show ip route output.

[ggnfs000]

ccna book says:

r1 is configured with following:
ip route 172.16.2.0 255.255.255.0 172.16.4.2
ip route 172.16.3.0 255.255.255.0 s0/0/1 (because of the quirk, it will show as directly connected as below)


result:
show ip route static
///
172.16.0.0/16 is variably subnetted, 10 subnets, 2 masks
S 172.16.2.0/24 [1/0]via 172.16.4.2
S 172.16.3.0/24 is directly connected, Serial 0/0/1


My understanding is that adding 172.16.x.x with 24 subnets will alloc 8 bits for subnets total of 256 subnets. So wondering why the status above says variably subnetted with 10 subnets. Perhaps the book shows the example from a larger configuration part of which not shown in the book?

[deanwebb]

It's quite possible that the config for the router being quoted had additional entries in the 172.16.x.x range. Cisco/Pearson aren't always telling you the whole picture.

[ggnfs000]

well, to challenge my guess, i created 3 routers on a packet tracer connected in a V-fashion with serial link.
On the bottom of V, which is a router that has connection to both two other router, add following routes:

Now I see, 6 subnets:

Router#show ip route
Codes: L - local, C - connected, S - static, 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 not set

     172.16.0.0/16 is variably subnetted, 6 subnets, 2 masks
C       172.16.1.0/24 is directly connected, GigabitEthernet0/0
L       172.16.1.1/32 is directly connected, GigabitEthernet0/0
C       172.16.4.0/24 is directly connected, Serial0/1/0
L       172.16.4.1/32 is directly connected, Serial0/1/0
C       172.16.5.0/24 is directly connected, Serial0/1/1
L       172.16.5.1/32 is directly connected, Serial0/1/1

Router#
Router#

Router#show ip route
Codes: L - local, C - connected, S - static, 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 not set

     172.16.0.0/16 is variably subnetted, 6 subnets, 2 masks
C       172.16.1.0/24 is directly connected, GigabitEthernet0/0
L       172.16.1.1/32 is directly connected, GigabitEthernet0/0
C       172.16.4.0/24 is directly connected, Serial0/1/0
L       172.16.4.1/32 is directly connected, Serial0/1/0
C       172.16.5.0/24 is directly connected, Serial0/1/1
L       172.16.5.1/32 is directly connected, Serial0/1/1

Router#
Router#

Makes no sense. I may guess it is talking about some of L and C which each having 3 but then it makes no sense for original post either.

[deanwebb]

But, if you count number of subnets and masks in the routing statement, you do have 6 and 2, like the statement says. That means that the book example left out 8 other subnets and one other mask.

[ggnfs000]

that thinking may work out. I am assuming the fact it is saying "variably subnetted" is referring to 24 and 32 masks then. Otherwise there was only 24 subnet masks were being used. BTw, packet tracer was amazing, building up and tearing up networks in few minutes.

[deanwebb]

There are some limits on what packet tracer can do, but it's really fun and quick for what it does do.

[icecream-guy]

I guess you learned that things are not always what they seem, and not always straight forward. Things are dumbed down in early training as not to overwhelm those learning, then one day, the educators will say, those things you learned, don't actually work that way, and show you the real way now.  Now you see why it's good to get in up to your elbows with the hands on, and why those paper certified have a read hard time in the hands on environment,  real production is never book easy. The Cisco answer is not always the correct answer in real life.

[wintermute000]

Seriously abandon packet tracer. Get into unetlab/eve-ng or GNS3 or CSRs on hypervisor of choice now. Read code real behaviour
NXOS also does the /32 route per interface ip behaviour

[deanwebb]

Seriously abandon packet tracer. Get into unetlab/eve-ng or GNS3 or CSRs on hypervisor of choice now. Read code real behaviour
NXOS also does the /32 route per interface ip behaviour

Packet tracer gets one to CCNA, and is pretty easy to use. After CCNA, absolutely get used to all the stuff that goes with real gear.