4 ms·

It's common on these provider "isolated" networks to use a small /24 subnet by default. I'm more surprised that AWS isn't sending a gratuitous ARP when IPs are

• windexh8er 12y ago
  That would mean that one of two things would need to occur: 1) Amazon sends GARP on behalf of the guest OS, from outside the kernel 2) Amazon has hooks into the guest OS to instruct the GARP to occur Both are very bad things with regard to customer / Amazon separation of privileges and control. I think every network engineer was probably yelling ARP at the screen early on in this write up and is likely one of the first things those seasoned in L2/L3 would look at first. Also, as others have stated IPv6 removes this problem altogether. With the complete gutting of the concept of a broadcast and replaced by announcements within multicast groups which are much more efficient when you're talking about "small" prefixes that house 18,446,744,073,709,552,000 hosts (/64). ARP tables wouldn't be able to scale or work efficiently. Overall this makes me think that it would be interesting to build a best practices guide around IPv4 and IPv6 networking within cloud provider environments. I think the gratuitous ARP on boot is a relatively safe practice, especially with regard to environments that are in continual flux. $0.02.