN10MB (Ethernet), capture size 96 bytes 05:39:07.928358 IP 192.168.1.101.34941 > 74.125.67.100.80: S 4254520618:4254520618(0) win 5840 <mss 1334,sackOK,timestamp 558838 0,nop,wscale 5> 05:39:10.751921 IP 192.168.1.101.34941 > 74.125.67.100.80: S 4254520618:4254520618(0) win 5840 <mss 1334,sackOK,timestamp 559588 0,nop,wscale 5> Where 74.125.67.100 is the IP it gets for google.com . Why isn't the MASQUERADE working? More precisely, I see that the source showing up as 192.168.1.101 -- shouldn't there be something to indicate that it came from the VPN? Edit: Some routes [from the client] $ ip route show table main 192.168.2.0/24 dev tap0 proto kernel scope link src 192.168.2.4 192.168.1.0/24 dev wlan0 proto kernel scope link src 192.168.1.101 metric 2 169.254.0.0/16 dev wlan0 scope link metric 1000 default via 192.168.1.1 dev wlan0 proto static $ ip route show table 200 default via 192.168.2.1 dev tap0

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• Port forwarding DD-WRT

  - by Pawel

  Hi, I'am runing locally service on port 81 (192.168.1.101) I would like to access server from outside MY.WAN.IP.ADDR:81. Everything is working fine on my local network, However can't access it from outside. Below iptables rules on the router. I am using dd-wrt and asus rt-n16 (everything is setup through standard port range forwarding in dd-wrt ) It might be something obvious, but I don't have any experience with routing. Any help will be really appreciated. Thanks. #iptables -t nat -vnL Chain PREROUTING (policy ACCEPT 1285 packets, 148K bytes) pkts bytes target prot opt in out source destination 3 252 DNAT icmp -- * * 0.0.0.0/0 MY.WAN.IP.ADDR to:192.168.1.1 5 300 DNAT tcp -- * * 0.0.0.0/0 MY.WAN.IP.ADDR tcp dpt:81 to:192.168.1.101 0 0 DNAT udp -- * * 0.0.0.0/0 MY.WAN.IP.ADDR udp dpt:81 to:192.168.1.101 298 39375 TRIGGER 0 -- * * 0.0.0.0/0 MY.WAN.IP.ADDR TRIGGER type:dnat match:0 relate:0 Chain POSTROUTING (policy ACCEPT 7 packets, 433 bytes) pkts bytes target prot opt in out source destination 747 91318 SNAT 0 -- * vlan2 0.0.0.0/0 0.0.0.0/0 to:MY.WAN.IP.ADDR 0 0 RETURN 0 -- * br0 0.0.0.0/0 0.0.0.0/0 PKTTYPE = broadcast Chain OUTPUT (policy ACCEPT 86 packets, 5673 bytes) pkts bytes target prot opt in out source destination # iptables -L Chain INPUT (policy ACCEPT) target prot opt source destination DROP tcp -- anywhere anywhere tcp dpt:webcache DROP tcp -- anywhere anywhere tcp dpt:www DROP tcp -- anywhere anywhere tcp dpt:https DROP tcp -- anywhere anywhere tcp dpt:69 DROP tcp -- anywhere anywhere tcp dpt:ssh DROP tcp -- anywhere anywhere tcp dpt:ssh DROP tcp -- anywhere anywhere tcp dpt:telnet DROP tcp -- anywhere anywhere tcp dpt:telnet Chain FORWARD (policy ACCEPT) target prot opt source destination ACCEPT 0 -- anywhere anywhere TCPMSS tcp -- anywhere anywhere tcp flags:SYN,RST/SYN TCPMSS clamp to PMTU lan2wan 0 -- anywhere anywhere ACCEPT 0 -- anywhere anywhere state RELATED,ESTABLISHED logaccept tcp -- anywhere pawel-ubuntu tcp dpt:81 logaccept udp -- anywhere pawel-ubuntu udp dpt:81 TRIGGER 0 -- anywhere anywhere TRIGGER type:in match:0 relate:0 trigger_out 0 -- anywhere anywhere logaccept 0 -- anywhere anywhere state NEW Chain OUTPUT (policy ACCEPT) target prot opt source destination Chain advgrp_1 (0 references) target prot opt source destination Chain advgrp_10 (0 references) target prot opt source destination Chain advgrp_2 (0 references) target prot opt source destination Chain advgrp_3 (0 references) target prot opt source destination Chain advgrp_4 (0 references) target prot opt source destination Chain advgrp_5 (0 references) target prot opt source destination Chain advgrp_6 (0 references) target prot opt source destination Chain advgrp_7 (0 references) target prot opt source destination Chain advgrp_8 (0 references) target prot opt source destination Chain advgrp_9 (0 references) target prot opt source destination Chain grp_1 (0 references) target prot opt source destination Chain grp_10 (0 references) target prot opt source destination Chain grp_2 (0 references) target prot opt source destination Chain grp_3 (0 references) target prot opt source destination Chain grp_4 (0 references) target prot opt source destination Chain grp_5 (0 references) target prot opt source destination Chain grp_6 (0 references) target prot opt source destination Chain grp_7 (0 references) target prot opt source destination Chain grp_8 (0 references) target prot opt source destination Chain grp_9 (0 references) target prot opt source destination Chain lan2wan (1 references) target prot opt source destination Chain logaccept (3 references) target prot opt source destination ACCEPT 0 -- anywhere anywhere Chain logdrop (0 references) target prot opt source destination DROP 0 -- anywhere anywhere Chain logreject (0 references) target prot opt source destination REJECT tcp -- anywhere anywhere tcp reject-with tcp-reset Chain trigger_out (1 references) target prot opt source destination #iptables -vnL FORWARD Chain FORWARD (policy ACCEPT 130 packets, 5327 bytes) pkts bytes target prot opt in out source destination 15 900 ACCEPT 0 -- br0 br0 0.0.0.0/0 0.0.0.0/0 390 20708 TCPMSS tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp flags:0x06/0x02 TCPMSS clamp to PMTU 182K 130M lan2wan 0 -- * * 0.0.0.0/0 0.0.0.0/0 179K 129M ACCEPT 0 -- * * 0.0.0.0/0 0.0.0.0/0 state RELATED,ESTABLISHED 0 0 logaccept tcp -- * * 0.0.0.0/0 192.168.1.101 tcp dpt:81 0 0 logaccept udp -- * * 0.0.0.0/0 192.168.1.101 udp dpt:81 0 0 TRIGGER 0 -- vlan2 br0 0.0.0.0/0 0.0.0.0/0 TRIGGER type:in match:0 relate:0 2612 768K trigger_out 0 -- br0 * 0.0.0.0/0 0.0.0.0/0 2482 762K logaccept 0 -- br0 * 0.0.0.0/0 0.0.0.0/0 state NEW

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• Logging communication between two VMs

  - by sYnfo

  Hi, I'm trying to set up "malware lab" described in this paper. So far, I've set up Windows guest system, adding one Host-only Network adapter, and setting this (sorry if the names aren't exactely correct, I don't have an english language version): - IP Address - 10.0.0.3 - Subnet mask - 255.255.255.0 - Default gateway - not set - Preferred DNS - 10.0.0.4 - Alternate DNS - not set And a Linux guest system - Ubuntu 9.04 - with two Network adapters - Bridged (eth0) and Host-only (eth1), and setting eth1 IP Address to 10.0.0.4, leaving the eth0 to be set by DHCP. Then, I have configured iptables as described in the paper, ie.: iptables -F -t nat iptables -F -t mangle iptables -t mangle -P PREROUTING ACCEPT iptables -t mangle -P OUTPUT ACCEPT iptables -t nat -P PREROUTING ACCEPT iptables -t nat -P POSTROUTING ACCEPT iptables -t nat -P OUTPUT ACCEPT iptables -t mangle -A PREROUTING -i eth0 -j ACCEPT iptables -t mangle -A PREROUTING -p udp -i eth1 -d 10.0.0.3 --dport 53 -j ACCEPT iptables -t mangle -A PREROUTING -p tcp -i eth1 --dport 80 -j ACCEPT iptables -t mangle -A PREROUTING -p tcp -i eth1 -d 10.0.0.3 --dport 6000:7000 -j ACCEPT iptables -t mangle -A PREROUTING -i eth1 -j ULOG iptables -t mangle -A PREROUTING -i eth1 -j DROP Now, when I try to ping the windows system from within the Linux system, it does not reply, I guess thats perfectly normal, because iptables is blocking ping responce. Same when I try to ping the Linux system from within the Windows. But when I try to access any web page from within the Windows system, I would expect that this action should get logged by iptables. But thing is, I don't see any of that kind of lines in log file (If I am looking in the right place, that is. :) It is at /var/log/messages, isn't it?). So, what do you think might be the problem here? I should note, that this is the first time I'm using linux, so don't expect ANY working knowledge of Linux at all... :) Also, since english is not my mother tongue, feel free to point out any gramatical mistakes... :) Thanks for any advice.

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• How to Unban an IP properly with Fail2Ban

  - by psp

  I'm using Fail2Ban on a server and I'm wondering how to unban an IP properly. I know I can work with IPTables directly: iptables -D fail2ban-ssh <number> But is there not a way to do it with the fail2ban-client? In the manuals it states something like: fail2ban-client get ssh actionunban <IP>. But that doesn't work. Also, I don't want to /etc/init.d/fail2ban restart as that would lose all the bans in the list.

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• IP tables gateway

  - by WojonsTech

  I am trying to make an iptables gateway. I ordered 3 dedicated server from my hosting company all with dual nics. One server has been given all the ip addresses and is connected directly to the internet and has its other nic connected to a switch where the other servers are all connected also. I want to setup iptables so for example the ip address 50.0.2.4 comes into my gateway server it fowards all the traffic to a private ip address using the second nic. This way the second nic can do what ever it needs and can respond back also. I also want it setup that if any of the other servers needs to download anything over the inernet it is able to do so and by using the same ip address that is used for its incomming traffic. Lastly I would like to be able to setup dns and other needed networking stuff that i maybe not thinking about.

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• How to drop packets in a custom Intrusion Detection System

  - by tzoukos

  Hi there, I'm trying to build a custom Intrusion Detection and Prevention System (IDS/IPS). I found a great utility named ROPE which can scan the packet payload and drop the packet that doesn't follow the rules, set by a script. This serves my purpose completely, since what I want to do is check the payload for some specific text and then drop it or allow it ( the string feature in iptables wouldn't do me any good, because I want to check more than one string in tha payload, like usernames, id's, etc ). However, ROPE is really old and despite my many attempts I haven't managed to install it properly. Do you know any similar program that will help me drop packets in iptables depending on the payload? Any suggestion is greatly appreciated :)

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• 32bit domU on 64bit dom0

  - by ModuleC

  I'm using 64bit Centos Dom0 with: 2.6.18-164.15.1.el5xen #1 SMP Wed Mar 17 12:04:23 EDT 2010 x86_64 x86_64 x86_64 GNU/Linux recently i migrated some 32bit Centos domUs on this node. As by specs 32bit domUs should work with 64bit dom0. DomUs are paravirtualized, and everything works, except iptables limit. Anyways runing csf on domU will return following messages in dmesg: ip_tables: (C) 2000-2006 Netfilter Core Team Netfilter messages via NETLINK v0.30. ip_conntrack version 2.4 (2080 buckets, 16640 max) - 304 bytes per conntrack ip_tables: limit match: invalid size 40 != 28 ip_tables: limit match: invalid size 40 != 28 ip_tables: limit match: invalid size 40 != 28 ip_tables: limit match: invalid size 40 != 28 ip_tables: limit match: invalid size 40 != 28 ip_tables: limit match: invalid size 40 != 28 ip_tables: limit match: invalid size 40 != 28 Doing lsmod on both dom0 and domU is listing all iptables modules required as loaded. I've found this http://www.mail-archive.com/[email protected]/msg189433.html But didn't find anything for centos on this issue. Am I missing something?

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• open mysql to any connection on ubuntu

  - by ThomasReggi

  I simply want to open up mysql to be accessible from any server ip. I have already commented out the bind-address in /etc/mysql/my.conf. I have already setup the user account within mysql. I have no clue whats stopping me from connecting. The more challenging I see this being the more I realize how much of a security risk it is, and I get that, I just want to be able to do it temporarily. I think that the iptables firewall is the last thing that is preventing me from achieving this, but sudo iptables -A INPUT -p tcp -m tcp --dport 3306 -j ACCEPT is seemingly doing nothing.

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• Block IP Address including ICMP using UFW

  - by dr jimbob

  I prefer ufw to iptables for configuring my software firewall. After reading about this vulnerability also on askubuntu, I decided to block the fixed IP of the control server: 212.7.208.65. I don't think I'm vulnerable to this particular worm (and understand the IP could easily change), but wanted to answer this particular comment about how you would configure a firewall to block it. I planned on using: # sudo ufw deny to 212.7.208.65 # sudo ufw deny from 212.7.208.65 However as a test that the rules were working, I tried pinging after I setup the rules and saw that my default ufw settings let ICMP through even from an IP address set to REJECT or DENY. # ping 212.7.208.65 PING 212.7.208.65 (212.7.208.65) 56(84) bytes of data. 64 bytes from 212.7.208.65: icmp_seq=1 ttl=52 time=79.6 ms ^C --- 212.7.208.65 ping statistics --- 1 packets transmitted, 1 received, 0% packet loss, time 0ms rtt min/avg/max/mdev = 79.630/79.630/79.630/0.000 ms Now, I'm worried that my ICMP settings are too generous (conceivably this or a future worm could setup an ICMP tunnel to bypass my firewall rules). I believe this is the relevant part of my iptables rules is given below (and even though grep doesn't show it; the rules are associated with the chains shown): # sudo iptables -L -n | grep -E '(INPUT|user-input|before-input|icmp |212.7.208.65)' Chain INPUT (policy DROP) ufw-before-input all -- 0.0.0.0/0 0.0.0.0/0 Chain ufw-before-input (1 references) ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmp type 3 ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmp type 4 ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmp type 11 ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmp type 12 ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmp type 8 ufw-user-input all -- 0.0.0.0/0 0.0.0.0/0 Chain ufw-user-input (1 references) DROP all -- 0.0.0.0/0 212.7.208.65 DROP all -- 212.7.208.65 0.0.0.0/0 How should I go about making it so ufw blocks ICMP when I specifically attempt to block an IP address? My /etc/ufw/before.rules has in part: # ok icmp codes -A ufw-before-input -p icmp --icmp-type destination-unreachable -j ACCEPT -A ufw-before-input -p icmp --icmp-type source-quench -j ACCEPT -A ufw-before-input -p icmp --icmp-type time-exceeded -j ACCEPT -A ufw-before-input -p icmp --icmp-type parameter-problem -j ACCEPT -A ufw-before-input -p icmp --icmp-type echo-request -j ACCEPT I'm tried changing ACCEPT above to ufw-user-input: # ok icmp codes -A ufw-before-input -p icmp --icmp-type destination-unreachable -j ufw-user-input -A ufw-before-input -p icmp --icmp-type source-quench -j ufw-user-input -A ufw-before-input -p icmp --icmp-type time-exceeded -j ufw-user-input -A ufw-before-input -p icmp --icmp-type parameter-problem -j ufw-user-input -A ufw-before-input -p icmp --icmp-type echo-request -j ufw-user-input But ufw wouldn't restart after that. I'm not sure why (still troubleshooting) and also not sure if this is sensible? Will there be any negative effects (besides forcing the software firewall to force ICMP through a few more rules)?

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• How much traffic a linux-based shaper would be able to chew

  - by facha

  Hi, everyone I have a linux based traffic shaper (iptables + tc htb policy). It works in bridge mode. Shapes traffic based on IPs and ports (there are about 100 rules in the "mangle" chain of iptables). Right now its throughoutput is about 100 mb/s (I don't remember pps, there are about 800 users in the network). Just was wondering - when I will hit the limit. How much traffic could a linux-based shaper possibly get throuhg it. If you have one under heavy load, please could you write what machine you use and what load there is. Or if you have any other info about the subj, please write as well. Thanks in advance.

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• HTTPS is not working in transparent proxy with Squid

  - by Supratik

  Hi I am using Squid proxy 3.1, all systems in the LAN connects to the internet through proxy. Direct connection is blocked using the iptables from the gateway server. There are some devices which does not have options for auto proxy or manual proxy and can only connect to the internet directly. So I enabled transparent proxy in Squid and redirected packets for port 80 and 443 to Squid proxy using iptables. Now the problem is it is working fine for HTTP port but HTTPS is not working. It is throwing "ssl_error_rx_record_too_long" error. If it is not possible through transparent proxy can you please suggest me another solution. Warm Regards Supratik

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• fail2ban with Cloudflare

  - by tatersalad58

  I'm using fail2ban to block web vulnerability scanners. It is working correctly when visiting the site if CloudFlare is bypassed, but a user can still access it if going through it. I have mod_cloudflare installed. Is it possible to block users with IPtables when using Cloudflare? Ubuntu Server 12.04 32-bit Access.log: 112.64.89.231 - - [29/Aug/2012:19:16:01 -0500] "GET /muieblackcat HTTP/1.1" 404 469 "-" "-" Jail.conf [apache-probe] enabled = true port = http,https filter = apache-probe logpath = /var/log/apache2/access.log action = iptables-multiport[name=apache-probe, port="http,https", protocol=tcp] maxretry = 1 bantime = 30 # Test Apache-probe.conf [Definition] failregex = ^<HOST>.*"GET \/muieblackcat HTTP\/1\.1".* ignoreregex =

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• Mail server hammering

  - by Rodrigo

  I've noticed a quick increase on smtp connections coming to my server, investigating it further i figured out that there's a botnet hammering my smtp server. I've tried to stop it by adding a rule at iptables: -N SMTP-BLOCK -A SMTP-BLOCK -m limit --limit 1/m --limit-burst 3 -j LOG --log-level notice --log-prefix "iptables SMTP-BLOCK " -A SMTP-BLOCK -m recent --name SMTPBLOCK --set -j DROP -A INPUT -p tcp --dport 25 -m state --state NEW -m recent --name SMTPBLOCK --rcheck --seconds 360 -j SMTP-BLOCK -A INPUT -p tcp --dport 25 -m state --state NEW -m recent --name SMTP --set -A INPUT -p tcp --dport 25 -m state --state NEW -m recent --name SMTP --rcheck --seconds 60 --hitcount 3 -j SMTP-BLOCK -A INPUT -p tcp --dport 25 -m state --state NEW -j ACCEPT That would avoid them from hammering "too fast", however the problem still, there's like 5 tries per second, it's going insane, i had to incrase the maximum number of childs of sendmail/dovecot. There's too many ips to filter out manually and simply changing the smtp to another port is not practical since i got many other clients on that server. I'm using sendmail with dovecot, any ideas to have this filtered out more efficiently?

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• Passing all traffic through Cloudflare

  - by Nick

  I am new to Linux System Administration and I am experimenting with iptables trying to learn how to really lock down a system with them. And one thing a friend of mine recommended was that there was a way to pass all incoming traffic through Cloudflare so even if attackers resolved the server ip they still couldn't (D)dos it directly. This is exactly what they said: "Simply config your servers iptables to only allow incoming connections from CloudFlares IP ranges then set it to allow only your IP/IP range to connect on port 21 (SSH)" Could someone help me on what command I'd need to run for Ubuntu to get this effect?

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