Learning by Doing: CISCO Certified Network ... - SCN Research

Input queue: 0/75/0 (size/max/drops); Total output drops: 0
Queueing strategy: weighted fair
Output queue: 0/1000/64/0 (size/max total/threshold/drops)
Conversations 0/0/256 (active/max active/max total)
Reserved Conversations 0/0 (allocated/max allocated)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
0 packets input, 0 bytes, 0 no buffer
Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
0 packets output, 0 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
0 output buffer failures, 0 output buffers swapped out
0 carrier transitions
DCD=down DSR=down DTR=down RTS=down CTS=down
Randy#
Let’s go back over some of those things I highlighted in this example. Note the
output from a show interface command. Pay special attention to the contents of
the first five lines…this is our “bread and butter” lines. Be sure you know what is
on which line and which line is in which order. We see a note about “MTU.”
This is the maximum transmission unit. If the router is requesting to send a
packet larger than the receiving router’s MTU, then the sending router will
fragment the outgoing information into allowable sizes. Isn’t that nice? They can
get along. Notice the default encapsulation type on serial lines is HDLC. We will
be changing this when we get to the WAN part. Finally we see a MAC address
per interface (necessary for proper routing to different interfaces). Guess what?
We can change this if we want…I wouldn’t worry about it right now. If a hacker
gets a request from a device with a MAC address they can determine which
company manufactured it. Remember OUI’s? Once I know it is a CISCO device
I can port scan to narrow down the devices. Once I know what device it
specifically is I can use my knowledge of that device, its security problems, and
gain access to it!
3. Time for the network layer. Check to be sure the routing protocol is enabled and
that you have the correct routing protocol enabled. Have you
advertised/associated/published your networks properly? Test your router-torouter
connectivity with ping or an extended ping command. Here is an example
of using ping from the Randy console to Ward Ethernet interface:
Randy#ping 192.168.4.1
You should see:
Randy#ping 192.168.4.1
191