Solved

"clear arp" can not clear arp in router or switch

Posted on 2013-06-16
8
652 Views
Last Modified: 2013-06-18
Hi Expert
Here is a question. After I used command "clear arp", I found the output of show arp is still same and did not have any change in router or switch. It looks like the command only can clear Age time, and cannot clear mac address. How to clear mac address ? Anyone can give me some suggestion ? Thank you

R1#sh arp
Protocol  Address          Age (min)  Hardware Addr   Type   Interface
Internet  10.0.0.11               0   c218.26d8.0000  ARPA   FastEthernet1/1
Internet  10.0.0.3                0   c219.26d8.0000  ARPA   FastEthernet1/1
Internet  10.0.0.1                -   c214.2070.f101  ARPA   FastEthernet1/1
0
Comment
Question by:EESky
  • 3
  • 3
  • 2
8 Comments
 
LVL 9

Expert Comment

by:Sandeep Gupta
ID: 39253181
clear ip arp

clear counters
0
 

Author Comment

by:EESky
ID: 39254540
The both commands can not work for the situation
0
 
LVL 4

Assisted Solution

by:MarcusSjogren
MarcusSjogren earned 500 total points
ID: 39254616
If "clear arp" and "clear ip arp" doesn't clear the output for "show arp" and "show ip arp" it means that your router is communicating with the IP addresses.

Could for instance be via Cisco CDP or similar which is running automatically in the background with a discovery function.

Marcus
0
PRTG Network Monitor: Intuitive Network Monitoring

Network Monitoring is essential to ensure that computer systems and network devices are running. Use PRTG to monitor LANs, servers, websites, applications and devices, bandwidth, virtual environments, remote systems, IoT, and many more. PRTG is easy to set up & use.

 
LVL 4

Expert Comment

by:MarcusSjogren
ID: 39254625
show arp will show you arp-table for all protocols including apple talk etc.
Show ip arp will only show IP to MAC bindings.
0
 

Author Comment

by:EESky
ID: 39255245
Yes, the command "clear arp" does not has the function which delete the record of relation of ip address and mac address. it can only update the age time of it. but it looks like that the cdp also cannot do that
0
 
LVL 4

Accepted Solution

by:
MarcusSjogren earned 500 total points
ID: 39255327
Hi,

May I ask why this is such a big issue for you? Both CDP and ARP feature automatic discovery functions and the discovery function cannot be removed.
Hence, the ARP table will have entries.

Type "arp -a", "arp -d *" and "arp -a" on your Windows PC, you will see a similar behavior.

Can you specify what devices 10.0 0.1,10.0.0.3 and 10.0.0.11 is?

Marcus
0
 
LVL 9

Expert Comment

by:Sandeep Gupta
ID: 39255756
try this as well

clear arp-cache

remember default arp timeout is 4hrs.
0
 

Author Comment

by:EESky
ID: 39257328
To Marcus, You are right. Thank you. And i found that once i changed ip address or mac address, the neighbor of the device can change the its own arp table immediately. it looks like that arp protocol send update message to neighbor so fast and frequently.
0

Featured Post

PRTG Network Monitor: Intuitive Network Monitoring

Network Monitoring is essential to ensure that computer systems and network devices are running. Use PRTG to monitor LANs, servers, websites, applications and devices, bandwidth, virtual environments, remote systems, IoT, and many more. PRTG is easy to set up & use.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
checking for updates 11 68
Multicast on 3750x cisco router 1 38
access vs trunk with voice vlan 2 44
Cisco switch suggestion 5 47
Creating an OSPF network that automatically (dynamically) reroutes network traffic over other connections to prevent network downtime.
Quality of Service (QoS) options are nearly endless when it comes to networks today. This article is merely one example of how it can be handled in a hub-n-spoke design using a 3-tier configuration.
After creating this article (http://www.experts-exchange.com/articles/23699/Setup-Mikrotik-routers-with-OSPF.html), I decided to make a video (no audio) to show you how to configure the routers and run some trace routes and pings between the 7 sites…
After creating this article (http://www.experts-exchange.com/articles/23699/Setup-Mikrotik-routers-with-OSPF.html), I decided to make a video (no audio) to show you how to configure the routers and run some trace routes and pings between the 7 sites…

776 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question