docs: add an up-to-date example for SNMP configuration

console/data/docs/02-configuration.md

@@ -289,21 +289,40 @@ The `snmp` provider accepts the following configuration keys:
 - `poller-retries` is the number of retries on unsuccessful SNMP requests.
 - `poller-timeout` tells how much time should the poller wait for an answer.
 
-For example:
+*Akvorado* will use SNMPv3 if there is a match for the `security-parameters`
+configuration option. Otherwise, it will use SNMPv2.
+
+For example, with SNMPv2 and trying both `private` and `@private` SNMPv2
+communities:
 
 ```yaml
 metadata:
   workers: 10
   providers:
     type: snmp
-    communities:
+    credentials:
       ::/0:
+        communities:
           - private
           - "@private"
 ```
 
-*Akvorado* will use SNMPv3 if there is a match for the `security-parameters`
-configuration option. Otherwise, it will use SNMPv2.
+And with SNMPv3:
+
+```yaml
+metadata:
+  workers: 10
+  providers:
+    type: snmp
+    credentials:
+      ::/0:
+        security-parameters:
+          user-name: monitoring
+          authentication-protocol: SHA
+          authentication-passphrase: "d$rkSec"
+          privacy-protocol: AES192
+          privacy-passphrase: "Cl0se"
+```
 
 #### gNMI provider
 

console/data/docs/05-troubleshooting.md

@@ -205,7 +205,6 @@ For the second case, use this one:
 $ curl -s http://127.0.0.1:8080/api/v0/outlet/metrics | grep 'akvorado_outlet_core.*errors'
 ```
 
-
 Here is a list of errors you may find:
 
 - `metadata cache miss` means interface information is missing from the metadata
@@ -219,6 +218,20 @@ Here is a list of errors you may find:
 - `input and output interfaces missing` means the flow does not contain input
   and output interface indexes. Fix this on the exporter.
 
+To check the SNMP configuration is correct, an convenient way is to use
+`tcpdump`. Notably, you can check the credentials are correct. If you don't get
+a `GetResponse` message, likely there is a misconfiguration on the exporter.
+
+```console
+# tcpdump -c3 -pni any port 161
+20:46:44.812243 IP 240.0.2.11.34554 > 240.0.2.13.161: C="private" GetRequest(95) .1.3.6.1.2.1.1.5.0 .1.3.6.1.2.1.2.2.1.2.11 .1.3.6.1.2.1.31.1.1.1.1.11 .1.3.6.1.2.1.31.1.1.1.18.11 .1.3.6.1.2.1.31.1.1.1.15.11
+20:46:45.144567 IP 240.0.2.13.161 > 240.0.2.11.34554: C="private" GetResponse(153) .1.3.6.1.2.1.1.5.0="dc3-edge1.example.com" .1.3.6.1.2.1.2.2.1.2.11="Gi0/0/0/11" .1.3.6.1.2.1.31.1.1.1.1.11="Gi0/0/0/11" .1.3.6.1.2.1.31.1.1.1.18.11="Transit: Lumen" .1.3.6.1.2.1.31.1.1.1.15.11=10000
+^C
+2 packets captured
+2 packets received by filter
+0 packets dropped by kernel
+```
+
 Another cause for metadata cache misses is that Docker cannot reach the
 exporters because Docker subnets may overlap with your router networks. To fix
 this, add this to `/etc/docker/daemon.json` and restart Docker:

outlet/metadata/provider/snmp/config_test.go

@@ -179,7 +179,7 @@ func TestConfigurationUnmarshallerHook(t *testing.T) {
 						"user-name":                 "alfred",
 						"authentication-protocol":   "sha",
 						"authentication-passphrase": "hello",
-						"privacy-protocol":          "aes",
+						"privacy-protocol":          "AES",
 						"privacy-passphrase":        "bye",
 					},
 				}