DOS commands for Network Engineers.

Link

  • To see the system information: systeminfo
  • Display Connection Configuration: ipconfig /all
  • Display DNS Cache Info Configuration: ipconfig /displaydns
  • Clear DNS Cache: ipconfig /flushdns
  • Release All IP Address Connections: ipconfig /release
  • Renew All IP Address Connections: ipconfig /renew
  • Re-Register the DNS connections: ipconfig /registerdns
  • Change/Modify DHCP Class ID: ipconfig /setclassid
  • Network Connections: control netconnections
  • Test Connectivity: ping supto.net
  • Displays the TCP/IP protocol sessions: netstat
  • Display Local Route: route
  • Display Resolved MAC Addresses: arp
  • Display Name of Computer Currently on: hostname
  • Display DHCP Class Information: ipconfig /showclassid
  • Name Server Lookup: nslookup google.com
  • Access and maintain a Microsoft File/Printer Sharing environment: net
  • For Traces the route: tracert supto.net  (press ctrl+break to came out of this command)
  • Combines functions of Ping and Tracert : pathping /?
  • Used to retrieve the information about a user on a network: finger

MPLS Circuit Troubleshooting

Link

In this scenario we are asked to validate a flapping interface.  

1] Find the serial interface and verify that it is up/up

 attga43c3#sho ip int br | include 10.112.210.45

 Serial9/1/1/20:0       10.112.210.45   YES manual up

2] Display the interface and note the errors

    attga43c3#sho int s9/1/1/20:0

        Serial9/1/1/20:0 is up, line protocol is up
          Hardware is cyBus 2CT3+
          Description: MNX | MYHOME SERVICES | MYHOUSE | GA | DHEC.123456..ATI | 23853 | 1305937 | 1364629 | USA | MIS |
          Internet address is 10.112.210.45/30
          MTU 1500 bytes, BW 1536 Kbit, DLY 20000 usec, rely 255/255, load 1/255
          Encapsulation PPP, crc 16, loopback not set
          Keepalive set (10 sec)
          LCP Open
          Listen: CDPCP
          Open: IPCP
          Last input 00:00:05, output 00:00:05, output hang never
          Last clearing of “show interface” counters never
          Input queue: 0/1000/0/0 (size/max/drops/flushes); Total output drops: 5
          Queueing strategy: VIP-based fair queuing
          5 minute input rate 0 bits/sec, 0 packets/sec
          5 minute output rate 0 bits/sec, 0 packets/sec
             6534487 packets input, 3035189030 bytes, 0 no buffer
             Received 0 broadcasts, 0 runts, 1 giants, 0 throttles
             116987 input errors, 7228 CRC, 51274 frame, 0 overrun, 0 ignored, 58484 abort
             5877595 packets output, 2144676741 bytes, 0 underruns
             0 output errors, 0 collisions, 170 interface resets
             0 output buffer failures, 0 output buffers swapped out
             166 carrier transitions no alarm present
          Timeslot(s) Used: 1-24, Transmitter delay is 0 flags, transmit queue length 5
          non-inverted data

3] Find the VRF and ping the VRF interface.

    attga43c3#sho ip vrf interface | include 10.112.210.45

        Serial9/1/1/20:0       12.112.210.45   1612 <— VRF

4] Run an extended Ping to the VRF

    Router3#ping vrf 1612   

        Protocol [ip]:
        Target IP address: 10.112.210.46
        Repeat count [5]: 5000
        Datagram size [100]: 1500
        Timeout in seconds [2]: 1
        Extended commands [n]:
        Sweep range of sizes [n]:
        Type escape sequence to abort.
        Sending 5000, 1500-byte ICMP Echos to 10.112.210.46, timeout is 1 seconds:
        !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

In the above ping I wanted to really hammer the heck out of circuit.  In this example we see that the circuit is clocking massive input errors and  no output. Instead of me writing what I did to correct this, I’m going to leave this post open for the reader to comment what they think I did.  Note the bold errors and circuit type.