Re: [conex] Preferential Drop
Dirk Kutscher <Dirk.Kutscher@neclab.eu> Wed, 12 February 2014 12:37 UTC
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From: Dirk Kutscher <Dirk.Kutscher@neclab.eu>
To: =?iso-8859-1?Q?Mirja_K=FChlewind?= <mirja.kuehlewind@ikr.uni-stuttgart.de>,
"conex@ietf.org" <conex@ietf.org>
Thread-Topic: [conex] Preferential Drop
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Date: Wed, 12 Feb 2014 12:36:42 +0000
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Subject: Re: [conex] Preferential Drop
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Hi, Thanks. Just a few comments: - it's probably useful to state in the table that "1" == top priority - "... it MAY preferentially drop packets" -- I actually think this should read "it SHOULD preferentially drop packet" -- we want to recommend it -- not say that it is really optional. (You would need to change the parentheses later in the text then, too...) - I don't think we need "if a router implements preferential drop it SHOULD also support ECN-marking" -- it's kind of implicit. The text later also seems to assume that ECN is implemented anyway. Dirk > -----Original Message----- > From: conex [mailto:conex-bounces@ietf.org] On Behalf Of Mirja Kühlewind > Sent: Mittwoch, 12. Februar 2014 12:39 > To: conex@ietf.org > Subject: [conex] Preferential Drop > > Hi group, > > I'm currently integrating text from the re-ECN documents on preferential > drop into the IPv6 CDO draft. > > Find the references from the re-ECN drafts here: > http://tools.ietf.org/html/draft-briscoe-conex-re-ecn-tcp-02#section-5.3 > http://tools.ietf.org/html/draft-briscoe-conex-re-ecn-motiv-02#section-5.1 > > Here is my current text: > "7. DDoS mitigation by using preferential drop > > If a router queue experiences very high load so that it has to drop > arriving packets, it MAY preferentially drop packets within the same > Diffserv PHB using the preference order given in Table 1 (1 means > drop first). Additionally, if a router implements preferential drop > it SHOULD also support ECN-marking. Preferential dropping can be > difficult to implement on some hardware, but if feasible it would > discriminate against attack traffic if done as part of the overall > policing framework as described in [RFC6789]. If nowhere else, > routers at the egress of a network SHOULD implement preferential drop > (stronger than the MAY above). > > +----------------------+------------+ > | | Preference | > +----------------------+------------+ > | Not-ConEx or no CDO | 1 | > | X (but not L,E or C) | 2 | > | X and L,E or C | 3 | > +----------------------+------------+ > > Table 1: Drop preference for ConEx packets > > A flooding attack is inherently about congestion of a resource. As > load focuses on a victim, upstream queues grow, requiring honest > sources to pre-load packets with a higher fraction of ConEx-marks. > > If ECN marking is supported by the downstream queues preferential > dropping provides the most benefits because if the queue is so > congested that it drops traffic, it will be CE-marking 100% of the > forwarded traffic. Honest sources will therefore be sending 100% > ConEx E-marked packets (and therefore being rate-limited at an > ingress policer). Senders under malicious control can either do the > same as honest sources, and be rate-limited at ingress, or they can > understate congestion. If the preferential drop ranking is > implemented on queues, these queues will preserve E/L-marked traffic > until last. So, the traffic from malicious sources will all be > automatically dropped first. Either way, the malicious sources > cannot send more than honest sources." > > The text in the re-ECN drafts assumes that a ConEx/re-ECN-capable router > will automatically also support ECN. The preferential drop works best if the > router uses ECN, because such a router will mark all packets before anything > gets dropped. If the router is not ECN-capable, it still might help but not that > much. Thus I added the following sentence: > "if a router implements preferential drop it SHOULD also support ECN- > marking" > > Not sure if I should write something like this because requiring to support > ECN might stop people from implementing the preferential drop. On the > otherhand ECN support would be helpful for ConEx anyway. But without a > deployed accurate ECN it's kind of useless.... > > Any thoughts? > > Mirja > > > _______________________________________________ > conex mailing list > conex@ietf.org > https://www.ietf.org/mailman/listinfo/conex
- [conex] Preferential Drop Mirja Kühlewind
- Re: [conex] Preferential Drop Dirk Kutscher
- Re: [conex] Preferential Drop Mirja Kuehlewind