1 Reply Latest reply: Nov 29, 2011 12:09 PM by Conwyn RSS

    802.1q trunk shows ARPA encapsulation. WHY?

    bearMedicine - CCNA

      Hi

       

      I have a weird situation where a trunk link is working in a lab environment. One end of the trunk is configured as an 802.1q trunk, yet it shows ARPA encapsulation in the 'show interface' command output. The other end of the link is not even configured as a trunk, yet it shows 802.1q encapsulation in its 'show interface' output. Can someone please explain this? Can ARPA and 802.1q interwork?

       

      Config and command output is shown below:

       

      "r1" (real names have been changed to protect the innocent   ) is a 7200.

      "r2" is a 4000 series switch

       

      r1#sh run int fa1/1

      Building configuration...

       

       

      Current configuration : 88 bytes

      !

      interface FastEthernet1/1

      description r2 3/25

      no ip address

      duplex full

      end

       

       

      r1#sh int fa1/1

      FastEthernet1/1 is up, line protocol is up

        Hardware is AmdFE, address is 000e.382d.f51d (bia 000e.382d.f51d)

        Description: r2 3/25

        MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,

           reliability 255/255, txload 7/255, rxload 6/255

        Encapsulation 802.1Q Virtual LAN, Vlan ID  1., loopback not set

        Keepalive set (10 sec)

        Full-duplex, 100Mb/s, 100BaseTX/FX

        ARP type: ARPA, ARP Timeout 04:00:00

        Last input 00:00:00, output 00:00:00, output hang never

        Last clearing of "show interface" counters never

       

       

      r2#sh run int gi3/25

      Building configuration...

       

       

      Current configuration : 170 bytes

      !

      interface GigabitEthernet3/25

      description Link to r1 fa1/1

      switchport trunk encapsulation dot1q

      switchport mode trunk

      load-interval 30

      duplex full

      speed 100

      end

       

       

      r2#sh int gi3/25

      GigabitEthernet3/25 is up, line protocol is up (connected)

        Hardware is Gigabit Ethernet Port, address is 0018.7306.2a88 (bia 0018.7306.2a88)

        Description: Link to r1 fa1/1

        MTU 1500 bytes, BW 100000 Kbit, DLY 10 usec,

           reliability 255/255, txload 7/255, rxload 8/255

      Encapsulation ARPA, loopback not set

        Keepalive set (10 sec)

        Full-duplex, 100Mb/s

        input flow-control is off, output flow-control is off

        ARP type: ARPA, ARP Timeout 04:00:00

        Last input 00:00:27, output never, output hang never

        Last clearing of "show interface" counters never

       

      Thanks, Bear