Archive for category Cisco

How Do I Decrypt Cisco Type 7 Passwords?

There are a lot of choices available online. But my personal favorites are:

The 1st option is an online only service. The 2nd option, however, allows you to download a utility called “Get Pass” from Boson’s site that you can carry around on your laptop in order to decrypt Cisco type 7 passwords.

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Gateway of Last Resort on a Cisco Router/Switch

Check out the following link on Cisco’s site:

Configuring a Gateway of Last Resort Using IP Commands

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Routing Protocol Resources on Cisco’s Site

The following links will take you to Cisco’s Site providing detailed explanation of each Routing Protocol & also tons of guides that can take you from novice to expert level:

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Time-Based ACL for ISDN Connectivity

There are 4 things to consider:

1. Define the Time-Range (under global config mode):
time-range isdn-hours
absolute start 00:00 01 January 2009
periodic weekdays 7:00 to 19:00

2. An Access List needs to be created for defining the interesting traffic & tying the Time-Range (under global config mode):
access-list 100 remark ACL for ISDN interesting traffic definition
access-list 100 deny ospf any any
access-list 100 permit ip any any time-range isdn-hours

3. Create a Dialer List with a Reference to access-list 100, as follows (under global config mode):
dialer-list 1 protocol ip list 100

4. Apply the Dialer List to the ISDN Interface (under global config mode):
interface BRI0
dialer-group 1

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How to Upgrade IOS Image on a Cisco Router/Switch?

There are a couple of pieces to this puzzle. Here is a list of things you need to successfully perform this operation:

1) Router or a Switch you would like to upgrade
2) Console Cable
3) Straight Through Ethernet Cable (CAT5)
4) PC
5) TFTP Server (http://www.solarwinds.com/products/freetools/)

Here is a step-by-step of what needs to be done to perform the upgrade:

1. First of all, you would need to connect your Console Cable’s RJ-45 end into the Router’s or Switch’s Console Port.
2. The other end of the Console Cable that has a DB9 Connector needs to be plugged into the Serial Port of the PC.
3. Now open up your favorite program to launch console. Or you can use Hyper-terminal (comes free with Windows). Here are a few snapshots of Hyper-Terminal settings to get you started:

com-portcom-port-properties

4. Once you are done. You should be at a user prompt followed by a “>” sign. Now type in “enable” to get to “#” prompt also known as exec prompt.
5. Now the other important piece of the puzzle you need to focus on is running a TFTP Server on your PC. Once you have the software downloaded as mentioned above, you can then go ahead & launch it.
6. Once the TFTP Server is running on a PC. Make sure you point the path on the Server to the appropriate IOS image. Here are a few snapshots of the SolarWinds TFTP Server config:

tftp-server-configtftp-server-config-2

7. Now the last piece of the puzzle is the Ethernet Connection between the Router/Switch & PC. Connect any of the available ethernet/fast-ethernet ports on your Router/Switch to your PC’s Ethernet Port via a CAT5 cable. Make sure its a stright-thru cable since you are connecting two dislike devices.
8. Now assign a manual IP address on each end of the Ethernet Connection. For Example: on the PC, assign 10.10.10.1 /24 & on the Router/Switch assign 10.10.10.2 /24. Once done, try pinging either from your PC’s command prompt or your Router/Switch’s CLI mode via the Hyper-Terminal or any Terminal program of your choice.
9. Here is the final step: type in the following command under exec prompt:
Router#copy tftp: flash:
hit enter
Address or name of remote host []?
here you have to type in the IP address of your TFTP Server, which in this case happens to be the same as your PC’s IP address.
10. Then ok all the way & the image push should start immediately.
11. Once the image is done pushing & you get a message indicating that the IOS image push was successful. Make sure you see the image on the flash. You can check this by typing in “show flash” under exec prompt.
12. And last but not least, don’t forget to REBOOT. Reboot is what forces the router to initialize the new IOS image. You can reboot the Router/Switch via “reload” command under exec prompt.

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Most Common TCP/UDP – Transport Layer Ports!!!

ultimate-port-list

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What is MPLS & Why is BGP required with MPLS Implementation?

FYI… The below-mentioned explanation is a very high-level overview of how MPLS & BGP work in conjunction. This post, by no means, contain detailed information regarding MPLS & BGP. If you need more information check out Cisco’s site (search keyword: MPLS, BGP) & you will find tons of material with great explanations.

MPLS (Multi-Protocol Label Switching) is basically a WAN technology that allows Routing on Layer2. Now I know, this sounds crazy but just hang in there for moment & I will explain myself. Review the below-mentioned diagram while keeping the OSI Model in mind & it will give you an idea:

mpls_protocolstack

As you can see, MPLS is stuffed between Layer2 (Data-Link) & Layer3 (Network), therefore its considered “Layer 2.5” Protocol. Do understand the underlying WAN mechanism or infrastructure is still based of off Layer 2 technologies such as Frame Relay, ATM, PPP, HDLC, etc. MPLS essentially adds the concept of Labels, which makes it a lot quicker to deliver packets to its destination since the Layer3 lookup is not required.

Now where does BGP come into play? Why is BGP required with MPLS Implementation? These questions come to mind because with Frame Relay, ATM, PPP, HDLC we did not need a Layer3 routing protocol. Well, here is the answer:

With strictly Layer2 WAN protocols provided by the service provider or carrier, we only need Layer2 information since we (customers) need to communicate to the provider on Layer2. With MPLS however, things are a bit different. The provider now communicates via BGP. In other words, in the old days provider would only care about Layer2 stuff & the upper layers were our responsibility as far as routing. But with MPLS, the provider now participates in the Routing process & is running BGP on their router. Hence we also have to use BGP on our router for the MPLS to work.

The following WAN Designs will further clarify the above explanation:

traditional-wan-design-vs-mpls-wan-design

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