[nsp] does it switch or route

[Stephen J. Wilcox]

On Tue, 20 May 2003, gab.seun jones.ewulomi wrote:

> The 69 adresses and the 10 addresses are all on the same Lan(all in the same
> physical building)

Yes but they are different IP Networks that you happen to have on the same 
physical systems, to the software they are separate.
 
> When I do a sh arp I see arp entries for 69 and 10 addresses.

Yes but your router has an IP on the interface configured in both networks, 
again think as tho they are two different networks

> An as far as I know when the router as learnt the ip to mac address(as long 
> as the aging time hasn't expired) and if
> it then hears a packet going to a 10 network in which it has already heard a
> 
> conversation(arp entry in router) the router will switch it or it will be a
> layer 2 conversation

ok its both! your looking too deep..

think of your network like this

<--L3-->Rtr<--L3-->
<--L2-->   <--L2-->
<-Host->   <-Host->
69/8       10/8

right the data starts at the host on the left src 69/8 destination 10/8. the 
host has no idea where the 10/8 net is so it sends it to the router default 
gateway on 69/8 address

to send to the router 69/8 the host and router have to have arp to determine how 
the L3 Ip address maps to the L2 network card address (MAC)

so the packet (L3) is put into an ethernet frame (L2), sent over the ethernet
(L2) to the router, the router takes the packet (L3) out of the frame (L2) 
decides it is going to a host on the 10/8 net which it has arp for already so it 
puts the packet (L3) into a frame (L2) and transmits onto the ethernet

so the receiving host gets the frame (L2) extracts the packet (L3) and theres 
your data.. so you see it has been routed over the router and the L2 arp and mac 
info is needed by the hardware to do the actual transmitting on the ethernet

.. any help or have i just really muddied the water for you!

Steve

> 
> please advice/correct if im wrong
> 
> regards,
> gab
> 
> 
> 
> >From: "Stephen J. Wilcox" <steve at telecomplete.co.uk>
> >To: "gab.seun jones.ewulomi" <seun_ewulomi at hotmail.com>
> >CC: cisco-nsp at puck.nether.net
> >Subject: Re: [nsp] does it switch or route
> >Date: Tue, 20 May 2003 15:38:07 +0100 (BST)
> >
> >
> >On Tue, 20 May 2003, gab.seun jones.ewulomi wrote:
> >
> > > H people,
> > >
> > > my apologies if this is somewhat a simple and trivial question.
> > >
> > > On my Lan we have end stations configured with a 10 and 69 network /8.
> > > On the default gateway(router) we have the 69.x.x.x ip adress on the
> > > interface and a 10.x.x.x secondary ip address on the same interface.
> > >
> > > My question is if the end stations on the the same lan e.g if a 69 
> >address
> > > pc wants to talk to a 10 adress pc is this switched or routed by the 
> >router
> >
> >I'm guessing your confused by the two terms..
> >
> >Ok to get from 10/8 to 69/8 the packets need to go via a router which is a 
> >layer
> >3 device capable of forwarding in the IP layer (this IP forwarding/routing 
> >is
> >required as the devices are in different networks)
> >
> >The end stations or even switches in the network are not capable of routing
> >packets between networks so the router is needed, all the end stations can 
> >do is
> >talk to other devices in the same network or push the packets at their 
> >default
> >gateway....
> >
> >hth
> >
> >  >
> > > your opinions and answers will be most appreciated
> > >
> > > regards,
> > > gab
> > >
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