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[possibly O-T] ip-sysctl calls and a few questions.

To: <netdev@xxxxxxxxxxx>
Subject: [possibly O-T] ip-sysctl calls and a few questions.
From: "Oskar Andreasson" <blueflux@xxxxxxxxxxx>
Date: Fri, 3 May 2002 16:07:58 +0200
Sender: owner-netdev@xxxxxxxxxxx
Hi All,

I hope this is no intrusion to this list or that it is off-topic, however, I 
will try to keep it as much to the core ipv4 area as possible. If you do 
respond, please CC replies directly to me since I am not on the list.

First off, I'm working on a larger document which contains a reference to all 
ipv4 sysctl calls available in linux. The reference part of the document is 
heavily based upon linux/Documentation/networking/ip-sysctl.txt document 
written by various writers, as it looks now. The main problem is that I have 
quite a problem understanding the behaviours of some variables/sysctl calls, 
and what they do. 

I will (try to :-)) briefly sum up all questions I have at this moment below:

ip_nonlocal_bind - how does this affect the ip stack? How and why will it break 
certain applications (according to ip-sysctl.txt)? A possible scenario when it 
may be used?

INET peer storage - one of the subtopics from the ip-sysctl.txt. What does this 
refer to? ARP tables and storage I assume, but I am not 100% sure? Would anyone 
care to give a very very brief explanation to this "section" and why a specific 
subsection on this in the document, but not 

tcp_max_syn_backlog - I haven't looked in the source code for this one myself, 
but the default values listed in the ip-sysctl.txt document are faulty in 
comparison to the default values I get on my own systems. Are these calculated 
at boot time, or is the document simply old?

tcp_fack - Does this variable turn on Fast Acknowledgement, and if so, in which 
RFC is this documented? RFC 2018, 2883 or some other? 

tcp_reordering - What does it mean? How does it work? Is there any RFC 
documenting this and what the default behaviour should be? 

tcp_adv_win_scale - I can say nothing but "hmmm" about the explanation in the 
ip-sysctl.txt document, and I understand pretty much nothing from what I've 
read in the source, though I haven't even tried very much so far. What do the 
different equations do as specified in ip-sysctl.txt? What do the variables 
used in them mean? Perhaps I'm just dumb or something :-).

icmp_ratemask - Both these are interconnected afaik, but they are not listed in 
the ip-sysctl.txt (seems they override the old variables that where available). 
From what I understand, ratemask tells which ICMP types (and codes?) are 
specified, and if to ratelimit these. How is this mask calculated? How is the 
ratelimit set, and in what measurement?

Those are the questions I have for now.. Sorry for the massive amount of 
questions, but I have collected them for a week or so :-). I really really hope 
this is not offtopic for this list and that noone will get too annoyed over the 
questions and that someone is able to reply to them.

Have nice day,

Oskar Andreasson
mailto: blueflux@xxxxxxxxxxx

PS. I will be gone over the weekend so there is no rush with any replies 
really, just thought I'd get them away before the list of questions grows too 
large. DS.

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