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    SVI

    Tim

      Hello Everyone

       

      I have some question about SVI (switch virtual interface)

       

      Q: I have switch 2960 with VLAN 20 & VLAN 50

      VLAN 10 : ip address 192.168.10.X 

      VLAN 20 ip address 192.168.20.X

       

      With no default gateway I am able to access the my server which is on different VLAN

       

      Can some explain how is working without default gateway my studies you can ping between same VLAN without switch  default-gateway but if any thing going to the different VLAN then they need a default-gateway to route right I am confuse

       

      Please help

       

        • 1. Re: SVI
          Conwyn

          Hi Tim

           

          If you have more than one SVI active then you have a L3 switch.

           

          So inter vlan routing will automatically route between the SVI for vlan A and the SVI for vlan B.

           

          I never realised 2960 supported L3 switch. Are you sure you have not got a router on a stick hiding somewhere.

           

          Proxy arp on the router monitors traffic and if it sees a requested for a route it knows about it replies with his arp and the routes the traffic.

           

          Regards Conwyn

          • 2. Re: SVI
            Keith Barker - CCIE RS/Security, CISSP

            Tim-

             

            To fully answer your question, (accurately), it would be helpful to know:

             

            VLANs on the switch (exactly)

            VLAN interfaces on the switch, including IP address

            Which port the server is connected to, and what VLAN is that port assigned

            What the IP address of the server is

             

            With that info, there is a better chance of getting a meaningful answer, that is also correct.

             

            Let us know.

             

            Keith

            • 3. Re: SVI
              Conwyn

              Hi Keith

               

              2960 is a L2 switch.

               

              Regards Conwyn

              • 4. Re: SVI
                Tim

                Thanks for your Help

                 

                What  happen I have a 3750 switch swith Multiple SVI on it

                 

                VL:21 ----> Accounting Users

                VL:31 ----> IT users

                VL:22 ----> Sales Users

                VL:10 ----> Switch Management VLAN

                 

                and the defaylt-gateway on the switch is 192.168.10.X

                 

                 

                and I have 48 ports distributed in VL:21 , VL:31 & VL:22  and the issues form the switch if I am trying to ping the VL:11 which is monitoring VLAN and I am geeting timeout form my 3750 switch I dont know why but I am doing ping between three VL: 21,22,23 thats fine and when I shudwon the 21,22,31 SVI and then I am able to ping from the 3750 switch to VLAN 111 I have not idea why

                 

                all the vlans are alreayd allowed on the trunk

                 

                This 3750 connected to the core and the core is doing the routing

                 

                can anyone clarify the why is like this

                 

                Thanks

                • 5. Re: SVI
                  Conwyn

                  Hi Tim

                   

                  If you have a 3750 without ip routing then it is a L2 switch

                   

                  ip default-gateway simply allows you to telnet to the management vlan

                   

                  If you have a 3750 with ip routing then it is a L3 switch. default-gateway is ignored. Use ip route 0.0.0.0 0.0.0.0 a.b.c.d  or ip default-network or routing protocol. Inter-vlan routing will occur naturally as well as inter routed port.

                   

                  Regards Conwyn

                  • 6. Re: SVI
                    Tim

                    Thanks for your reply

                     

                     

                    Yes your are right 2960 is just layer 2 switch but why we define multipe SVI on layer switch as we know is not gona perfrom routing  and how the traffic from VLAN A to VLAB will go I think throught the default gate way correct

                     

                    but in my case the 2960 has two vlan 110,100 and SVI are up and the server on 110 VLAN is able to ping across the network and switch and switch have no default-gateway define I have ni idea how they are communicating

                     

                    Please help me out

                     

                    Thanks

                    • 7. Re: SVI
                      Conwyn

                      Hi Tim

                       

                      Please post your config

                       

                      Regards Conwyn

                      • 8. Re: SVI
                        Tim

                        Please see the attchment for 2960 switch this switch have no default-gateway define and servers connected to that switch si fine they can communicate accross the network I have no idea how

                         

                        Please see attchment

                         

                        Thanks

                        • 9. Re: SVI
                          Conwyn

                          Hi Tim

                           

                          2960 do support multiple SVI since 12.2 (something) but not routing. I think traffic is going down gi0/1 and the core is using proxy arp to do the routing for you.

                           

                          Regards Conwyn

                          • 10. Re: SVI
                            Tim

                            Thanks for your help I will appreciate that

                             

                            if you don't mind I have qucik question that let say SVI just for to access the swicth from different VLAN right if I shutdown all the SVI and If I don't define default gateway how gona traffic will travel to different VLAN or diffent switch my asnwer I will get time out because switch dont know how to take the traffic right so It means the default-gateway is used to carry traffic to different vlan or different switch right  if this right then why in some forum says default gateway is used for switch remote management please advise

                             

                            onece again thanks very much for yout time

                             

                            Thanks

                            • 11. Re: SVI
                              Conwyn

                              Hi Tim

                               

                              For a L2 switch such as the 2960 the int vlan x is used for switch management via telnet.

                               

                              default-gateway is used to allow the switch management output to get back to the person doing the telnet.

                               

                              It is nothing to do with inter-vlan routing.

                               

                              It is unfortuate that they call L2 switches SVI they should be called Management VI (MVI) to avoid confusion.

                               

                              I believe you have intervlan routing because your trunk to the core is using proxy-arp on the core. You could switch off g0/1 and see if you still have inter vlan traffic

                               

                              Regards Conwyn

                              • 12. Re: SVI
                                Tim

                                Thanks

                                My last question if you don't mind is there any command to check proxy arp is enbal on my switches Please advise

                                I am very happy I learn new thing

                                Thanks

                                • 13. Re: SVI
                                  Conwyn

                                  Hi Tim

                                   

                                  The proxy arp will be on your router or L3 switch. On the 2960 you have a trunk on 0/1 I assume there is router or L3 switch on the other end

                                   

                                  show ip int gi0/0

                                   

                                  GigabitEthernet0/0 is up, line protocol is up
                                    Internet address is /20
                                    Broadcast address is 255.255.255.255
                                    Helper address is not set
                                    Directed broadcast forwarding is disabled
                                      Proxy ARP is enabled

                                   

                                  Regards Conwyn

                                  • 14. Re: SVI
                                    Tim

                                    Thanks for your Help

                                     

                                    Your are expert

                                     

                                    Thanks

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