Sunday, July 4, 2010

How to find firewall in a network

Traceroute is often used for network troubleshooting. By showing a list of routers traversed, it allows the user to identify the path taken to reach a particular destination on the network. This can help identify routing problems or firewalls that may be blocking ICMP traffic, or high port UDP in UNIX ping, to a site.
http://en.wikipedia.org/wiki/Traceroute#Uses

Basic step by step how to find a firewall in a network

1. Traceroute to the source ip
2. Traceroute to the destination ip
3. Access to the last hop device
4. If the device is a Cisco router, do sh ip route on this device
5. nslookup to find device's hostname or ip address 

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