Subject: Same global address on Multiple Interface of an IP6 node

From: "Suvendu M" <[email-masked]>
Date: Thu, 24 Jul 2003 16:30:17 +0530

All,

I have a generic question on Ipv6.It is :

Can a single global address (say 2222::1111) be configured on multiple
interfaces of a single ip6 node. If so is there any specific purpose for
doing that ??
What about link-local address, how would it be used, if single link local
address is configured on multiple interface of a same node.

Thanks in advance for your response.

Regards,
Suvendu

***************************************************************************
This message is proprietary to Future Software Limited (FSL) 
and is intended solely for the use of the individual to whom it
is addressed. It may contain  privileged or confidential information 
and should not be circulated or used for any purpose other than for 
what it is intended. 

If you have received this message in error, please notify the
originator immediately. If you are not the intended recipient,
you are notified that you are strictly prohibited from using,
copying, altering, or disclosing the contents of this message. 
FSL accepts no responsibility for loss or damage arising from 
the use of the information transmitted by this email including
damage from virus.
***************************************************************************
--------------------------------------------------------------------
IETF IPng Working Group Mailing List
IPng Home Page:                      http://playground.sun.com/ipng
FTP archive:                      ftp://playground.sun.com/pub/ipng
Direct all administrative requests to [email-masked]
--------------------------------------------------------------------

---

From: Robert Elz <[email-masked]>
Date: Thu, 24 Jul 2003 19:10:30 +0700

Date:        Thu, 24 Jul 2003 16:30:17 +0530
    From:        "Suvendu M" <[email-masked]>
    Message-ID:  <[email-masked]>

  | Can a single global address (say 2222::1111) be configured on multiple
  | interfaces of a single ip6 node.

Depends what the implementation allows, but I doubt many would permit
that - the address (with the prefix length) generally also defines
the prefix for the link, and those need to be unique for routing to
work.

  | If so is there any specific purpose for doing that ??

Not that I can think of.

  | What about link-local address, how would it be used, if single link local
  | address is configured on multiple interface of a same node.

This one is impossible to achieve.   You can set addresses with the same
bit pattern, but they're all different addresses, as they're in different
scopes.   Whether or not the bit patterns look similar, there's no great
magic to how LL addresses are used - if there's more than one possible
scope (ie: there's more that one interface, usually excluding the loopback
interface, that no-one I know of enables LL addresses on) then the scope
must always accompany the address for it to have any meaning at all.
in that sense, the scope is part of the address.

[Of course, if the multiple interfaces concerned were bridged together,
then they would all be in one link, all have one scope, and having just
a single LL address for the collection of them would make perfect sense].

kre

---

From: Roy Brabson <[email-masked]>
Date: Thu, 24 Jul 2003 08:58:46 -0400

> interfaces of a single ip6 node.

Yes, it can.  There are a few ways to accomplish this.  If all the 
interfaces are on the same lan, then you could have a "primary" and a 
"backup" interface.  If the interfaces are on different lans, you can run 
a dynamic routing protocol and advertise the address as being reachable 
through each physical interface on a node.  In this case, the address 
isn't really configured on the multiple interfaces per-se (you instead 
have a "virtual" interface which is assigned the IP address), but the 
result is any interface on the node may be used.  There are other methods 
which may be used as well.

> If so is there any specific purpose for doing that ??

Redundancy.  If one interface goes down, traffic will automatically switch 
to the another interface without disrupting existing connections.

> address is configured on multiple interface of a same node.

I'm not sure it is particularly useful.  Link-local addresses are really 
intended to be used for bootstraping, configuration discovery, route table 
maintenance, and the like.  Most, if not all, of these protocols work on a 
per-interface basis.  I suppose it could allow an interface to act as a 
"hot standby" for another interface, automatically switching over if the 
primary interface fails.  But this would only work if the interfaces are 
on the same physical lan.  If they are on different lans, then the two 
interfaces are in different link-local scope zones and are treated as 
unique addresses.

Roy

---

From: "Todd T. Fries" <[email-masked]>
Date: Thu, 24 Jul 2003 08:30:26 -0500

I understand there are tricks for faster thoroughput on IPv4 with regards
to multiple interfaces (network cards) and a single IP address.  Say,
two 100mbit cards plugged into the same 100mbit switch.  Is this `trick'
available with IPv6 in any fashion?
-- 
Todd Fries .. [email-masked]

Free Daemon Consulting, LLC                    Land: 405-748-4596
http://FreeDaemonConsulting.com              Mobile: 405-203-6124
"..in support of free software solutions."

Key fingerprint: 37E7 D3EB 74D0 8D66 A68D  B866 0326 204E 3F42 004A
            Key: http://todd.fries.net/pgp.txt

(last updated 2003/03/13 07:14:10)

Penned by Roy Brabson on Thu, Jul 24, 2003 at 08:58:46AM -0400, we have:
| > Can a single global address (say 2222::1111) be configured on multiple
| > interfaces of a single ip6 node.
| 
| Yes, it can.  There are a few ways to accomplish this.  If all the 
| interfaces are on the same lan, then you could have a "primary" and a 
| "backup" interface.  If the interfaces are on different lans, you can run 
| a dynamic routing protocol and advertise the address as being reachable 
| through each physical interface on a node.  In this case, the address 
| isn't really configured on the multiple interfaces per-se (you instead 
| have a "virtual" interface which is assigned the IP address), but the 
| result is any interface on the node may be used.  There are other methods 
| which may be used as well.
| 
| > If so is there any specific purpose for doing that ??
| 
| Redundancy.  If one interface goes down, traffic will automatically switch 
| to the another interface without disrupting existing connections.
| 
| > What about link-local address, how would it be used, if single link 
| local
| > address is configured on multiple interface of a same node.
| 
| I'm not sure it is particularly useful.  Link-local addresses are really 
| intended to be used for bootstraping, configuration discovery, route table 
| maintenance, and the like.  Most, if not all, of these protocols work on a 
| per-interface basis.  I suppose it could allow an interface to act as a 
| "hot standby" for another interface, automatically switching over if the 
| primary interface fails.  But this would only work if the interfaces are 
| on the same physical lan.  If they are on different lans, then the two 
| interfaces are in different link-local scope zones and are treated as 
| unique addresses.
| 
| Roy
| --------------------------------------------------------------------
| IETF IPng Working Group Mailing List
| IPng Home Page:                      http://playground.sun.com/ipng
| FTP archive:                      ftp://playground.sun.com/pub/ipng
| Direct all administrative requests to [email-masked]
| --------------------------------------------------------------------
--------------------------------------------------------------------
IETF IPng Working Group Mailing List
IPng Home Page:                      http://playground.sun.com/ipng
FTP archive:                      ftp://playground.sun.com/pub/ipng
Direct all administrative requests to [email-masked]
--------------------------------------------------------------------

---

From: Erik Nordmark <[email-masked]>
Date: Wed, 30 Jul 2003 13:44:48 +0200 (CEST)

> to the another interface without disrupting existing connections.

I think there is some confusion between the conceptual descrption of IPv6
(using terms like "interface" and "link" as per RFC 2460) and how one
can actually build a system using e.g. Ethernet cards.

At the conceptual level a global unicast address can only be assigned
to one interface in the Internet.
But since the "interface" is an abstraction that is provided to IP
there is nothing to prevent an implementation whicb uses multiple Ethernet
cards attached to the same or different Ethernet switches as long as this
is transparent to IP. An example of such an approach is IEEE 802.3ad which 
provides what looks like a single aggregate, with a single MAC address,
on top of multiple Ethernet cards. (If you read the IEEE 802 specs be aware
that the definition of "link" is subtle but completely different between
those specs and RFC 2460.)

So far so good. There might be cases where you want to use a slightly different
implementation technique where the abstraction has multiple MAC addresses; for
instance one per participating Ethernet card. There isn't much in the RFCs to
guide such an approach, but as long as it interoperates with other
implementations it would be ok. There is a subtle part of RFC 2461 which tries
to make this easier - the ability to omit the source link-layer address option
in router advertisements be able build routers which give different link-layer
addresses (for the same IP address) to different hosts using unicast neighbor
advertisements. But details on how to build such a "load balance across
multiple MAC addresses" thing for a router or for a host are left as a detail
for the reader :-)

But if you are only concerned about redundancy and not load spreading across
the Ethernet cards life is probably simpler.

  Erik