ARP detstination mac-address 0000.0000.0000

Unanswered Question

Internet Router--->3550 Switch-->Nortel Contivity>>

All the devices are having public IP addresses and are in Vlan 100.

Sometimes the Internet Router is not able to ping or connect to the Contivity where as the switch is able to access both the devices (Internet Rtr & Contivity).

While checking on the switch & Internet rtr i capture the following logs.

Switch#sh log

Mar 25 11:17:17.990 EDT: IP ARP: creating incomplete entry for IP address: interface Vlan100

Mar 25 11:17:17.990 EDT: IP ARP: sent req src 0012.800b.a780,dst 0000.0000.0000 Vlan100

Internet RTR#sh log

Mar 25 11:17:17 EDT: IP ARP: rcvd req src 0012.800b.a780, dst GigabitEthernet0/1

Mar 25 11:20:54 EDT: IP ARP: rcvd req src 0018.b964.66fc, dst GigabitEthernet0/1

We have done a static ARPA entry in internet rtr for Contivity but still the issue remains same. The moment the issue persists again i tried to clear the arp on switch but it didn't make router to get reply from Contivity when i did the same clear arp-cache on internet rtr, it started getting communicate with Contivity.

I am not able to find the solution of this issue and the reason for that, now every time i have to do clear ip arp-cache on rtr whenever the issue comes down.

Also i want to understand the situation when a dest mac-address can be 0000.0000.0000.

Any help on this will be appreciated.


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Richard Burts Wed, 03/26/2008 - 08:17
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I am not clear what the issue is with Contivity. When you have the problem would you do show arp before you do the clear arp and see what is in the arp table for that address?

The other part of your question is more easy to answer. When you send an arp request you know the destination IP address that you want to reach but do not know the destination MAC address. So in the arp request the destination MAC address is all zero (zero because you do not know what it is).




Thanks for you reply on this.

The outage issue between rtr & contivity use to get resolve when i do clear arp on rtr, at the time of this outage i have checked the arp entry on rtr. Since it is a manual entry on rtr, it shows as same it show in working nature.

in the outage time:

Internet rtr can't ping to contivity.

switch can ping to internet rtr and contivity.

contivity can't ping to internet rtr.

There is one more logs which are related to "creating incomplete entry for IP address:" when this can be generate?

Your provided information is helpout me to understand dst mac all zero. Thanks

Richard Burts Wed, 03/26/2008 - 08:55
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If a router receives a packet to forward to a destination address which is on a local LAN but the destination IP address does not appear in the arp table then the router creates an incomplete entry in the ARP table (it is incomplete because the router does not have the destination MAC address and is attempting to learn it). The router creates the incomplete entry in the ARP table and sends an ARP request. If the router receives an ARP response then it puts the destination MAC address into the ARP table and the entry is now complete. If no ARP response is received the router will purge the incomplete entry. Note that the router can not forward the IP packet that caused the incomplete entry and the router will drop that IP packet.

In considering the problem with contivity I had been assuming that the problem was on rtr. But it occurs to me that it is quite possible (and even likely given the fact that you mention which is that in the problem the switch can still ping contivity ) that the problem is on contivity. I wonder if for some reason contivity gets an incorrect MAC for rtr? I suspect that clear arp on rtr fixes the problem because as it clears the arp table I believe that rtr will send a gratuitous arp which refreshes the ARP entry in contivity. In the time of the problem can you check the table in contivity?



Hi Rick,

The ownership of contivity is not under my supervision, there is a diffrent team to manage contivity. Still i'll ask them to check the ARP table on contivity, if there is any available option for that, at the time of outage. Sometimes this outage get restored itself after couple of minutes, we have started clearing arp process from past 2-3 days only.

Thanks rick i'll get back to you with the ARP table information on the contivity soon..

alsarinetworks Wed, 09/24/2014 - 03:59
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To do this more clear, the devices involved are:

Internet Router   --->3550 Switch        -->Nortel Contivity -->>

How is the connection scheme? Is configured in interface vlan 100 on switch, and rtr and Contivity conenected to L2 switch ports assigned to vlan 100? o are the three devices connected to a fourth device via L2 switch ports?

On the oterh hand, ¿who is


vijaysiwan17 Wed, 09/24/2014 - 08:47
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It is permanent or sometime ping problem between Internet router and NC  Rupesh?



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