Firewall Configuration in Linux in Centos 6.2
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@Lakshmana said:
@scottalanmiller
I have to assign IP for the VM machines I going to install.The requirements are 512 MB RAM,10 GB Hard disk and Centos minimal desktop.I have to use 3 NIC.That is One NIC for allowing WAN,one NIC for LAN and other for my VMmachineYes, but the IP has nothing to do with the firewall. The firewall in Linux works off ports as a rule. You can restrict access to the machine from certain IP ranges, but the default is to either allow all IPs to a port or deny all.
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@Lakshmana said:
@scottalanmiller
I have to assign IP for the VM machines I going to install.The requirements are 512 MB RAM,10 GB Hard disk and Centos minimal desktop.I have to use 3 NIC.That is One NIC for allowing WAN,one NIC for LAN and other for my VMmachineSure, but why are you connecting that to configuring the firewall? Setting up the basic networking and configuring the firewall are unrelated activities.
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@scottalanmiller said:
@Lakshmana said:
@scottalanmiller
I have to assign IP for the VM machines I going to install.The requirements are 512 MB RAM,10 GB Hard disk and Centos minimal desktop.I have to use 3 NIC.That is One NIC for allowing WAN,one NIC for LAN and other for my VMmachineSure, but why are you connecting that to configuring the firewall? Setting up the basic networking and configuring the firewall are unrelated activities.
Wait are you configuring this machine as a VM Host or either a router/gateway device? Something seems odd.
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I think that you should back up and talk to us about your goals, rather than getting stuck in small technical details. You are asking tiny questions that are very specific but are not telling us what you are trying to accomplish. So the information that we give you might be dangerous or wrong because you were not sure what question to ask.
You are skipping the steps that allow a community like this to help you help yourself. We need a bigger picture so that we can help with solutions before you get stuck or into a dangerous position.
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@thecreativeone91 said:
http://community.spiceworks.com/topic/254525-asking-better-questions - Just Saying.
http://mangolassi.it/topic/306/asking-better-questions
We've had a local copy too for a long time
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@scottalanmiller said:
I think that you should back up and talk to us about your goals, rather than getting stuck in small technical details. You are asking tiny questions that are very specific but are not telling us what you are trying to accomplish. So the information that we give you might be dangerous or wrong because you were not sure what question to ask.
You are skipping the steps that allow a community like this to help you help yourself. We need a bigger picture so that we can help with solutions before you get stuck or into a dangerous position.
I second this. You are so hung up on "how do I do this or that" that you are probably shooting yourself in the foot when it comes to the big picture.
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@thanksajdotcom Ok Dont get angry.I will confirm my situation and after that I will ask my queries without confusing others
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@Lakshmana said:
@thanksajdotcom Ok Dont get angry.I will confirm my situation and after that I will ask my queries without confusing others
I'm not angry. If you think this is anger, you've obviously never seen me get heated. Lol
No, but what we are trying to emphasize is that you need to think big picture, give us all the details of what the big picture goals are, and how you've gone about attacking the problem. Once we have the macro-level info, we can start helping you with the micro-level problems. But without the big picture, we could give you the right answers to the wrong questions.
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@thanksajdotcom Ok I understood
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How to block the SSH port in the IP table.I used the following command but it does not work?
My aim is that when I try to access the machine in Putty,the Centos machine should not be taken in the Putty/sbin/iptables -A INPUT -p tcp --destination-port {PORT-NUMBER-HERE} -j DROP
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@Lakshmana said:
How to block the SSH port in the IP table.I used the following command but it does not work?
My aim is that when I try to access the machine in Putty,the Centos machine should not be taken in the Putty/sbin/iptables -A INPUT -p tcp --destination-port {PORT-NUMBER-HERE} -j DROP
I want to say this is missing something at the end but I might be wrong. IPTables isn't my specialty.
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@Lakshmana said:
How to block the SSH port in the IP table.I used the following command but it does not work?
My aim is that when I try to access the machine in Putty,the Centos machine should not be taken in the Putty/sbin/iptables -A INPUT -p tcp --destination-port {PORT-NUMBER-HERE} -j DROP
You don't block port by port, you simply need to stop allowing it. You need to block everything. Show us your entire config file. IPtables can't be discussed without seeing the file you are asking about.
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@scottalanmiller said:
@Lakshmana said:
How to block the SSH port in the IP table.I used the following command but it does not work?
My aim is that when I try to access the machine in Putty,the Centos machine should not be taken in the Putty/sbin/iptables -A INPUT -p tcp --destination-port {PORT-NUMBER-HERE} -j DROP
You don't block port by port, you simply need to stop allowing it. You need to block everything. Show us your entire config file. IPtables can't be discussed without seeing the file you are asking about.
And don't forget that the traffic will follow the first matching rule in iptables. If you wanted to allow SSH for only certain ips, for example, you could put ACCEPT rules above the general DROP rule for SSH in the iptables config. That way those specific ips could get in as expected, but all others get blocked.
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In firewalls, the standard format is allow whatever you want through, whether that's opening specific ports, or whatever, and then there is the good ole "deny all" rule you put at the bottom. The syntax may vary from firewall to firewall, but the principal is the same. Allow what you want, IN THE ORDER YOU WANT THE PRIORITY TO BE, like @NetworkNerd said, and then deny the rest. Once you open EXACTLY what you want open, you shut the doors to everything else. That's how firewalls work.
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@thanksajdotcom said:
In firewalls, the standard format is allow whatever you want through, whether that's opening specific ports, or whatever, and then there is the good ole "deny all" rule you put at the bottom.
This isn't necessarily true. It really depends on the case. There are many cases when you'll want some deny rules before allow. It's about planning the processing order of the rules for that specific use, especially when you get into router with lots of networks running off of it. Deny rules can be used to "filter" down allow rules that come after it.
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@thecreativeone91 said:
@thanksajdotcom said:
In firewalls, the standard format is allow whatever you want through, whether that's opening specific ports, or whatever, and then there is the good ole "deny all" rule you put at the bottom.
This isn't necessarily true. It really depends on the case. There are many cases when you'll want some deny rules before allow. It's about planning the processing order of the rules for that specific use, especially when you get into router with lots of networks running off of it. Deny rules can be used to "filter" down allow rules that come after it.
This is true. I'm not denying that. However, most people allow what they want and deny the rest. It's much rarer to deny the specific things you don't want and allow the rest. I see that more internally than a public facing firewall.
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We lead with geo-specific deny rules to block regions before allowing ports.
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@scottalanmiller said:
We lead with geo-specific deny rules to block regions before allowing ports.
And in that case it makes sense. You're blocking all traffic from China or Russia, for example. Then you allow the ports you want open but those countries are blocked, and maybe every other country is fine (hopefully you haven't blocked Spain... ;)), and then you deny the rest. That also makes logistical sense. I don't disagree with @thecreativeone91. It all comes down to what your objective is and then determining the best way to approach it.
