From: ccie2be (ccie2be@nyc.rr.com)
Date: Fri Dec 03 2004 - 16:51:33 GMT-3
Andrew,
Thanks for your comprehensive reply.
The Cisco documentation is extremely vague and exceedingly poorly written on
this.
For example, on page 53 of the Implementing basic connectivity for IPv6, it
says,
For a point to multipoint interface "you MAY need to configure multiple
explicit mappings" meaning one frame map to the remote (Global or
Site-Local) unicast address and a 2nd frame map to the remote link-local
address where both remote addresses refer to the same remote interface.
It also says that configuring both mappings "Ensures" that IGP's will work
properly. What the heck does "Ensure" mean? Does it mean that with only one
mapping, it won't work? If so, then shouldn't they just say, "For IGP's to
work over a p2m interface, 2 mappings are REQUIRED." Or, does "Ensure" mean
that sometimes one mapping will suffice but other times, it won't? And, if
that's the case, when will one mapping suffice? And, which mapping, the one
to the remote link-local address or one the remote global ipv6 address?
It also doesn't explain why both mappings are needed for the IGP's to work.
Does each mapping have a different role to play in this process?
In conclusion, I can say with great confidence, this documentation sucks -
BIG TIME.
Getting back to the original issue, I don't know if you're right or wrong
about needing to explicitly define the link-local address. The way I read
it, as long as the frame map ipv6 statement maps to the remote link-local
address, things should work regardless of whether the link-local address was
explicitly defined or automatically generated.
BTW, the Syngress book, Configuring IPv6 for Cisco IOS, on page 171 shows an
example of configuring 2 frame map statements to each remote, but it also
says the map to the remote link-local address does NOT need to be
configured. The book is a couple years old, so maybe that's no longer true
or maybe that's wrong - I don't know which.
I just hope I can get all this confusion cleared up in the next few weeks
before I take the lab.
Thanks, Tim
----- Original Message -----
From: "Edwards, Andrew M" <andrew.m.edwards@boeing.com>
To: "ccie2be" <ccie2be@nyc.rr.com>; "Group Study" <ccielab@groupstudy.com>
Sent: Friday, December 03, 2004 1:40 PM
Subject: RE: IPv6 link local address
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@nyc.rr.com]
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
This archive was generated by hypermail 2.1.4 : Mon Jan 03 2005 - 10:31:24 GMT-3