Freebsd 5.1 <-> Win XP Networking problems

[epilogue]

On Wed, 14 Jul 2004 23:06:38 -0400
epilogue <epilogue at allstream.net> wrote:

> On Wed, 14 Jul 2004 16:40:10 -0600
> Danny MacMillan <flowers at users.sourceforge.net> wrote:
> 
> > On Wed, Jul 14, 2004 at 03:41:04AM -0600, Matthew Seaman wrote:
> > > On Tue, Jul 13, 2004 at 02:32:46PM -0700, Darren Pilgrim wrote:
> > > 
> > > > > 	ifconfig_ed0="inet 192.168.1.0/24  netmask 255.255.0.0"
> > > > > 	ifconfig_vr0="inet 192.168.0.0/24  netmask 255.255.0.0"
> > > > 
> > > > 192.168.1.0/24 and 192.168.0.0/24 are blocks of addresses in CIDR
> > > > notation, not the actual addresses to be fed to ifconfig.  You need
> > > > to pick addresses within the netblock to use for myserver and all
> > > > the other machines on your network.  Since myserver can reach the
> > > > internet just fine, you should keep the IP address for vr0 the
> > > > same, just lengthen the netmask to allow the use of 192.168.1.0/24
> > > > on the LAN.
> > > 
> > > ifconfig(8) understands CIDR notation just fine, although it's not
> > > usual to configure an interface using the '.0' /network/ address. 
> > > Look on it as a third alternate way of specifying the netmask, so
> > > that the following three examples are equivalent:
> > > 
> > > 	ifconfig fxp0 inet 192.168.123.74/29
> > >         ifconfig fxp0 inet 192.168.123.74 netmask 0xfffffff8
> > >         ifconfig fxp0 inet 192.168.123.74 netmask 255.255.255.248
> > > 
> > > Those correspond to the slightly contrived example of the /29 network
> > > starting with network address 192.168.123.72 and running up to the
> > > broadcast address 192.168.123.79
> > > 
> > > Note: you can give a broadcast address on the ifconfig command line,
> > > but usually it's not necessary as a standard value will be calculated
> > > from any ip number forming part of that network and from the netmask.
> > > However you can't in general use ip address + broadcast to do the
> > > converse, as there isn't necessarily a unique solution.
> > 
> > I apologize for asking this question here, but I've googled and read
> > arp(4) and arp(1) and nothing I can see gives a clear answer (at least
> > clear to me).  It is related to this thread.
> > 
> > Is it the subnet mask that lets my computer know that for an IP address
> > located external to my network it should send the packet to the router
> > (using the router's MAC address) instead of arp-ing for the MAC address
> > of the target node?
> 
> hello danny,
> 
> i'm only going to speak to the part immediately above...
> 
> kind of yes, but mostly no.

er, how about we forget that i said 'kind of yes, but mostly no' and go
with 'yes, for machines off your network'?  i don't know how that
slipped in there.    ;)

> the subnet mask simply provides a mathematical
> means to segment a single ip block into smaller separate networks.
> technically, the computer will look at it's local network (defined by the
> block and subnet mask) to determine if the target machine is local.  if
> not, your machine knows the target machine must be on another network and
> it forwards the packets to the only other place it can, whatever gateway
> you've defined (ie. your local router), which then forwards it up the
> point-to-point connection to its gateway (your ISP's router), which
> continues to forward it based on IP...
> 
> afaik, MAC addresses have nothing to do with this directly.  yes, MAC
> addresses (OSI model - data link - layer 2) are mapped to IP addresses
> (OSI model - network - layer 3) and vice versa.  these are kept in a
> cache in order to speed up routing, somewhat like having a DNS cache can
> avoid much of the processing wasted on resolving frequently used
> addresses.  generally speaking, this cache is volatile in nature and can
> be cleared manually or by power-cycling a router, to provide two
> examples.
> 
> In case you're curious, this doc is a good primer on IP Addressing and
> subnetting.
> 
> "Understanding IP Addressing: Everything You Ever Wanted To Know"
> http://www.3com.com/other/pdfs/infra/corpinfo/en_US/501302.pdf
> 
> for more about the ISO model, see google.  sorry i don't have an
> interesting link handy.
> 
> hoping that this answered at least part of your question, and crossing
> my fingers that i didn't muddle up any of these details (it has been a
> while since i've looked at this).
> 
> 
> cheers,
> epi
> 
> 
> > This is the only way I can see that this would
> > make sense, as arp -a doesn't seem to return the MAC addresses of boxes
> > on the other side of my router under any circumstances.  I read a
> > document online that suggested that a router would recursively ARP for
> > a non-local MAC address but this seems insane and highly improbable to
> > me.  More likely is that my computer, knowing that an IP address is
> > not local by examining the network address, would choose a route from
> > its routing table, arp for that router's MAC address, and send the
> > packet thither.  But is that what actually happens?
> > 
> > Pointers to documentation explaining this accepted with my thanks.
> > 
> > --
> > Danny MacMillan
> > 
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