07-23-2012 07:40 AM - edited 03-04-2019 05:02 PM
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”
07-23-2012 07:49 AM
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
07-25-2012 12:42 PM
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?
07-25-2012 01:04 PM
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.
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