TCPDUMP - A MUST !

tcpdump is one of the most powerful linux/unix commands that helps us to analyze the network packet mainly for troubleshooting purpose. It mainly captures packets received or transferred over a network on a specific interface .

tcpdump is mainly used on linux/unix distro and can be easily installed.

INSTALLING TCPDUMP

$ sudo apt-get install tcpdump [On Debian, Ubuntu and Mint]

$ sudo yum install tcpdump [On RHEL/CentOS/Fedora and Rocky Linux/AlmaLinux]

$ sudo emerge -a sys-apps/tcpdump [On Gentoo Linux]

$ sudo pacman -S tcpdump [On Arch Linux]

$ sudo zypper install tcpdump [On OpenSUSE]

TCPDUMP COMMANDS

1. CAPTURE HOST

# tcpdump -i < interface name > host <host ip >

# tcpdump -i eth0 host 10.1.1.1

2. NO DOMAIN LOOKUP

# tcpdump -i eth0 -n host 8.8.8.8

3. NO DOMAIN AND PROTOCOL LOOKUP

# tcpdump -i eth0 -nn host 8.8.8.8

4. CAPTURE SERVICE

# tcpdump -i eth0 -nn port 443

5. CAPTURE HOST AND SERVICE

# tcpdump -i eth0 -nn host 118.91.171.10 and port 80

6. CAPTURE HOST AND PROTOCOL

# tcpdump -i eth0 -nn host 118.91.171.10 and udp

7. NEGATE FILTER

# tcpdump -i eth0 -nn host 118.91.171.10 and not icmp -c 5

8. COMPLEX COMBINATION

# tcpdump -i eth0 -nn "dst 8.8.8.8 or dst 1.1.1.1" and port 443 -c 10

9. CAPTURE MAC ADDRESS

#tcpdump -i eth0 -nn -e host 8.8.8.8 and icmp -c 100

10. VPN TRAFFIC

#tcpdump -i eth0 -nn host 118.91.171.10 and esp -c 50 ( FOR PHASE II )

#tcpdump -i eth0 -nn host 118.91.171.10 and udp and port 500 -c 100 ( IKE PHASE I )

11. VERBOSE ( PROVIDES HEADER LEVEL INFO )

#tcpdump -i eth0 -nn -vv host 118.91.171.10 and tcp -c 100

12. SAVE THE CAPTURE FILES

#tcpdump -i eth0 -nn -vv host 118.91.171.10 and port 80 -c 100 > /var/log/capture.txt

#tcpdump -i eth0 -nn -vv host 118.91.171.10 and port 80 -c 100 > /var/log/capture.cap

13 . CAPTURE NETWORK

#tcpdump -i eth0 -nn net 118.91.171.0/24

Note : Capturing for network can only be for classful network and we cannot define classless network. tcpdump will simply not capture the packet

Comments

SAN Switch Zoning with Brocade

Zoning in Brocade SAN Switch Let's begin with resetting the switch completely. In my environment I have two brocade SAN Switch connecting to 2 Dell R940 server configured with VMware. The SAN switch will be having connectivity between Dell Unity 500 storage and Dell R940 servers. Multipathing will be done between the server and storage with the help of SAN Switch. Multipathing, also called SAN multipathing or I/O multipathing, is the establishment of multiple physical routes between a server and the storage device that supports. It results in better fault tolerance and performance enhancement. DESIGN The idea behind zoning is that intended WWPN talk with each other . This is more like ACL in the world of Ethernet. To see the devices which are logged into the switch the following commands can be executed. SAN-A:admin> switchshow switchName: SAN-A switchType: 118.1 switchState: Online switchMode: Native switchRole: Principal switchDomain: 1 switchId: ...

SSL Decryption FortiGate

We have pretty much heard about SSL decryption and of malware hiding inside an encrypted traffic. A large amount of traffic in the internet is pretty much encrypted which basically means that bad things like malware, virus, ransomware can hide inside this encrypted traffic. If majority of these traffic are encrypted our Firewalls are not able to analyze these traffic which can easily infect our organization and the investment which we have done in these firewalls are wasted. There does come around a solution for this and as my topic suggest SSL Decryption also know as Deep Packet Inspection as by some IT folks. The image that I have attached down below clearly suggest about what I am trying to explain. Using deep packet inspection, the firewall simply decrypts the encrypted traffic happening between client and server, inspects the content to find the threats and block them , then forwards it to the destination re-encrypting it . We will need to first setup the SSL/SSH in...

Upgrade Catalyst C9500

Upgrading Catalyst 9500 series switch is relatively easy. The one that I'm going to upgrade today is on Install mode containing packages.conf file. Install mode consumes far less resources in compared to the traditional bundle mode and has some advantage like auto upgrade when configured in stacked mode. We can talk about the difference between bundle and install mode later on. Let's focus on upgrading the Catalyst 9500 switch. Switch I am trying to upgrade is in 17.03.03 which has some bugs and security vulnerabilities. I am upgrading it from 17.03.03 to 17.6.5(MD) golden image present in the cisco download site for C9500 series switch and also reading down the linked document from cisco that is what they recommend. You can have a look at it . https://www.cisco.com/c/en/us/support/docs/switches/catalyst-9300-series-switches/221498-recommended-releases-for-catalyst-9200-9.html We will first need to create FTP username and password in the switch. The username and password must b...

Packet Pushers

Search This Blog