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If a networking device has attained Link Local Address and attains a Link Local Address - say - 169.254.111.135. Now if DHCP got enabled in the device and it acquires an IP from DHCP server in network - should the device give away Link Local Address?

What is the ideal situation in such a case for the device to do?

Programmer
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Is defined on RFC 3927 section 1.9:

If a host finds that an interface that was previously configured with an IPv4 Link-Local address now has an operable routable address available, the host MUST use the routable address when initiating new communications, and MUST cease dvertising the availability of the IPv4 Link-Local address through whatever mechanisms that address had been made known to others. The host SHOULD continue to use the IPv4 Link-Local address for communications already underway, and MAY continue to accept new communications addressed to the IPv4 Link-Local address. Ways in which an operable routable address might become available on an interface include:

  • Manual configuration
  • Address assignment through DHCP
  • Roaming of the host to a network on which a previously assigned address becomes operable

So yes, if the device gets assigned a DHCP address then Link Local one should be dropped. Check https://www.rfc-editor.org/rfc/rfc3927#section-1.9

Community
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Nahuel Greco
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For IPv4, it is usual to drop the Link Local Address when an IP address is obtained by another means. Once you have attained a different IP address the Link Local Address doesn't have much use.

For IPv6, the Link Local Address is retained.

BillThor
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  • Thanks for the details. Please confirm the state when Link Local Address needs to be dropped - when we send DHCP Discover or receive DHCP offer - I am not sure what's the Link Local RFC states? – Programmer Jun 25 '18 at 12:08
  • Can you please provide some references of how to test Link Local addressing method - I mean how Link Local addressing method should behave the RFC 3927 is cryptic to conclude the test cases – Programmer Jun 25 '18 at 13:09