Skip navigation
Cisco Learning Home > Certifications > Routing & Switching (CCNA) > Discussions

_Communities

This Question is Answered
5651 Views 7 Replies Latest reply: Sep 9, 2011 8:52 AM by Elvin Arias RSS

Currently Being Moderated

"show ip route" shows info "variably subnetted"

Sep 7, 2011 6:11 AM

abenmao 2 posts since
Sep 7, 2011

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

  • cadetalain 2,642 posts since
    Sep 18, 2008
    Currently Being Moderated
    1. Sep 7, 2011 7:55 AM (in response to abenmao)
    Re: "show ip route" shows info "variably subnetted"

    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.

  • Keneil Facey 200 posts since
    Oct 1, 2010
    Currently Being Moderated
    2. Sep 7, 2011 1:23 PM (in response to abenmao)
    Re: "show ip route" shows info "variably subnetted"

    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

  • Elvin Arias 1,855 posts since
    Mar 12, 2010
    Currently Being Moderated
    3. Sep 7, 2011 8:56 PM (in response to abenmao)
    Re: "show ip route" shows info "variably subnetted"

    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

  • Brian 2,968 posts since
    Aug 17, 2009
    Currently Being Moderated
    4. Sep 7, 2011 11:26 PM (in response to abenmao)
    Re: "show ip route" shows info "variably subnetted"

    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

  • Brian 2,968 posts since
    Aug 17, 2009
    Currently Being Moderated
    5. Sep 7, 2011 11:42 PM (in response to Brian)
    Re: "show ip route" shows info "variably subnetted"

    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

  • Elvin Arias 1,855 posts since
    Mar 12, 2010
    Currently Being Moderated
    7. Sep 9, 2011 8:52 AM (in response to abenmao)
    Re: "show ip route" shows info "variably subnetted"

    Hi abenmao,

     

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

     

    Elvin.

Actions

More Like This

  • Retrieving data ...

Bookmarked By (0)