Subject: [MEXT] ICMP error...?

From: "Pedro Pinheiro" <[email-masked]>
Date: Thu, 6 Dec 2007 12:58:19 -0000

Hi all,

I don't know if this subject has already been discussed. If so, please
forgive me and point to me where can I find a answer.
My question is relative to NEMO Basic Support protocol.

If a packet from a CN to a MNN (or vice-versa) goes into a MRHA packet and
this is traversing the Internet, don't matter if destined to HA or to CoA's
MR, and any router has to generate a ICMP error (unreachable, ...) it will
generate it destined to the HA's or CoA's IP. 
In this situation how will the HA or MR find out the origin of the packet
inside the MRHA? The icmp will not forward the MRHA packet so that HA or MR
could see inside it and return a ICMP error to the CN or MNN. 

I hope I have made myself clear.
Thank you in advance.
Pedro Vapi

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Universidade de Coimbra
Pedro Pinheiro
Eng, MSc
[email-masked]
Centro de Informatica 
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3001-401 COIMBRA
tel: +351 239 853 170
fax: +351 239 853 189
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From: Alexandru Petrescu <[email-masked]>
Date: Thu, 06 Dec 2007 13:17:35 -0800

> generate it destined to the HA's or CoA's IP. 

Right...

> inside the MRHA?

The origin of the packet is the src field of that ICMP Error, right?

Not sure where the error happens exactly (between CN and HA?  between HA 
and MR?)

Alex

> The icmp will not forward the MRHA packet so that HA or MR

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From: "Pedro Pinheiro" <[email-masked]>
Date: Fri, 7 Dec 2007 10:46:23 -0000

> Not sure where the error happens exactly (between CN and HA?  between

Let me try to exemplify.
Suppose those scenarios:

1) Comunication from MNN to CN:

The normal situation is:
MNN ----> MR ======> Router on the Internet ======> HA -------> CN

----> means "normal" traffic
====> means MRHA traffic with the "normal" traffic encapsulated inside.

Now, imagine that the "Router on the Internet" has a problem and needs to
drop the packet and generate an icmp error. 
This is the situation I am talking about! 
In this point, the icmp error will be forward to the MR's CoA with the icmp
error message. 
Now, what I am asking is: when MR receives this icmp error, how will he
forward it to the right MNN? It has lost the MNN IP. And, with that, when
will the MNN will know that the packet has been drop? Only in the timeout
time?

2) On the opposite way, we have the packet from CN to MNN

CN ------> HA =====> A router ======> MR ------> MNN

If the packet is drop in the "A router" point and it generates a icmp error,
then it will forward it to the HA IP. How will the HA knows the IP of the CN
so that he can inform that this packet has been lost?

Uffff... it's hard to explain :D
Well, in fact this is a problem that affects all tunnel situations (GRE,
VPN, etc.)

Best regards,
Pedro Vapi

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From: Brian Haley <[email-masked]>
Date: Fri, 07 Dec 2007 09:26:39 -0500

Hi Pedro,

> will the MNN will know that the packet has been drop? Only in the timeout

Well, if it follows the ICMPv6 rules, the error message should contain 
as much of the original packet as possible, which should include the 
original IP source address once the tunnel header is stripped-off.  Or 
am I missing something?

-Brian