7 Replies Latest reply: Sep 9, 2011 8:52 AM by Elvin Arias RSS

    "show ip route" shows info "variably subnetted"

    abenmao

      Hi there,

       

      I have 2 cisco routers: 1841. One is in use, the other is standby. On the production router,I have the following info:

       

      gts#show ip interface brief

      Interface                  IP-Address      OK? Method Status                Protocol

      FastEthernet0/0            203.122.221.193 YES NVRAM  up                    up

      FastEthernet0/1            58.183.230.130  YES NVRAM  up                    up

      Loopback0                  unassigned      YES unset  up                    up

       

      gts#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

             i - IS-IS, su - IS-IS summary, 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, + - replicated route

       

      Gateway of last resort is 58.183.230.129 to network 0.0.0.0

       

      S*    0.0.0.0/0 [1/0] via 58.183.230.129

            58.0.0.0/8 is variably subnetted, 2 subnets, 2 masks

      C        58.183.230.128/30 is directly connected, FastEthernet0/1

      L        58.183.230.130/32 is directly connected, FastEthernet0/1

            203.122.221.0/24 is variably subnetted, 2 subnets, 2 masks

      C        203.122.221.192/28 is directly connected, FastEthernet0/0

      L        203.122.221.193/32 is directly connected, FastEthernet0/0

      gts#

       

      Now I'm trying to configure the standby router in the same way as the production one does. But I have no idea about how to get the configuration "variably subnetted". The result of "show ip route"  on my standby router is as follows

      203.122.221.0/28 is subnetted, 1 subnets

        203.122.221.192 is directly connected

      58.0.0.0/30 is subnetted, 1 subnets

        58.183.230.128 is directly connected

       

      thank you for the help

      Alex

        • 1. Re: "show ip route" shows info "variably subnetted"
          cadetalain

          Hi,

           

          the output you are seeing here is due to IOS version 15 and the other one is IOS version 12 where you won't see same output because you haven't got the Local /32 entries in version 12.

           

          Alain.

          • 2. Re: "show ip route" shows info "variably subnetted"
            Keneil Facey

            Hi,

             

            To get that output you need to subnet beyond the classful boundary and to subent using different masks.

             

             

            So for example,

             

            If you have two Loopback interfaces, both should fall within a classful boundary but with different masks.

             

            eg. Loopback 1 and Loopback 2 fall in the 192.168.1.0/24 classfull boundary

             

            but Loopback 1 has a /29 mask while Loopback 2 has a /30 mask

             

             

            R4(config)#inter lo 0

            R4(config-if)#

            %LINK-5-CHANGED: Interface Loopback0, changed state to up

            %LINEPROTO-5-UPDOWN: Line protocol on Interface Loopback0, changed state to up

            R4(config-if)#

            R4(config-if)#ip add

            R4(config-if)#ip address 192.168.1.1 255.255.255.248

            R4(config-if)#inte lo 1

            %LINK-5-CHANGED: Interface Loopback1, changed state to up

            %LINEPROTO-5-UPDOWN: Line protocol on Interface Loopback1, changed state to up

            R4(config-if)#

            R4(config-if)#ip ad

            R4(config-if)#ip address 192.168.1.9 255.255.255.252

            R4(config-if)#end

             

             

            this should produce the following result

            R4#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 not set

             

                 192.168.1.0/24 is variably subnetted, 2 subnets, 2 masks

            C       192.168.1.0/29 is directly connected, Loopback0

            C       192.168.1.8/30 is directly connected, Loopback1

            R4#

             

            Hope this helps

            Keneil

            • 3. Re: "show ip route" shows info "variably subnetted"
              Elvin Arias

              Hi abenmao,

               

              This is related to how the Cisco IOS classify the routes in the routing table. There are basically two types of routes:

              1- Level 1 routes

              2- Level 2 routes

               

              The level 1 routes are subdivided in two groups:

              1.1- Level 1 final routes.

              1.2- Level 1 parent routes.

               

              A level 1 final route is a route that has an exit interface or next-hop and a subnet mask lower or equal than it's default class, i.e: 192.168.1.0/24, 172.16.1.0/16, 12.0.0.0/8, 192.168.0.0/16, a default route, a supernet.

               

              Look at this example:

               

              R1(config)#interface loo

              R1(config)#interface loopback 1

              R1(config-if)#ip address 192.168.2.1 255.255.255.0

              R1(config-if)#exit

              R1(config)#do show ip route

               

              output ommited

               

              Gateway of last resort is not set

               

              C    192.168.2.0/24 is directly connected, Loopback1

               

              Lets look what happens if we add a lower mask to a class b route:

               

              R1(config)#interface loopback 2

              R1(config-if)#ip address 172.16.1.0 255.252.0.0

              R1(config-if)#do sh ip route

               

              output ommited

               

              Gateway of last resort is not set

               

              C    172.16.0.0/14 is directly connected, Loopback2

              C    192.168.2.0/24 is directly connected, Loopback1

               

              The route was added and any route was additionally created. This comprobe the statement about the level 1 final routes.

               

              Now, the level 2 routes are routes that have a higher mask than it's default class and an exit inteface attached to it. Lets see the following example:

               

              R1(config-if)#exit

              R1(config)#int lo3

              R1(config-if)#ip address 192.168.3.1 255.255.255.128

              R1(config-if)#do show ip route

               

              output ommited

               

              Gateway of last resort is not set

               

              C    172.16.0.0/14 is directly connected, Loopback2

              C    192.168.2.0/24 is directly connected, Loopback1

                   192.168.3.0/25 is subnetted, 1 subnets

              C       192.168.3.0 is directly connected, Loopback3

               

              The highlited route is a level 2 final route because the subnet mask is higher than its class default.

               

              Note that a second route was created whe we added the level 2 final route:

               

              R1(config-if)#do show ip route

               

              output ommited

               

              Gateway of last resort is not set

               

              C    172.16.0.0/14 is directly connected, Loopback2

              C    192.168.2.0/24 is directly connected, Loopback1

                   192.168.3.0/25 is subnetted, 1 subnets

              C       192.168.3.0 is directly connected, Loopback3

               

              This is called a level 1 parent route. A level 1 parent route is a route that doesn't have any next-hop or exit interface. These are automagically created when you add a level two route .

               

              Elvin.

               

              El mensaje fue editado por: Elvin Arias

              • 4. Re: "show ip route" shows info "variably subnetted"
                Brian

                On the "active" router you have more than one subnet identified and therefore, it is variably subnetted.

                 

                58.0.0.0/8 is variably subnetted, 2 subnets, 2 masks

                  58.183.230.128/30 is directly connected, FastEthernet0/1

                  58.183.230.130/32 is directly connected, FastEthernet0/1

                203.122.221.0/24 is variably subnetted, 2 subnets, 2 masks

                  203.122.221.192/28 is directly connected, FastEthernet0/0

                  203.122.221.193/32 is directly connected, FastEthernet0/0

                 

                and on the "standby" router you identified only one subnet for each major network.

                 

                203.122.221.0/28 is subnetted, 1 subnets

                  203.122.221.192 is directly connected

                58.0.0.0/30 is subnetted, 1 subnets

                  58.183.230.128 is directly connected

                 

                HTH

                 

                • 5. Re: "show ip route" shows info "variably subnetted"
                  Brian

                  Here is a little better explanation.  Take the example below.  I configured the following on each of the loopback interfaces.

                   

                  interface Loopback1

                  ip address 192.168.1.1 255.255.255.128

                  !

                  interface Loopback2

                  ip address 192.168.1.129 255.255.255.192

                  !

                  interface Loopback3

                  ip address 172.16.3.1 255.255.255.0

                  !

                  interface Loopback4

                  ip address 172.16.4.1 255.255.255.0

                  !

                   

                  Pay particular attention to the subnet masks used on each interface and then look carefully at the output of the routing table below.

                   

                  Router#sh ip rou
                  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 not set

                       172.16.0.0/24 is subnetted, 2 subnets
                  C       172.16.3.0 is directly connected, Loopback3   <--- usewd the same subnet mask for both subnets of the major network 172.16.0.0/16
                  C       172.16.4.0 is directly connected, Loopback4   <--- usewd the same subnet mask for both subnets of the major network 172.16.0.0/16
                       192.168.1.0/24 is variably subnetted, 2 subnets, 2 masks
                  C       192.168.1.0/25 is directly connected, Loopback1   <--- used a /25 prefix-length
                  C       192.168.1.128/26 is directly connected, Loopback2   <--- used a /26 prefix-length
                  Router#

                   

                  When the same mask or prefix-length was used the routing table showed them as "is subnetted".  Where as when we used a different subnet mask or prefix-length for each the routing table showed them as "is variably subnetted".

                   

                  HTH

                   

                  • 6. Re: "show ip route" shows info "variably subnetted"
                    abenmao

                    thank you for all the input. It's my first question. I was surprised to see so many helpful hands right here. Apologize to Elvin Arias.the system doesn't allow me to give credits to all helpful answers.

                     

                    thank you once again for the time everybody put in. It is so warm here

                    • 7. Re: "show ip route" shows info "variably subnetted"
                      Elvin Arias

                      Hi abenmao,

                       

                      Im not here for the points, just for help!. But will be for the next time .

                       

                      Elvin.