DUPADDR problem on the same interface

[robertreymund]

Hello everybody!

I'm trying to configure my network like this:

ISP – (VDSL) Router from ISP in bridge mode – Cisco 876 FastEthernet 3 with VLAN4

This means the VLAN4 will be my WAN interface. VLAN1, 2 and 3 are connected to the internet through VLAN4.

My Problem: The internet is working fine, but after 2-5 minutes I have the following error in the log:

000045: *Jul 23 13:33:12.003 PCTime: %IP-4-DUPADDR: Duplicate address 178.195.XX.XX on Vlan4, sourced by 98d6.bb71.35f1

So I checked the mac-addresses:

routerHome#sh mac-address-table vlan 4

Destination Address  Address Type  VLAN  Destination Port

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

0004.201e.dac6          Dynamic       4     FastEthernet3

001f.9e66.1804          Self          4     Vlan4

0024.932b.1940          Dynamic       4     FastEthernet3

0090.d063.ff00          Dynamic       4     FastEthernet3

0090.d063.ff04          Dynamic       4     FastEthernet3

78d6.f093.ad17          Dynamic       4     FastEthernet3

98d6.bb71.35f1          Dynamic       4     FastEthernet3

routerHome#show arp

Protocol  Address          Age (min)  Hardware Addr   Type   Interface

Internet  178.195.XX.1            1   0090.d063.ff04  ARPA   Vlan4

Internet  178.195.XX.XX           -   001f.9e66.1804  ARPA   Vlan4

Why does the VLAN4 has problems with one of his own mac addresses?

You’ll find my configuration and many other interesting logs in the file “problemdubmac_techsupport.txt”

[Alessio Andreoli]

this is a duplicate

by the way the answer is the same... before issuing show ip arp or show arp you should issu a broadcast :

ping 255.255.255.255

and then issuing again the show arp

HTH

Alessio

[robertreymund]

Thank you for your answer. Here is the output:

routerHome#ping 255.255.255.255

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 255.255.255.255, timeout is 2 seconds:

.....

routerHome#sh arp

Protocol  Address          Age (min)  Hardware Addr   Type   Interface

Internet  192.168.1.1             -   001f.9e66.1804  ARPA   Vlan1

Internet  192.168.1.33            0   f0de.f180.3539  ARPA   Vlan1

Internet  192.168.1.81            0   f0de.f180.3539  ARPA   Vlan1

Internet  192.168.2.1             -   001f.9e66.1804  ARPA   Vlan2

Internet  192.168.3.1             -   001f.9e66.1804  ARPA   Vlan3

How can I prevent this dublicate address problem?

[paolo bevilacqua]

Seems to me the duplicate is some other customer on the same subnet, thing about which you can't do anything.

Complain to ISP and try get him shut down, or your address changed.