top button
Flag Notify
    Connect to us
      Site Registration

Site Registration

NetFilter: How to set tcp flags?

+1 vote

How do i set tcp flags ? I tried

 nft add rule filter output tcp flags {syn,rst} counter

but failed ... also can some point me to valid syntaxes ..

posted Sep 25, 2013 by Mandeep Sehgal

Looking for an answer?  Promote on:
Facebook Share Button Twitter Share Button LinkedIn Share Button

Similar Questions
+1 vote

Is there a way to find out if there any iptables rules set on a machine ?

There are some indirect ways which will not always work; for example, I know that on most hosts, iptables -S will return the following output (when no iptable rules are set)

So you can check whether or not the number of output lines is greater than 3 (as an indication of whether or not iptables rules are set). But there are hosts on which there are more chains then these 3; these chains are set by application/services, even without any iptable rules which are set. And after running iptables -F on these machines, iptables -S will still show more than 3 chains, even that there are no iptables rules set in these chains.

So the question is - is there a way to know whether or not netfilter rules are set on a host, regardless of the number of chains ?

+1 vote

I've done some digging but really can't find a good explanation of the syntax for matching TCP flags in nftables. In iptables a rule can be written like:


How do I do the equivalent in nftables? Also are we still able to use the "ALL" and "NONE" keywords?

+1 vote

Could someone help me understand the correct use of the protocol filter parameter --state. I figure it would be something like this "conntrack -L -p TCP --state ESTABLISHED" but 2 different versions of conntrack-tools give the same error (conntrack v1.2.1 (conntrack-tools): unknown option --state, Try conntrack -h or conntrack --help for more information.)

Is ts a deprecated parameter? What I'm trying to do is to selectively delete entries that are in a particular state. For instance TCP SYN_SENT, or UDP UNREPLIED.

+2 votes

We can set bandwidth for UDP while TCP uses its maximum bandwidth...why it is like this?

0 votes

Is it possible to bind multiple address families in netfilter queue? I see IPv4 show up in my queue, but not ARP. With error code removed, here is how I'm calling nfq_bind:

netfilterqueue_handle = nfq_open();
netfilterqueue_queue = nfq_create_queue( netfilterqueue_handle, 0,

nfq_bind_pf( netfilterqueue_handle, AF_INET );
nfq_bind_pf( netfilterqueue_handle, NF_ARP );

I'm thinking the more likely possibility is the iptable rules I'm using to send traffic to the queue are too restrictive. Here are the rules I have:

# Generated by iptables-save v1.4.21 on Sat Feb 14 10:40:46 2015
:INPUT ACCEPT [56:4995]
:OUTPUT ACCEPT [56:4496]
# Completed on Sat Feb 14 10:40:46 2015
# Generated by iptables-save v1.4.21 on Sat Feb 14 10:40:46 2015
:INPUT ACCEPT [1017:217421]
:FORWARD DROP [53:2307]
:OUTPUT ACCEPT [934:211104]
:MYRA - [0:0]
-A FORWARD -m conntrack --ctstate RELATED,ESTABLISHED -j MYRA
-A FORWARD -s -o eth0 -m conntrack --ctstate NEW -j MYRA
-A MYRA -j NFQUEUE --queue-num 0 --queue-bypass
# Completed on Sat Feb 14 10:40:46 2015

Do I have to add another FORWARD line to get ARP to jump to MYRA? What would it look like?