[TCPIP]
[reactos.git] / reactos / lib / drivers / lwip / doc / snmp_agent.txt
1 SNMPv1 agent for lwIP
2
3 Author: Christiaan Simons
4
5 This is a brief introduction how to use and configure the SNMP agent.
6 Note the agent uses the raw-API UDP interface so you may also want to
7 read rawapi.txt to gain a better understanding of the SNMP message handling.
8
9 0 Agent Capabilities
10 ====================
11
12 SNMPv1 per RFC1157
13 This is an old(er) standard but is still widely supported.
14 For SNMPv2c and v3 have a greater complexity and need many
15 more lines of code. IMHO this breaks the idea of "lightweight IP".
16
17 Note the S in SNMP stands for "Simple". Note that "Simple" is
18 relative. SNMP is simple compared to the complex ISO network
19 management protocols CMIP (Common Management Information Protocol)
20 and CMOT (CMip Over Tcp).
21
22 MIB II per RFC1213
23 The standard lwIP stack management information base.
24 This is a required MIB, so this is always enabled.
25 When builing lwIP without TCP, the mib-2.tcp group is omitted.
26 The groups EGP, CMOT and transmission are disabled by default.
27
28 Most mib-2 objects are not writable except:
29 sysName, sysLocation, sysContact, snmpEnableAuthenTraps.
30 Writing to or changing the ARP and IP address and route
31 tables is not possible.
32
33 Note lwIP has a very limited notion of IP routing. It currently
34 doen't have a route table and doesn't have a notion of the U,G,H flags.
35 Instead lwIP uses the interface list with only one default interface
36 acting as a single gateway interface (G) for the default route.
37
38 The agent returns a "virtual table" with the default route 0.0.0.0
39 for the default interface and network routes (no H) for each
40 network interface in the netif_list.
41 All routes are considered to be up (U).
42
43 Loading additional MIBs
44 MIBs can only be added in compile-time, not in run-time.
45 There is no MIB compiler thus additional MIBs must be hand coded.
46
47 Large SNMP message support
48 The packet decoding and encoding routines are designed
49 to use pbuf-chains. Larger payloads than the minimum
50 SNMP requirement of 484 octets are supported if the
51 PBUF_POOL_SIZE and IP_REASS_BUFSIZE are set to match your
52 local requirement.
53
54 1 Building the Agent
55 ====================
56
57 First of all you'll need to add the following define
58 to your local lwipopts.h:
59
60 #define LWIP_SNMP 1
61
62 and add the source files in lwip/src/core/snmp
63 and some snmp headers in lwip/src/include/lwip to your makefile.
64
65 Note you'll might need to adapt you network driver to update
66 the mib2 variables for your interface.
67
68 2 Running the Agent
69 ===================
70
71 The following function calls must be made in your program to
72 actually get the SNMP agent running.
73
74 Before starting the agent you should supply pointers
75 to non-volatile memory for sysContact, sysLocation,
76 and snmpEnableAuthenTraps. You can do this by calling
77
78 snmp_set_syscontact()
79 snmp_set_syslocation()
80 snmp_set_snmpenableauthentraps()
81
82 Additionally you may want to set
83
84 snmp_set_sysdescr()
85 snmp_set_sysobjid() (if you have a private MIB)
86 snmp_set_sysname()
87
88 Also before starting the agent you need to setup
89 one or more trap destinations using these calls:
90
91 snmp_trap_dst_enable();
92 snmp_trap_dst_ip_set();
93
94 In the lwIP initialisation sequence call snmp_init() just after
95 the call to udp_init().
96
97 Exactly every 10 msec the SNMP uptime timestamp must be updated with
98 snmp_inc_sysuptime(). You should call this from a timer interrupt
99 or a timer signal handler depending on your runtime environment.
100
101 An alternative way to update the SNMP uptime timestamp is to do a call like
102 snmp_add_sysuptime(100) each 1000ms (which is bigger "step", but call to
103 a lower frequency). Another one is to not call snmp_inc_sysuptime() or
104 snmp_add_sysuptime(), and to define the SNMP_GET_SYSUPTIME(sysuptime) macro.
105 This one is undefined by default in mib2.c. SNMP_GET_SYSUPTIME is called inside
106 snmp_get_sysuptime(u32_t *value), and enable to change "sysuptime" value only
107 when it's queried (any function which need "sysuptime" have to call
108 snmp_get_sysuptime).
109
110
111 3 Private MIBs
112 ==============
113
114 If want to extend the agent with your own private MIB you'll need to
115 add the following define to your local lwipopts.h:
116
117 #define SNMP_PRIVATE_MIB 1
118
119 You must provide the private_mib.h and associated files yourself.
120 Note we don't have a "MIB compiler" that generates C source from a MIB,
121 so you're required to do some serious coding if you enable this!
122
123 Note the lwIP enterprise ID (26381) is assigned to the lwIP project,
124 ALL OBJECT IDENTIFIERS LIVING UNDER THIS ID ARE ASSIGNED BY THE lwIP
125 MAINTAINERS!
126
127 If you need to create your own private MIB you'll need
128 to apply for your own enterprise ID with IANA: http://www.iana.org/numbers.html
129
130 You can set it by passing a struct snmp_obj_id to the agent
131 using snmp_set_sysobjid(&my_object_id), just before snmp_init().
132
133 Note the object identifiers for thes MIB-2 and your private MIB
134 tree must be kept in sorted ascending (lexicographical) order.
135 This to ensure correct getnext operation.
136
137 An example for a private MIB is part of the "minimal Unix" project:
138 contrib/ports/unix/proj/minimal/lwip_prvmib.c
139
140 The next chapter gives a more detailed description of the
141 MIB-2 tree and the optional private MIB.
142
143 4 The Gory Details
144 ==================
145
146 4.0 Object identifiers and the MIB tree.
147
148 We have three distinct parts for all object identifiers:
149
150 The prefix
151 .iso.org.dod.internet
152
153 the middle part
154 .mgmt.mib-2.ip.ipNetToMediaTable.ipNetToMediaEntry.ipNetToMediaPhysAddress
155
156 and the index part
157 .1.192.168.0.1
158
159 Objects located above the .internet hierarchy aren't supported.
160 Currently only the .mgmt sub-tree is available and
161 when the SNMP_PRIVATE_MIB is enabled the .private tree
162 becomes available too.
163
164 Object identifiers from incoming requests are checked
165 for a matching prefix, middle part and index part
166 or are expanded(*) for GetNext requests with short
167 or inexisting names in the request.
168 (* we call this "expansion" but this also
169 resembles the "auto-completion" operation)
170
171 The middle part is usually located in ROM (const)
172 to preserve precious RAM on small microcontrollers.
173 However RAM location is possible for a dynamically
174 changing private tree.
175
176 The index part is handled by functions which in
177 turn use dynamically allocated index trees from RAM.
178 These trees are updated by e.g. the etharp code
179 when new entries are made or removed form the ARP cache.
180
181 /** @todo more gory details */