Show ip route / routing table

Question

hi all,
i have a question regarding the output of the "show ip route" command:
C         192.168.30.0/24 is directly connected, Ethernet0                                  
            172.16.0.0/24 is subnetted, 1 subnets
S          172.16.1.0 is directly connected, Ethernet0
               192.168.38.0/24 is variably subnetted, 2 subnets, 2 masks
S       192.168.38.0/24 is directly connected, Ethernet0
S       192.168.38.0/25 [1/0] via 192.168.30.40
     10.0.0.0/32 is subnetted, 1 subnets
C       10.1.1.1 is directly connected, Loopback1
I understand why lines 4,5 and 6 are present. Its cause the network 192.168.38.0 is supposed to have a /24 mask but there is also a network with a /25 mask and thus it says this network is variably subnetted.
But why doesnt it show the same for line 2 and 3? Shouldnt it say 172.16.0.0/16 is subnetted? I understand why is doesnt show "variably subnetted" as there is only on subnet but why not 172.16.0.0/16?
And the same for the last two lines. Why not 10.0.0.0/8 but /32? Even though its a loopback interface still the network 10.0.0.0 is supposed to have a /8 mask by nature.
And it might be a stupid question but does a static router always have a metric of 0? I guess so as they dont have to compete with other routes, right?
I mean a static route goes always straight into the routing table and the metric is actually just for comparison reasons within a routing protocol to see what is the best route which should be suggested for being written into the routing table.
Also i tried to put static routes permanently into the routing table with the "permanent" command but always when i detach the cable of the corresponding interface the routes get kicked out of the RT. Is there a trick or something i have to be aware of?
thanks for any help!

Answer 1

I will take the easy part of the question first. One of the basic principles of IOS is that it will put routes into the routing table is the corresponding interface is in the up state. And that IOS will withdraw a route from the routing table is the corresponding interface is in the down state. So when you disconnect the interface then the route using that interface is withdrawn.
The more complex part of the question is the aspect of metrics with static routes. My explanation here would start from the point that the reason we use metrics is so that we can compare routes learned within a protocol and determine whether one is better than the other. This makes sense for RIP, it makes sense for OSPF, and it makes sense for EIGRP. But it does not make sense for static routes. To try to make it a bit more clear: if RIP or OSPF or EIGRP learn a route to a subnet that goes via FastEther0/0 and also learn a route to that subnet that goes via FastEther0/1 then we compare the routes and if one has a more attractive metric then that is the one that gets put into the routing table. But with static routes if there is a static route for a subnet that goes via FastEther0/0 and also a static route for that subnet that goes via FastEther0/1 then there is no comparison and both routes are put into the routing table. Since we do not do comparisons with static routes then there is no concept of metric associated with the static route and IOS puts a default value into the metric field of a static route.
HTH
Rick