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

[Andrew 👽 Yourtchenko <[e-mail]>]

On 9/20/14, 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
>
>>On the same subnet ? You wrote that the replies were indeed amplified
>>and sent, or did I misunderstand ?
>
> The replies on the same subnet appear to be blocked in one case and not
> blocked in another case.
> So, one cannot make a blanket statement (at least based on two data
> points!).
>

With the test I did within my home network, I saw amplified replies on
both, so one can not make a blanket statement indeed and it depends on
the OS and the setup.

>
>> 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.
>
>>This is all link-local. The reason Smurf is dangerous is that one can
>>send the request from across the internet. Here it's on the same
>>segment - so it's a customer-provider relationship, and there are ton
>>of the existing operational mechanisms that can be used to take care
>>of this if this is a concern - documenting them might be useful.
>>Saying that the hosts should not reply altogether - not; for the
>>reasons outlined in the previous mail.
>
>>(Of course this is just my experience, would be interesting to hear
>>others' opinions).
>
> As I said in another response, in IPv6 subnets, there may be many other
> nodes
> on link with you.   We were using the
>  Ping to FF02::1 as a graphic example of how
> it is possible to impact both yourself and other nodes without even meaning
> to.

So you ping ff02::1 on a network with X hosts, where X is large. So
each of these X hosts has to process 1 packet and generate 1 packet,
you have to process X responses, you populate ND cache on your hosts
with X entries, each of the X hosts populates their ND cache with your
address.

Your host is quite obviously impacted. But the others process a 1/X
share of the load compared to you, an equivalent to a regular 1 host
exchange. So I don't see how they are impacted.

>
> We discovered this by accident.   We were doing testing for another
> purpose and were quite surprised to see that both servers were seeing all
> the
> multicast packets and even more surprised when we did the PING to FF02::1.

Nick has a good point this whole situation would benefit of some more
debugging.

>
>>
>>
>>>>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!
>
> No, the more focused the doc is, the better.
>
>>
>>>
>>>>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.
>
>>If you were not spoofing the source, then the only DoS target was
>>yourself, and the inter-customer resource isolation should take care
>>of the rest. This is relates to "Oops I don't know what I'm doing"
>>part.
>
> Actually, not.  In this case, there was no inter-customer resource
> isolation.  So, we were impacting everyone.   As I say, we discovered
> this by accident.

Again, it's obvious to see how you're impacting yourself but it's
unclear to me how were you impacting the others.

I did a quick test in my lab, and the only node that significantly
grew the ND cache in my test was the one sending the ping. The rest
just added only the sender's address. Sure, the sender also triggered
NUD on the addresses, but again it is only the sender that was
impacted - the rest had just 1 packet to handle, which is not much.

Please help me understand where is the problem ?

>
> I am thinking that the bigger question that we should address is
> node isolation.  I think that people implementing IPv6 have got the
> /64 for subnet in their heads pretty well.  But, not the other part
> about how multicast - and other packets impact nodes on link with you.
> And that they should do node isolation.
>
> What do you think?

Give each vhost a routed /64 and use link-local next-hops - this will
give the same "broadcast profile" as for IPv4, and reduce the hoster's
resources needed to manage the allocated addresses, and still allows
to sell 65536 vhosts, assuming the said hoster has only /48.

Then on the shared segment that carries the routed traffic,
intra-subnet apply the same security policy to the ff02::1 IPv6
traffic as you do to IPv4 x.x.x.255 originated within and destined for
that subnet - private VLANs, p2p links, or nothing.

--a

>
>>Now, if you start to spoof your source and send the traffic at high
>>rates, we're into the ToS violation territory, and the hosting company
>>probably assumes a certain degree of good citizenship from its clients
>>towards each other.
>
>>If you were to try this kind of link-local smurf, why not
>>try stealing other VM's IPv4 addresses and running MITM on them ? Or
>>try spoofing the default router ? Or try sweep-scanning their entire
>>/64 from Internet at high rate ? Or get into legacy and try
>>ARP-flooding with broadcast ARP requests/replies at line rate ?
>
>>There usually is a very simple mitigation to all of the above: first
>>warn the hosting customer that is being naughty, then terminate the
>>contract. I know for sure it is being practiced.
>
> We discovered this by accident & were using the example of Ping FF02::1 to
> illustrate what can happen.
>
>
>
> --a
>
>>
>> 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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>>>>
>>
>