Tools & Tricks    

Here we provide short tips and reminders to things that will save time.

Blocking traffic

How to block traffic.
  • Protocol blocking: Use your firewall or router ACL to stop the traffic. This tactic applies to inward and outward traffic.
  • Website access: Use your DNS server to point the clients to an alternate IP address. keeps the network traffic clean. Alternately you can use a web server to provide a reminder that they are going somewhere bad and to record who is trying to going where they should not.

    Linux - Stuff

    Bash Commands
    CLUI commands we hardly ever use
  • at This command allows you to schedule a task to run once at a given time such as rebooting a server
    at 8:00
    at> reboot
    at> (CTRL+d to exit)

  • /usr/sbin/sendmail -bt sendmail test mode
    # /usr/sbin/sendmail -bt
    ADDRESS TEST MODE (ruleset 3 NOT automatically invoked)
    Enter [ruleset] [address]
    > 3,0

    > (CTRL+d to exit)

  • TCPdump to ignore SSH
    Issue tcpdump -i eth0 -n 'port ! 22' when you need to use TCPdump on an SSH connection

  • linking files
    Issue ln -s [source] [target] when you need to make a soft link. This is similar to the windows "shortcut" concept.

  • Linux Permissions
    Here is a summary of the meanings for individual octal digit values:
    	0 --- no permission
    	1 --x execute 
    	2 -w- write 
    	3 -wx write and execute
    	4 r-- read
    	5 r-x read and execute
    	6 rw- read and write
    	7 rwx read, write and execute

    Cisco - Stuff

  • PING command reply codes are:
    	Character 	Description
    	! 	Each exclamation point indicates receipt of a reply.
    	. 	Each period indicates the network server timed out while waiting for a reply.
    	U 	A destination unreachable error PDU was received.
    	Q 	Source quench (destination too busy).
    	M 	Could not fragment.
    	? 	Unknown packet type.
    	& 	Packet lifetime exceeded.
  • TRACE command reply codes are:
    	Character 	Description
    	! 		success
    	* 		time out
    	N 		network unreachable
    	H 		host unreachable
    	P 		protocol unreachable
    	A 		admin denied
    	Q 		source quench received (congestion)
    	? 		unknown (any other ICMP message)
  • Top Talkers Enter the following commands in global config mode
    ip flow-cache entries 4000
    ip flow-cache timeout inactive 100
    ip flow-top-talkers
    top 10
    sort-by bytes
    Then on the interface that is showing the heavy load add the commands depending on the traffic direction ip flow ingress or ip flow egress
    To see the results issue the command sh ip flow top-talkers
  • CPU Load sh proc cpu sort
  • Cisco ASA - Showing Preshared Keys To view the password unencrypted, type more system:running-config VPN
    Things to watch for when creating L2L VPN connections
  • Ensure that the name of the Tunnel-Group matches the IP address of the remote-peer.
  • Ensure the remote-peer is configured to send the IP address as the identifier
  • Ensure that remote-peer and the local firewall have the same LANs configured to be tunneled
  • Ensure that the re-key times match

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