119 lines
4.7 KiB
Markdown
119 lines
4.7 KiB
Markdown
# VPP's Interface AgentX
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This is an SNMP agent that implements the [Agentx](https://datatracker.ietf.org/doc/html/rfc2257)
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protocol. It connects to VPP's `statseg` (statistics memory segment) by MMAPing
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it, so the user running the agent must have read access to `/run/vpp/stats.sock`.
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It also connects to VPP's API endpoint, so the user running the agent must
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have read/write access to `/run/vpp/api.sock`. Both of these are typically accomplished
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by running the agent as group `vpp`.
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The agent connects to SNMP's `agentx` socket, which can be either a TCP socket
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(by default `localhost:705`), or a unix domain socket (by default `/var/agentx/master`)
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the latter being readable only by root. It's preferable to run as unprivileged user,
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so a TCP socket is preferred (and the default).
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The agent incorporates a refactored/modified [pyagentx](https://github.com/hosthvo/pyagentx).
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The upstream pyagentx code uses a threadpool and message queue, but it was not very stable.
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Often, due to lack of proper locking, updaters would overwrite parts of the MIB and as a
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result, any reads that were ongoing would abruptly be truncated. I refactored the code to
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be single-threaded, greatly simplifying the design (and eliminating the need for locking).
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To respect the original authors, this code is released with the same BSD 2-clause license.
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## Building
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Install `pyinstaller` to build a binary distribution
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```
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sudo pip install pyinstaller
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pyinstaller vpp-snmp-agent.py --onefile
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## Run it on console
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dist/vpp-snmp-agent -h
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usage: vpp-snmp-agent [-h] [-a ADDRESS] [-p PERIOD] [-d]
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optional arguments:
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-h, --help show this help message and exit
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-a ADDRESS Location of the SNMPd agent (unix-path or host:port), default localhost:705
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-p PERIOD Period to poll VPP, default 30 (seconds)
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-c CONFIG Optional vppcfg YAML configuration file, default empty
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-d Enable debug, default False
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## Install
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sudo cp dist/vpp-snmp-agent /usr/sbin/
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```
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## Configuration file
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This SNMP Agent will read a [vppcfg](https://github.com/pimvanpelt/vppcfg) configuration file,
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which provides a mapping between VPP interface names, Linux Control Plane interface names, and
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descriptions. From the upstream `vppcfg` configuration file, it will only consume the `interfaces`
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block, and ignore the rest. An example snippet:
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```
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interfaces:
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GigabitEthernet3/0/0:
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description: "Infra: Some interface"
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lcp: e0
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mtu: 9000
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sub-interfaces:
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100:
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description: "Cust: Some sub-interface"
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200:
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description: "Cust: Some sub-interface with LCP"
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lcp: e0.200
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20011:
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description: "Cust: Some QinQ sub-interface with LCP"
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encapsulation:
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dot1q: 200
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inner-dot1q: 11
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exact-match: true
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lcp: e0.200.11
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```
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This configuration file is completely optional. If the `-c` flag is empty, or it's set but the file does
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not exist, the Agent will simply enumerate all interfaces, and set the `ifAlias` OID to the same value as
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the `ifName`. However, if the config file is read, it will change the behavior as follows:
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* The `ifAlias` OID for an interface will be set to the `description` field.
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* Any `tapNN` interface names from VPP will be matched to their PHY by looking up their Linux Control Plane
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interface:
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* The `ifName` field will be rewritten to the _LIP_ `host-if`, which is specified by the `lcp`
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field. For example, `tap3` above will become `e0` while `tap3.20011` will become `e0.200.11`.
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* The `ifAlias` OID for a TAP will be set to the string `LCP ` followed by its PHY `ifName`. For example,
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`e0.200.11` will become `LCP GigabitEthernet3/0/0.20011 (tap3)`
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## SNMPd config
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First, configure the snmpd to accept agentx connections by adding (at least) the following
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to `snmpd.conf`:
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```
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master agentx
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agentXSocket tcp:localhost:705,unix:/var/agentx-dataplane/master
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```
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and restart snmpd to pick up the changes. Simply run `./vpp-snmp-agent.py` and it
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will connect to the snmpd on localhost:705, and expose the IFMib by periodically
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polling VPP. Observe the console output.
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## Running in production
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Meant to be run on Ubuntu, copy `*.service`, disable the main snmpd, enable
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the one that runs in the dataplane network namespace and start it all up:
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```
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sudo cp netns-dataplane.service /usr/lib/systemd/system/
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sudo cp snmpd-dataplane.service /usr/lib/systemd/system/
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sudo cp vpp-snmp-agent.service /usr/lib/systemd/system/
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sudo systemctl daemon-reload
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sudo systemctl stop snmpd
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sudo systemctl disable snmpd
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sudo systemctl enable netns-dataplane
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sudo systemctl start netns-dataplane
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sudo systemctl enable snmpd-dataplane
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sudo systemctl start snmpd-dataplane
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sudo systemctl enable vpp-snmp-agent
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sudo systemctl start vpp-snmp-agent
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```
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