linux firewall, iptables forwarding problem
Hi,
I am new to the linux, but I need to set up a simple firewall for the local network.
I have Ubuntu kernel 2.6 installed, two NIC cards with a one static IP address to internet, I am using bridge-utilities bridge two interfaces together. The bridge is up and fine.
Now I am really stock at this point.
I set default policy to DROP for Forward and enabled forwarding.
Then add rules like these:
iptables -P INPUT DROP
iptables -P FORWARD DROP
iptables -P OUTPUT ACCEPT
iptables -A FORWARD -i eth0 -o eth1 -m state --state ESTABLISHED,RELATED -j ACCEPT
iptables -A FORWARD -i eth1 -o eth0 -j ACCEPT
the local computer can not access internet, but if I changed default FORWARD policy to ACCEPT,
the local computer then can access internet.
I really don't understand why, Please help!
weiwei
Comments
-
The issue is with the order of operation in your rules, add the "-P" entries on the end to make them the final actions. This will allow the forwarding rules to be caught and used before the packets are being dropped.0
-
Thank you very much for replying, did the firewall check the default policy very last?
weiwei0 -
weiwei wrote:iptables -A FORWARD -i eth0 -o eth1 -m state --state ESTABLISHED,RELATED -j ACCEPT
iptables -A FORWARD -i eth1 -o eth0 -j ACCEPT
Why do the state have to be ESTABLISHED or RELATED? Like this newly generated packets won't get through your rules and will be DROPed as that is your default policy.
Try changing that
Regards0 -
The default policy must be set last, iptables reads the rules in the order they are input so whatever is last will be default for anything that does not find a matching rule in the preceding rules.0
-
mfillpot wrote:The default policy must be set last, iptables reads the rules in the order they are input so whatever is last will be default for anything that does not find a matching rule in the preceding rules.
AFAIK this is not true.
The policies are only applied whenever all the other rules fail.0 -
This was the sort of problem i faced in Linux Firewall that is in Forwarding iptables.
i hav 3 NICs
eth0 is my internet interface
eth1 is DMZ interface (doesnt really act like a dmz yet)
eth2 is my local lanI want to forward the ports to the server on the DMZ
I looked on google on more sites on how to forward ports and it says :
iptables -t nat -A PREROUTING -p tcp -d $INET_IP --dport 25 -j DNAT --to $DMZ_SERVER1:80
is this command correct?
thanks for your reply
EDIT:
no worried thanks again for your reply fixed it. USed these commands$IPTABLES -A FORWARD -p tcp -i $INETIF --destination-port 80 --destination 192.168.2.2 -j ACCEPT
$IPTABLES -t nat -A PREROUTING -p tcp -i $INETIF --destination-port 80 -j DNAT --to-destination 192.168.2.2:80 __________________
rm -rf /0
Categories
- All Categories
- 49 LFX Mentorship
- 102 LFX Mentorship: Linux Kernel
- 552 Linux Foundation Boot Camps
- 296 Cloud Engineer Boot Camp
- 118 Advanced Cloud Engineer Boot Camp
- 52 DevOps Engineer Boot Camp
- 53 Cloud Native Developer Boot Camp
- 4 Express Training Courses
- 4 Express Courses - Discussion Forum
- 1.9K Training Courses
- 18 LFC110 Class Forum
- 6 LFC131 Class Forum
- 25 LFD102 Class Forum
- 150 LFD103 Class Forum
- 17 LFD121 Class Forum
- LFD137 Class Forum
- 61 LFD201 Class Forum
- LFD210 Class Forum
- LFD210-CN Class Forum
- 1 LFD213 Class Forum - Discontinued
- 128 LFD232 Class Forum
- LFD237 Class Forum
- 23 LFD254 Class Forum
- 597 LFD259 Class Forum
- 102 LFD272 Class Forum
- 1 LFD272-JP クラス フォーラム
- LFD273 Class Forum
- 2 LFS145 Class Forum
- 24 LFS200 Class Forum
- 739 LFS201 Class Forum
- 1 LFS201-JP クラス フォーラム
- 3 LFS203 Class Forum
- 69 LFS207 Class Forum
- 300 LFS211 Class Forum
- 54 LFS216 Class Forum
- 47 LFS241 Class Forum
- 41 LFS242 Class Forum
- 37 LFS243 Class Forum
- 11 LFS244 Class Forum
- 33 LFS250 Class Forum
- 1 LFS250-JP クラス フォーラム
- LFS251 Class Forum
- 140 LFS253 Class Forum
- LFS254 Class Forum
- 1K LFS258 Class Forum
- 10 LFS258-JP クラス フォーラム
- 92 LFS260 Class Forum
- 129 LFS261 Class Forum
- 32 LFS262 Class Forum
- 79 LFS263 Class Forum
- 15 LFS264 Class Forum
- 11 LFS266 Class Forum
- 17 LFS267 Class Forum
- 17 LFS268 Class Forum
- 23 LFS269 Class Forum
- 203 LFS272 Class Forum
- 1 LFS272-JP クラス フォーラム
- LFS281 Class Forum
- 221 LFW211 Class Forum
- 167 LFW212 Class Forum
- SKF100 Class Forum
- 901 Hardware
- 219 Drivers
- 74 I/O Devices
- 44 Monitors
- 115 Multimedia
- 208 Networking
- 101 Printers & Scanners
- 85 Storage
- 761 Linux Distributions
- 88 Debian
- 66 Fedora
- 15 Linux Mint
- 13 Mageia
- 24 openSUSE
- 141 Red Hat Enterprise
- 33 Slackware
- 13 SUSE Enterprise
- 356 Ubuntu
- 477 Linux System Administration
- 41 Cloud Computing
- 69 Command Line/Scripting
- Github systems admin projects
- 95 Linux Security
- 77 Network Management
- 108 System Management
- 49 Web Management
- 66 Mobile Computing
- 23 Android
- 29 Development
- 1.2K New to Linux
- 1.1K Getting Started with Linux
- 536 Off Topic
- 131 Introductions
- 216 Small Talk
- 21 Study Material
- 817 Programming and Development
- 275 Kernel Development
- 508 Software Development
- 928 Software
- 260 Applications
- 184 Command Line
- 3 Compiling/Installing
- 76 Games
- 316 Installation
- 59 All In Program
- 59 All In Forum
Upcoming Training
-
August 20, 2018
Kubernetes Administration (LFS458)
-
August 20, 2018
Linux System Administration (LFS301)
-
August 27, 2018
Open Source Virtualization (LFS462)
-
August 27, 2018
Linux Kernel Debugging and Security (LFD440)