Static route, Default Network, Default gateway, what’s the difference?

New engineers will sometimes find themselves confused when it comes to the  differences of defining a route.   When to use ip default-gateway and ip default-network and lastly when to use ip route 0.0.0.0 0.0.0.0 [interface] Below is brief breakdown between the three.

1) Default Gateway (ip default-gateway x.x.x.x)
This command serves non-routing network device that need to reach any network outside its own subnet or outside of its local network. The command is to function when the network device is not in routing mode. Typically the command exists in Layer-2 switches or switches that are in bridging mode only.  In order for this command to function in a router, ip routing must be disabled. When the ip routing is disabled, the router becomes merely a host, similar to your regular PC. To reach any network outside its own subnet or outside of its local network, the device needs to have a default-gateway.

2) Default Network (ip default-network a.b.c.d)
This command establishes a default subnet or network for specific routing-speaking network device. Therefore the ip routing must be enabled on the device.With this command in place, your Layer-3 network device will actually route packets unlike the default-gateway command. Second this command does not specify the next hop address, it specifies a network to be considered as default. In order for this command to set a default network, you must already have a static route in your routing table. You can tell if this is working if from a sh ip route there is a “gateway of last resort” configured.

3) Gateway of Last Resort (ip route 0.0.0.0 0.0.0.0 next-hop-ip/exit-interface)
This command also requires ip routing to be enabled. This command sets a default route for anything not in your routing table. After this command is entered it will show a “gateway of last resort” configured in your ip route table.

My preliminary Cisco router setup

As a potential engineer one of the many basic skills you’ll need to master in your career is setting up a newly purchased router. Surprisingly I know a lot of Engineers that have worked in NOC’s (Network Operations Centers) for years, troubleshooting all sorts Cisco devices and various issues and never really having to configure anything. This is truly one of the down sizes of working in a large company; you tend to get pigeon-toed into doing on particular thing all the time.

Two skills are needed to know from memory.

• Basic setup a router or switch

• Basic password recovery for a router or switch Continue reading

Custom Cisco menu configuration

A while ago I stumbled upon a great piece of code that could make your Cisco router a little less intimidating for your tier one tech support staff.   The tier one team is useless the first ones that the customer engages when calling in a trouble. 

Most of the time tier one is responsible for taking the customer information, creating a ticket and performing some basic trouble shooting steps,  i.e. verify links and change passwords or provide application assistance, anything more in depth is forwarded to the tie 2 or 3  group.

With a simple menu configured on a Cisco router you can perform  basic show  commands that any tier 1 or 2 can use without the fear causing any intrusive down time to the production network, and the person performing the commands does not need to know the  proper command syntax .

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Network Address Translation

Network Address Translation, sometimes called Network Address Translator (NAT), was originally outlined in RFC 1631 in 1994. This was to allow devices on the inside network the use of private IP addresses that are presently defined in RFC 1918. NAT makes it possible to have a very big internal network with thousands of local addresses represented by a handful of global addresses or possibly a single global address.

basicnat

We will setup a basic static and dynamic NAT configuration.

To the left we have a basic example of how NAT operates.  Starting from the bottom we have our …

  • Inside Local Addresses
  • Outside Local Address
  • Inside Global Address
  • Outside Global Address
Our ISP has given us the following IP range.  189.45.23.56/29, looking at this subnet we can tell that our network starts on the 8th subnet range and this will give us 6 usable addresses

(For simplicity we will not be using subnet-zero)

  • Network ID: 189.45.23.56 (Will always be even)
  • First usable address: 189.45.23.57 (Will always be odd)
  • Last usable address: 189.45.23.62 (Will always be even)
  • Broadcast address: 189.45.23.63 (Remember BrODDcast, always odd)
  • Netmask of: 255.255.255.248

For more subnet information refer to The Last Subnet Doc

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