Re: [Sidrops] WG Adoption call draft-azimov-sidrops-aspa-verification

"Sriram, Kotikalapudi (Fed)" <kotikalapudi.sriram@nist.gov> Sun, 03 March 2019 01:36 UTC

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From: "Sriram, Kotikalapudi (Fed)" <kotikalapudi.sriram@nist.gov>
To: Alexander Azimov <a.e.azimov@gmail.com>
CC: "sidrops-chairs@ietf.org" <sidrops-chairs@ietf.org>, "sidrops@ietf.org" <sidrops@ietf.org>
Thread-Topic: [Sidrops] WG Adoption call draft-azimov-sidrops-aspa-verification
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Date: Sun, 3 Mar 2019 01:36:08 +0000
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Subject: Re: [Sidrops] WG Adoption call draft-azimov-sidrops-aspa-verification
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Hi Alex,

So, yes there are things we need to careful about in the design.
Also, got to be careful about claiming, “this mechanism
guarantees detection of both malicious and accidental route leaks”. 

There is a new Comment #0 that I have added here.
And I have other comments inline below. 

Comment#0:
One more thing occurred to me. This is very basic. 
Consider these frequently occurring examples of route leaks:

AS1 (Tier 1)----P2C---->AS2 (customer)----C2P-----> AS3
AS1 (Tier 1)----p2p---->AS2 (Tier 1)----p2p-----> AS3 (Tier 1)

AS2 leaks the route learned from AS1 in both cases above. 
AS1 being a Tier 1, never has to create an ASPA (has no providers).  
Regardless of whether AS2 created an ASPA or not,
AS3 is not able to detect the leaks in both cases above
(per algorithm in the draft).
This same issue arises even in the example of Comment #2
if AS3 in that example were a Tier 1.

>>Comment #1
--- snip ---

>Can you please clarify to me next scenario with three ISPs: 
> - Victim advertises /23 to Upstream, does use BGPSec, 
>    has ROA record with maxlength 24
> - Upstream, does use BGPSec
> - Attacker, advertises /24 that belongs to Victim, adds its ASN at 
>    the beginning of ASPath, doesn't use BGPSec
>Will Upstream, according to RFC8205, accept the hijacked route from Attacker?
>Anyway, I'm open for discussion about proper wording here.

The idea of a BGPsec cloud (some call it island) needs to be understood.
I hope you had chance to read RFC 8205 Section 7.9 – 
the idea of contiguous BGPsec ASes.
A group of contiguous BGPsec ASes decides that they 
require signed updates (i.e., BGPsec) from Day X *within their cloud*. 
What that means is that they have knowledge that they are 
contiguous (all connected to each other by some # of hops),
and they all do BGPsec. And they decide that BGPsec must be done
end-to-end within their BGPsec cloud. 
Then from Day X, they require signed/valid paths for prefixes 
that *originate within their BGPsec cloud*.
(Prefixes originated from outside the cloud may be unsigned
and may possibly be subject to signature stripping.) 
Then in your example, the attack is not possible within the cloud
(i.e., if attacker strips the signatures for any prefix that originated 
in that BGPsec cloud, his unsigned update is Invalid and not accepted;
it would be the same as the attacker himself suppressing the update.)

The wording I can suggest is: 
BGPsec [RFC 8205] is computationally expensive and it is uncertain 
when its adoption/deployment may happen.

Just FYI…
BGPsec is computationally expensive but there are optimization
efforts that may be helpful (if BGPsec adoption ever gets going):

http://www.freepatentsonline.com/y2019/0036943.html    
(Juniper’s BGPsec optimization patent)

https://www.nanog.org/meetings/abstract?id=3043 
   
https://www.sciencedirect.com/science/article/pii/S0140366417303365   

 >>Comment #2: Improvement of the algorithm for detection
---- snip -----

> This suggestion sounds great but it has an issue. Imagine that AS3 and AS4
> have what is commonly named 'complex' relation. So they are both
> customer-provider to one another. And in your scenario, where only AS4
> creates ASPA it may result in rejection of valid routes, which will make
> AS4 quite unhappy...

Yes, agree. ASPA has a shortcoming nevertheless.

>> Comment #3:
--- snip ---

> Fully agreed. Simplicity comes with its own cost.
> And that's why we still need community-based leak detection that can work
> per-prefix. And it's our duty as-coauthors (and my debt, which I need to
> admit) to finally push it forward.
> I'm going to add an explicit statement in the next version of the draft.

Yes, the per-prefix solution (existing WG draft) is a necessary component.

>> Comment #4: Not all malicious leaks / hijacks are detected
>>
>> In the topology below, AS2 leaks the path it learned from its peer AS4 to
>> its provider AS3 with path modification to avoid route leak detection,
>> or one may think of it as a hijack with feasible path insertion.
>> In either case, the Update: p2 AS2 AS1 from AS2 to AS3 is
>> illegitimate but defies detection despite all ASes participating in ASPA.
>>
>>          AS3                                                              AS5
>>               \  p1 AS2 AS1                                     /
>>                 \ p2 AS2 AS1                                 /
>>                    \                                                 /
>>                      \         <----p2 AS4 AS1--    /
>>                        AS2 -------p2p----------AS4
>>                           \                              /
>>                              \ p1 AS1           /p2 AS1
>>                                  \                 /
>>                                       AS1
>>                                    (p1, p2)
>>

> Thinking about it as hijack adds simplicity to the picture. Customers may
> still be hijacked by its direct or indirect providers. While it
> significantly limits the attacker vector and highly unlikely to happen in
> the real world, it must be clearly stated in the draft. Pushed to stack.

It is both. Hard to rule out malicious leak with path modification.
When considering malicious scenarios, the above would not be unlikely.
I think this is typically what the determined attacker (AS2) might do to
maliciously increase their revenue.  

>> Comment #5: Path verification vs. path feasibility
>>
>> Based on the above examples, in the draft, perhaps it is better to say
>>
>> that the path is assessed feasible rather than say that the path is
>> verified.
>>

> I'm not a native speaker but for me 'feasibility' sounds a bit odd. I
> would be glad to learn other opinions from the wg members. Anyway, this
> question should not become a showstopper.

BGPsec provides hard assurance that path seen in the update is correct.
ASPA can provide confirmation that the path is possible/feasible.
It cannot assure that path seen in the update is the actual path
that the update traversed. This is clear from the above example (Comm. #4).

We can meet in Prague. I'll be happy to discuss 
and we can try to help resolve these (to the extent possible). 

Thanks.

Sriram