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5275 Views 13 Replies Latest reply: Jul 12, 2012 6:06 AM by Brian RSS

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Static Route Question

Mar 22, 2013 9:47 AM

Brian 22 posts since
Feb 7, 2010

I have a question regarding static routing. Using packet tracer I created 3 routers, R1, R2, R3 and each router has a switch attached, with one host on each switch. Now the host I have attached can ping everyone on the network but R1 cannot ping R3 and vice versa. I don't understand why the hosts can ping everything on the network but R1 and R3 cannot ping one another unless I add an additional static route under R1 200.100.30.0 /30 193.168.21.2 and for R3 193.168.21.0 /30 200.100.30.1.

Below is the syntax that allows all the host to ping through the network except R1 cannot ping R3.
R1                                               R2                                                       R3
Fa 0/0: 182.0.0.1 /16                   Fa0/0:195.0.0.1 /24                    Fa0/0: 196.0.0.1 /24
S0/0: 193.168.21.1 /30                S0/0: 200.100.30.1 /30                S0/0: 200.100.30.2
                                                  S0/1: 193.168.21.2 /30

The static route I have on
R1 195.0.0.0 /24 193.168.21.2
      196.0.0.0 /24 193.168.21.2

R2 196.0.0.0 /24 200.100.30.2
      182.0.0.0 /16 193.168.21.1

R3: 182.0.0.0 /16 200.100.30.1
       195.0.0.0 /24 200.100.30.1

 

Thanks,

Brian

  • Keith Barker - CCIE RS/Security, CISSP 5,351 posts since
    Jul 3, 2009
    Currently Being Moderated
    1. Aug 24, 2010 7:27 PM (in response to Brian)
    Re: Static Route Question

    Hello Brian-

     

    You can PING from R1 to R3, just not to the interface on the serial interface of R3, from the serial interface of R1.

     

    From R1 if you ping 196.0.0.1 and source the ping from R1's 182.0.0.1 the ping will work.

     

    The problem is that R1 doesn't have a route to the serial interface of R3, and R3 doesn't have a route to the serial interface of R1.

     

    On R1, if you issue a "show ip route" you will notice there is no route to the 200.100.30.0/30 network.   And on R3, you will see that there is no route back to the 196.168.21.0/30 network that R1 is connected to.

     

    Best wishes,

     

    Keith Barker

  • suntao 1 posts since
    Jun 3, 2010
    Currently Being Moderated
    3. Aug 24, 2010 8:17 PM (in response to Brian)
    Re: Static Route Question

    In your situation, R1 only recognize three networks, it does not know how to get R3, if  static route  200.100.30.0 /30 193.168.21.2  is not added.

    but I think there is a better way to do that:

     

    R1: 0.0.0.0 0.0.0.0 193.168.21.2

     

    R2: 196.0.0.0 /24 200.100.30.2
          182.0.0.0 /16 193.168.21.1

     

    R3: 0.0.0.0 0.0.0.0 200.100.30.1

     

     

    best regards

  • Keith Barker - CCIE RS/Security, CISSP 5,351 posts since
    Jul 3, 2009
    Currently Being Moderated
    5. Aug 24, 2010 8:41 PM (in response to Brian)
    Re: Static Route Question

    From R1 I ping 196.0.0.1 which failed. I have a host attached to R1 which can ping 196.0.0.1 which is why I am confuse, shouldn't the host ping fail as well since there is no route in the routing table?

     

    Hello Brian-

     

    Excellent question.

     

    I want you to pretend you are literally R3.   You have routes to the 196 and 200 networks because you are attached to them.   You also have routes to the 182 and 195 networks, because you have static routes for those.

     

    So now for the fun part.

     

    The PC, on the 182 network pings you.  Do you know how to reply to the PING at 182?  Yes, you have a static route.

     

    Now R1 pings you, (and he sources his ping from his serial interface at 193.168.21.1).   Do you (playing the part of R3) know how to return the PING packet to the 193 network?  No.  You only know about how to reach networks 196, 200, 182 and 195.

     

    In reality, R1 couldn't ping R3 at the 200 network address interface, because R1 doesn't have a route there either.

     

    Does that help?

     

    Keith Barker

  • Keith Barker - CCIE RS/Security, CISSP 5,351 posts since
    Jul 3, 2009
    Currently Being Moderated
    6. Aug 24, 2010 8:43 PM (in response to Brian)
    Re: Static Route Question

    I see that R1 only recognizes three networks, 196.0.0.0 network is one of those network that R1 recognizes so shouldn't the ping work?. I have a host attached to R1 and from the host I can ping 196.0.0.1 but from R1 the ping fails. Im still a bit confuse with this since R1 does not know how to get to R3 shouldn't the host that is attached to R1 ping fail as well because I don't have the 200.100.30.0 network in the routing table?

    Take a look at my earlier post, from a few minutes ago. 

     

    Do you still have questions?

     

    Keith

  • Wendell Odom 342 posts since
    Jun 19, 2008
    Currently Being Moderated
    8. Aug 25, 2010 3:07 AM (in response to Brian)
    Re: Static Route Question

    Brian,

    when you say "it gets dropped by R2"... where are you doing the trace command, what options are you using, and what's the last IP address shown in the output? The reason I ask is that the last IP address listed in trace output doesn't translate to "that router dropped the packet".

     

    I would have expected that if you did the trace from R1, it would list R2's serial IP address (193.168.21.2), and then just asterisks, which doesn't mean that it got dropped by R2 necessarily. If R2's serial is the last IP address shown, it means it either got dropped by R2 due to no route, or the packet was dropped in the data plane (eg, ACL) between R2 and R3, or that R3 doesn't have a route to the source of the original packet  (193.168.21.1 if you didn't tell the trace command to use R1'a Fs0/0 as the source), or the packet is dropped in the data plane on the way back from R3 to R1. In this case, if on R1 you did simply "trace x", where X is an address on R3's LAN, and you see 193.168.21.2 and no more, from earlier discussion, it's the same problem as with your original ping - R3 has no route back to R1's serial IP of 193.168.21.1. Try on R1 "trace x source f0/0".

  • Keith Barker - CCIE RS/Security, CISSP 5,351 posts since
    Jul 3, 2009
    Currently Being Moderated
    9. Aug 25, 2010 8:31 AM (in response to Brian)
    Re: Static Route Question

    I understand it now! Just one more question from R1 pinging R3 196 network I performed a traceroute to see where the packet gets dropped. I notice it gets dropped by R2. Since R1 has a route to 196, shouldn't it be able to get to R3 network and then get dropped because there is no route back to R1?

    Hello Brian -

     

    When you did a trace from R1 to the 196 address of R3, if you saw a return of the IP address from R2, that means R2 can reach you.   It is the missing IP address of R3 in the results of the trace, that indicate R3 can't get back to the 193 network of R1.

     

    Wendell's comments are spot on.

     

    Best wishes,

     

    Keith Barker

  • zeroone 253 posts since
    Jan 13, 2010
    Currently Being Moderated
    10. Aug 25, 2010 8:38 AM (in response to Brian)
    Re: Static Route Question

    Is that a way you can send me packet tracer file you are working? I would like to troubleshoot. Thanks.

  • devaprem 29 posts since
    Apr 8, 2010
    Currently Being Moderated
    12. Jul 11, 2012 3:26 AM (in response to Brian)
    Re: Static Route Question

    Hi All

     

    I have one more question ,  is this route ( an additional static route under R1 200.100.30.0 /30 193.168.21.2)  really needed for this setup to work , i dont think so because the static entry on R3 (R3 193.168.21.0 /30 200.100.30.1) is enough for the succesfull ping between R1 to R3 .

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