Subject: [mobile-ip] Question on ll-scoped addresses

From: Alexandru Petrescu <[email-masked]>
Date: Wed, 23 Apr 2003 19:03:29 +0200

Hi, I need a clarification on link-local addresses, thanks for any input.

When the L bit is set, the HA is supposed to defend the ll address of MN
(with DAD).  Does it imply that HA will intercept the ll-addressed
packets that are supposed to reach MN?

If the HA will intercept those packets, what would the HA do with those
packets?

Alex
GBU

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From: Jari Arkko <[email-masked]>
Date: Wed, 23 Apr 2003 21:09:37 +0300

> If the HA will intercept those packets, what would the HA do with those

It has to send the NAs, but if there any intercepted packets, those
will be discarded and an ICMP sent to the sender.

Section 10.4.1:

    ...
    If the Link-Layer Address
    Compatibility (L) flag has been specified in the Binding Update, the
    home agent MUST do the same for the link-local address of the mobile
    node.

Section 10.4.2:

    However, packets addressed to the mobile node's link-local address
    MUST NOT be tunneled to the mobile node.  Instead, such a packet MUST
    be discarded, and the home agent SHOULD return an ICMP Destination
    Unreachable, Code 3, message to the packet's Source Address (unless
    this Source Address is a multicast address).  Packets addressed to

Jari

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From: Alexandru Petrescu <[email-masked]>
Date: Thu, 24 Apr 2003 14:23:38 +0200

Jari Arkko wrote:
>> When the L bit is set, the HA is supposed to defend the ll address
>>  of MN (with DAD).  Does it imply that HA will intercept the 
>> ll-addressed packets that are supposed to reach MN?
>> 
>> If the HA will intercept those packets, what would the HA do with 
>> those packets?
> 
> 

Ok, I see.  So they will be discarded.  But, in the other way around,
what happens to packets that are sent by MN (that is away from home),
that has src=its link-local address and dst=a link local address of a
host attached to the home link.  Will those be discarded?

Alex
GBU

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From: Jari Arkko <[email-masked]>
Date: Thu, 24 Apr 2003 15:53:48 +0300

> host attached to the home link.  Will those be discarded?

They will be sent to the link-local peer on the visited network, if
there happens to be a node with the same address ;-)

Per Section 11.3.1, in order to use reverse tunneling the packet
must have a home address as a source address (with the exception
of MLD packets).

--Jari

---

From: Alexandru Petrescu <[email-masked]>
Date: Thu, 24 Apr 2003 16:08:00 +0200

Jari Arkko wrote:
> Per Section 11.3.1, in order to use reverse tunneling the packet must
>  have a home address as a source address (with the exception of MLD 
> packets).

Ok, MN's ll-scoped address is not a home address (although it looks like
one since the HA defends it).

When you say "with the exception of MLD packets", does this imply that
when a MN is away from home, and wants to join a group (through the
bidir tunnel), and sends an Unsolicited Report that has its source
address its link-local address, will this packet be forwarded by the HA
on the home link?  Or will this packet be processed by the HA itself?

Alex
GBU