Re: [v6ops] new draft: draft-elkins-v6ops-multicast-virtual-nodes

[Nalini Elkins <[e-mail]>]

On 20/09/2014 04:54, Nalini Elkins wrote:
> On Windows, I did a :  ping ff02::1 -n 10
>
> where the -n is the count.
>
> So for each 1 ping request I send out, each of my neighbors sends me 10
> responses.

The "-n" parameter specifies how many icmp echo requests are sent out, not 
how many replies are solicited.

> Such as what?  BTW, I have sent Nick the trace & can send to you as well.

>The pcap file shows 10 icmp echo requests and 2840 echo replies, and that 
>the echo replies used 284 unique link-local ipv6 addresses associated with 
>284 unique MAC addresses.  This looks both correct and consistent with the 
>figures in the draft.  The lesson is that if you have a lot of ipv6 hosts 
>on the same broadcast domain, you will get lots of echo replies from a ping 
>to ff02::1.

This is the point we were trying to make.  But, we were using Ping to illustrate
that much layer 2 communication will occur - such as multicast.

Also, I was wrong in my explanation of multicast ping amplification.   How it
works is this:

Situation:  node A is on a subnet with 25 other nodes (B-Z)

1.  Node A sends 10 ICMP ping requests to FF02::1
2.  Nodes B through Z send Node A back ICMP 10 ping replies each

Impact: with very little work by Node A, he has made B - Z do work &
created network congestion with 250+ packets.

>Nalini, if you feel that there is an issue here, you should talk to your 

>hosting provider and suggest that they don't put as many ipv6 hosts on the 
>same broadcast domain.  This isn't a protocol level problem: it's expected 
>and correct behaviour.

I think people will be quite surprised at this behavior.   We think that the
issues of how many hosts are on a broadcast domain and node isolation
should be addressed.   We will add this to our draft.




Because It is not just ICMP but all link local and multicast communication.  I tell 
you, I do not think that people are not considering this in their network design.  
We are using the hosting company as an example of what really is happening in 
the wild.

Nick