On Wed, 2010-09-15 at 13:39 +0530, Abraham Varricatt wrote:
> On Tue, Sep 14, 2010 at 10:13 PM, Abraham Varricatt <abraham.varricatt
> +s...@googlemail.com> wrote:
> > What is the relationship between the SNMP reported "interfaces" (in
> > MIB-II, I think) and the physical ports on a system? I'm having a
> hard
> > time finding anything on the web.
>
> I've done some more investigation/study into this and well, could
> someone please confirm if I've got my facts right below?
>
> An "interface" refers to a connection into a sub-network and is
> uniquely identified by a MAC ID. In the case of a router having 4
> physical ports, it is usually seen that these 4 ports are connected to
> the "LAN" network and that to anyone connecting to any of the 4 ports
> will see the same MAC ID on the other end. To visualize it,
>
> +---------------------------------------------------------------+
> | Device: router MAC: AA:AA:AA:AA:AA:AA IP:192.168.1.1 |
> | |
> | Port-1 Port-2 Port-3 Port-4 |
> | |^| |^| |^| |^| |
> +----------------------------------|-------------|--------------+
> | |
> | |
> +-------------------------+
> | +----------= Device:
> PC-B |
> | | MAC:
> BB:BB:BB:BB:BB:BB |
> | | IP:
> 192.168.1.10 |
> |
> +-------------------------+
> |
> |
> |
> +------------------------+
> +------------------------= Device:
> PC-C |
> | MAC:
> CC:CC:CC:CC:CC:CC |
> | IP:
> 192.168.1.20 |
>
> +------------------------+
>
>
>
> In the above, consider Port-1 and Port-2 as empty (nothing is
> connected there). For the router it has a single "LAN" interface and
> this interface is shared by the 4 ports. 2 systems are connected to
> Port-3 and Port-4 respectively. Both PC-B and PC-C will see the router
> as having the same IP and MAC ID (indicated in figure).
>
> What I need to confirm is, if we have an SNMP agent running on the
> switch, will it be able to distinguish between the 4 ports? I'm
> guessing NO. Thinking along the same lines, suppose PC-B (acting as an
> SNMP manager) asks the router the status of its 'lone' interface, it
> should reply that it's active. i.e. using SNMPv2 (or standard MIB-II)
> there is no way for the agent to respond back the status of the
> individual ports.
>
> Using SNMP is it possible for the router to respond back to a manager
> the status of the individual ports? i.e. to tell PC-B that Port-1 &
> Port-2 are empty but Port-3 & Port-4 are occupied?
>
>
> I'm sorry if these questions seem noob-ish, but the book I have with
> me doesn't really explain this issue in a way that I understand. Also,
> the above theory is my "best-fit" explanation to my router's behavior
> (a Linksys WRT54GL running DD-WRT).
Here I think the problem is the router architecture.
My understanding is that internally almost all wifi routers have a
computer with three interfaces, external, wifi and internal.
The internal interface is then soldered to a hub (or, in the best of all
worlds, a switch) and to that hub the four ports labeled internal are
connected.
EXT----COMPUTER----WIFI
|
HUB------INTERNAL1-4
/MF
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