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

[Nalini Elkins <[e-mail]>]

On 9/19/14, Nalini Elkins <[e-mail]> wrote:
>
>>A directed broadcast ping on IPv4 gives pretty much the same result.
>>Did you test the effects of that ?
>
> I had not.  But, since you mentioned it, I did it on two different Windows
> machines.  The one that is the server in question had the following results:
>
> C:\Users\Administrator>ping x.x.x.255
>
> Pinging x.x.x.255 with 32 bytes of data:
> Request timed out.
> Request timed out.
> Request timed out.
> Request timed out.
>
> Ping statistics for x.x.x.255:
>     Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),
>
> Arp cache was not updated.   I did a packet trace in the background and
> indeed no ICMP replies were seen.
>
> I did the same ping x.x.x.255 on one of my client PCs and saw:
>
> Pinging x.x.x.255 with 32 bytes of data:
> Request timed out.
> Request timed out.
> Request timed out.
> Request timed out.
>
> But this time the packet trace showed that actually ICMP replies were sent.
>

>So, besides this cosmetic difference the behavior is identical for the
>case of IPv4 ping ?

Andrew, I think you may have misunderstand me.  The behavior is very definitely not
identical in IPv4.   In IPv4, many people block or disable directed broadcast PING.  Such
PINGs can be used for amplification in Smurf attacks.

http://www.techrepublic.com/article/understanding-a-smurf-attack-is-the-first-step-toward-thwarting-one/

Ping to FF02::1 is definitely amplification when 10 echo requests can create 2,000+ 
echo replies.   When you do a Ping on Linux, it is continuous until you stop it.
So, you may very easily do amplification without even meaning to.


>>Of course, private VLANs or (if we are talking VMs) or just using p2p
>>links with /128s would help this in the environments where the hosts
>>can not be trusted - and this of course is not virtual/physical
>>specific.
>
> Yes.  We wanted to bring up the topic of isolation of nodes for discussion.

>This is a useful topic in general - especially in light of the
>MLD-related thread, but the draft seems to focus on a very corner case
>- there are many much better reasons not to do large L2 networks.

We wanted to pick one specific instance.  Maybe we went TOO small!

>
>>If we're talking specifically virtual environment, here's an approach
>>on how to use ebtables to isolate the hosts:
>
>>ebtables -P FORWARD DROP
>>ebtables -F FORWARD
>>ebtables -A FORWARD -i $uplinkPort -j ACCEPT # let the traffic flow
>>from uplink to any ports
>>ebtables -A FORWARD -o $uplinkPort -j ACCEPT # let the traffic flow
>>from any ports to uplink
>
>>(source:http://serverfault.com/questions/388544/is-it-possible-to-enable-port-isolation-on-linux-bridges)
>
> I think this is very good.  But, unfortunately not very well known.   Also,
> is this possible for all platforms or just Linux?

>This was just my first google.com search result when searching for
>"private vlans linux".

>The first google.com search result on "private vlans windows" brings
>up http://blogs.technet.com/b/scvmm/archive/2013/06/04/logical-networks-part-iv-pvlan-isolation.aspx
>which seems to document similar technique.

>"private vlan vmware" results in
>http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1010691
>as its first hit.

>Would an IETF publication be easier to find than the above ?

Maybe not but the hosting company who provided us the service where we did this real life test does not seem to have read any of the documents you reference.

What to do is a good question.  IPv6 implementation at end user sites is new to many & mistakes are being made.  I do not know what is the answer.

>
>>So looks like the question at hand is:
>
>>"Should IPv6 nodes respond to Ping to FF0x::1?"
>
>>Which can be rephrased differently to ease the start of the discussion:
>
>>"What are the legitimate uses of a ping to ff0x::1 ?"
>
>>Right ?
>
> Yes.

>Allright, so I'll mention my use of ping6 ff0x::1:

>* quick check to find "a few hosts that are alive on this link"
>(obviously not to be done on large segments).

>* A way to trigger the remote side's ND process without having to do
>one myself (I know the multicast packet to all-hosts *will* usually
>get received regardless of the underlying issues with the L2.5
>infrastructure (snooping, etc.)

>* A way to further debug malfunctioning L2.5 infra, by comparing the
>reaction to pings to ff02::1, solicited node multicast, other
>multicast groups, etc.

>Summary: the ff02::1 current ping behavior does help in a non-trivial
>amount of cases.

>The security aspects the draft mentions indeed do exist, but in a
>properly configured network can be easily mitigated as I've shown
>above. So I'd be against changing the functionality in the existing
>stacks.

I don't know, Andrew.  I worry about the broadcast nature of the ping.
I feel like it is trouble waiting to happen.


--a

>
> --a
>
>
> On 9/19/14, [e-mail] <[e-mail]> wrote:
>> A new draft has been posted, at
>> http://tools.ietf.org/html/draft-elkins-v6ops-multicast-virtual-nodes.
>> Please take a look at it and comment.
>>
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