Will route packets for food…
Tag Archives: ccna
Cisco Switch IOS SSH and Line Logging
Cisco messages can be annoying when you are working a switch that logs ACL rules on a Cisco switch, so something that I’ve found quite useful is editing the line configuration to make the command you are typing in on a Cisco switch be re-printed below the log message.
It’s pretty simple to use, and all you need to do is this, in “configure terminal”.
line con 0
logging synchronous
line vty 0 4
logging synchronous
line vty 5 15
logging synchronous
Another handy tip is enabling SSH. SSH is secure unlike telnet, meaning passwords or important information can’t be seen if an attacker was able to log packets.
SSH is fairly easy to enable, first off make sure you have a username configured or radius, enable the ssh transport under the lines, set a domain-name and then generate some keys.
line vty 0 15
login local
transport input telnet ssh
!
username admin password god
ip domain-name internaluse.net
! out of config mode run
crypto key generate rsa
Make sure you put down 1024 for the RSA keys, other most SSH clients will turn you down.
TCP, UDP and their place in the world…
When setting up servers and services I used to wonder why people would use UDP. It’s annoying to setup and test with firewalls, however lately while doing my CCNA study I have learned the important uses of UDP and TCP.
TCP has lots of features, like error recovery and acknowledgment which UDP doesn’t support. Both use “ports” and both have error detection. So why use UDP?
I’ve linked to a flickr scan of TCP header. As you can see a TCP header is 20 Bytes long, without it’s payload, where as if you look at a UDP header it’s only 8 Bits long. UDP already has the advantage of being smaller in size, but what really makes UDP useful is it’s lack of error recovery.
In services like VoIP , Video Conferencing and Gaming, by the time TCP has detected an error, sent a request for the missing packet, and continued on it’s way it has interrupted the call, making TCP a bad choice. Since UDP doesn’t have error handling, it doesn’t matter if a packet was lost or damaged, because UDP won’t request (or check) for the missing packet and continue on it’s merry way. Thus keeping the call at low latency.
Ps. Now that I have gotten half way through the first Cisco CCNA book I might share a few other network tips, tricks or info.