Jay, I now understand the confusion -- You are speaking of the dotted decimal representation of the 32 bit IP address without regard to masking. I am speaking of the masked address which results in a (mask length) network number part and a (32 - mask length) host number. This means you think of address components as octets (bytes) and I think of the effective network number and the effective host number, the sizes of which are determined only by the mask. Or another way to this is that the routers and hosts do not see the dotted notation except in the configuration dialogs. Internal to the routing processes the effective network number determines the routing between subnets and a broadcast address is any address where the host number is all ones. Another way to look at this is to say you are thinking about IP addressing in a "classful" manner whilst I am speaking in a "classless" manner. Believe me, the transition from classful to classless thinking in IP addressing is not an easy thing. None of the RFCs are simple to understand. So, I guess I'm not in trouble after all. Regards. JimC At 8:49 PM -0400 4/14/98, Jay R. Ashworth wrote:
On Tue, Apr 14, 1998 at 04:52:06PM -0400, James R. Cutler wrote:
I have a B assignment. I have switched infrastructure segments with /22 masking. Do you mean to say that the host number range on each /22 masked segment is not continuous 1 through 1022, but has several holes instead.? The network seems to be working properly. I may be in big trouble!
None of my TCP/IP courses or books or Cisco CDs have prepared me for such a surprise. Please point me to a text which will explain this.
None of my study of TCP in the past 5 years has prepared me for the idea that someone might think that any component of an IP address might be greater than 255. They're decimal representations of _8 bit_ numbers.
No matter _where_ the net/subnet break is, you _still_ _write_ them as AAA.BBB.CCC.DDD.
Yes, conceptually, you might _read_ the addresses that way, but I'm pretty sure that not one piece of equipment you own will let you _write_ them that way, will they?
Now, to get back to the conversation at hand: the proposition was that blocking ingress to addresses ending in .255 makes it much more difficult for your network to be used as a "smurf amplifier" (and if you don't know what that is, you haven't been following the discussin (and links) on this list in the last month or 3).
Yes, if you have internal networks larger than a /24, then that means you'll lose extra addresses if you do this.
The point is that if you _don't_ avoid using host addresses that end in .255 _whether that address is a broadcast address based on your netmask or not_, then you're likely to find yourself with hosts that either can't talk, or can't be talked _to_.
Now have I made myself clear?
Cheers, -- jra -- Jay R. Ashworth jra@baylink.com Member of the Technical Staff Unsolicited Commercial Emailers Sued The Suncoast Freenet "Two words: Darth Doogie." -- Jason Colby, Tampa Bay, Florida on alt.fan.heinlein +1 813 790 7592
Managing Editor, Top Of The Key sports e-zine ------------ http://www.totk.com
- James R. Cutler EDS , 800 Tower Drive, Troy, MI 48098 Phone: +1 248 265 7514 FAX: +1 248 265 7514 EDS Internal Web: <http://www.iscg.eds.com/cutler/> World Wide Web: <http://www.ltu.edu/midecus/dechtm/cutler/cutler.htm>
Anyone mind sharing that conversation? On Wed, 15 Apr 1998, James R. Cutler wrote: :Jay, : :I now understand the confusion -- You are speaking of the :dotted decimal representation of the 32 bit IP address without :regard to masking. I am speaking of the masked address which :results in a (mask length) network number part and a :(32 - mask length) host number. This means you think of :address components as octets (bytes) and I think of the :effective network number and the effective host number, the :sizes of which are determined only by the mask. : :Or another way to this is that the routers and hosts do not :see the dotted notation except in the configuration dialogs. :Internal to the routing processes the effective network :number determines the routing between subnets and a broadcast :address is any address where the host number is all ones. : :Another way to look at this is to say you are thinking about :IP addressing in a "classful" manner whilst I am speaking in :a "classless" manner. Believe me, the transition from classful :to classless thinking in IP addressing is not an easy thing. :None of the RFCs are simple to understand. : :So, I guess I'm not in trouble after all. : :Regards. : : JimC : : :At 8:49 PM -0400 4/14/98, Jay R. Ashworth wrote: :>On Tue, Apr 14, 1998 at 04:52:06PM -0400, James R. Cutler wrote: :>> I have a B assignment. I have switched infrastructure segments :>> with /22 masking. Do you mean to say that the host number :>> range on each /22 masked segment is not continuous 1 through 1022, :>> but has several holes instead.? The network seems to be working :>> properly. I may be in big trouble! :>> :>> None of my TCP/IP courses or books or Cisco CDs have prepared me for :>> such a surprise. Please point me to a text which will explain this. :> :>None of my study of TCP in the past 5 years has prepared me for the :>idea that someone might think that any component of an IP address might :>be greater than 255. They're decimal representations of _8 bit_ :>numbers. :> :>No matter _where_ the net/subnet break is, you _still_ _write_ them as :>AAA.BBB.CCC.DDD. :> :>Yes, conceptually, you might _read_ the addresses that way, but I'm :>pretty sure that not one piece of equipment you own will let you :>_write_ them that way, will they? :> :>Now, to get back to the conversation at hand: the proposition was that :>blocking ingress to addresses ending in .255 makes it much more :>difficult for your network to be used as a "smurf amplifier" (and if :>you don't know what that is, you haven't been following the discussin :>(and links) on this list in the last month or 3). :> :>Yes, if you have internal networks larger than a /24, then that means :>you'll lose extra addresses if you do this. :> :>The point is that if you _don't_ avoid using host addresses that end in :>.255 _whether that address is a broadcast address based on your netmask :>or not_, then you're likely to find yourself with hosts that either can't :>talk, or can't be talked _to_. :> :>Now have I made myself clear? :> :>Cheers, :>-- jra :>-- :>Jay R. Ashworth jra@baylink.com :>Member of the Technical Staff Unsolicited Commercial Emailers Sued :>The Suncoast Freenet "Two words: Darth Doogie." -- Jason Colby, :>Tampa Bay, Florida on alt.fan.heinlein +1 813 790 7592 :> :>Managing Editor, Top Of The Key sports e-zine ------------ http://www.totk.com : :- :James R. Cutler :EDS , 800 Tower Drive, Troy, MI 48098 :Phone: +1 248 265 7514 FAX: +1 248 265 7514 :EDS Internal Web: <http://www.iscg.eds.com/cutler/> :World Wide Web: <http://www.ltu.edu/midecus/dechtm/cutler/cutler.htm> : -- Regards, Jason A. Lixfeld jlixfeld@idirect.ca iDirect Network Operations jlixfeld@torontointernetxchange.net --------------------------------------------------------------------- TUCOWS Interactive Ltd. o/a | "A Different Kind of Internet Company" Internet Direct Canada Inc. | "FREE BANDWIDTH for Toronto Area IAPs" 5415 Dundas Street West | http://www.torontointernetxchange.net Suite 301, Toronto Ontario | (416) 236-5806 (T) M9B-1B5 CANADA | (416) 236-5804 (F) ---------------------------------------------------------------------
On Fri, Apr 17, 1998 at 03:32:35PM -0400, jlixfeld@idirect.ca wrote:
:I now understand the confusion -- You are speaking of the :dotted decimal representation of the 32 bit IP address without :regard to masking. I am speaking of the masked address which :results in a (mask length) network number part and a :(32 - mask length) host number. This means you think of :address components as octets (bytes) and I think of the :effective network number and the effective host number, the :sizes of which are determined only by the mask. Anyone mind sharing that conversation?
Oh, he carboned that? I took it off the list when it became obvious to the most casual observer that it didn't belong here. What he was saying was that he doesn't look at IP addresses as AAA.BBB.CCC.DDD. He looks at them as NNNNNNN.HHH,. for whatever decimal split is appropriate for the length of his netmask... which must make him awfully lonely. :-) Cheers, -- jra -- Jay R. Ashworth jra@baylink.com Member of the Technical Staff Unsolicited Commercial Emailers Sued The Suncoast Freenet "Two words: Darth Doogie." -- Jason Colby, Tampa Bay, Florida on alt.fan.heinlein +1 813 790 7592 Managing Editor, Top Of The Key sports e-zine ------------ http://www.totk.com
participants (3)
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James R. Cutler -
Jay R. Ashworth -
jlixfeld＠idirect.ca