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Apple provides an SNMP Manager that implements an architecture for doing
network management on a Macintosh computer. This Technote describes how the
SNMP manager finds network cards on a Macintosh and explains how you can make
the SNMP Manager recognize new types of network cards. This Technote is a
supplement to the information provided in the Developers kit for SNMP available
on the E.T.O. CD-ROM in the MacSNMP Programmer's Guide.. The kit defines
the interfaces to actually gather the information.
[June 01 1993]
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Introduction
This Technote assumes that you know something about SNMP and how it works. It
also assumes that you know something about the Macintosh computer's resource
manager and driver architecture. This note provides information additional to
that provided in the MacSNMP Programmer's Guide. The method that the
SNMP Manager uses to find a networking card depends on the slot manager;
therefore, machines that do not support the slot manager will not support
SNMP-managed network cards.
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Network Management Framework
In the IETF (Internet Engineering Task Force) framework for network management
there are MIBs (Management Information Bases) for practically every known
device, including Ethernet cards, Token Ring cards, FDDI cards, LocalTalk,
SMDS, ATM, and others. A MIB describes a mini database that a device must
support in order to be network manageable. MIBs consist of groups, each of
which contains variables and/or rows of variables (tables). One of the standard
groups in the standard TCP/IP MIB II (RFC 1213) is the interfaces (if) group.
The ifGroup contains variables that describe any (and every) network
card. It defines statistics (identified as variables) such as number of packets
sent, number of bytes sent, number of bytes received, and so on. As documented
in the MacSNMP Programmer's Guide, the SNMP Manager makes a driver call
to a network card to determine this information. But how does it find the
driver?
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Finding the Driver
The SNMP Manager looks through all of the slots (including the pseudo slot for
a .ENET0 device) using the Slot Manager. It searches for any device
that has the SpBlock.spCategory set to catNetwork (=4.) It
assumes that this (and only this category) is a network card. It then
looks in its STR# resource (resource ID = 1) for the driver name,
using the SpBlock.spCType as the index. The shipping resource is
listed below.
resource 'STR#' (1,"Driver Names for cards"){
{
".ENET",".TOKN","","","","","","",
"","","","","","","","",
".FDDI"
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Please note that since the spCType of an FDDI card is 17, there are 14
blank entries in this resource. When the original (pre-FDDI final
specifications) code for the SNMP Manager was done, FDDI was going to have an
spCType of 3. It is unknown why this changed, but Apple Developer
Technical Service has promised to be more compact in the future.
The reason for this hack is that the driver name for many cards is not
correctly stored in the SpBlock, while the spCType always is.
The SNMP Manager then checks to see if a driver of that name is opened for that
slot. If it is, it can then proceed to make the parameter block based
statistics calls to gather the information defined in the ifTable in the
ifGroup.
The ifTable in the ifGroup is defined in ASN.1 notation in RFC 1213 as:
IfEntry ::=
SEQUENCE {
ifIndex INTEGER,
ifDescr DisplayString,
ifType INTEGER,
ifMtu INTEGER,
ifSpeed Gauge,
ifPhysAddress PhysAddress,
ifAdminStatus INTEGER,
ifOperStatus INTEGER,
ifLastChange TimeTicks,
ifInOctets Counter,
ifInUcastPkts Counter,
ifInNUcastPkts Counter,
ifInDiscards Counter,
ifInErrors Counter,
ifInUnknownProtos Counter,
ifOutOctets Counter,
ifOutUcastPkts Counter,
ifOutNUcastPkts Counter,
ifOutDiscards Counter,
ifOutErrors Counter,
ifOutQLen Gauge,
ifSpecific OBJECT IDENTIFIER
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The SNMP Manager controls the index, as this must be the same for various other
tables. Additionally, the ifTable requires that we return an object ID that
describes the ifSpecific system on the card and an integer describing
the ifType. This tells network management stations where to go to get
information specific to this type of network card (things like how many times a
Token Ring got a bad token or how many times packet length overruns occurred on
an Ethernet card). The SNMP Manager finds this object
identifier by using the SpBlock.spCType as the index into
another resource of type `ifSP'. It also finds the ifType in this resource;
this number is defined in RFC 1213 for several networking systems. This
resources is defined as:
/*-------------ifSP * ifSpecific Enumerated Object IDs-----------------*/
type 'ifSP' {
integer = $$Countof(OIDEnum); /* Number of specific Object IDs */
wide array OIDEnum {
unsigned long; /* ifType, from RFC 1213 */
wide array ObjectID { /* Object ID for this card type */
unsigned integer = $$Countof(ID); /* Num of IDs in OID */
wide array ID {
unsigned long; /* an ID */ };
};
};
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And the resource that is shipping with the card looks like the following:
data 'ifSP' (1, "ifSpecific Enumerated") {
$"0011" //Three entries in table
$"0000 0006" // Enet type
$"0008" //ENET Object ID
$"0000 0001"
$"0000 0003"
$"0000 0006"
$"0000 0001"
$"0000 0002"
$"0000 0001"
$"0000 000A"
$"0000 0007"
$"0000 0009" // Token ring type
$"0008" //Token ring Object ID
$"0000 0001"
$"0000 0003"
$"0000 0006"
$"0000 0001"
$"0000 0002"
$"0000 0001"
$"0000 000A"
$"0000 0009"
$"0000 0000 0000" // #3 type + oid ID
$"0000 0000 0000" // #4 type + oid ID
$"0000 0000 0000" // #5 type + oid ID
$"0000 0000 0000" // #6 type + oid ID
$"0000 0000 0000" // #7 type + oid ID
$"0000 0000 0000" // #8 type + oid ID
$"0000 0000 0000" // #9 type + oid ID
$"0000 0000 0000" // #10 type + oid ID
$"0000 0000 0000" // #11 type + oid ID
$"0000 0000 0000" // #12 type + oid ID
$"0000 0000 0000" // #13 type + oid ID
$"0000 0000 0000" // #14 type + oid ID
$"0000 0000 0000" // #15 type + oid ID
$"0000 0000 0000" // #16 type + oid ID
$"0000 000F" // FDDI Type
$"0008" //FDDI Object ID
$"0000 0001"
$"0000 0003"
$"0000 0006"
$"0000 0001"
$"0000 0002"
$"0000 0001"
$"0000 000A"
$"0000 000E"
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Please note again that since the spCType of FDDI is 17, there are 14
blank entries in this resource.
Both of these resources are stored in the SNMP Manager file in the Extensions
folder. If you are releasing a new type of networking card and want it to be
network manageable, you must perform the following steps.
To support the generic ifGroup (minimum support to claim network compatibility)
you must:
- implement the driver call described in the MacSNMP Programmer's Guide for network cards; specifically, it must support the following driver selector: 242 (
LapGetLinkStatus).
- ensure that the STR# resource of ID #1 in the SNMP Manager file in the Extensions folder has the name of your network driver in the correct string (the one that has an index equal to the
spCType of your card).
- ensure that the `ifSP' resource of ID #1 in the same place has the correct entry for your network card's object ID. This object ID will only be used for display.
When adding your entry to either of these resources, please don't overwrite the
entire resource. Just add your specific entries to the resource. Other cards or
future release may have already altered the resources beyond what is listed
above and you would not want to erase useful information and cause other
people's hardware to fail.
To support the specific MIB for your network group is a bit more complicated.
The shipping SNMP Manager defines a driver interface for Ethernet and Token
Ring cards to use to return the network specific statistics. And future
versions of the AppleTalk Connection Product will have Agents that can actually
report these values to the SNMP Manager. The Agent will depend upon the correct
driver name from the STR# resource described above. Thus, if you are building
an Ethernet or Token Ring card you will only have to implement the correct
driver calls as documented in the MacSNMP Programmer's Guide to become
fully network manageable.
If you are building a third type of card, the problem is more difficult. First
the IETF has not defined MIBs for most other types of cards, and second there
is no definition for which selector returns which information from the card's
driver. As new cards become available Apple may provide Link Layer agents that
can manage these new cards. Apple Developer Technical Support should be
notified if you are building a new card. There are several procedures to define
new card interfaces, and they can recommend the best alternative for your card
type.
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Conclusion
Please talk to Apple Developer Technical Support if you are developing a new
type of networking card for the Macintosh.
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References
Inside Macintosh, Volume V, Slot manager
Designing Cards and Drivers for the Macintosh Family
MacSNMP Programmer's Guide
RFC 1157, A Simple Network Management Protocol
RFC 1213, Management Information Base for Network Management of
TCP/IP-Based Internets: MIB-II
RFC 1155, Structure and Identification of Management Information for
TCP/IP- Based Internets
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