Last Call Review of draft-ietf-opsawg-large-flow-load-balancing-11
review-ietf-opsawg-large-flow-load-balancing-11-secdir-lc-nir-2014-05-02-00

Hi

I have reviewed this document as part of the security directorate's
ongoing effort to review all IETF documents being processed by the
IESG.  These comments were written primarily for the benefit of the
security area directors.  Document editors and WG chairs should treat
these comments just like any other last call comments.

tl;dr version: the document is ready.

I was a little surprised by the way the document is organized, and I’m not sure
who the target audience is. On the one hand it is very verbose on explanations
(that’s a good thing!) and I could very well understand it even though I lack
any background on the matter.  On the other hand, the order in which things are
explained seems strange:

The introduction talks about large flows vs small flows, long-lived flows vs
short-lived flows, and Large flows vs Small flows (no, I’m not repeating
myself, capitalize Large is different from lower-case large and in fact means
both “large” and “long-lived”).  But three things are totally missing: What is
a flow? How large does a flow have to be to be considered “large” (lower case),
and how long must a flow continue to be considered “long-lived”. Even the
terminology section (1.2) defines Large, Small and small again, but not what a
flow is.  These concepts are finally explained in sections 4.1, 4.3.1, and
4.3.2.

The document describes how load balancing can be achieved by moving large flows
around between links and by removing loaded links from the hash table, so that
Small (or actually un-classified) new flows will not go to overloaded links.
This is an improvement over the assumed default that is statically assigning
flows to links based on a hash.

The document has a short security considerations section that says that it does
not impact the security of the Internet infrastructure or applications. I tend
to agree, because the parts of the network where these protocols tends to be
mostly stateless, so moving flows from one component to another should not make
a difference. It would be different if there were supposed to be firewalls on
the nodes. The security considerations also says that load balancing might help
in resisting DoS attacks, for example if an attacker can create traffic where
the hash would collide with some Large flow. With load balancing either the
attacker’s flow or the Large flow is moved, eliminating the contention. Again,
I tend to agree, although this will allow a more powerful attacker to overload
all the links, not just the ones they can target with the hash function. Still,
an attacker powerful enough to overload all the links is likely to be able to
create traffic that collides with all links anyway.

I don’t think there’s anything missing from the security considerations.

Hope this helps

Yoav