Quite often on many lists we will hear the term Best Current Practice (BCP) 38 bandied about and further recommendations to implement [1] [2][3][4] (See NANOG Mailing list archive) . Some will say ‘it will aid in DDoS mitigation’ and even others will even state ‘All Internet Service Providers (ISP) should implement this." Now before the philosophical discussions ensue in the comments, it might be a good idea to discuss, technically, what it is? And perhaps what it can do?

BCP 38 A.K.A. RFC 2827 (thank you for correction from our readers) [5] is a best practice methodology around ingress traffic filtering. The specific purpose as stated in the RFC abstract “to prohibit DoS attacks which use forged IP addresses to be propagated    from 'behind' an Internet Service Provider's (ISP) aggregation point.” [5]

The BCP 38 outlines the concept of “restricting transit traffic” that comes from a “downstream network to known, and internally advertised prefixes” [5, p.4]. In an overly simplified diagram (My interpretation of the RFC, comments and corrections welcome), it means the ISP says:

Let us know if you are using or have implemented BCP38? We recommend it and do feel that it has technical merit and can help reduce risk!

UPDATE

A reader noted (see comments) that a purposeful effort by NANOG to get more information out can be found at @ http://www.bcp38.info.

References:

[1] https://isc.sans.edu/diary/A+Chargen-based+DDoS%3F+Chargen+is+still+a+thing%3F/15647

[2] https://isc.sans.edu/diary/Disaster+Preparedness+-+Are+We+Shaken+or+Stirred%3F/11431

[3] https://isc.sans.edu/forums/diary/Where+Were+You+During+the+Great+DDoS+Cybergeddon+of+2013+/15496

[4] https://isc.sans.edu/podcastdetail.html?id=3260

[5] http://tools.ietf.org/html/bcp38

Richard Porter

--- ISC Handler on Duty

Twitter: @packetalien

Blog: http://packetalien.com

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