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RE: IPv6 link local address posted 12/03/2004
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Tim,

Here is what I've got from this so far....


Link-local addresses are used by routers to verify neighbor reachability
and keep track of the neighbor routers.  

They do this for network management and routing functions like ICMP
redirects, router advertisements, stateless autoconfiguration of end
hosts, etc.

When it comes to NBMA networks, the link-local address becomes
important.  As near as I have been able to tell, the remote nodes
link-local address is the one that you will map for Frame or ATM to work
with routing protocols (namely OSPF and ISIS over NBMA).

EX:

R1:
Ipv6 unicast-routing

Ipv6 router ospf 1
 Router-id 1.1.1.1

Int s0/0
 Encap frame
 Ipv6 address 2001:1:1:1::/64 eui-64		
 Ipv6 address fe80::e0:f727:e400:a link-local
 Frame map ipv6 fe80::e0:f727:e400:B 100 broadcast
 Frame map ipv6 2001:1:1:1:e0:f727:e400:B 100
 Ipv6 ospf 1 area 0

R2:

Ipv6 unicast-routing

Ipv6 router ospf 1
 Router-id 2.2.2.2

Int s0/0
 Encap frame
 Ipv6 address 2001:1:1:1::/64 eui-64
 Ipv6 address fe80::e0:f727:e400:B link-local
 Frame map ipv6 fe80::e0:f727:e400:a 100 broadcast
 Frame map ipv6 2001:1:1:1:e0:f727:e400:a 101
 Ipv6 ospf 1 area 0

Notice that the link-local address is statically set here.  I did this,
and I think this is the right thing to do, because the link-local
address is built by the available system mac addresses on the unit for
non-multiaccess nodes.  There is a pecking order to determine the
link-local from the available pool, and forbid that the next time the
router reboots it decides to use a different link-local address on the
local node that my remote node is no longer statically mapped too.

If that's not correct, I'm sure someone will let me know.  8)

andy


-----Original Message-----
From: ccie2be [mailto:ccie2be@xxxxxxxxxx] 
Sent: Friday, December 03, 2004 4:34 AM
To: Group Study
Subject: IPv6 link local address


Hi guys,

Since ipv6 automatically creates a link local address for every
interface configured with a unicast ipv6 address, why would anyone want
to use the link-local option on the following command?

int e0/0
ipv6 address <ipv6-addr> </length | link-local>


Also, what ipv6 addresses are allowed when the link-local option is
used?

In other words, does the ip v6 address have to start with FE80::/10 or
can any allowed ipv6 unicast address be used and then ipv6 will
automatically construct a legal link-local address from the unicast
address?

Thanks, Tim

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