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arp entry after copy tftp command

Hello,

We have a system in VLAN 1, it has IP 146.103.0.113. The catalysts have interface VLAN1 disabled and no ip address assigned. Sometimes, we cannot SSH or telnet from itnetadm towards the catalysts. We can do so from another system called Monalisa (, 146.103.0.112, you can ssh from itnetadm towards monalisa). When this condition exists, and I do a show ARP on the catalyst, I can see the MAC address of itnetadm directly in the ARP cash of the switch on its VLAN 1 interface. That is the reason why the ssh does not work: the switch answers the ssh tcp setup directly, because it has a direct ARP entry, but I don't know why. Bug? There is no reason why the switch has an ARP entry of a node on another subnet.

Itnetadm is also syslog server and tftp server. We can induce  this situation by doing a copy run tftp://146.103.0.113/test.cfg on the cli. After doing that, the arp entry of itnetadm apprears again (for no reason in my opinion) in the ARP cahce, but this time, on vlan 142, with the MAC address of the router instead of the MAC address of Itnetadm.

See the result in the arp table:

cat5131#sh arp

Protocol  Address          Age (min)  Hardware Addr   Type   Interface

Internet  10.14.2.1              44   0000.0c07.ac8e  ARPA   Vlan142

Internet  10.14.2.118             -   7cad.7431.2941  ARPA   Vlan142

Internet  146.103.0.113           7   0017.a4a7.effc  ARPA   Vlan1

cat5131#

cat5131#clear arp

cat5131#

cat5131#

cat5131#

cat5131#copy run tftp://146.103.0.113/test.cfg

Address or name of remote host [146.103.0.113]?

Destination filename [test.cfg]?

!!

43581 bytes copied in 3.129 secs (13928 bytes/sec)

cat5131#sh arp

Protocol  Address          Age (min)  Hardware Addr   Type   Interface

Internet  10.14.2.1               0   0000.0c07.ac8e  ARPA   Vlan142

Internet  10.14.2.118             -   7cad.7431.2941  ARPA   Vlan142

Internet  146.103.0.113           0   547f.eeb0.c9c1  ARPA   Vlan142

cat5131#

If I do a debug arp , i see some messages arp gleaning ....

What is the explanation of the arp gleaning because this message appear after the command " copy running-config to tftp "

Thanks for your help,

kind regards,

1 REPLY
VIP Purple

arp entry after copy tftp command

HI jose,

Check this link:

very well written by Leo

https://supportforums.cisco.com/thread/2007044

Regards

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