cancel
Showing results for 
Search instead for 
Did you mean: 
cancel
3573
Views
0
Helpful
2
Replies

ARP "incomplete" entry

Wassim Aouadi
Level 4
Level 4

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

cadet alain
VIP Alumni
VIP Alumni

Hi,

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

Regards.

Alain

Don't forget to rate helpful posts.

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)

Getting Started

Find answers to your questions by entering keywords or phrases in the Search bar above. New here? Use these resources to familiarize yourself with the community:

Innovations in Cisco Full Stack Observability - A new webinar from Cisco