[Cu-wireless] Re: Cu-wireless digest, Vol 1 #119 - 6 msgs
mmorenz at mail1-0.chcgil.ameritech.net
mmorenz at mail1-0.chcgil.ameritech.net
Fri May 3 09:25:23 CDT 2002
####REPLIES INLINE...FIRST THOUGH, I WANT TO SAY THAT I AM
ENCOURAGED BY THE CONCRETE PROPOSALS AND DISUCSSION THAT'S
> Message: 3
> Date: Thu, 2 May 2002 14:21:32 -0500
> From: Jon Dugan <jdugan at ncsa.uiuc.edu>
> To: cu-wireless at lists.groogroo.com
> Subject: Re: [Cu-wireless] Re: Cu-wireless digest, Vol 1
#118 - 4 msgs
> I apologize for missing the Tuesday meeting, I had plans
the predated the
> change to Tuesdays. I will be there not the next Tuesday
(out of town on
> business) but the following Tuesday.
> On Thu, May 02, 2002 at 07:53:24AM -0500, The Morenz Family
> > >From: David Young <dyoung at onthejob.net>
> > >I can understand the desire to keep the routing tables
compact, but subnet
> > >routing seems unnatural for a wireless network. Will OSPF
bog down if
> > >we do not use subnets? Every host in a subnet needs to be
> > >routed, anyway....
> Why does every host in the subnet need to be routed
individually? I am
> trying to understand what problem you are trying to
> architecture you are building toward.
####THAT'S MY BIG KEY, AS WELL. I AM HOPEFUL THAT WE WILL SEE A
DEFINITION OF JUST-WHAT-THE-NETWORK-IS-DESIGNED-TO-DO. THE
ANSWER THAT THE NETWORK IS "SELF-JUSTIFYING" IS NOT SATISFYING
TO ME AND I DON'T THINK IT BODES WELL FOR THE PROJECT.
I ONCE HAD A VETERAN SYSADMIN SAY THAT THERE'S A DIFFERENCE
BETWEEN 'AD HOC' AND 'POINTLESS'. IF I'M IN NEW YORK AND I
WAN'T TO GET TO L.A. BY ANY MEANS NECESSARY, THEN THAT'S 'AD
HOC'. IF I'M IN NEW YORK AND I DON'T KNOW WHERE I WANT TO
> > The whole idea of subnet routing is that things in a subnet
> > individually routed. So, if you are individually routing
> > elements of a subnet then you are not using subnet
routing. Am I
> > missing something?
> No that is absolutely correct. Routing works in the
following manner, there
> are three components to a route table entry:
> 1. the network address
> 2. the mask
> 3. the next hop
> The network address specifys the high bits of interest.
The mask specifies
> how many of those bits are interesting and the next hop
determines what the
> next hop router is (that is the next Layer 3 device).
> So for example, NCSA has the 22.214.171.124/16 block of
address space. The /16
> notation means that the higest 16 bits make up the
legitimate prefix. This
> is equivalent to a 255.255.0.0 netmask. A network address
with a mask is
> often referred to as a prefix. A /24 is the most typical
length for a
> subnet, it has a netmask of 255.255.255.0.
> Routes are always matches in longest prefix order, that is
if you are trying
> to forward a packet to 126.96.36.199 and you have the
following two routes:
> Prefix Next Hop
> -------------- ----------------
> 188.8.131.52/16 141.142.x.y
> 184.108.40.206/24 141.142.a.b
> You will select the second route because it has a longer
> for example outside of NCSA we only announce the /16.
> I'm not sure what the current proposed architecture is,
however it seems
> reasonable that you would want to use subnet routing. If
we use the RFC
> 1918 address space 10.0.0.0/8 and dividie that up amongts
the various nodes,
> we should have plenty of room for growth. We could
allocate a /16's to major
> aggregation point which would hand out /24's to their
downstreams. This is
> essential the same as the BxNode and CxNode from the
Seattle Wireless stuff.
####THIS (USING THE Bx NODES AS UPSTEAM ROUTERS IS SLIGHTLY
DIFFERENT THAN WHAT ZACH DESCRIBED ON TUESDAY. I LIKE THIS
SETUP AS WELL)####
> In this sort of a model, the CxNodes would advertise their
> into OSPF. Each BxNode would collect all the routes from
> Cx nodes and exchange routes with other Bx nodes.
> I have given some thought to a routing architecture, but
I'm afraid I'm out
> of time right now (the day job calls).
> One last question which routing protocol implementation did
you have in
> mind? GateD? Zebra?
> > My understanding is that a few thousand entries in the
> > is no big deal. Millions are a problem. Are you talking
> > Champaign-Urbana? If so, what is the point of subnet
> Correct. We really don't need to worry about the size of
the routing table
> until it gets into the 100,000 range or so. A P133 can
handle stuff under
> 100,000 routes with no major problem.
> > ####(THERE SEEMS TO BE SOME CONFUSION REGARDING
> > ROUTING" IS A REDUNDANT TERM. ALL LAYER 3 PACKET SWITCHING
IS DONE BY
> > NETWORK (OR "SUBNET") NUMBER. ROUTERS DO NOT, IN FACT *CAN
> > ABOUT HOSTS...THEY ONLY ROUTE TO NETWORKS.)
> A router can in fact provide a route to a single host. You
can specify a
> route with a mask that is 32 bits long. This route will
cover a single
> host. This is known as a host route or a /32.
####THIS IS A VALID POINT, JON. BUT SO AS NOT TO CONFUSE THOSE
WHO ARE LESS FAMILIAR WITH ROUTING (FOR WHOM THE TERM "HOST
ROUTE" MIGHT BE MISLEADING), IT SHOULD BE NOTED THAT
TECHNICALLY THE ROUTER IS NOT ROUTING TO A *HOST*, BUT RATHER
TO A NETWORK THAT CONTAINS ONLY ONE HOST (HENCE THE /32 MASK).
SO, AS I SAID BEFORE: ALL ROUTING IS DONE BY NETWORKS.
FROM A DESIGN STANDPOINT, IF THE NETWORK WILL HAVE A
PREPONDERANCE OF /32 OR "HOST" ROUTES AND IF, AS DAVID SAID
EARLIER, THE HOSTS WILL BE GROUPED "ARBITRARILY" INTO VARIOUS
NETWORKS, THEN THE OBVIOUS QUESTION TO ME IS WHY WE ARE ROUTING
AT ALL? THERE IS ALREADY A PROTOCOL FOR CREATING REDUNDANCY AND
AVOIDING LOOPS IN A NETWORK THAT SWITCHES BY INDIVIDUAL ADDRESS
AND THAT IS SPANNING TREE PROTOCOL (AS USED IN A FULLY-BRIDGED
WHEN I'VE ASKED THIS BEFORE, I BELIEVE SOMEONE SAID THAT WE
WANT TO MAKE SURE AND USE THE SHORTEST PATH, BUT STP CAN BE
TWEAKED TO DO THIS MUCH MORE EASILY THAN TRYING TO IMPLEMENT
OSPF IN A NIGHTMARE OF OVERLAPPING AREAS OR BY RE-ENGINEERING
IP TO ADD SOME SORT OF NEW FUNCTIONALITY (INTERFACE_ID, ETC).
ANYWAY, I LIKE THIS DISCUSSION. GOOD MEAT.
Mark A. Morenz, MS Ed, CCNA+BSCN, CCAI
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