Crib Notes


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. 127.0.0.1 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.

    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 PIX have the same LANs configured to be tunneled
  • Ensure that the re-key times match

    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 tester@testdomain.com

  • 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.


  • 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
    In Cisco routers, the codes for a traceroute command reply are: 
    	! -- 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)
    • eSubnet Fragment

    Receive insights into networking, security
    and IT management from our newsletter