On Tue, Sep 14, 2010 at 10:13 PM, Abraham Varricatt <
abraham.varricatt+s...@googlemail.com<abraham.varricatt%2bs...@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).
Still a bit puzzled,
Abraham Varricatt
------------------------------------------------------------------------------
Start uncovering the many advantages of virtual appliances
and start using them to simplify application deployment and
accelerate your shift to cloud computing.
http://p.sf.net/sfu/novell-sfdev2dev
_______________________________________________
Net-snmp-coders mailing list
Net-snmp-coders@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/net-snmp-coders
