ip version 6 (ipv6) Configuration on Linux

AutoConfiguration,
Auto configuration  is completely independent. Getting the mac address of the card and giving a random ipv6 address.

Static ipv6 configuration
# ——————————————————————————-
auto lo
iface lo inet loopback

auto eth0
allow-hotplug eth0
iface eth0 inet dhcp

iface eth0 inet6 static
address 2001:db8::xxxx:yyyy
netmask 64
gateway 2001:db8::xxxx:yy:zzzz
# —————————————————————————–
Your /etc/hosts file should read
127.0.0.1 localhost
127.0.1.1 serverubuntu//change this to 127.0.0.1
192.168.1.199 serverubuntu//add your static IP

# The following lines are desirable for IPv6 capable hosts
::1 localhost ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters

#— Network Fail logs
#systemctl status network.service
network.service – LSB: Bring up/down networking
Loaded: loaded (/etc/rc.d/init.d/network)
Active: failed since Thu, 09 Feb 2012 00:11:18 -0500; 8min ago
CGroup: name=systemd:/system/network.service
├ 3850 /bin/bash ./ifup 59173567_autom tica boot
├ 3859 nmcli con up uuid 32aea3d4-ce65-42d1-a3ed-6a42c17a2111
├ 25236 /bin/bash ./ifup 59173567_autom tica boot
├ 25245 nmcli con up uuid 32aea3d4-ce65-42d1-a3ed-6a42c17a2111
├ 25507 /bin/bash ./ifup 59173567_autom tica boot
├ 25516 nmcli con up uuid 32aea3d4-ce65-42d1-a3ed-6a42c17a2111
├ 25903 /bin/bash ./ifup 59173567_autom tica boot
├ 25912 nmcli con up uuid 32aea3d4-ce65-42d1-a3ed-6a42c17a2111
├ 26168 /bin/bash ./ifup 59173567_autom tica boot
├ 26177 nmcli con up uuid 32aea3d4-ce65-42d1-a3ed-6a42c17a2111
├ 26427 /bin/bash ./ifup 59173567_autom tica boot
├ 26436 nmcli con up uuid 32aea3d4-ce65-42d1-a3ed-6a42c17a2111
├ 26686 /bin/bash ./ifup 59173567_autom tica boot
├ 26695 nmcli con up uuid 32aea3d4-ce65-42d1-a3ed-6a42c17a2111
├ 27471 /bin/bash ./ifup ALEJANDRO_autom tica boot
├ 27480 nmcli con up uuid f8a46744-7098-4eb6-8902-34df1bd351f5
├ 28228 /bin/bash ./ifup Auto_58915877 boot
├ 28234 nmcli con up uuid 80a61972-1616-431e-bcf3-d4660386ec35
├ 29174 /bin/bash ./ifup Auto_58915877 boot
└ 29180 nmcli con up uuid 80a61972-1616-431e-bcf3-d4660386ec35
#————————————————————————————
Route Commands

#————————————————————————————

Centos Configuration  or  RedHat

/etc/sysconfig/network

cat /etc/sysctl.conf

 

 

 

#————————————————————————————

Tcpdump Best Practices

List of interfaces on which tcpdump can listen:


Listen on interface eth0:

Listen on any available interface :

Be verbose while capturing packets:

More verbose while capturing packets:

Very verbose while capturing packets:

Verbose and print the data of each packet in both hex and ASCII, excluding the link level header:

Verbose and print the data of each packet in both hex and ASCII, also including the link level header:

Less verbose (than the default) while capturing packets:

Limit the capture to 100 packets:

Record the packet capture to a file called capture.cap:

Record the packet capture to a file called capture.cap but display on-screen how many packets have been captured in real-time:

Display the packets of a file called capture.cap:

Display the packets using maximum detail of a file called capture.cap:

Display IP addresses and port numbers instead of domain and service names when capturing packets

Capture any packets where the destination host is 192.168.5.1. Display IP addresses and port numbers:

Capture any packets where the source host is 192.168.5.1. Display IP addresses and port numbers:

Capture any packets where the source or destination host is 192.168.5.1. Display IP addresses and port numbers:

Capture any packets where the destination network is 192.168.5.0/24. Display IP addresses and port numbers:

Capture any packets where the source network is 192.168.1.0/24. Display IP addresses and port numbers:

Capture any packets where the source or destination network is 192.168.5.0/24. Display IP addresses and port numbers:

Capture any packets where the destination port is 23. Display IP addresses and port numbers:

Capture any packets where the destination port is is between 1 and 1023 inclusive. Display IP addresses and port numbers:

Capture only TCP packets where the destination port is is between 1 and 1023 inclusive. Display IP addresses and port numbers:

Capture only UDP packets where the destination port is is between 1 and 1023 inclusive. Display IP addresses and port numbers:

Capture any packets with destination IP 192.168.1.1 and destination port 23. Display IP addresses and port numbers:

Capture any packets with destination IP 192.168.5.1 and destination port 80 or 443. Display IP addresses and port numbers:

Capture any ICMP packets:

Capture any ARP packets:

Capture either ICMP or ARP packets:

Capture any packets that are broadcast or multicast:

Capture 500 bytes of data for each packet rather than the default of 68 bytes:

Capture all bytes of data within the packet:

 

delete route commandline linux terminal

 

setup a bridge without ip address

 

32 iptables examples to manage firewall

  1. Allow user

  2.  
  3. Deny User
  4. Allow  port for a user.

Great

25 Most Frequently Used Linux IPTables Rules Examples

 

Kutay Zorlu

 

Introduction

Iptables is a firewall that plays an essential role in network security for most Linux systems. While many iptables tutorials will teach you how to create firewall rules to secure your server, this one will focus on a different aspect of firewall management: listing and deleting rules.

In this tutorial, we will cover how to do the following iptables tasks:

List rules
Clear Packet and Byte Counters
Delete rules
Flush chains (delete all rules in a chain)
Flush all chains and tables, delete all chains, and accept all traffic
Note: When working with firewalls, take care not to lock yourself out of your own server by blocking SSH traffic (port 22, by default). If you lose access due to your firewall settings, you may need to connect to it via the console to fix your access. Once you are connected via the console, you can change your firewall rules to allow SSH access (or allow all traffic). If your saved firewall rules allow SSH access, another method is to reboot your server.

Prerequisites
Before you start using this tutorial, you should have a separate, non-root superuser account—a user with sudo privileges—set up on your server. If you need to set this up, follow the appropriate guide:

Initial Server Setup with Ubuntu 14.04
Initial Server Setup with CentOS 6
Let’s look at how to list rules first. There are two different ways to view your active iptables rules: in a table or as a list of rule specifications. Both methods provide roughly the same information in different formats.

List Rules by Specification
To list out all of the active iptables rules by specification, run the iptables command with the -S option:

sudo iptables -S
Example: Rule Specification Listing

As you can see, the output looks just like the commands that were used to create them, without the preceding iptables command. This will also look similar to the iptables rules configuration files, if you’ve ever used iptables-persistent or iptables save.

List Specific Chain

If you want to limit the output to a specific chain (INPUT, OUTPUT, TCP, etc.), you can specify the chain name directly after the -S option. For example, to show all of the rule specifications in the TCP chain, you would run this command:

sudo iptables -S TCP
Example: TCP Chain Rule Specification Listing
-N TCP
-A TCP -p tcp -m tcp –dport 22 -j ACCEPT
Let’s take a look at the alternative way to view the active iptables rules, as a table of rules.

List Rules as Tables
Listing the iptables rules in the table view can be useful for comparing different rules against each other,

To output all of the active iptables rules in a table, run the iptables command with the -L option:

sudo iptables -L
This will output all of current rules sorted by chain.

If you want to limit the output to a specific chain (INPUT, OUTPUT, TCP, etc.), you can specify the chain name directly after the -L option.

Let’s take a look at an example INPUT chain:

sudo iptables -L INPUT
Example: Input Chain Rule Table Listing
Chain INPUT (policy DROP)
target prot opt source destination
ACCEPT all — anywhere anywhere ctstate RELATED,ESTABLISHED
ACCEPT all — anywhere anywhere
DROP all — anywhere anywhere ctstate INVALID
UDP udp — anywhere anywhere ctstate NEW
TCP tcp — anywhere anywhere tcp flags:FIN,SYN,RST,ACK/SYN ctstate NEW
ICMP icmp — anywhere anywhere ctstate NEW
REJECT udp — anywhere anywhere reject-with icmp-port-unreachable
REJECT tcp — anywhere anywhere reject-with tcp-reset
REJECT all — anywhere anywhere reject-with icmp-proto-unreachable
The first line of output indicates the chain name (INPUT, in this case), followed by its default policy (DROP). The next line consists of the headers of each column in the table, and is followed by the chain’s rules. Let’s go over what each header indicates:

target: If a packet matches the rule, the target specifies what should be done with it. For example, a packet can be accepted, dropped, logged, or sent to another chain to be compared against more rules
prot: The protocol, such as tcp, udp, icmp, or all
opt: Rarely used, this column indicates IP options
source: The source IP address or subnet of the traffic, or anywhere
destination: The destination IP address or subnet of the traffic, or anywhere
The last column, which is not labeled, indicates the options of a rule. That is, any part of the rule that isn’t indicated by the previous columns. This could be anything from source and destination ports, to the connection state of the packet.

Show Packet Counts and Aggregate Size

When listing iptables rules, it is also possible to show the number of packets, and the aggregate size of the packets in bytes, that matched each particular rule. This is often useful when trying to get a rough idea of which rules are matching against packets. To do so, simply use the -L and -v option together.

For example, let’s look at the INPUT chain again, with the -v option:

sudo iptables -L INPUT -v
Example: Verbose Listing
Chain INPUT (policy DROP 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
284K 42M ACCEPT all — any any anywhere anywhere ctstate RELATED,ESTABLISHED
0 0 ACCEPT all — lo any anywhere anywhere
0 0 DROP all — any any anywhere anywhere ctstate INVALID
396 63275 UDP udp — any any anywhere anywhere ctstate NEW
17067 1005K TCP tcp — any any anywhere anywhere tcp flags:FIN,SYN,RST,ACK/SYN ctstate NEW
2410 154K ICMP icmp — any any anywhere anywhere ctstate NEW
396 63275 REJECT udp — any any anywhere anywhere reject-with icmp-port-unreachable
2916 179K REJECT all — any any anywhere anywhere reject-with icmp-proto-unreachable
0 0 ACCEPT tcp — any any anywhere anywhere tcp dpt:ssh ctstate NEW,ESTABLISHED
Note that the listing now has two additional columns, pkts and bytes.

Now that you know how to list the active firewall rules in a variety of ways, let’s look at how you can reset the packet and byte counters.

Reset Packet Counts and Aggregate Size
If you want to clear, or zero, the packet and byte counters for your rules, use the -Z option. They also reset if a reboot occurs. This is useful if you want to see if your server is receiving new traffic that matches your existing rules.

To clear the counters for all chains and rules, use the -Z option by itself:

sudo iptables -Z
To clear the counters for all rules in a specific chain, use the -Z option and specify the chain. For example, to clear the INPUT chain counters run this command:

sudo iptables -Z INPUT
If you want to clear the counters for a specific rule, specify the chain name and the rule number. For example, to zero the counters for the 1st rule in the INPUT chain, run this:

sudo iptables -Z INPUT 1
Now that you know how to reset the iptables packet and byte counters, let’s look at the two methods that can be used to delete them.

Delete Rule by Specification
One of the ways to delete iptables rules is by rule specification. To do so, you can run the iptables command with the -D option followed by the rule specification. If you want to delete rules using this method, you can use the output of the rules list, iptables -S, for some help.

For example, if you want to delete the rule that drops invalid incoming packets (-A INPUT -m conntrack –ctstate INVALID -j DROP), you could run this command:

sudo iptables -D INPUT -m conntrack –ctstate INVALID -j DROP
Note that the -A option, which is used to indicate the rule position at creation time, should be excluded here.

Delete Rule by Chain and Number
The other way to delete iptables rules is by its chain and line number. To determine a rule’s line number, list the rules in the table format and add the –line-numbers option:

sudo iptables -L –line-numbers
[secondary_output Example Output: Rules with Line Numbers]
Chain INPUT (policy DROP)
num target prot opt source destination
1    ACCEPT all — anywhere anywhere ctstate RELATED,ESTABLISHED
2   ACCEPT all — anywhere anywhere
3   DROP all — anywhere anywhere ctstate INVALID
4   UDP udp — anywhere anywhere ctstate NEW
5   TCP tcp — anywhere anywhere tcp flags:FIN,SYN,RST,ACK/SYN ctstate NEW
6   ICMP icmp — anywhere anywhere ctstate NEW
7   REJECT udp — anywhere anywhere reject-with icmp-port-unreachable
8   REJECT tcp — anywhere anywhere reject-with tcp-reset
9   REJECT all — anywhere anywhere reject-with icmp-proto-unreachable
10  ACCEPT tcp — anywhere anywhere tcp dpt:ssh ctstate NEW,ESTABLISHED

This adds the line number to each rule row, indicated by the num header.

Once you know which rule you want to delete, note the chain and line number of the rule. Then run the iptables -D command followed by the chain and rule number.

For example, if we want to delete the input rule that drops invalid packets, we can see that it’s rule 3 of the INPUT chain. So we should run this command:

sudo iptables -D INPUT 3
Now that you know how to delete individual firewall rules, let’s go over how you can flush chains of rules.

Flush Chains
Iptables offers a way to delete all rules in a chain, or flush a chain. This section will cover the variety of ways to do this.

Note: Be careful to not lock yourself out of your server, via SSH, by flushing a chain with a default policy of drop or deny. If you do, you may need to connect to it via the console to fix your access.

Flush a Single Chain

To flush a specific chain, which will delete all of the rules in the chain, you may use the -F, or the equivalent –flush, option and the name of the chain to flush.

For example, to delete all of the rules in the INPUT chain, run this command:

Flush All Chains

To flush all chains, which will delete all of the firewall rules, you may use the -F, or the equivalent –flush, option by itself:

sudo iptables -F
Flush All Rules, Delete All Chains, and Accept All
This section will show you how to flush all of your firewall rules, tables, and chains, and allow all network traffic.

Note: This will effectively disable your firewall. You should only follow this section if you want to start over the configuration of your firewall.

First, set the default policies for each of the built-in chains to ACCEPT. The main reason to do this is to ensure that you won’t be locked out from your server via SSH:

Then flush the nat and mangle tables, flush all chains (-F), and delete all non-default chains (-X):

Your firewall will now allow all network traffic. If you list your rules now, you will will see there are none, and only the three default chains (INPUT, FORWARD, and OUTPUT) remain.

 

Linux ethernet device set speed of interface

 

How to Rename Eth0 Network Interface Card Name [ Udev ]