sub-net routing question

[marthter]

Hi Lennart,

Thank you for your reply...

On 11-08-17 05:22 PM, Lennart Sorensen wrote:
> On Wed, Aug 17, 2011 at 03:40:18PM -0400, marthter wrote:
>> ...
>> Picture three routers and two computers...
>>
>> "middle router" has (for now) nothing connected to WAN, just LAN
>> "left router" has its WAN jack connected to a LAN jack of middle router
>> "right router" has its WAN jack connected to a LAN jack of middle router
>> "left computer" is connected to LAN jack of left router
>> "right computer" is connected to LAN jack of right router
> Are you actually using routers, or just your typical little one wan port
> and a switch type boxes?
um yes and no.  No they are not 48 port rack mount routers.  Yes they 
have one WAN port and four LAN ports (whether the LAN side is just a 
switch or more intelligent or not I don't know).

They are running OpenWRT (which I guess makes this on-topic : - )

However that is not really the point of the question.  I was trying to 
keep the question general, almost as a thought experiment.... if I can 
distill it maybe further it would be something like:

How can one set up three routers and two computers in a hierarchical 
network?
   - if possible using just address/netmask/gateway settings (and 
whatever routes the computers and routers add for you automatically 
based on gateway)
   - but if necessary, with manually added route(s), preferably only on 
the middle router

I guess from all the various networking stuff I've read and played with 
over the years (I mean I've been able to set up a lot of simple LANs for 
people but clearly I've read no Cisco textbooks), I always thought that 
the "right" (or most efficient) way to do this, was both to wire them in 
a tree layout, and to define the logical numbering of addresses and 
subnets in a tree layout that mimics the wiring.

> A lot of the cheap boxes can only route between a wan port and an internal
> switch (with one subnet on it).
If I understand this, I think this means my left router and right router 
are still fine, and this is maybe an issue in my middle router, but it 
would just be broadcasting to its four LAN ports and would eventually 
switch packets to the right ports.

> Some are more advanced and can setup vlan's for specific ports, which
> would allow you to have other switches on different ports with different
> subnets and route between them (there is no need for multiple routers
> to do that, just one decent router and some switches).
Maybe another way to phrase it is, aside from an all-switches network, 
what is the simplest "hello world" heirarchical network that would get 
the most mileage out of the basic address/netmask/gateway setup (which 
I'm most familiar with), and require the fewest custom/manual routing 
rules in the fewest places?

> If you do have multiple routers, some support using RIP or OSPF or ISIS
> to share the routing info with each other, so that you don't have to
> add each route manually to each router.  It can also be used to create
> redundant routes in some cases so a cable or port failure won't take
> out the whole network.
I'd just like to know how to structure it first before improving the 
robustness or maintainability.

Thank you
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