Unix & Linux
Sponsored by
Sponsored logo

Questions tagged [netfilter]

Ask Question

The tag has no usage guidance.

104 questions
Newest
Active
Bountied
Unanswered
Filter by
Sorted by
Tagged with
0
votes
1answer
31 views

Get netfilter statistics on the command line

I am finally switching from the old iptables to the new netfilter (specifically using firewalld) to configure my computers and servers but so far I have failed to find any newer alternative to the ...
1
vote
1answer
64 views

Nftables default drop chain problem

I'd like to take a default drop approach to my firewall rules. I've created some rules for testing purposes: table bridge vmbrfilter { chain forward { type filter hook forward priority -...
0
votes
0answers
20 views

ipvlan mode l2 IP address takeover

Let's suppose that I have 2 ipvlan mode l2 network interfaces: A and B, and A is in a network namespace. When B receives a packet, is it possible to distinguish in a netfilter (iptables) rule whether ...
0
votes
0answers
120 views

Linux tc filter add - errors RTNETLINK answers: Operation not supported

I'm working on the network simulation to create some traffic on specific ports , and trying to inject the network delay. I'm using the linux tc utility to do this operations. So i'm new to the tc ...
1
vote
1answer
52 views

marked packets not detected by routing policy database

I have a following mangle table rule in a lab server which marks UDP traffic with 1 if the destination address is 6.6.6.6: $ sudo iptables -t mangle -L PREROUTING 2 -v -n --line-numbers 2 17 ...
0
votes
0answers
75 views

ufw and iptables-nft not working

I have upgraded to Buster. It's running on a physical server, no VM. The setup is as folows: Kernel modules lsmod | grep nf nf_log_ipv6 16384 5 nf_reject_ipv6 16384 1 ...
-1
votes
1answer
48 views

Qemu network traffic filtering with iptables

I need to filter both outcoming and incoming traffic of the guest system on Qemu (Linux). The host system is Linux too. I think iptables is a good tool, but I don't know how to use it here. What ...
0
votes
1answer
48 views

How set MAC address filtering on linux?

I need to block any incoming connection from a MAC address different from a specific one (which is static and well known). This MAC address should generate only non-IP connection: this is the reason ...
0
votes
1answer
632 views

Debian update to Buster, iptables throwing an error in

I've just updated my old Debian Jessie server to Buster, and I'm having some issues with iptables. I understand that the backend has been changed with the update, but I have absolutely no knowledge or ...
0
votes
1answer
16 views

netfilter fails to properly replace destination IP of UDP response package

We have small kuberentes cluster running (CentOS 7, Kuberenetes 1.13 + Flannel) and after some tweaking TCP configuration (see below), we noticed that DNS was not working properly. I don't think that ...
1
vote
1answer
705 views

Check whether iptables or nftables are in use

Given a host that is in an unknown state of configuration, I would like to know if there is an effective way of non-interactively determining if the firewall rule set in place is managed by iptables ...
0
votes
1answer
38 views

How is netfilter able to track the out-of-band data-connections of FTP to be in RELATED state with control-connection?

An article at this URI https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/6/html/security_guide/sect-security_guide-firewalls-iptables_and_connection_tracking RELATED — A packet ...
0
votes
0answers
81 views

Why my system can only do port forwarding when I ssh to it?

I use debian 10 with kernel 4.19 and nftables as port forwarding tool. The rule is like table ip nat { chain prerouting { type nat hook prerouting priority -100; policy accept; ip ...
0
votes
0answers
126 views

How to drop all lldp packets on a specific port using IPTables?

I have lldp packets sent on a specific port (6633) and i need to drop only and only if they are lldp packets, because i have another traffic that cant be dropped, so i can't just drop all traffic on ...
0
votes
0answers
44 views

How ipset timeout works?

Is the expiry checked for every received packet if the ip should be removed from ipset or is there something in the background running every second and removing expired ip addresses?
1
vote
0answers
121 views

firewalld updating ipset entry timeout

I have been trying to figure out how to update the timeout of an ipset entry, with no luck so far, when using native ipset I would just simply use: $ ipset add foo 192.168.0.5 timout N -exist but ...
1
vote
1answer
249 views

Does upset hash:net,port support 0.0.0.0/0

Is there a way to add 0.0.0.0/0 to ipset type hash:net,port? It appears to only support prefix lengths of 1-32 but what if I want an entry in my ipset hash to support all ip traffic on a given port? ...
1
vote
0answers
116 views

Netfilter bypass through Firejail

For isolation, I run Firefox through Xephyr with Openbox. In the Firejail profile, I set net enp2a1 to isolate the network through network namespaces. But I don’t like that a regular user can override ...
1
vote
1answer
35 views

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>:...
0
votes
0answers
20 views

Use Netfilter to programatically set packet destination and route them

I'm new to iptables and its modules and I would like help in rapping my head around it. The Problem Managing large scale NAT routing. I need to handle more then 100,000 static IPs (and growing) and ...
1
vote
0answers
46 views

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 | | | | ...
0
votes
1answer
40 views

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 ...
1
vote
1answer
534 views

Example command to set same DSCP value in the IP header for return packets within the same TCP connection

I have seen connmark or ctinfo could work for this but couldn't find a simple effective command to make it work (Not familiar within this area). The command can be applied to the TCP termination node ...
-1
votes
1answer
258 views

Failing service during boot, which one + solution?

System: Linux Mint 19.3 "Tricia" - Cinnamon (64-bit), based on Ubuntu 18.04, kernel 5.3.0-24-generic Problem duration: literally for a year or so. Problem description: since I have too large a ...
1
vote
0answers
158 views

arptables-nft persistence

Introduction This is on Debian Buster with kernel 4.19.0-6 I've installed iptables-persistent and netfilter-persistent versions 1.0.11 and added a basic rule to arptables-nft to block all LAN ...
1
vote
1answer
285 views

How to clone the output of the MASQUERADE target with a TEE?

The Netfilter's extensions man page states that: MASQUERADE: This target is only valid in the nat table, in the POSTROUTING chain QUESTION: How to clone the output of the MASQUERADE target with a ...
1
vote
1answer
1k views

nftables meter error: syntax error, unexpected saddr, expecting comma or '}'

I have below nftable rule to add a connection rate meter: nft add rule ip filter input tcp dport @rate_limit meter syn4-meter \{ ip saddr . tcp dport timeout 5m limit rate 20/minute \} counter ...
0
votes
1answer
243 views

Systemtap can not resolve probe point although it is shown in probe list

I'm trying to debug netfilter synproxy module with systemtap. This is probe point I'm trying to add. # stap -l 'module("ipt_SYNPROXY").statement("*")' | grep send_client_synack module("ipt_SYNPROXY")...
5
votes
1answer
5k views

nftables rule: No such file or directory error

I am trying to apply below nftables rule which I adopted from this guide: nft add rule filter INPUT tcp flags != syn counter drop somehow this is ending up with: Error: Could not process rule: No ...
3
votes
1answer
3k views

Best way to filter/limit ARP packets on embedded Linux

I have an embedded Linux on some network device. Because this device is pretty important I have to make many network tests (I have a separate device for that). These tests include flooding my device ...
0
votes
1answer
3k views

Changing Destination IP address using iptables and DNAT

I am trying to experiment with DNAT in PREROUTING. I found a tutorial here. It contains the following sentence: This is done in the PREROUTING chain, just as the packet comes in; this means that ...
1
vote
1answer
1k views

iptables-restore failed in Debian buster/sid if it has --multiport option in the rules file

I have /etc/iptables/rule.v4 file contains many rule, the below is the line where I see the issue -A INPUT -p tcp -m multiport --dports 22 -j ACCEPT -A INPUT -p udp -m multiport --dports 16384:32768 -...
0
votes
0answers
200 views

Packet traversal in the Linux networking stack

I am trying to understand the packet traversal in Linux. I found a diagram from link. My linux box has the following routing table: default via 192.168.2.1 dev wlan0 proto static metric 1024 169....
3
votes
2answers
1k views

How can I transform UDP to TCP with netfilter?

I have a wonderful ISP blocking all UDP traffic (except DNS to its own DNS servers). However, I want to use UDP for my VPN solution. I have root over both VPN endpoints, and both of them are using ...
1
vote
1answer
974 views

Is there any way to view nfmark like ctmark?

I understand that iptables --set-mark does not add mark "on" the packets. The MARK target is for associating a mark with the packet in the kernel data structures. The packet itself is not modified. ...
2
votes
1answer
7k views

How does iptable work with linux bridge?

Setup: VM1 --- Bridge -- VM2 VM1 and 2 are on same subnet. Bridge has 2 interfaces added to brctl bridge. When I block VM2 ip using uptables -A FORWARD -s (VM1 ip) -j DENY it doesn't work. I ...
6
votes
0answers
281 views

Multicast ICMPv6 comes back with conntrack state invalid

I was playing arround with the Multicast feature of IPv6. $ ping ff02::2%wlp3s0 This should normally result in an echo-reply from all the routers on your local network segment (Wikipedia - IPv6). So ...
1
vote
1answer
132 views

iptables blocking local traffic

My local machine IP: 192.168.0.35 What I did: Answer that i tried here!! sudo iptables -t nat -A OUTPUT -p tcp --dport 80 -j DNAT --to-destination 192.168.0.35:80 The error: Now I can not access ...
1
vote
1answer
320 views

iptables Masquerade leave out some local packet?

In openwrt i have config lan forward to wan with masqenabled. And my lan network is 192.168.100.0/24. when some pc ping with other network ip e.g: 192.168.1.15, tcpdump will get some local packet in ...
1
vote
3answers
2k views

in iptables, does MASQUERADE match only on NEW connections (SYN packets)?

I observed that MASQUERADE target does not match on packets in the reply direction (in terms of netfilter conntrack). I've a single simple -t nat -A POSTROUTING -s 10.a.0.0/16 -d 10.b.0.0/16 -j ...
2
votes
1answer
930 views

Masquerade rule with netfilter-persistent

I use netfilter-persistent to manage a firewall. I would like to share a connection between two interfaces using masquerading (example, or another). When I run those operations by invoking iptables ...
2
votes
1answer
188 views

Packet meta class applied, but captured VLAN priority is wrong

My linux home router sits between my ISP (Orange) and my home network. On the WAN side, Orange provide internet in a VLAN tagged 832. Some control messages (ARP, DHCP, ICMPv6 "router discovery" types,...
1
vote
1answer
168 views

How does one use tc to add latency to a ratelimit?

I read that there's another tool for netfilter that allows you to add latency to a ratelimit. Does anyone have an example of this?
5
votes
1answer
10k views

How --set-mark option works on Netfilter (IPTABLES)?

On Netfilter, you have the option --set-mark for packets that pass through the mangle table. The majority of tutorials and examples over the Internet, say that this just adds a mark on the packet, ...
5
votes
2answers
3k views

Is there a way to do layer 7 filtering in Linux?

The L7-filter project appears to be 15 years old, requires kernel patches with no support for kernels past version 2.6, and most of the pattern files it has appear to have been written in 2003. ...
2
votes
1answer
2k views

multicast traffic is able to poke a hole into the netfilter connection tracking system

I have an IPTV solution at home where the ISP sends me hundreds of large UDP datagrams per second from 10.4.4.5 port 10 to 239.3.5.3 port 10, i.e. it is using multicast. My current iptables ...
1
vote
2answers
761 views

Send TCP packet to the same source [closed]

I want to design a system which reduce travel time of packet what is happening in reality is I send a SYN bit from client side, this bit travel through router then to server and server reply SYN+ACK ...
1
vote
0answers
528 views

iptables connlimit-above allowing more connections than desired

I'm trying to set a per-ip connection limit on a kubernetes node using iptables connlimit. Since each container on the VM has a different source IP (overlay net), using connlimit should work. I added ...
8
votes
2answers
6k views

What are the essential iptables rules for IPv6 to work properly?

I had a problem where I lost connectivity to a server on the IPv6 address after some time and it turned out to be caused by DHCPv6 client packets (port 546) being dropped by the default INPUT policy ...
0
votes
0answers
154 views

When are inverse NAT manipulation applied by netfilter/iptables?

If there is a DNAT rule in the PREROUTING chain like this one: iptables -t nat -A PREROUTING -j DNAT --to-destination x.x.x.x All packets reaching the stack from a network interface will first pass ...

1
2 3