[SCFN] router vs. switch

[Kevin Stevens]

On Oct 12, 2009, at 18:16, green bean wrote:

> Our head of IT [who never even heard of m0n0wall or pfSense, hes a  
> Windoze-only person]
> says that:
> we have a standard D-Link wireless router. one of the ports is  
> marked WAN, the rest are LAN.
> he says you cannot use the WAN port as an uplink because its feed  
> from other switches upstream,
> instead of directly off our [satellite] modem.
> True?

Maybe.  It wouldn't properly be an uplink in the normal sense of the  
term, and you'd have to use a different address space behind it (which  
is probably what he objects to)

> He says we should use it as a switch, only using the LAN ports,  
> putting the feed from upstream switches into one of those LAN ports.
> Does this make sense?

Yes.  That's how I use all my SOHO routers.  I don't need the routing  
or firewall capabilities, those are handled at my perimeter.

> In switches and hubs, all ports are numbered, none of them marked  
> "uplink."
> He says if port 1 is used as an uplink, the port next to it should  
> be kept vacant,
> because it wont work.
> True?

Not as a general rule.  If he knows something specific about your  
particular router, it might be.

>  We have a 24 port switch [other switches are upstream] which i  
> plugged my laptop into.
> I cant get a regular [192.168 etc] IP, windoze gives me a useless  
> 169.etc IP and says limited or no connectivity of course.
> I tried ipconfig/release and ipconfig/renew but that didnt help.

So you aren't getting DHCP service on that port.  That could be any  
number of things.

> So I move downstream to a D-Link wireless router with one of its LAN  
> ports connected to the 24 port switch.
> Its WAN port is kept vacant for the "reason" discussed above.
> I plug into another of its LAN ports and I get a regular 192.168.etc  
> IP.
> This doesnt make sense because im downstream from the 24 port switch  
> which wouldnt give me a regular IP.

Yes, it does.  Your router has a DHCP server built into it, so when  
you plug in you are getting DHCP from there.  Incidentally you may be  
screwing up requests from other hosts on that broadcast domain.

> Im guessing the 24 port switch had no more IPs to give out even  
> though it had vacant ports.
> Can this be true?

Switches, per se, don't provide DHCP services.  The router connected  
to it upstream (not yours) probably has a BOOTP forwarder on it to  
send DHCP requests to a server somewhere; or may possibly have a DHCP  
server capability built into it.  As per above, there could be any  
number of reasons why you couldn't pull DHCP directly from that 24- 
port switch:  it might have port security enabled and not even be  
talking to your laptop; it might not have DHCP forwarding enabled  
upstream on the router, etc. etc.

You really shouldn't be doing what you're doing since you don't know  
the potential consequences.  You could easily be screwing up  
communications elsewhere in your network.  Everything your network  
admin says is accurate, so I suggest you stop calling him names and  
work with him.

KeS