[colug-432] modems routers switches Oh my!

[Vince Herried]

*I"m not a networking expert.*

Every now  and then I get consulted about a home network and lately it seems
that there are two routers involved.
In the latest example a person has a cable modem ( Motorola SB5100 ) /
router connected to a vonage box
then connected to another router.  She wants to dump her router and buy one
with more ports.  At present
no WIFI is involved.  I suggested a switch or even a hub rather than another
router.
I sent them following image.

https://docs.google.com/drawings/d/1mw66Z8FzkwC8O8AGVmRmRBJ3mpUt_uqqoBhE7yyliBQ/edit

Modem -> Vonage -> Router ( assuming connected to WAN port) -> devices....


So what is going on here,  I have always thought that having two routers in
series was bad!
The manual for  the SB5100 shows a simple graphic showing the output plugged
into a switch or hub with  up to 32 devices so
obviously it is a router ( with a single RJ45 output ).  Apparently there is
no web interface to this SB5100.


What kind of real life issues are there when you have two NATs going on at
the same time.
Obviously it can't be as bad as I thought, because it has been running that
way for years.


BTW:  My system topology is modem/router -> LAN port of a WIFI router ( DHCP
disabled ) -> switch ( I ran out of ports )

approximately like this graphic.
https://docs.google.com/drawings/d/1--ib9LAZ-yvVw8BXlv2tHhp8COXM5aE5dwC-mPoUskU/edit?authkey=CKOCot4D&hl=en_US

Do manufacturers continue to make modem/routers with a single port which
seems to encourage this misuse?
We can't expect the home user to, gasp, read the owners manual can we.


Any one have any real life explanations of problems caused by two NATS?

----
I just ordered a new fancy WIFI box with a bunch of goodies ( router of
course,  bit torrent, uPnP, FTP, ... )
I guess I'm just going to have to bite the bullet and see what I can break
by
miss configuring it.  ( router -> another router -> devices )

If I'm all wet, let the flames arise.

-- 
Vince Herried
Vince at planetvince.info
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