Archived from groups: alt.internet.wireless (
More info?)
"Ron Bandes" <RunderscoreBandes @yah00.com> wrote in
news:CQfoc.26316$CC4.11102477@news4.srv.hcvlny.cv.net:
> The MAC address does not come into play only during DHCP negotiation.
> Every IP packet is encapsulated in an Ethernet frame that has a source
> MAC and a destination MAC.
>
> Also, you don't tell the computer to use one of the router's static IP
> addresses. The router assigns a dynamic IP address to the computer
> from a pool of IP addresses. It just isn't true that the router
> doesn't care about the MAC.
Well, I don't know how else to put it about the use of a static IP. As I
understood it, if the router's DHCP IP(s) started from 192.168.1.100
through 192.168.1.150 that's the pool you speak of.
Now if I wanted to use 192.168.1.2 which I understand is a static IP,
then I would have to go to the NIC's configuration screen and enter IP
192.168.1.2 subnet 255.255.255.0 and Default Gateway 192.168.1.1 (Device
IP).
I am only speaking in the context of the OP's post and the MAC and his
mis-understanding of how (basic) things were working; of course the MAC
comes into play when one looks at the picture of network traffic.
>
> However, the original poster needn't worry about a conflict in MAC
> addresses. The TCP/IP protocol suite is layered. IP is a
> Network-layer protocol that understands how to get a packet across an
> internetwork: from network to network to network. But IP doesn't
> understand the details of how to physically get a packet across even a
> single network. It's like IP is a navigator, not a driver.
>
> To continue the navigator/driver analogy, some networks are like
> roads, some are like oceans, some are like air routes. You need
> different drivers to drive cars, boats, and airplanes. These are
> different Data-Link Layer protocols, like Ethernet, PPP (used on
> dialup), and DSL. So after IP determines which network needs to be
> traversed next, it stuffs the IP packet into a Data-Link Layer frame
> that is appropriate for that network type; for your LAN that would be
> Ethernet. Then Ethernet takes over and "drives" the Ethernet frame
> (containing the IP packet) across the LAN from your computer to your
> router. Ethernet knows nothing about IP addresses, so it is using MAC
> addresses to find the router on the Ethernet LAN. So on a LAN, every
> interface (on both computers and routers) have both an IP address and
> a MAC address. When the frame arrives at the router, the packet is
> removed from the Ethernet frame and the frame is discarded. The
> router determines which network the packet must traverse next. It
> then encapsulates the packet in a new frame, and off we go again.
> Remember, not all networks are Ethernet, so in general we can't reuse
> the frame. Also, the destination MAC address in the frame is just the
> next destination, not the final destination. The destination IP
> address in the packet is for the final destination, and it doesn't
> change as the packet makes its way through many networks.
>
> Since MAC addresses are used only to traverse a single network, and
> not an internetwork, it doesn't matter if interfaces on different
> networks have the same MAC address. The only reason that MAC
> addresses are made to be universally unique is that the manufacturer
> doesn't know which two devices will be connected to the same network.
> At home you have three networks in a typical setup: your Ethernet
> LAN, another Ethernet between your router and your broadband modem,
> and the broadband network that connects your modem to the ISP. The
> router's LAN ports are on the Ethernet LAN, the router's WAN port is
> on the other Ethernet between the router and the broadband modem. It
> doesn't matter if the router's WAN port has the same MAC address as a
> computer on the LAN because they're on different networks.
I do appreciate your explaination on all of this, because I certainly
don't have this kind of in-depth knowledge in this area.
However, it's to my understanding that the modem is the device that gets
the public IP from the ISP and the first device behind the modem such as
router, a direct connect computer's NIC, or FW appliance uses the public
IP assigned to the modem --- excuse my lack of words to better describe
this.
I bring the above up because of another discussion I was having with an
OP and his mis-understanding of (excuse me for saying it *stealthing*)
the router ports and the public IP being hidden. This was based on the
Gibson Port scan and stealth check on a router where port 113 was
*closed* and not stealthed. The FTP server needed 113.
I told him it was the modem that was issued the public IP from the ISP
not the router. So, the public IP is known and that so called hiding of
the public IP meant nothing in something discovering the public IP and
stopping port scans.
Also, what's the deal with putting a dummy IP into the DMZ of the router
to redirect unsolicited inbound traffic to the dummy IP in the DMZ of the
router? Is that effective or useless? Also, I port forward port 113 to
the DMZ IP, since one port scan reported that port as being open, which I
don't have any IDENT. The scan reported back 113 was closed when I did
the forwarding.
Can you comment on it?
Duane
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