Questions tagged [firewall]

A firewall is a program that controls the incoming and outgoing network traffic on a system. Use this tag for all questions related to firewall configuration and operation.

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How to check if any firewall is already installed

I have a Debian 10 VPS (virtual private server). How to check if any firewall is already installed? I dont have a list of all existing firewalls, so I hope there is a more general way.
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Is it possible to bind to a port that has a entry for DNAT in iptables?

I have added a DNAT entry (in the host) for a port (say 30001) in PREROUTING using iptables $ sudo iptables -t nat -A PREROUTING -p tcp --dport 30001 -j DNAT --to-destination <my guest vm ip>:...
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iptables: MultiWAN and portforwarding & port redirection

I'm running Gentoo Linux, so using plain iptbales to manage my firewall and networking. I usually use wan0 for all my traffic, but since I have already a web-server behind that i would like wan1 (bind ...
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STUN server Coturn and LAN clients

I have a Zimbra Server, and I need to make Zimbra Talk (Connect), which uses WebRTC, to work for my users both internally and externally. My users are behind an UTM and they are masqueraded. So I ...
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Ubuntu ufw Lightsail not opening port 80

I have port 80 open from AWS lightsail console, and ufw status shows that port 80 should be open. And yet, I cannot curl into port 80 nor can I telnet or ping or launch a server. I've checked ...
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Iptables outbound block denies inbound

I'm trying to block only outbound connections to specific IP addresses, however I want to allow inbound connections from the same IP addresses. From what I understand about blocking outbound ...
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Ubuntu (18.04.4 LTS) - iptables keeps reloading

I'm not sure when this started, I've noticed it just today. Here is the problem: I have an ubuntu server with CSF installed, today I got an notice that my server was unreachable. I thought CSF blocked ...
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How would I go about creating an outbound firewall?

Firewall being an overwhelming word, but I want all new connections to prompt a dialog where I can choose what happens to it, so that the correct nftable rules can be applied. Akin to open snitch but ...
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Tomcat: Activate a Tomcat Filter on specific source IP addresses

I am a Tomcat N00b so my search terminology for google may be lacking. But so far I have not found the answer to my question(s). I have a scenario where I have some traffic coming in through a WAF ...
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Nftables conflicting tables: Include multiple *.nft only loads first inet table?

Configuration: /etc/sysconfig/nftables.conf contains an include: "include /etc/nftables/my-filter*.nft" /etc/nftables contains my-filter1.nft with "table inet default {" my-filter2.nft with "table ...
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How does Linux route packets destined for another interface? [duplicate]

How are packets routed inside a single linux machine? Imagine the following setup: +--------------------+ | apache on | | 192.168.1.30:80 | | | | ...
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Kill switch using iptables & filtering by group id

I am trying to set up a kill switch using iptables, because my VPN client doesn´t do so. I liked the approach of allowing packets based on group id described here: https://weekly-geekly.github.io/...
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Iptables rule under attack

I have this example on IPtables Iptable is on the Host. This host has 2 ethernets connected eth0(192.168.0.2) where the LAN is connected and eth1(151.100.4.3) where it is connection to the internet. ...
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Two files with saved iptables rules

I have got CentOs and here are my all saved rules /etc/sysconfig/iptables. I want to create another file with rules which will be loaded form systemctl start iptables.service as well. Have you got any ...
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Firewall (iptables) with host-shared bridge and containers

I have configured LXC container with a host-shared bridge. The host is a debian server. The bridge configuration look like this : auto br0 iface br0 inet dhcp bridge_ports eth0 ...
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Need to determine if firewall is blocking an outbound connection

I don't have direct control over the firewall. I'm trying to troubleshoot a connection to a SFTP site from a Unix machine. Pinging the host results in a timeout, and nmap is telling me the host may be ...
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Blocking internet access to some application with a specific wifi

I’m looking into a solution to prevent some application to accessing the internet when I’m connected to a specific wifi access point. My exact use case is that I would like to disable dropbox, spotify ...
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How can I port scan a host from itself without using the loopback interface?

I'm trying to audit firewall rules on a host. This is typically pretty straightforward to do with nmap or a similar scanning tool. The problem is that I can only run the audit on the host itself. ...
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“Reverse” an SSH connection from destination to target [duplicate]

I have two machines A and B which are in different subnets, both behind separate firewalls. Machine A can see B, but B cannot see A. I have a user account (non-root) on both machines, I can SSH B from ...
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LXLE: Enable ssh without being logged in to console session?

I am building a machine that I would like to used as a headless server on a home network. I've plumped for LXLE as a distribution as it's lightweight and does most of what I need. I would like to be ...
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IP Filter via Firewall vs /etc/ssh/sshd_config

Typically I just use a local firewall (FirewallD, UFW, IPTables) on my personal linux boxes. At my work, we use Jamf (previously Casper suite) to managed our Macs, which uses SSH (remote login) for ...
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Cannot remove a firewall service previously created

I've added a new service in my CentOS server using the following command: firewall-cmd --permanent --add-service=wiremock sudo firewall-cmd --reload then I've removed it through firewall-cmd --...
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How can I add a comment to a firewalld rich rule?

In iptables, I can add a comment or a note to a firewall rule using the built-in comment extension, which provides access to the --comment flag to iptables -I. I find this useful to record why a ...
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Why ufw blocks connection when they're allowed?

I have the following set of rules sudo ufw status numbered Status: active To Action From -- ------ ---- [ 1] 41337/tcp ...
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How to connect from one server to another server's postgresql database by configuring firewall

I am trying to connect from Ubuntu 16.04 server to Gentoo server's PostgreSQL database. But I cannot connect to it. Ubuntu server has internet with static IP: 93.154.53.88. In my Gentoo server has IP: ...
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SSH to VPS works from specific IP but fails with Mobile Data (3G/4G)

The VPS (remote location) has UFW installed and the issue is that when I connect from my own computer / every device connected to my router it works perfectly fine but as soon as I use my phone's data ...
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Iptable order of rules with example

I had question about IPtables. Let's start with this example of my book: What rules you would set for a mail server accepting connections for EMSTP (port 465) and IMAP (port 993) having a ...
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iptables add ip,port and also IP

Now I perform this: create blockipset hash:ip add blockipset 192.168.1.5 -exist add blockipset 192.168.3.115 -exist Is it possible for iptables and ipset to block ip,port and ip? for example, the ...
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Is there an interactive firewall on Linux, one that gives popup on anything trying to connect to anything?

I used ZoneAlarm and a few other programs for a long time on Windows, just because I could control anything from system services to any software connecting to any IP address. I don't find the idea of ...
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Fail2ban & nftables errors, IPs not banned

So I've been experimenting with nftables in CentOS 8 and things are going pretty well, but I'm having a weird problem with fail2ban. Fail2ban cannot ban IPs with nftables-multiport or nftables-...
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HTTPS connections are generating incoming connections

I have a lot of records in my firewall log that are related to HTTPS traffic. For some reason incoming connections are being made to ephemeral ports and they are blocked by my firewall because these ...
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110 views

nftables allow redis only from specific IP addresses

I am configuring a REDIS server and I want to allow connections only from a set of specific IP addresses. This is a Debian 10 server, and the recommended framework to use is nft, which I haven't used ...
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ipfw dummynet per ip fair traffic shaping

I want to shape traffic in such way, that no specific user could exhaust WAN connection that much so other users would be affected. I have ISP link with 100Mbits/s bandwidth and sometimes some users ...
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Hole punching a VPN kill-switch

I use firewalld's direct rules to block all incoming and outgoing connections except for on a tun interface, making a kill switch for my VPN connections (similar to here). I have since whitelisted ...
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409 views

Firewall rules based on Domain name instead of IP address

I am running Guacamole remote desktop gateway test setup to manage access to cloud VM instances. As I got one strange POC request from one client to restrict Guacamole RDG access to one specific ...
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Looking for a simple but effective firewall

I just freshly install a new machine running on linuxmint-19.2-xfce-64bit. I set the Gufw to block all incoming and outgoing traffic but my system still receive an IP address! The software manager ...
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1answer
129 views

firewall: nftable counter rules

A few months ago, I migrated the firewall of a debian laptop from iptables to nftables, using debian's recommended procedure, and all seems to have been fine. Now, months later, I'm scrutinizing the ...
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Login to a Ubuntu vps via ssh,while ssh is blocked by firewall

Unfortunately my English is not good and I apologize for that. I have a Ubuntu vps. When I was trying to enable the firewall, I forgot to open the ssh port. And after restarting, my access to vps was ...
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1answer
882 views

Port forwarding & NAT with nftables

I have an OpenWRT gateway (self-built 19.07, kernel 4.14.156) that sits on a public IP address in front of my private network. I am using nftables (not iptables). I would like to expose a non-...
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nftables chains and priority problem [duplicate]

I have two output chains like this: chain OUT { type filter hook output priority 0; policy accept; ct state established,related accept oif "lo" counter packets 0 bytes 0 accept ip ...
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248 views

Why are my network connections being rejected?

I have a CentOS 8 guest running on a Fedora 31 host. The guest is attached to a bridge network, virbr0, and has address 192.168.122.217. I can log into the guest via ssh at that address. If I start a ...
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CentOS 8 firewalld + nftables or just nftables

I've been on CentOS 7 for a long time and was used to building my custom iptables configurations on a variety of both personal and business boxes. I've recently started working with CentOS 8 and ...
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iptables - default action at the end of user-defined chain

I'm reading iptables' man page at https://linux.die.net/man/8/iptables, and I've got a question regarding the use of user-defined chains: In the Targets section, it says If the end of a built-in ...
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135 views

How to Limit Number of connection to specific port in linux?

I would like to limit number of connection to some ports. for example: I would like to allow just 2 connection for ports between 2300 to 2500 on my server. But I don't know how can I do that using ...
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How to close 22 (so I can open it)

I have been trying to get ssh to work between an Ubuntu VM and my Xubuntu system. (Note: My Xubuntu system is running on Chrome OS) SSH has hangs until a timeout, this tells me that something is ...
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Will this firewall configuration prevent unencrypted traffic?

All incoming and outgoing traffic denied. Allowed outgoing ports: 53,67,68,443 Since I have not allowed port 80 and since programs use port 443 for https traffic by default, will this configuration ...
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How to route network traffic through an interface on another host?

I have limited networking knowledge, so please bear with me :) I have a host that runs a VM that has 2 interfaces (ens33 and crc). My host has an interface (eth0) that is on the same subnet as "ens33"...
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Why does UFW use a different sysctl.conf file?

There are a lot of network-related settings in /etc/sysctl.conf and a number of files in /etc/sysctl.d/. My data centre operator who has preconfigured the Ubuntu OS to work best in their environment ...
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nftables rules not blocking traffic

I am testing NFtables and am attempting to set up a basic routing firewall on a linux machine with 2 interfaces, ens37 and ens38. Here is the ifconfig output for these 2 interfaces. ens37: flags=4163&...
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ufw & iptables don't block incoming connection

I enable ufw and I tried to block all the traffic from one server, but I can't. It only blocks ssh, all the other ports are open. I test it with telnet. I want to allow all ports for some IPs, and ...

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