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To: python-list@python.org
From: Dennis Lee Bieber <wlfraed@ix.netcom.com>
Subject: Re: Can post a code but afraid of plagiarism
Date: Wed, 22 Jan 2014 22:36:32 -0500
Organization: IISS Elusive Unicorn
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On Wed, 22 Jan 2014 08:33:30 -0800 (PST), indar kumar
<indarkumar59@gmail.com> declaimed the following:

>On Saturday, January 18, 2014 3:21:42 PM UTC-7, indar kumar wrote:
>> Hi,
>> 
>> 
>> 
>> I want to show a code for review but afraid of plagiarism issues. Kindly, suggest how can I post it for review here without masking it visible for public
>
>Description of each of the commands:

	The following appears to be only ONE "command"

>• config
>
>? Parameters: <host_id> <mac addr> <ip addr> <cache timeout>
>? <cache timeout> is the host's ARP cache timeout, in seconds
>? Actions:
>? Update simulator's configuration database.
>• If <host_id> already exists, its information should be updated. Otherwise, it should
>be added.
>? Print “<host_id> connected.”
>? Have the host send a gratuitous ARP request .

http://en.wikipedia.org/wiki/Address_Resolution_Protocol#ARP_announcements


>• If any other hosts have an outdated entry for the MAC or IP address, they should
>update their caches.
>• If there are any responses to that request, that means that somebody else has this IP
>address. If that is the case, you should print:
>Error: <host_id> detected IP address conflict. It will be disconnected.

	That does not follow ARP protocol... BEFORE claiming the IP address,
the "new host" is supposed to send an ARP Probe

http://en.wikipedia.org/wiki/Address_Resolution_Protocol#ARP_probe


	Sending the probe (using a local "IP" address of 0.0.0.0, but with the
correct hardware MAC address) asking if anyone is using the IP address the
local configuration is claiming is supposed to be the test to confirm no
one else has the same IP.

	If no one responds with the configuration IP address, THEN the local
host can send an ARP announcement claiming the IP address, which other
nodes then use to update their cache lists. Note that an ARP announcement
is used to provide the local MAC/IP pair to OTHER nodes. It does not answer
how the local node obtains the information of the other nodes. It may be
possible to have the nodes receiving a broadcast ARP announcement respond
with a direct (that is, TO the original sender only) -- but that could
result in an infinite loop if the original then tries to respond back...


	Note that "host id" is NOT part of the ARP protocol. I'm going to
presume that no actual network traffic (or even interprocess communication)
is being used here -- just a simple single threaded program. If so, "host
id" would probably be used as a dictionary key to identify the ARP cache
for that simulated host. The data value (nothing currently seems to be
using the cache timeout value so I'm going to ignore it) would be, itself,
a dictionary using IP values as keys, with the corresponding MAC address as
the data value. OTOH: since you do need to keep the IP and MAC of the
host... The structure is probably going to look like:

{ hostid : (hostMAC, hostIP, hostTimeout, { otherIP : otherMAC, ...}), ...}

Pseudo-code (and not even using Python syntax <evil grin> [not validated
REXX either])

do forever
	parse pull host MAC IP timeout
	simulation.host.cache = {}		#create/reset this host's cache
	say "sending ARP probe" MAC ff:ff:ff:ff:ff:ff 0.0.0.0 IP
	foreach node in simulation
		if node.hostid = host
			continue	#skip ourselves
		else
			if node.hostIP = IP
				#this IP is assigned elsewhere
				say "sending ARP response" node.MAC MAC node.hostIP IP
				say "error"
				simulation.host = ""	#delete the config host, invalid
	if host in simulation
		#it didn't get deleted, so the IP must be available
		say "sendign ARP announcement" MAC 0:0:0:0:0:0  IP IP
		foreach node in simulation
			if node.hostid = host
				continue
			else
				#update cache with new MAC/IP pair

	Of course, if the IP changed, but not the MAC, the old IP with the MAC
will be left behind... This is where the timeout would come into play, if
each entry had a time-to-purge entry (clock time when entered + timeout
value); then whenever the cache was checked/updated you'd delete any entry
that had a purge time lower than the current clock time.

-- 
	Wulfraed                 Dennis Lee Bieber         AF6VN
    wlfraed@ix.netcom.com    HTTP://wlfraed.home.netcom.com/