Subject: [Mip6] Clarification on sending ICMP error in RFC 3775

From: Ranjitsinh Wable <[email-masked]>
Date: Thu, 19 Oct 2006 10:13:21 +0530

Dear All,

I  was going through the RFC 3775. Section 9.2 of the RFC says that when
 received packet is erroneous then ipv6 node(CN) should send the ICMP
 packet.  And message has to be sent to the directly to the source of a
 packet. And the Binding cache should not be used for the same.

Section 9.2 RFC 3775.

    The Payload Proto field MUST be IPPROTO_NONE (59 decimal).
    Otherwise, the node MUST discard the message and SHOULD send ICMP
    Parameter Problem, Code 0, directly to the Source Address of the
    packet as specified in RFC 2463 [14].  Thus no Binding Cache
    information is used in sending the ICMP message.  The Pointer
    field in the ICMP message SHOULD point at the Payload Proto field.

Section 10.2 of the RFC says that HA should also follow the same rules
specified in the section 9.2.

I have small question on this. Now lets say that the MN returned home and
sent a BU(De-registration) with palyload proto not equal to 59.
BU packet is sent from the home link. So it will have only IPv6 header and
mobility header and some additional payload header.
IPv6 Source address will be the HoA of the MN. HA will have the valid
Binding cache for the MN.

In the above case HA should send ICMP error message to the MN not using the
binding cache and it should be directly sent to HoA of the MN.
If HA is still intercepting the packets for the MN (as valid binding cache 
is
present), how the ICMP error message will be sent to MN address.

1) Whether the HA should send NS to resolve the HoA of MN? but in this case
HA itself is defending the MN HoA. (This may require special routing)

RFC says(section 11.5.4) it is possible for MN to respond to the NS by
 sending the unicast NA. This case is required for sending the BA to MN by 
HA.
And it is assumed that time the BU for De-registration is accepted.
and HA is no longer serving/ defending the MN HoA.
    OR
2) Whether HA should tunnel the packet without using binding cache?
But in this case packet will be unneccessarily sent to foreign network.
OR
3) HA silently discard the errenous packet?

IMHO Section 9.2 holds good for CN but may not be for HA.
Kindly let me know your views on the same.

Thanks and Regards,

Wable R. U.

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