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Asked: 2009-12-22 23:04:49 +0800 CST

Duplicate IP address detection with multiple NICs

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I am using arping -D to detect duplicate IP addresses within a network when setting up servers. (The network is controlled by someone else, and we have had many issues with IP allocation in the past.) It works fine as long as my host has a single NIC on a given VLAN, but when my host has more than one (I have one with 9 NICs on one VLAN and 1 on the other), arping -D always returns false collisions.

The problem is that all 9 of my NICs respond to an ARP request for any of the IPs on those NICs. (These are real physical NICs, not aliases or anything.) I send out one ARP request packet, and get 9 ARP is-at ARP replies, one for each MAC address.

I could implement my own solution by sniffing packets and checking for any replies with a MAC address other than the local NICs', but it seems like there ought to be an easier way.

linux

1 Answers

  1. Best Answer

    First, don't have nine NIC's on the same subnet, if you want bandwidth use bonding, if you need addresses use ip addr.

    To fix the arp issue just set the following sysctl's:

    net.ipv4.conf.all.arp_ignore = 1
net.ipv4.conf.all.arp_announce = 2
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