Can someone tell me why do I have arp table entry outside interface network?

Server has 2 interfaces, both on the same network:

ip route
default via dev eth0 proto static metric 1024 dev eth0 proto kernel scope link src dev eth1 proto kernel scope link src

arp -n
Address HWtype HWaddress Flags Mask Iface ether d4:d7:48:b5:a3:c1 C eth1 ether d4:d7:48:b5:a3:c1 C eth0

And then, when I ping (from eth0) I get icmp reply but arp table does not change.
But when I ping -I eth1 I get icmp reply and there is a new entry in arp table: ether d4:d7:48:b5:a3:c1 C eth1

But, when I add 'ip route add default via dev eth1' to the routing table and ping from eth1 there is no new arp table entry for
Why is that?

NOTE: Both interfaces are connected to Cisco switch with 'ip local-proxy-arp' on the SVI with ip which is default gw, and both are in Private VLAN.

2 Answers 2


It sounds like the Cisco interface your eth0 is connected to is configured with ip local-proxy-arp but the Cisco interface your eth1 connects to is actually configured with ip proxy-arp instead. This would account for the switch taking responsibility over the data-link addressing of an IP outside of the locally configured LAN.

Can you please verify this on the switch configuration? If I am incorrect, please post the results of show run int [PORT_FOR_ETH0] and show run int [PORT_FOR_ETH1]?

  • Well... the server is VMware virtual machine which is connected via vDS with private vlan to Cisco. I did't write this info, because I think it is irrelevant. And on Cisco is only ip local-proxy-arp.
    – Vangass
    Apr 16, 2015 at 7:21

OK. Everything is correct.
If there is no default gateway configured on the interface and there is proxy-arp configured on switch port, then if you ping ip address outside network configured on the iface, you will get arp entry in your arp table with ip address outside current network.
Thats the normal behaviour :].
I've checked this manually on lab switch.

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