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6257 Views 14 Replies Latest reply: Apr 28, 2009 5:38 PM by Erick RSS

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CAN'T PING ACROSS SWITCH

Apr 28, 2009 2:13 PM

Stephanie 49 posts since
Nov 10, 2008

Alright I have just had it with this problem. Sometimes like when I first start my day with labs I can set my ethernet interfaces on my routers with an IP addrss plug them into a switch and bam I can ping across. Today I made a vlan put my interfaces in the newly created vlan and yes I could still ping. Yet today is no different then any day, the afternoon arrives and I get to another lab where I want to ping across my ethernet interfaces leave them in the default vlan no ping, make a new vlan no ping.

I know it doesn't have to do with the time of day but every afternoon my steady speed comes to a grinding hault. Usually I say whatever and put them in a vlan then give the vlan an ip address and then continue, without any rhyme or reason but dead frustrated. Now I've come to a lab where I can no longer ignore the fact that it just doesn't work. I'm taking my test in a few days. I do not want this to be an issue that prevents me from passing. Though I doubt their equipment will be as quarky as mine. The lab I am trying to configure now has all ethernet interfaces configured with different ip network addresses, but they still need to ping. I have frame relay running, and rip v2 on 2 of my routers. One of my routers does not have an interface to connect to my frame switch and therefore needs to broadcast it's Rip update packets through the ethernet. I shut my serial interfaces just to make sure it wasn't just that one router causing me trouble.

Someone anyone, I've got to get this resolved.

And I can't do a simple copy paste to show my configs, so what do I do about that?

  • Currently Being Moderated
    2. Apr 28, 2009 2:42 PM (in response to Stephanie)
    Re: CAN'T PING ACROSS SWITCH

    With regards to you RIP problem:

     

    Are the interfaces sharing the updates on the same subnet?

     

    You can use the no validate-update-source command in router configuration mode to see if that helps, but I would be careful with this command as it may indicate problems with the IP addressing scheme used.

  • Currently Being Moderated
    4. Apr 28, 2009 2:50 PM (in response to Stephanie)
    Re: CAN'T PING ACROSS SWITCH

    No.  I don't believe so, but if I am wrong I'm sure one of the experts will jump in and correct me.  I am pretty sure if is for classful routing protocols that share update information regularly.  Link-state protocols only share routing nforamtion if there is a change in the network topology and the routers must become neighbors based on a set of criteria which depends on the protocol.  Once the routers reach a neighbor state, there is no need to validate a routing update because they are already considered neighbors.

     

    HTH

     

    Erick

  • Currently Being Moderated
    6. Apr 28, 2009 3:14 PM (in response to Stephanie)
    Re: CAN'T PING ACROSS SWITCH

    Can you give a copy of your running-cong and your show ip route results?  How may routers are you using?  Do you have RIP running over frame-relay?  If you you may in fact be having a split horizon issue.  Try the no ip split-horizon command if you are configuring RIP over frame-relay.  If you are configuring RIP over ethernet, I would try plugging your router into a different switch port and work your way up from layer one until you get to layer 3.

  • Paul Stewart  -  CCIE Security, CCSI 6,986 posts since
    Jul 18, 2008
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    7. Apr 28, 2009 3:10 PM (in response to Stephanie)
    Re: CAN'T PING ACROSS SWITCH

    I would first determine if this is a hop by hop issue that is causing the routing table to not update, or if the routing table is not updating and causing an end to end issue.  Try pinging devices that are on the same layer 3 network.  If this fails, troubleshoot it from layer to.  Look at the ARP cache on the layer 3 devices and the mac address tables in the switch (show mac-address-table).  Adjacent connectivity of the layer three devices needs to be in tact before you get to concerned about troubleshooting the routing table.  On the positive side, this is an excellent troubleshooting opportunity for you to work through.

  • Paul Stewart  -  CCIE Security, CCSI 6,986 posts since
    Jul 18, 2008
    Currently Being Moderated
    10. Apr 28, 2009 5:14 PM (in response to Stephanie)
    Re: CAN'T PING ACROSS SWITCH

    I'm not sure I follow you now.  You have 3 subnets in one vlan.  They cannont reach each other via this vlan because they are on different subnets.  They could route through the rest of the network (if the routers have another physical path).  However, if any router that the packet would traverse has a route through this vlan to a discontiguous address, it will not work.  This could happen if the router is not properly validating the source before inserting it into the route table. In other words if it receives a route update to an address that it is not connected to.  It could recursively route, but you will have a lot of stange issues. Basically, the three interfaces posted in the trouble.doc will not communicate with each other and should not be in the same vlan.

  • Currently Being Moderated
    11. Apr 28, 2009 5:21 PM (in response to Stephanie)
    Re: CAN'T PING ACROSS SWITCH

    Hi!

     

    I am assuming that R1 and R2 are connected to a switch with their ethernet interfaces?

     

    Why do you have your ethernet interfaces configured to be on different subnets if they are on the same segment? Turn RIP off completely and try configuring your routers that are connected to the switch to be on the same subnet and then try pinging from there?  If pings are successful, try configuring loopback interfaces on your routers and advertise your loopback interfaces into RIP

     

    Erick

  • Currently Being Moderated
    14. Apr 28, 2009 5:38 PM (in response to Stephanie)
    Re: CAN'T PING ACROSS SWITCH

    No problem.  I hope it works out.

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