Tuesday, December 11, 2012

CCDP - ARCH - Route filtering

Filter routes inbound to a router via a 'distribute-list' cmd to prevent inbound rutes from being learned.

Filter routes outbound to a neighbour via a 'redistribute [protocol] [process number] route-map FILTER' cmd and a deny statement on the FILTER route-map to stop routes from being advertised towards a neighbour.

CCDP - ARCH - Migrate Routing Protocols By Manipulating the AD

High level steps to move from one RP to another by manipulating the AD:
1) Configure the new RP and manually set the AD to be Higher (and therefore less preferred) than the current RP
2) Configure all devices as necessary and then check the topology using appropriate show commands
3) Ensure the new RP has all the required routes in its database
4) Either by increasing the AD on the current RP or by reducing the AD on the New RP change the AD so that the new RP is the preferred RP to use
5) Use show commands to ensure that the new RP is populating the routing table correctly (there shouldn't be any routes learned via the old protocol - if there are some then troubleshoot accordingly)
6) Remove the old RP from the routers
7) Move to normal running

Wednesday, November 14, 2012

CCDP - ARCH - UDLD (UniDirectional Link Detection):

  • Used where there are fibre links between switches (but can also be applied to Copper interfaces)
  • Interface could be seen as Up/Up but due to a mismatch on the tx/rx pairs the comms become unidirectional 
  • UDLD Normal mode error-disabled the end that detected the unidirectional state - default mode
  • UDLD Agressive mode disables both ends - set it with the [agressive] switch
  • Uses 15 sec hello timer
  • Can be applied globally or on the interface

Monday, November 12, 2012

CCDP - ARCH - STP tools

The following tools can be used to manage STP and L2 switching loops:

  • PortFast: applied to a port connecting to an end user/host. Transitions the ports straight to forwarding
  • UplinkFast: Offers L2 link load balancing, up to 5 secs convergence time once a link fails
  • BackboneFast: Invoked when an inferor BPDU is received on a root port or blocked port. Reduces convergence times after an indirect failure.
  • Loop Guard: Stops a bridging loop by preventing an Alternate port or Root port becoming a Designated port.
  • Root Guard: Protects the Root switch by preventing other switches from taking the Root role.
  • BPDU Guard: Apply to PortFast enabled ports. If the port recieves a BPDU the port gets shutdown
  • UDLD (UniDirectional Link Detection): Detects when one-way connection exists on a copper/fibre link. Interface moves to a shutdown state and an alarm is triggered.
  • Bridge Assurance: If a port that should receive BPDU's suddenly stops receiving them the port is moved to an 'Inconsistant' state and shutdown. Prevents potential loops

Sunday, July 15, 2012

Thoughts on the CCDA exam...

I sat the CCDA exam the other day and was stunned to find that I hadn't passed it. Sitting here now I'm still little confused if I'm honest. The exam consists of 55 questions to be completed in 75 minutes which is plenty of  time. I finished with 15 minutes go and that was after I made myself slow down.

Thinking on I'm trying to remember the style of questions I faced and to be honest I'm struggling to remember specifics. I'm not going to challenge the NDA you sign so all I say is that standard of question is no more technically challenging than the level you get in the Office Cert Guide by Bruno and Jordan. I can think of one area however I probably did fall down on. The test papers.

In the Offical Cert Guide and on the Cisco Learning Network there are practice question that you can try. When ever I did them I passed with flying colours. In the practice exams I did 3 attempts and pass them all by a good margin so I felt I was ready. At no point during the exam did I feel that it was getting the better of me and I think there were only 2 questions where I felt I needed to guess. As a result I was actually shocked when it said I hadn't met the grade.

I'm about to reschedule the exam for a few weeks time and today I reviewed the Offical Cert Guide and compared it to the Exam Topics list off the Cisco Learning Network. The main thing that lept out  to me was that while the Exam topics are set out one way, the Offical Cert Guide is set out in a different structure. As a result it's not immediately clear how the study material relates to the exam objectives.

I'm going to spend this week comparing and contrasting the material I have and will ramp up the exam practice. Finally I'll be reviewing (again) Enterprise Architecture, and Network Services.

Onwards and upwards...

Thursday, June 28, 2012

Password recovery on a Cisco ME3400 Switch

Continuing my notes on password recovery on various bits of kit. Today's task was an ME3400 Switch.

Perform the following steps to regain access to your switch:
  1. Power up the switch and send the Break sequence (dependant on the system you are working from) to access Password Recovery
  2. Load the helper files:                                         switch#load_helper
  3. Next, verify the name of your config file:            switch#dir
  4. Rename said config file:                                     switch#rename flash:config.txt flash:config.txt.old
  5. Reboot the system:                                           switch#boot
  6. Next you'll be prompt to enter the auto config process. Enter No
  7. Enter the PRIV EXEC mode:                           switch>en
  8. Rename your config file:                                   switch#rename flash:config.txt.old flash:config.txt
  9. Copy the config in the Memory:                       switch#copy flash:config.txt system:running-config
  10. Next change your passwords as you see fit
  11. Last part is to check the state of your interfaces. You may need to #no shut your appropriate ports.
     Finally apply your changes via switch#wr mem and reboot.

Monday, June 25, 2012

CCNP - ENTERPRISE - Duplex Mismatch

Right, not done any posts for a while so here we go with a note on Duplex Mismatches...

A Duplex Mismatch occurs when 2 devices are directly connected with different duplex modes. One end might be set to auto whilst the other could be set mannually to Full Duplex.

The situation is usually the result of manual configuration of an interface and the result can cause a number of effects on the network.

The most common situation for a duplex mismatch is the example above, one end set to auto (negotiate) and the other set to Full Duplex. With one end trying to negotiate whilst the other end is not the result is that the negotiation fails and the interface fails back to Ethernet standards and sets it's self to half duplex. This default action when negotiation fails allows for older hubs to be in operation in the network.

With one end now automatically set to Half Duplex and the other end manually set to Full Duplex you get the duplex mismatch.

The activity observed on the network can be varied. For example a duplex mismatch will not affect PING as the single packets are sent at 1 second intervals and therefore the link can process the traffic with out any issue being observed. Telnet will be seen as slow but you should still be able to run your session.

The main issue you will see is when both ends of the link attempt to send traffic at the same time. The end set Full Duplex can sendand receive data at the same time. No problems there, however, the end set to Half Duplex will not receive any data because it is busy sending first. The combination will result in packets from the Full Duplex end being lost whilst packets from the Half Duplex end will be slow or lost as that end perceives a collision is occurring and will run CSMA/CD.

As packets are now being lost TCP attempts to perform error recovery and retransmit the packets. This will fail as well due to the mismatch in place.

In the Full Duplex end you will see Frame Check Sequence errors and/or runt frames as packets are lost in transit.

The key to the operation to configure both ends the same. Use only Auto OR Full.

Simply change the setting on one end of the link to match the configuration of the other end.

Tuesday, March 13, 2012

Off topic - HR: The Spark Way

Have you got to perform a company restructure? need reduce head count? not sure where to start in your vast empire? Never fear the patented Spark method is here to help!

Step one : Obtain a list of all employees in the company and make sure their Job title is included.
Step two : Tell an educated but uninformed individual the job title of the first employee in the list and ask them to describe what that person does
Step three : If the first word out of the individual's mouth is 'Err???....???' then that person can be chopped :o)
Step four : Repeat for all employees and you'll have your list of jobs that can be culled.

Marvellous! :o)

Monday, January 23, 2012

Upgrade IOS on an ASR-1002F

Steps to upgrade IOS on an ARS-1002F are as follows:
  1. Copy your IOS .bin file to a USB stick and connect it to USB0 on the front of the ASR
  2.  Connect the power and press 'Escape' on startup to access ROMMON
  3. At the prompt do > boot usb0:
  4. The router will boot using the ASR image you have on the USB
  5. Once booted do #copy usb0:asr10~7q.bin bootflash:
  6. Confirm the location and the .bin file will transfer
  7. Next, set the system to boot from bootflash - #boot system flash bootflash:asr10~7q.bin
  8. Next set the config-register to ensure it boots properly - (config)#config-register 0x2102
  9. Write this - #wr mem
  10. Finally reload the asr and ensure it boots correctly - #reload

Friday, January 20, 2012

Password Recovery on a Catalyst 3750-E

Password recovery on a Catalyst 3750-E

  • Press and hold the Mode button on the front of the system then connect the power
  • Continue holding until the SYS LED blinks from green, to amber, to green, then turns solid green.
  • Release Mode and you should have a prompt for – switch:
  • Do – switch: flash_init
  • Next do – switch: dir flash:
  • Next do - switch:  rename flash:config.text flash:config.old
  • Next do – switch: boot
  • Once the system reboots you can either save the blank config and work from a clean install                   #wr mem
  • Or, recover the old config and reset the password:   
                       #rename flash:config.old flash:config.text
  • Then do - #copy flash:config.text system:running-config
  • Change all the passwords and apply an appropriate user account:
          (config)#enable secret [password]
          (config)#username Trevor password [password]
          (config)#line con 0
                        password [password]
          (config)#line vty 0 4
                       password [password]
  • Finally save the config and reload -
                     #wr mem

Password Recovery on a Cisco 5580

 Steps to reset a password on a Cisco ASA 5580
  • Boot the system and press escape as the system loads
  • At ROMMON set confreg to 0x41 - >confreg 0x41
  • then reload >boot
  • When prompted type 'No' to by pass the auto configuration steps.
  • Once at the command prompt copy the start-up config to running config:
           #conf t
          (config)#copy start run
  • Next change the password to on of your choice:
         (config)#password [password]
         (config)#enable password [password]
  • Add a user account with priv 15 access:
         (config)#username Trevor password [password] priv 15
  • Change the configuration register back to the correct one:
         (config)#config-register 0x1
  • Finally write this and then reload:
          #wr mem
  •  Test and you should be good.