Query : agentIP option in hsflowd.conf file to select agent ip address

[koppulanagender-sys]

1. While exploring agentIP i saw below options in https://sflow.net/host-sflow-linux-config.php.

->As per below options agentIP is selected based on available IP addresses on the device and to boost priority below options can be used in hsflowd.conf file.

AGENT CIDR
agent.cidr = 10.0.0.0/8
Prefer an IP address that falls into this range.

agent.cidr = !192.168.0.0/16
Prefer an IP address that does NOT fall into this range.

AGENT INTERFACE
agent = eth0
Select the IP address associated with this interface.

2. But while iam exploring the code, i saw one more option where even if the ip address is not present on the device, with below option agentIP can be selected.
   ->It can be any valid IPV4/IPV6 address and valid hostname .

agentIP = 2.2.2.2

Query :
1.May i know why this agentIP option is not provided in the document.(https://sflow.net/host-sflow-linux-config.php.)
2.My use case will be solved if i use agentIP in hsflowd.conf file , can i use this option

[sflow]

This option is not documented because it is usually a very bad idea to use it(!) In a large network it can be irretrievably confusing if an agent reports sFlow using an IP address that actually belongs to some other device. If you are in a test lab and this is a convenient short-cut then of course, no problem. Otherwise I would advise against it.

[koppulanagender-sys]

Below is the definition of sFlowAgentAddress from RFC 3176: https://datatracker.ietf.org/doc/html/rfc3176

sFlowAgentAddress OBJECT-TYPE
SYNTAX InetAddress
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The IP address associated with this agent. In the case of a
multi-homed agent, this should be the loopback address of the
agent. The sFlowAgent address must provide SNMP connectivity
to the agent. The address should be an invariant that does not
change as interfaces are reconfigured, enabled, disabled,
added or removed. A manager should be able to use the
sFlowAgentAddress as a unique key that will identify this
agent over extended periods of time so that a history can
be maintained."
::= { sFlowAgent 3 }

My use case gets solved by 2 options:

1.Using agentIP = 2.2.2.2 in hsflowd.conf
->I understand it accepts any valid ipv4/ipv6 ip,In large networks we might use a Agent IP which belongs to some other device.

2.Using agent.cidr = 192.168.30.1/32 in hsflowd.conf
->I understand here it checks if the mentioned ip address is present on the device , if present it uses this as agent IP or else it selects based on available IP addresses on device.

Query :

If either of the above options is used to configure the agent address, would that be considered non-compliant with RFC 3176 (sFlowAgentAddress), or is one of these approaches acceptable and i can use it.?

[sflow]

I think it would be safer to use the agent.cidr approach if you can. There you are saying "use this address provided it has been assigned to one of your interfaces, otherwise fall back on the address that is deemed most likely to be stable, unique and reachable."

I don't think there is a compliance problem, but please note that the authority for sFlow v5 is sflow.org.

Some sFlow implementations avoided this problem by requiring that the user choose the agent-address in the device CLI. In the case of hsflowd we wanted to make it possible for every device in the network to have the same configuration. That makes it easier to configure with Puppet/Ansible Kubernetes configmap or DNS-SD, so it scales better for large deployments.