When I change the IPv4 address on my Juniper router interface, it causes router to send out the gratuitous ARP message: As you can see, I first set the IPv4 address to 10.10.10.126 and then changed it to 10.10.10.65. However, are there operating-system platforms, which do not send gratuitous ARP message in case IPv4 address is changed? asked 06 Mar '13, 08:32  mrtn |
2 Answers:
RFC 5227 requires every host to perform IP address conflict detection before beginning to use an IPv4 address, regardless of how that address is assigned (manually, DHCP, other). See section 2.1 of the RFC. Almost all implementations perform the IP address conflict detection by sending gratuitous ARPs. Technically, this is an error, because the RFC requires them to send ARP probes instead of gratuitous ARPs, but using gratuitous ARPs for this purpose is accepted practice. In a gratuitous ARP, the target IP address and the sender IP address are the same. In an ARP probe, the sender IP address is 0.0.0.0. So there should not be any operating systems that don't perform IP address conflict detection with either a gratuitous ARP or an ARP probe when their IP address is changed. Given the wide variety of implementations, complete with bugs, it wouldn't surprise me if somewhere there is a non-compliant implementation that does not conform to this requirement. answered 06 Mar '13, 09:09  Jim Aragon edited 06 Mar '13, 19:08 |
a gratuitous ARP is sent by many (current) OSes while the system boots and if the link of an interface goes down and comes back up. I don't think there is a requirement in any RFC to send an gratuitous ARP after an IP change. So, you may or may not see such an ARP after an IP change. Some loadbalancer and/or cluster software will issue a gratuitous ARP after a failover has taken place, but that depends on the software used and also it's configuration. Regards answered 06 Mar '13, 08:46  Kurt Knochner ♦ |
