TCPDUMP and Other Networking Tools

SUMMARY

TCPDUMP and Other Networking Tools

ISSUE

Purpose

This article provides examples for the uses of the tcpdump command to diagnose and troubleshoot various networking issues.

Applies To

All Unitrends backup appliance software versions

TCPDUMP

tcpdump - dump traffic on a network

Examples

Show incoming packets on port 1194 from source 24.39.64.20

tcpdump -lnni eth0 port 1194 and src host 24.39.64.20

Show outgoing packets on port 1194 to destination 24.39.64.20

tcpdump -lnni eth0 port 1194 and dst host 24.39.64.20

Show contents of packets

tcpdump -lnni eth0 -s0 -x port 1194 and src host 24.39.64.20

IPTABLES

iptables - administration tool for IPv4 packet filtering and NAT

Display Firewall Rules

iptables -L

ROUTE

route -- manually manipulate the routing tables

Examples

List routing table

route

Set default gateway

route add default gw 192.168.0.1 eth0

Static routes

/etc/sysconfig/network-scripts/route-eth0

10.10.10.0/24 via 192.168.0.1 dev eth0

172.16.1.0/24 via 192.168.0.1 dev eth0

 

WGET

Determine external ip address

wget -q -O - checkip.dyndns.org|sed -e 's/.*Current IP Address: //' -e 's/<.*$//'

Third Party Links

TCPDUMP Man Page

ROUTE Man Page

CentOS: IPTABLES

WGET Man Page

http://www.cyberciti.biz/tips/configuring-static-routes-in-debian-or-red-hat-linux-systems.html

http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/5/html/Deployment_Guide/s1-networkscripts-static-routes.html

http://www.cyberciti.biz/faq/linux-setup-default-gateway-with-route-command/

NOTES

Brandon Nelson - 6/18/2018 - Removed broken link. 
20180809jmaynard- updated link
20191114jmaynard - updated link