Clever Geek Handbook

Packet Tracer. Lab: Configuring Floating Static Routes

Network topology





Tasks



  1. Creating a basic static default route
  2. Deploying a Floating Static Route
  3. Checking for switching to a floating static route when the main route fails


General information



So, to begin with, a few words about what a static, and even a floating route is. Unlike dynamic routing, static routing requires you to independently build a route to a specific network. A floating static route is used to provide a backup path to the destination network in the event of a primary route failure.



On the example of our network, the "Border Router" so far has only directly connected routes to networks ISP1, ISP2, LAN_1 and LAN_2.







Creating a basic static default route



Before talking about the backup route, you first need to build the main route. Suppose the main route from the border router goes through ISP1 to the Internet, and the route through ISP2 is the backup one. To do this, set the default static route on the border router in global configuration mode: 



Edge_Router>en
Edge_Router#conf t
Edge_Router(config)#ip route 0.0.0.0 0.0.0.0 s0/0/0


Where:



  • the first 32 bits of zeros are the destination network address;
  • the second 32 bits of zeros are the netmask;
  • s0 / 0/0 is the outgoing interface of the border router that is connected to the ISP1 network.


This entry means that if packets arriving at the border router from LAN_1 or LAN_2 contain the address of a destination network that is not in the routing table, they will be forwarded through the s0 / 0/0 interface.







Let's check the routing table of the border router and send an echo request to the web server from PC-A or PC-B:











We see that the default static route entry has been added to the routing table (as evidenced by the S * entry). Let's trace the route from PC-A or PC-B to the web server:







The first transition is made from PC-B to the local IP address of the border router 192.168.11.1. The second hop is from the border router to 10.10.10.1 (ISP1). Remember, in the future we will compare the transitions.



Deploying a Floating Static Route



So, we have built the main static route. Next, we create, in fact, a floating static route through the ISP2 network. The process of creating a floating static route is no different from a regular default static route, except that the first additionally specifies the administrative distance. Administrative distance refers to the reliability of the route. The fact is that the administrative distance of a static route is equal to one, which means absolute priority over dynamic routing protocols, for which the administrative distance is many times greater, except for local routes - for them it is equal to zero. Accordingly, when creating a static floating route, you should specify an administrative distance greater than one, for example, 5. Thus,the floating route will not take precedence over the primary static route, but when it is unavailable, the default route will be considered primary.







The syntax for specifying a floating static route is as follows: 



Edge_Router(config)#ip route 0.0.0.0 0.0.0.0 s0/0/1 5


Where:



  • 5 - this is the value of the administrative distance;
  • s0 / 0/1 - the output interface of the border router connected to the ISP2 network.


I would like to say right away that while the main route is in working condition, the floating static route will not be displayed in the routing table . To be more convincing, we will display the contents of the routing table while the main route is in good condition: You







can see that the routing table still displays the main static default route with the output interface Serial0 / 0/0 and no other static routes in the routing table is displayed.



Checking for switching to a floating static route when the main route fails



And now for the fun part: let's simulate the failure of the main route. This can be done by disabling the interface at the software level, or simply removing the connection between the router and ISP1. Disable the Serial0 / 0/0 interface of the main route: 



Edge_Router>en
Edge_Router#conf t
Edge_Router(config)#int s0/0/0
Edge_Router(config-if)#shutdown


... and we immediately run to look at the routing table:







In the figure above, you can see that after the failure of the main static route, the output interface Serial0 / 0/0 changed to Serial0 / 0/1. In the first trace that we did earlier, the next hop from the border router was to the IP address 10.10.10.1. Compare the hops by retracing the fallback route:







Now the hop from the edge router to the web server is via IP address 10.10.10.5 (ISP2).



Of course, static routes can be viewed by displaying the current router configuration: 



Edge_Router>en
Edge_Router#show run




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