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12255 Views 6 Replies Latest reply: Apr 3, 2013 3:33 AM by William RSS

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What is a stub network?

Apr 28, 2011 11:21 PM

srijeeb2111 20 posts since
Aug 4, 2010

Can somebody explain to me in details with figure what a stub network is and how it is related to default routing?

  • sid 32 posts since
    Sep 30, 2009
    Currently Being Moderated
    1. Apr 28, 2011 11:47 PM (in response to srijeeb2111)
    Re: What is a stub network?

    Purpose of a stub area is to block external type 5 LSA’s and replace them with a default route.

     

    Read more: http://www.ciscowizard.com/2011/04/ospf-areas.html#ixzz1KtNRWd56

  • Keith Barker - CCIE RS/Security, CISSP 5,351 posts since
    Jul 3, 2009
    Currently Being Moderated
    2. Apr 29, 2011 2:57 PM (in response to srijeeb2111)
    Re: What is a stub network?

    small wan graphic with 624 and extra IPv6.png

     

    Hello-

     

    Looking at the topology, consider R7.   It has some locally connected networks (not all shown), and then 1 path out, for everything else (through the interface ser  0/0.1 that goes up to R1.      R7's networks would be considered (generally speaking) stub networks, as they don't lead to any additional networks.  R7 is the end of the line.

     

    In that light, R7 would be a good candidate to use a default route, with R1 being the next hop, or specifiying that R7's ser0/0.1 should be used for the default route, because everything else (other than locally attached networks) lives off of that interface.

     

    Example:

     

    R7#show ip route     

    <snip>

     

         1.0.0.0/24 is subnetted, 1 subnets

    D       1.1.1.0 [90/2297856] via 23.1.2.137, 02:42:49, Serial0/0.1

         2.0.0.0/24 is subnetted, 1 subnets

    D       2.2.2.0 [90/2809856] via 23.1.2.137, 02:42:49, Serial0/0.1

         3.0.0.0/24 is subnetted, 1 subnets

    D       3.3.3.0 [90/2809856] via 23.1.2.137, 02:42:49, Serial0/0.1

         4.0.0.0/24 is subnetted, 1 subnets

    D       4.4.4.0 [90/2809856] via 23.1.2.137, 02:42:36, Serial0/0.1

         5.0.0.0/24 is subnetted, 1 subnets

    D       5.5.5.0 [90/2809856] via 23.1.2.137, 02:40:44, Serial0/0.1

         6.0.0.0/24 is subnetted, 1 subnets

    D       6.6.6.0 [90/2809856] via 23.1.2.137, 02:42:49, Serial0/0.1

         23.0.0.0/8 is variably subnetted, 6 subnets, 3 masks

    D       23.1.2.148/30 [90/2681856] via 23.1.2.137, 02:42:50, Serial0/0.1

    D       23.1.2.144/30 [90/2681856] via 23.1.2.137, 02:42:50, Serial0/0.1

    D       23.1.2.146/32 [90/2681856] via 23.1.2.137, 02:42:50, Serial0/0.1

    D       23.1.2.128/29 [90/2681856] via 23.1.2.137, 02:42:50, Serial0/0.1

    D       23.1.2.140/30 [90/2681856] via 23.1.2.137, 02:42:50, Serial0/0.1

    C       23.1.2.136/30 is directly connected, Serial0/0.1

         7.0.0.0/24 is subnetted, 1 subnets

    C       7.7.7.0 is directly connected, Loopback0

         9.0.0.0/24 is subnetted, 1 subnets

    D       9.9.9.0 [90/2323456] via 23.1.2.137, 02:42:50, Serial0/0.1

         10.0.0.0/24 is subnetted, 1 subnets

    D       10.19.0.0 [90/2195456] via 23.1.2.137, 02:42:50, Serial0/0.1

    R7#



    R7#ping 23.1.2.150


    Type escape sequence to abort.

    Sending 5, 100-byte ICMP Echos to 23.1.2.150, timeout is 2 seconds:

    !!!!!

    Success rate is 100 percent (5/5), round-trip min/avg/max = 8/12/20 ms

    R7#conf t

    Enter configuration commands, one per line.  End with CNTL/Z.

     

    Now, we can remove the eigrp, and add 1 static route:

     

    R7(config)#no router eigrp 1


    %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 23.1.2.137 (Serial0/0.1) is down: interface down

    R7(config)#ip route 0.0.0.0 0.0.0.0 serial0/0.1

    R7(config)#do show ip route

    Codes: 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


    Gateway of last resort is 0.0.0.0 to network 0.0.0.0


         23.0.0.0/30 is subnetted, 1 subnets

    C       23.1.2.136 is directly connected, Serial0/0.1

         7.0.0.0/24 is subnetted, 1 subnets

    C       7.7.7.0 is directly connected, Loopback0

    S*   0.0.0.0/0 is directly connected, Serial0/0.1

     


    We still have full connectivity.

     

    R7#ping 23.1.2.150


    Type escape sequence to abort.

    Sending 5, 100-byte ICMP Echos to 23.1.2.150, timeout is 2 seconds:

    !!!!!

    Success rate is 100 percent (5/5), round-trip min/avg/max = 4/11/24 ms

    R7#

     

    R1 is directly connected to the WAN networks, which are not stub, as there are more routers with more networks behind them.   As a result, using a default route on R1, wouldn't work.

     

    Best wishes,

     

    Keith

  • Martin 13,077 posts since
    Jan 16, 2009
    Currently Being Moderated
    3. Apr 29, 2011 3:42 PM (in response to srijeeb2111)
    Re: What is a stub network?

    there is ONLY ONE way IN and OUT off Stub routers;

     

    if you Searach this forum for stub router you will find more details;

  • Scott Morris - CCDE/4xCCIE/2xJNCIE 8,398 posts since
    Oct 7, 2008
    Currently Being Moderated
    4. Apr 30, 2011 9:47 PM (in response to srijeeb2111)
    Re: What is a stub network?

    The object of a stub area is to maintain reachability, but limit the overall size of the database (and therefore impact of recalculations on the devices).

     

    Scott

  • William 1 posts since
    Feb 12, 2013

    After looking at several explinations of this now this one makes complete sense, thanks Keith for clearifying!

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