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Enthusiast

ARP "incomplete" entry

Hi,

I plugged an IP device into a 2960 Catalyst switch. The port is up, but there is no MAC address learned on it:

TNSWAGCS01002(config-if)#do sh mac add int fa0/16

          Mac Address Table

-------------------------------------------

Vlan    Mac Address       Type        Ports

----    -----------       --------    -----

TNSWAGCS01002(config-if)#

TNSWAGCS01002(config-if)#do sh int fa0/16

FastEthernet0/16 is up, line protocol is up (connected)

  Hardware is Fast Ethernet, address is 0064.40ee.f510 (bia 0064.40ee.f510)

  Description: --- STC ---

  MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec,

     reliability 255/255, txload 1/255, rxload 1/255

  Encapsulation ARPA, loopback not set

  Keepalive set (10 sec)

  Half-duplex, 10Mb/s, media type is 10/100BaseTX

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

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

  Last input never, output 00:00:01, output hang never

  Last clearing of "show interface" counters never

  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0

  Queueing strategy: fifo

  Output queue: 0/0 (size/max)

  5 minute input rate 0 bits/sec, 0 packets/sec

  5 minute output rate 0 bits/sec, 0 packets/sec

     14432 packets input, 923648 bytes, 0 no buffer

     Received 1392 broadcasts (0 multicasts)

     0 runts, 0 giants, 0 throttles

     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored

     0 watchdog, 0 multicast, 0 pause input

     0 input packets with dribble condition detected

     48956 packets output, 3586289 bytes, 0 underruns

     0 output errors, 0 collisions, 18 interface resets

     0 babbles, 0 late collision, 0 deferred

     0 lost carrier, 0 no carrier, 0 PAUSE output

     0 output buffer failures, 0 output buffers swapped out

TNSWAGCS01002(config-if)#

TNSWAGCS01002(config-if)#

interface FastEthernet0/16

description --- STC ---

switchport access vlan 1400

switchport mode access

switchport port-security

switchport port-security violation restrict

switchport port-security mac-address sticky

priority-queue out

mls qos trust cos

spanning-tree portfast

spanning-tree bpduguard enable

end

I read that it may be a L1/L2 issue. We tried with another ethernet cable. We also tried with another IP device of the same model. That did not solve the issue.

Any idea would be appreciated.

Wass

2 REPLIES 2
Highlighted
Advisor

Hi,

what is happening if you ping any IP from this device ?

Regards.

Alain

Don't forget to rate helpful posts.
Highlighted

Hi Alain,

There are no issues with this switch. One of the symptoms of the issue is that a ping from the gateway to the host fails. The ARP "incomplete" entry appears on the connected router:

Internet  10.101.13.62            -   1cdf.0f1a.4258  ARPA   GigabitEthernet0/0.1300

Internet  10.101.13.65            0   Incomplete      ARPA  

Internet  10.101.13.70            -   1cdf.0f1a.4258  ARPA   GigabitEthernet0/0.1400

I did ARP debugs:

- debug arp

- debug arp table

- debug arp interface

- debug arp database

The debug output is in the file attached. Please note that:

- the IP address of the device generating the "incomplete ARP" is 10.101.13.65

- the IP address of the gateway is 10.101.13.70 (subinterface on the branch router)

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