Questions tagged [netfilter]
The netfilter tag has no usage guidance.
0
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20 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 ...
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0answers
14 views
Keep conntrack state for current ssh connection on netfilter rule flush/reload
When i am reloading netfilter with a new ruleset that drops invalid packets
flush ruleset
...
ct state invalid counter log prefix "Drop input invalid " drop comment "drop invalid packets"
...
over ...
0
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1answer
48 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
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1answer
43 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 -...
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0answers
20 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....
2
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2answers
70 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 ...
0
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1answer
42 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. ...
0
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1answer
112 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 ...
4
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0answers
60 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 ...
0
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0answers
60 views
Show iptables, ebtables etc rules created by libvirt
I'm using libvirt with qemu on a ubuntu bionic system. I'd like to inspect what network filtering rules are actually created in the system for the nwfilter rules when I run a qemu/kvm guest with ...
1
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1answer
46 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
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1answer
37 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
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3answers
245 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 ...
0
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1answer
76 views
Masquerade rule with netfilter-persitent
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
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1answer
34 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
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1answer
26 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?
1
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1answer
760 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, ...
4
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1answer
454 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
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1answer
417 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
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2answers
231 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 ...
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0answers
203 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 ...
5
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2answers
1k 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
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0answers
58 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 ...
0
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2answers
302 views
How to establish a man-in-the-middle scenario with ebtables and iptables
For testing and educational purposes I want so set up a man-in-the-middle scenario as follows:
Host T is the target host that is to be "cloned"
Host M is the man in the middle with interfaces eth0 ...
0
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1answer
463 views
How to match both UDP and TCP for given ports in one line with nftables
How can i do this in a single line?
tcp dport 53 counter accept comment "accept DNS"
udp dport 53 counter accept comment "accept DNS"
0
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0answers
112 views
How to use wildcard in a list with nftables
I'd like to use wildcards in a list with nftables. I tried this, but it gives me an error when I'm loading it:
iifname {"virbr*", "vboxnet*"} accept
oifname {"virbr*", "vboxnet*"} ct state ...
0
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1answer
323 views
nftables, add output rule syntax
I'm a bit frustrated by the lack of comprehensive documentation of nftables and currently I'm failing to get even a simple example to work. I'm trying just create a output rule. Here's my only table:
...
0
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1answer
2k views
URL Filtering with IP tables
I've been trying to set up URL filtering with Iptables. I have set up two interfaces. Traffic flows in from one interface and flows out from the other.
Below are the Iptables I have configured:
*...
0
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1answer
739 views
blocking YouTube not working for Google Chrome
I have some rules on the FILTER table of Netfilter, which block HTTPS access to some websites:
-A FORWARD -s 10.255.255.0/26 -p tcp -m tcp --dport 443 -m string --string "facebook.com" --algo bm -j ...
0
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1answer
649 views
When and how to use chain priorities in nftables
When configuring a chain in nftables, one has to provide a priority value. Almost all online examples set a piority of 0; sometimes, a value of 100 gets used with certain hooks (output, postrouting).
...
3
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1answer
2k views
nf_register_hook not found in linux kernel 4.13-rc2 and later
I just started learning about netfilter and I was trying to make a simple netfilter module, all the tutorials and HOW TOs register a hook function with nf_register_hook(), but I could not find one in ...
2
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1answer
319 views
How to disable implicit source port mapping on outgoing UDP packets sent through NAT in iptables?
iptables is re-writing the source port on my UDP packets that go out of a tun interface. I have NAT rules setup with port X forwarded (details below). When an application behind the NAT receives a ...
0
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1answer
489 views
iptable string matching to find application type / application layer protoco
I would like to know is it possible to match the type of applications/application layer protocols using iptables string matching extension?
2
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3answers
362 views
removed lib modules folder after every reboot
uname -r: 4.13.0-16-generic (ubuntu 17.10 server)
I have a problem that iptables doesn't work after a reboot:
iptables-apply /etc/network/iptables
[ ok ] Stopping fail2ban (via systemctl): fail2ban....
2
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1answer
2k views
Is iptables string matching still supported?
I was reading the book Linux Firewalls - Attack Detection and Response (by M. Rash, No Starch Press, 1 Ed., Oct. 2007). In one of its chapter it discusses string matching using iptables. I was ...
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1answer
3k views
What is the difference between NAT OUTPUT chain and NAT POSTROUTING chain?
IF Nating is done in OUTPUT chain of the NAT table, then what is the function of SNAT in POSTROUTING
0
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1answer
1k views
iptables/netfilter: “nf_nat_ftp” is not working well with recent Linux kernels
I'm facing the following issue with Linux kernel 4.10-28-generic, embedded in Ubuntu-16.04.02-LTE.
My machine has two ethernet adapters, namely the following ones:
enp0s3: 198.168.56.2 (internal ...
3
votes
1answer
3k views
How to list all network connections Centos 7 (Connection tracking)
I have a box with Centos 7 installed.
I am trying to configure some iptables rules and playing with the mangle table and markings
For example on my router I am able to see established network ...
0
votes
1answer
2k views
How can I see the kernel logs?
I run Ubuntu 16.04
In the linux kernel there are certain log statement for conditions on packet filtering which I'd like to see if they are actually triggered.
One example is:
/* Smaller that ...
1
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1answer
379 views
Filtering and queue the packet of a process using iptable
I am trying to queue the packets of a process so I can use libnetfilter_queue to modify them.
I know that I should use --pid-owner processid to filter packets of a process and iptables -I <table ...
0
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1answer
442 views
OUTPUT chain rules in iptables
netfilter seems to allow rejected traffic from my INPUT chain to go through my OUTPUT chain. Here are the rules from the INPUT chain that are applied to the packets in question:
LOG all -- ...
0
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1answer
6k views
tcpdump ip range
I'm using nfsen and I need to apply a filter to get specific ip range and I can't find the syntax. I searched in the doc of nfdump and tcpdump but nothing.
For now the netflows captured provides from ...
2
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1answer
780 views
How do packets traverse tc/netfilter physical, VLAN and bridge interfaces?
Given the following setup on a router that performs NAT between two networks A and B:
eth0 - physical interface - no ip address
eth0.1 - VLAN interface for network A - no ip address
eth0.2 - VLAN ...
1
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1answer
221 views
iptables ERROR target
When I list the iptables rules for filter table with iptables -t filter -L -vvv --line-numbers command, then I see entry numbers from 0 to 124 under the debug output. Last entry is following:
Entry ...
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0answers
101 views
The correct way of implementing adblocking with uzbl?
I though about running some proxy on localhost, but will I be able to filter https? I've tried to use scripts from wiki, but they are not seem to work.
Another idea is to implement adblocking using /...
3
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1answer
1k views
IPTables redirect all UDP packets including ESTABLISHED
We currently have some rules setup in IPtables that look like the below:
-A PREROUTING -d dstip/32 -p udp -m udp --dport 27035 -m u32 --u32 "0x0>>0x16&0x3c@0x8=0xffffffff&&0x0>&...
2
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0answers
309 views
Match-set via libiptc
Could anyone share any examples that use match-set for iptables via the libiptc library?
I have tried using the iptables v1.4.21 and the code from https://bani.com.br/2012/05/programmatically-...
1
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1answer
682 views
-o in iptables is for specifying the interface for OUTPUT, FORWARD, and POSTROUTING Correct?
Reading in detail about iptables / netfilter here, when I read about the -o argument:
"Indicates the interface through which the outgoing packets are sent
through the INPUT, FORWARD, and ...
1
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0answers
198 views
Iptables packet src ip not NATed in case of icmp reply and tcp ack
I am using iptables in conjunction with net-filter queue in order to alter packets programmatically.
Im using iptables rules over ubuntu lab with 2 NICs eth0 to the internet and eth1 to the LAN I ...
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0answers
74 views
Log internet access
For a WiFi hotspot I want to record each guest's internet access.
Not the full data, only source/dest/timestamp/duration.
I didn't found any open source software to do this.
Question 1: does someone ...
