5 Replies Latest reply: Feb 19, 2019 1:58 AM by Sergey RSS

    L3 interface with encapsulation dot1q

    Mickael

      Hello everyone,

       

      I have a question regarding the following configuration :

      interface Ethernet1/54.4

        description IPN-POD2

        mtu 9150

        encapsulation dot1q 4

        medium p2p

        vrf member fabric-mpod

        ip unnumbered loopback0

        ip ospf dead-interval 3

        ip ospf hello-interval 1

        ip ospf network point-to-point

        ip router ospf 1 area 0.0.0.0

        ip pim sparse-mode

        no shutdown

       

      Some colleagues told me that the encapsulation dot1q 4 is only local to the interface and is not corresponding to "Vlan 4"
      Is this right?

       

      I'm a bit confused about it

       

      Thanks

       

      Mickael

         
        • 1. Re: L3 interface with encapsulation dot1q
          Sergey

          Mickael,

           

          The encapsulation and VLAN number on the subinterface means that the subinterface will tag outgoing packets with VLAN 4 tag and will expect received packets to have a tag of 4 as well. It is not clear what you mean by "corresponding to VLAN 4". If this is a router, then routers don't have VLAN databases, as switches do, so in that respect it is correct. There is no VLAN 4 existing as a layer 2 entity on the router. Instead, it can use VLAN tags on subinterfaces to differentiate multiple connections on a single physical interface.

          • 2. Re: L3 interface with encapsulation dot1q
            Mickael

            For exemple if i Have 2 L3 switch with the configuration above

            Does that mean if I add a host in access vlan4, do the show mac adresse table will short the mac of host and the one of the links between the 2 switch?

            • 3. Re: L3 interface with encapsulation dot1q
              Conwyn

              Hi Mickael

               

              For a L3 switch

               

              config t

              vlan 4

              int vlan4

              ip address ...

               

              int Ethernet1/54

              switch mode trunk

              switchport trunk add vlan 4

               

              You can trunk as many vlans as you wish.

               

              Regards Conwyn

              • 4. Re: L3 interface with encapsulation dot1q
                Mickael

                Yes I know but I tried the following :

                interface Ethernet1/54.4

                  description IPN-POD2

                  mtu 9150

                  encapsulation dot1q 4

                  medium p2p

                  vrf member fabric-mpod

                  ip address 1.1.1.1/30

                  ip ospf dead-interval 30

                  ip ospf hello-interval 1

                  ip ospf network point-to-point

                  ip router ospf 1 area 0.0.0.0

                  ip pim sparse-mode

                  no shutdown

                 

                On both switches with ip 1.1.1.1 and 1.1.1.2
                Once I create the instance vlan 4 on the switches , and I do show mac address-table vlan 4 , I dont see the mac of 1.1.1.1 and 1.1.1.2, why?

                • 5. Re: L3 interface with encapsulation dot1q
                  Sergey

                  Mickael,

                   

                  The switches don't support sub-interface configurations. On the switch you can either have a Layer 3 port with no subinterfaces or you can have VLANs with SVI interfaces in each corresponding VLAN.