Re: [Sidrops] ASPA false leak

"Jakob Heitz (jheitz)" <jheitz@cisco.com> Wed, 16 October 2019 21:31 UTC

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From: "Jakob Heitz (jheitz)" <jheitz@cisco.com>
To: Alexander Azimov <a.e.azimov@gmail.com>, Randy Bush <randy@psg.com>
CC: Ben Maddison <benm=40workonline.africa@dmarc.ietf.org>, SIDR Operations WG <sidrops@ietf.org>
Thread-Topic: [Sidrops] ASPA false leak
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Date: Wed, 16 Oct 2019 21:31:46 +0000
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Archived-At: <https://mailarchive.ietf.org/arch/msg/sidrops/V3tR0nQuwqKEt2rfWY7SkeP9pgM>
Subject: Re: [Sidrops] ASPA false leak
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So, should AS5 just drop the traffic?

Regards,
Jakob.

From: Alexander Azimov <a.e.azimov@gmail.com>
Sent: Wednesday, October 16, 2019 1:41 PM
To: Randy Bush <randy@psg.com>
Cc: Ben Maddison <benm=40workonline.africa@dmarc.ietf.org>rg>; Jakob Heitz (jheitz) <jheitz@cisco.com>om>; SIDR Operations WG <sidrops@ietf.org>
Subject: Re: [Sidrops] ASPA false leak

And another real-world scenario.

The significant number of route leaks today happens when an ISP is using the prefix-list of their customers as the only egress filter (no ingress filters/no communities).
In this case, just like in your scenario, it starts to leak customer's prefixes when it gets them from providers/peers, thus spoiling TE of their customers. More then, the customer even can't redirect traffic from such misconfigured upstream provider even if it experiences a service degradation.

I don't believe we should legitimize such behavior.

ср, 16 окт. 2019 г. в 09:42, Randy Bush <randy@psg.com<mailto:randy@psg.com>>:
>> Consider the topology:
>>
>>    AS5      AS3
>>      \     /   \
>>       \   /     \
>>        AS4     AS2
>>          \     /
>>           \   /
>>            AS1
>>
>> AS1 has providers AS2 and AS4.
>> AS2 has provider  AS3.
>> AS4 has providers AS3 and AS5.
>>
>> AS5 receives a route with AS-path (4 3 2 1).
>> ASPA would declare that AS4 leaked the route from AS3 to AS5.
>> However, AS4 is an authorized provider for AS1.
>> Even though AS4 has a path to AS1, it chose to use an alternative
>> valid path to reach AS1.
>
> and that alternate path sure looks a lot like a route leak.

lemme try a different way

the attacker A3 wishes tio siphon jelly beans from A5's traffic to A1.
so she convinces A4 to prefer the A4 A3 A2 A1 path, which A4 then
announces to A5 as her best path.  profit.

randy

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--
Best regards,
Alexander Azimov