Floating Route & Email Packet Tracer Activity

Please click here to download topology RIPv2 Bkup and Email.pka

I made up the packet tracer file "RIPv2 Backup and Email.pka" as a supporting activity to assist my students in understanding "Routing Concepts" of CCNA Exploration curriculum and at the same time in response to their question of other usage of static and static default routes.

I often explain to my students that under certain circumstances, a simple static route may be all the backup solution you need just as ISDN as a backup to frame relay. This static route can coexist with the dynamic route but it just doesn't show in the routing table. Therefore, it is called "Floating Route". In case the interface that is advertised in dynamic routing protocol fails, the static route will kick in and replace the major dynamic route as a back up to provide network availability to local network users.

I explain that we can configure a static route as long as the AD of the static route is higher than current dynamic route AD; it won't be used unless the main route leaves the routing table.  The route "floats" in the routing table and isn't seen unless the primary route leaves the table.

The packet tracer file with the topology shown below is created in that purpose and I also take the opportunity to help them review VLSM addressing skills as well as how to configure Email and DNS server in Packet Tracer.

The whole activity is just to prove to the students that using static route as backup sometimes can solve the problem that happens when the main dynamic routes are down. As availability is vital to any networks, this simple solution sometimes saves money and headache caused when any type of dynamic routing failures take place.

In this packet tracer activity, I use default static route as a backup.

I explain that they learned how to write a default static route in their CCNA studies, but they also remember that the default AD of a static route is either 1 or 0... and both of those values are less than 120!   To change the AD of a static route, configure the desired distance at the end of the ip route command.

R1(config)#ip route 0.0.0.0 0.0.0.0 s0/0/0  ?
  <1-255>    Distance metric for this route
  A.B.C.D    Forwarding router's address
  name       Specify name of the next hop
  permanent  permanent route
  tag        Set tag for this route
 

R1(config)#ip route 0.0.0.0 0.0.0.0 s0/0/1  200

The default static route has an AD that's only one higher than that of the RIPv2 route, but that's enough to make the route "float" and not yet be seen in the routing table.

R1#show ip route

Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP

       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area

       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2

       E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP

       i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area

       * - candidate default, U - per-user static route, o - ODR

       P - periodic downloaded static route

Gateway of last resort is 172.16.6.5 to network 0.0.0.0

     10.0.0.0/30 is subnetted, 1 subnets

C       10.10.10.8 is directly connected, Serial0/0/1

     172.16.0.0/16 is variably subnetted, 4 subnets, 3 masks

C       172.16.0.0/22 is directly connected, FastEthernet0/0

R       172.16.4.0/23 [120/1] via 172.16.6.5, 00:00:04, Serial0/0/0

R       172.16.6.0/30 [120/1] via 172.16.6.5, 00:00:04, Serial0/0/0

C       172.16.6.4/30 is directly connected, Serial0/0/0

R*   0.0.0.0/0 [120/2] via 172.16.6.5, 00:00:04, Serial0/0/0

Let's see the effect on the routing table when the Serial0/0/0 interface is closed.

R1(config)#int s0/0/0

R1(config-if)#shutdown

%LINK-5-CHANGED: Interface Serial0/0/0, changed state to administratively down

%LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/0/0, changed state to down

R1#show ip route

Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP

       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area

       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2

       E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP

       i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area

       * - candidate default, U - per-user static route, o - ODR

       P - periodic downloaded static route

Gateway of last resort is 0.0.0.0 to network 0.0.0.0

     10.0.0.0/30 is subnetted, 1 subnets

C       10.10.10.8 is directly connected, Serial0/0/1

     172.16.0.0/22 is subnetted, 1 subnets

C       172.16.0.0 is directly connected, FastEthernet0/0

S*   0.0.0.0/0 is directly connected, Serial0/0/1

When the link comes up again,

R1(config)#int s0/0/0

R1(config-if)# no shutdown

%LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/0/0, changed state to up

R1#show ip route

Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP

       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area

       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2

       E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP

       i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area

       * - candidate default, U - per-user static route, o - ODR

       P - periodic downloaded static route

Gateway of last resort is 172.16.6.5 to network 0.0.0.0

     10.0.0.0/30 is subnetted, 1 subnets

C       10.10.10.8 is directly connected, Serial0/0/1

     172.16.0.0/16 is variably subnetted, 4 subnets, 3 masks

C       172.16.0.0/22 is directly connected, FastEthernet0/0

R       172.16.4.0/23 [120/1] via 172.16.6.5, 00:00:04, Serial0/0/0

R       172.16.6.0/30 [120/1] via 172.16.6.5, 00:00:04, Serial0/0/0

C       172.16.6.4/30 is directly connected, Serial0/0/0

R*   0.0.0.0/0 [120/2] via 172.16.6.5, 00:00:04, Serial0/0/0

Simply by adjusting the administrative distance of a static route, we've got a backup route that takes little configuration. Floating static routes are an important step in training and working in production networks, so I tell my students to make sure they can write one when needed!