A Firewall is an application or hardware device used to inspect and filter network traffic.

learn more… | top users | synonyms

9
votes
3answers
4k views

What are the named ports for iptables?

When setting up iptables you can name the port ssh which will use port 22. Is there a list of all the named ports? Specifically I need ssh, http, https and mysql.
9
votes
3answers
20k views

Linux/iptables: best way to clear all rules, leaving anything open

Currently have this snippet: iptables -F // flush all chains iptables -t nat -F iptables -t mangle -F iptables -X // delete all chains Is there a possibility that some impervious rule will stay ...
9
votes
3answers
289 views

advantages in closing a port where no services are running

Are there advantages in closing a port where no services are running? What do I gain in terminating a connection at iptables level instead of what does it next (I guess OS).
9
votes
3answers
6k views

Rate limiting with UFW: setting limits

UFW's man page mentions that it can setup iptables rate limiting for me: ufw supports connection rate limiting, which is useful for protecting against brute-force login attacks. ufw ...
9
votes
1answer
82k views

TCP/IP ports necessary for CIFS/SMB operation

If I want to allow Windows networked drives between two firewalled computers, do I need to open ports 137-139, or is port 445 sufficient? I have to submit a form and get approval to open firewall ...
9
votes
5answers
4k views

Managing parallel rules for ipv4 and ipv6 iptables?

We've recently started experimenting with IPv6, and one of the first issues we're having to contend with is dealing with a completely separate set of firewall (Linux iptables/ip6ables) rules for the ...
9
votes
1answer
547 views

Kerberos authentication, service host and access to KDC

I have a web application (hostname: service.domain.com) and I wish to use Kerberos authentication to identify users that are logged into a Windows domain. Microsoft AD (Windows Server 2008 R2) is ...
8
votes
11answers
3k views

SOHO - throttle bittorrent traffic from problem users

I manage the network in a small office (SW dev is my "real job"), and there are a couple of users who beat the hell out of our internet connection by running bittorrent. Between the almost crippling ...
8
votes
2answers
491 views

How to configure a small network of computers within a larger university network?

I have a small computer lab (8 HP workstations, 1 HP server, 2 NAS boxes, 1 HP networked printer) where currently all the devices are connected directly to my university's network. Each device has an ...
8
votes
4answers
1k views

Slow down individual connections passing through a Linux router?

We have a Linux server acting as a router/firewall for our office. Occasionally someone will upload a large file that takes up all our bandwidth. I don't want to implement any complex rules or traffic ...
8
votes
2answers
362 views

Is it reasonable to use Nagios to check that a service is NOT available?

Suppose I have a server with a private interface and a public interface. Public might have things like HTTP(S) servers, private might have MySQL and SSH. Obviously Nagios is useful to check that the ...
8
votes
4answers
2k views

OpenBSD/FreeBSD Firewall w/ GUI that is compatible with Intel 82574L Gigabit LAN NICs

I recently purchased a server to run m0n0wall or pfSense but I've learned since then that both of these firewall products are based on versions of FreeBSD which weren't yet compatible with the NICs in ...
8
votes
2answers
1k views

Linux iptables / conntrack performance issue

I have a test-setup in the lab with 4 machines: 2 old P4 machines (t1, t2) 1 Xeon 5420 DP 2.5 GHz 8 GB RAM (t3) Intel e1000 1 Xeon 5420 DP 2.5 GHz 8 GB RAM (t4) Intel e1000 to test linux firewall ...
7
votes
4answers
17k views

Firewall blocking FTP server on Windows 2008 R2

I can access the FTP site without problems from the local machine, but it times out from the remote machine. If I turn the firewall off COMPLETELY, it works. Obviously, this isn't really a ...
7
votes
2answers
5k views

Virtualized firewall under Hyper-V?

We are currently considering installing an instance of pfSense on our Hyper-V R2 based server to act as a content filter, captive portal and general firewall. Although it is usually bad practice to ...
7
votes
3answers
680 views

What is the ip range of EC2

I'd like to setup a rule to block ssh request from EC2 since I've been seeing a large amount of ssh based attack from there and was wondering if anyone knew what their IP ranges are. EDIT: Thank you ...
7
votes
6answers
392 views

Firewall anti-patterns?

What are some of the most common and wrong ways to configure a firewall? I'll start the list with the following: Blindly blocking ICMP. This was common practice in 1998 when smurf attacks were all ...
7
votes
2answers
5k views

tcp flags in iptables: What's the difference between RST SYN and RST and SYN RST ? When to use ALL?

I'm working on a firewall for a virtual dedicated server and one of the things I'm looking into is port scanners. TCP flags are used for protection. I have 2 questions. The rule: -p tcp ...
7
votes
3answers
2k views

Running a webserver behind a firewall, is it secure?

Currently we have a Linux-based firewall which NAT-ing our public IP address to give internet access to our staff's PCs and a Windows Server 2003 for internal filesharing. I want to host Redmine/SVN ...
7
votes
2answers
3k views

pfSense Firewall or Linksys/Cisco router for small offices

I'm about to start switching some networks around for multiple small offices. Each office has about 10 to 15 users and 10 to 15 computers. Each office has a spread of generic routers and access ...
7
votes
7answers
8k views

Linux equivalent of pfsync+carp for failover firewall/routing

I'm currently using a linux box to handle my firewall/NAT using iptables. It has two NICs, one link to a LAN switch, one to our egress Internet provider. I'm looking at upgrade this box to two boxes ...
7
votes
3answers
10k views

Disabling Windows Server 2008 firewall

I applied a Windows firewall rule that blocks all tcp connection and thus kicked myself out of remote desktop on a dedicated server. I managed to get into recovery via VNC, which is basically a ...
7
votes
4answers
6k views

What to do with an out-of-warranty Barracuda Spam/Web filter?

I'm working with an organization that would like to start using a old Barracuda Spam Filter 300 unit. I've sold and configured plenty of these, but was surprised to see that this unit's warranty ...
7
votes
9answers
2k views

Need prosumer router/firewall/vpn/vlan/nat advice [closed]

Looking for a recommendation on a device (or devices I guess) to do router/firewall/vpn/vlan/nat functons for my home network. Right now, I'm doing this with an IPCop box, but I'd prefer a little ...
7
votes
2answers
751 views

Why are people trying to connect to my network on TCP port 445?

I was playing with my new syslog server and had my m0n0wall firewall logs forwarded as a test, I noticed a bunch of recent firewall log entries that say that it blocked other WAN IPs from my ISP (I ...
7
votes
2answers
169 views

Still worthwhile to firewall/filter ssh access except from specific IPs?

A number of years ago now, there were several remote exploits for OpenSSH which prompted many admins including myself to start filtering port 22 at the network perimeter, permitting only IP addresses ...
7
votes
3answers
10k views

IPTables: allow SSH access only, nothing else in or out

How do you configure IPTables so that it will only allow SSH in, and allow no other traffic in or out? Any safety precautions anyone can recommend? I have a server that I believe has been migrated ...
7
votes
2answers
302 views

Debugging iptables and common firewall pitfalls?

This is a proposed Canonical Question about understanding and debugging the software firewall on Linux systems. In response to EEAA's answer and @Shog's comment that we need a suitable canonical ...
7
votes
2answers
3k views

Block IP on EC2. Firewall or other options?

My EC2 (Fedora AMI) based service is being heavily hit by a rogue misconfigured client. What options do I have to block the IP of this rogue client?
7
votes
1answer
781 views

Cisco FWSM -> ASA upgrade broke our mail server

We send mail with unicode asian characters to our mail server on the other side of our WAN... immediately after upgrading from a FWSM running 2.3(2) to an ASA5550 running 8.2(5), we saw failures on ...
6
votes
3answers
630 views

What's wrong with using windows firewall?

I was developing a system which requires connection between two computers. I decided to connect the two machines together via direct ethernet cable. My boss didn't like it as there is no firewall in ...
6
votes
5answers
6k views

Making iptables easier to maintain

My network is completely locked down except for a few sites which are whitelisted. This is all done through iptables, which looks something like this: # Allow traffic to google.com iptables -A ...
6
votes
2answers
522 views

For an internet-facing, all-roles-in-one Exchange server, what do I need to let through the firewall?

As the result of a recent penetration test, in which we did not fare well, it has been brought to my attention that our internet facing, all-roles-in-one, Exchange 2010 SP3 server has no firewall in ...
6
votes
4answers
3k views

SSH from A through B to C, using private key on B

I'm looking for a simple way to SSH from my local machine, A, through a proxy, B, to a destination host, C. The private key that goes with the public key on C is on B, and I can't put that key on my ...
6
votes
9answers
22k views

block Torrent through firewall

is there a way to block users on firewall level from using torrents?
6
votes
2answers
401 views

When an IP or a block of IPs are assigned to you, do the network admins just add them to a router?

Let's say there is a router to the internet and a router separates your network from others within a data center. When the data center provided gives you IP addresses, do they just take a [set] of ...
6
votes
3answers
320 views

Is there already a recommended IPv6 Firewall setup?

I'd like to switch from private-IPv4-subnet-behind-NAT to IPv6, but of course I have no intention of exposing my users' workstations "unprotected" to the net. Some obvious points up-front: Allow ...
6
votes
6answers
8k views

Why block outbound ICMP?

This question is slightly related to "Why Block Port 22 Outbound?". I don't see how this can be a notable security risk.
6
votes
2answers
751 views

Gigabit network with a 100 megabit firewall

We have set up all the equipment necessary to have a gigabit network. All servers + workstations are running gigabit cards, just bought a 16 port switch that can handle gigabit as well. My concern is ...
6
votes
2answers
12k views

opening port 80 on Ubuntu AWS

I'm running a tomcat server on an ubuntu machine hosted in an AWS instance. I can reach the server via public_ip:8080 but when i change the listening port on server.xml from 8080 to 80 connection is ...
6
votes
6answers
3k views

How reliable are IP address-based firewall restrictions?

On some of my production systems that need to be accessible outside of the LAN I will sometimes add a firewall restriction at the edge to only permit traffic on, say, RDP from a specific origin IP ...
6
votes
2answers
2k views

Running multiple services on Port 443, Tunnel SSH over HTTPS

Situation: I want to tunnel SSH sessions through HTTPS. I have a very restrictive firewall/proxy which only allows HTTP, FTP and HTTPS traffic. What works: Setting up a tunnel through the proxy to a ...
6
votes
1answer
15k views

Which firewall ports do I need to open in order for a domain trust to work?

I have two Active Directory domains in two different forests; each domain has two DCs (all of them Windows Server 2008 R2). The domains are also in different networks, with a firewall connecting them. ...
6
votes
1answer
830 views

Block outgoing connections for certaing uids (root, apache, nobody)

With iptables in CentOS 5 and 6 Linux - how can you please prevent processes running as root, apache or nobody from initiating outgoing connections? On CentOS 5 Linux I've tried putting these lines ...
6
votes
5answers
12k views

How do I scan a firewall to find open outgoing ports?

I'm looking for a tool that I can use within a firewalled network to scan the firewall to find open outgoing ports. I've done some research and found Firewalk but it hasn't been maintained in 10 ...
6
votes
1answer
129 views

Tools for detecting network traffic filtering [closed]

In Iran we have an ongoing problem with the govt. blocking and manipulating various network protocols. I'm looking for a tool, framework or platform to help us analyze and report on any of these ...
6
votes
5answers
5k views

“No route to host” with ssl but not with telnet

I have a strange problem with connecting to a https site from one of my servers. When I type: telnet puppet 8140 I am presented with a standard telnet console and can talk to the Server as ...
6
votes
2answers
3k views

Is there a secure way to allow IIS 7 in a DMZ to access a DB server behind the firewall?

Our network admins are adamant that it is insecure for our web servers, which are hosted in the DMZ, to access the DB server behind our firewall. To get round the problem, we access the data via web ...
6
votes
3answers
14k views

Firewall rule to allow access to windows updates or other resources on a CDN?

What's the best way to poke a firewall hole in a border firewall to allow windows updates? As far as I can tell, the windows update sites are hosted on a content distribution network that can ...
6
votes
5answers
2k views

DDoS Protection Services - are they good enough? [duplicate]

first of all, I understand that it's better to have DDoS protections on data center level. But our DC is not ready to provide good quality of protection. So we thinking about using some external DDoS ...