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I really need to know this for a linux server, but since it also applies to client OSes, I figured the question should be posed here instead of server fault.

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up vote 13 down vote accepted

According to the replies to this post to the linux-net mailing list,

  • At one point, the Linux kernel had a limit of 255 aliases per physical interface device.
  • As of Linux kernel version 2.2, there is no (practical) limit, with the second response citing personal experience with having aliased over 5,000 addresses to a single ethernet card.

Of course, binding large numbers of aliases to a single device will impose memory requirements and may have performance implications, so it's entirely possible that your hardware may limit the number of aliases you can add, even if the kernel itself doesn't.

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There's no need to create aliases for this; ip addr add can bind the addresses to a single device. – Ignacio Vazquez-Abrams Jan 11 '11 at 10:03
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Yes, and it does so by aliasing additional addresses onto the same device. Whether the alias is named (eth0:0) or not, it's still an alias. Granted, the authors of the ip(8) man page choose not to use the term "alias" because it treats all addresses as equal, pretty much the entire rest of the world agrees that assigning multiple addresses to the same interface is called "IP aliasing". – Dave Sherohman Jan 11 '11 at 15:32
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At some point I had the need to assign lots of IPv6 addresses to a single host, and once I reached around 4000 addresses neighbor discovery broke. The exact number of addresses it took to break neighbor discovery varied a bit between experiments, but it was always quite close to 4000. – kasperd Dec 16 '15 at 0:31

The maximum would be 4,294,967,294 IP addresses (assuming you're talking about IPV4, you have enough RAM, and we take out one for the broadcast address and one for the network address).

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More than you could ever possibly need. Use ip addr add to add addresses to an interface.

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