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Link Local Address

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  Link Local Address InuY4sha <riccardomanfrin@email.it> - 2011-09-13 06:59 -0700
    Re: Link Local Address Ivan Shmakov <ivan@gray.siamics.net> - 2011-09-13 21:36 +0700

#581 — Link Local Address

Can a Link Local Address be routable? 
What ISO/OSI layer is a Link Local Address bounded to? L2 or L3?

Thanks

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#582

>>>>> InuY4sha  <riccardomanfrin@email.it> writes:

 > Can a Link Local Address be routable?  What ISO/OSI layer is a Link
 > Local Address bounded to? L2 or L3?

	Why this question sounds like a homework assignment, I wonder?

	For the second part, a shared-media link layer (such as
	Ethernet, even though it's more point-to-point these days)
	generally employs some kind of addressing: as all the nodes
	receive the message sent (the media is shared, remember?), there
	has to be a way for the receiving node to determine whether the
	message is targeted at it.

	However, as the link layer has no knowledge whatsoever about
	anything beyond its own link, the only addresses it may ever get
	are the link local ones.

	On the other hand, the /network/ layer covers a /network/ of
	multiple links.  It may, however, for some specific needs (such
	as autoconfiguration) have to use some kind of “generic”,
	predefined addresses, whose scope we, however, have to limit to
	a specific link.  To distinguish these addresses from the
	network-wide addresses (which are the ones we've introduced the
	network layer for in the first place) we call them “link local.”

	As for the routing, it's sometimes stated that the network level
	addresses are introduced to uniquely name all the nodes in the
	network.  It's not quite true — the Media Access Control
	sublayer addresses (as per Ethernet) are already sufficiently
	unique; and, IPv6 link local (and, sometimes, global) addresses
	are derived from them.  Think, however, of what a kind of
	routing table it will require to support forwarding to such
	addresses at the scale of Internet.  Hopefully, this will allow
	you to attain the enlightment.

-- 
FSF associate member #7257	Coming soon: Software Freedom Day
http://mail.sf-day.org/lists/listinfo/ planning-ru (ru), sfd-discuss (en)

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