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

    CAN'T PING ACROSS SWITCH

    Stephanie

      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?

        • 1. Re: CAN'T PING ACROSS SWITCH
          Stephanie

          I did a debug ip rip on the router that only has the ethernet connection the output is telling me that it is ignoring the v2 updates because it is coming from a bad source. Why is it a bad source, and how do I make it a good source?

          • 2. Re: CAN'T PING ACROSS SWITCH
            Erick

            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.

            • 3. Re: CAN'T PING ACROSS SWITCH
              Stephanie

              No, and I found something. Yea I issued the no validate-update-source command. Granted this is the first RIP config that I encountered this problem with. The command worked. I never heard of it before, but I was looking around and found it. Will this work on other routing protocols?

              • 4. Re: CAN'T PING ACROSS SWITCH
                Erick

                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

                • 5. Re: CAN'T PING ACROSS SWITCH
                  Stephanie

                  My routing tables still aren't updating completely. I have to take a break, then I am going to see if split horizon has anything to do with it, but I don't think it should at this point. I have to investigate. Like I said this is the first lab that RIP is my protocol running. Actually this is the first lab with any networking protocol running. There has to be something else, because before the interfaces were on the same subnet and I couldn't ping across the switch, and basically that was the jist of my configuration, so let me know if you have any other ideas. The switch always see's the CDP neighbors, but still wouln't carry a ping over to the routers.

                  • 6. Re: CAN'T PING ACROSS SWITCH
                    Erick

                    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.

                    • 7. Re: CAN'T PING ACROSS SWITCH
                      Paul Stewart  -  CCIE Security

                      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.

                      • 8. Re: CAN'T PING ACROSS SWITCH
                        Stephanie

                        Here are my runs. I can ping across Serial links that are configured for the same network. My ethernets are configured for the different networks, and I can no longer ping. Please take a look.

                        • 9. Re: CAN'T PING ACROSS SWITCH
                          Stephanie

                          Since I came back from my break the router with no serial link can't ping the other routers anymore. Please take a look. I'm telling you the devices know how to get to the addresses, but they are not be forwarded and their interfaces are in vlan 2 that I created. I could do anoher scenario where all the ethernets are in the same subnet and interfaces on the switch are access for the same vlan and they won't ping. It's got to be within the switch, I did change it to vtp transparent before I left, I turn it back to server, but no difference, and I really don't think that should be of a matter since I'm only using 1 switch.

                          • 10. Re: CAN'T PING ACROSS SWITCH
                            Paul Stewart  -  CCIE Security

                            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.

                            • 11. Re: CAN'T PING ACROSS SWITCH
                              Erick

                              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

                              • 12. Re: CAN'T PING ACROSS SWITCH
                                Stephanie

                                O'kay, there's logic. I'm glad to have it solidified in my mind. So basically, this lab I'm looking at isn't so good. This is all well and good, but would you please keep your eye out for my next post. I'm going to go back and configure a much simpler lab where this was my trouble, and logically it should have worked, but I ended up changing the vlan to have an ip address which I shouldn't have to do if the interfaces are configured for the same network. So bare with me if you're available to, because this question, yes has been answered, and I thank you, but my head against the wall is going to continue..

                                • 13. Re: CAN'T PING ACROSS SWITCH
                                  Stephanie

                                  Yes this is exactly what I'm going to do, you've been right thus far, but hang on while I do another quick config. Don't you know that I'm going to do it this time and it will probably work, because I've got help. If it does I will be back. This problem has arrisin too many times when the ethernets are configured for the same network, so if it does work now, I will be back, probably afternoon time.

                                  • 14. Re: CAN'T PING ACROSS SWITCH
                                    Erick

                                    No problem.  I hope it works out.