mirror of https://github.com/hashicorp/consul
237 lines
9.6 KiB
Markdown
237 lines
9.6 KiB
Markdown
---
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layout: docs
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page_title: Network Segments (Enterprise)
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description: >-
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Network segments enable LAN gossip in a datacenter when network rules or firewalls prevent specific sets of clients from communicating directly. Learn about configuring server and client agents to operate in segmented networks.
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---
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# Network Segments
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<EnterpriseAlert>
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This feature requires version 0.9.3+ of
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self-managed Consul Enterprise.
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Refer to the{' '}
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<a href="/consul/docs/enterprise#consul-enterprise-feature-availability">enterprise feature matrix</a>
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{' '}for additional information.
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</EnterpriseAlert>
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Consul requires full connectivity between all agents (servers and clients) in a
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[datacenter](/docs/agent/config/cli-flags#_datacenter) within a given
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LAN gossip pool. By default, all Consul agents will be a part of one shared Serf LAN
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gossip pool known as the `<default>` network segment, thus requiring full mesh
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connectivity within the datacenter.
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In some environments, full connectivity between all agents is not possible—known as a
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"segmented network". This is usually the result of business policies enforced through
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network rules or firewalls. To use Consul in a segmented network, you must break up
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the LAN gossip pool along network communication boundaries into separate "network
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segments". Network segments are isolated LAN gossip pools that only require full
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connectivity between agent members on the same segment.
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Complete the [Network Segments](https://learn.hashicorp.com/tutorials/consul/network-partition-datacenters) tutorial to learn more about network segments.
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-> **Info:** Network segments enable you to operate a Consul datacenter without full
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mesh (LAN) connectivity between agents. To federate multiple Consul datacenters
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without full mesh (WAN) connectivity between all server agents in all datacenters,
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use [Network Areas (Enterprise)](/docs/enterprise/federation).
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# Consul Networking Models
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To help set context for this feature, it is useful to understand the various
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Consul networking models and their capabilities.
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**Cluster:** A set of Consul servers forming a Raft quorum along with a
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collection of Consul clients, all set to the same
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[datacenter](/docs/agent/config/cli-flags#_datacenter), and joined together to form
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what we will call a "local cluster". Consul clients discover the Consul servers
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in their local cluster through the gossip mechanism and make RPC requests to
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them. LAN Gossip (OSS) is an open intra-cluster networking model, and Network
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Segments (Enterprise) creates multiple segments within one cluster.
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**Federated Cluster:** A set of connected clusters, each representing a unique Consul “datacenter”. These Consul servers are federated together
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over the WAN. Consul clients make use of resources in federated clusters by
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forwarding RPCs through the Consul servers in their local cluster, but they
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never interact with remote Consul servers directly. There are two tutorials that
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will guide you through inter-cluster network models:
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1. [WAN gossip (OSS)](https://learn.hashicorp.com/consul/security-networking/datacenters)
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1. [Network Areas (Enterprise)](https://learn.hashicorp.com/tutorials/consul/federation-network-areas).
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**LAN Gossip Pool**: A set of Consul agents that have full mesh connectivity
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among themselves, and use Serf to maintain a shared view of the members of the
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pool for different purposes, like finding a Consul server in a local cluster,
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or finding servers in a remote cluster. A **segmented** LAN Gossip Pool limits a
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group of agents to only connect with the agents in its segment.
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# Network Segments Configuration
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## Server Configuration
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Server agents are members of all segments. The datacenter includes a `<default>`
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segment, as well as additional segments defined in the
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[`segments`](/docs/agent/config/config-files#segments) server agent configuration option.
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Each additional segment is defined by:
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- a non-empty name
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- a unique port
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- optionally, a custom bind and advertise address for the additional segment's
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Serf LAN listener on the server
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~> **Note:** Prior to Consul 1.7.3, a Consul server agent configured with too
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many network segments may not be able to start due to [limitations](https://learn.hashicorp.com/tutorials/consul/network-partition-datacenters#network-segments-limitations)
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in Serf.
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### Example Server Configuration
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The following server agent configuration will create two user-defined network
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segments: `alpha` and `beta`.
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<CodeTabs heading="Example network segments configuration for server agents">
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```hcl
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segments = [
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{
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name = "alpha"
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bind = "{{GetPrivateIP}}"
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advertise = "{{GetPrivateIP}}"
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port = 8303
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},
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{
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name = "beta"
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bind = "{{GetPrivateIP}}"
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advertise = "{{GetPrivateIP}}"
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port = 8304
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}
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]
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```
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```json
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{
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"segments": [
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{
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"name": "alpha",
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"bind": "{{GetPrivateIP}}",
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"advertise": "{{GetPrivateIP}}",
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"port": 8303
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},
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{
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"name": "beta",
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"bind": "{{GetPrivateIP}}",
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"advertise": "{{GetPrivateIP}}",
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"port": 8304
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}
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]
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}
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```
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</CodeTabs>
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The server [agent configuration](/docs/agent/config/config-files) options relevant to network
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segments are:
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- [`ports.serf_lan`](/docs/agent/config/config-files#serf_lan_port): The Serf LAN port on this server
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for the `<default>` network segment's gossip pool.
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- [`segments`](/docs/agent/config/config-files#segments): A list of user-defined network segments
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on this server, including their names and Serf LAN ports.
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## Client Configuration
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Each client agent can only be a member of one segment at a time. This will be the
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`<default>` segment unless otherwise specified in the agent's
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[`segment`](/docs/agent/config/cli-flags#_segment) agent configuration option.
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### Join a Client to a Segment ((#join_a_client_to_a_segment))
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For a client agent to [join](/commands/join) the Consul
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datacenter, it must connect to another agent (client or server) within its
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configured segment.
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<Tabs>
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<Tab heading="Join via another client">
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Clients A and B specify the same segment S. Client B is already joined to the segment S
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LAN gossip pool. Client A wants to join via Client B. In order to do so, Client A
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must connect to Client B's configured [Serf LAN port](/docs/agent/config/config-files#serf_lan_port).
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</Tab>
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<Tab heading="Join via a server">
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Client A specifies segment S and wants to join the segment S gossip pool via Server 1.
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In order to do so, Client A must connect to Server 1's configured [Serf LAN port
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for segment S](/docs/agent/config/config-files#segment_port).
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</Tab>
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</Tabs>
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There are several methods to specify the port used by the join operation, listed in order
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of precedence:
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1. **Specify an explicit port in the join address**. This can be done at the CLI when starting
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the agent (e.g., `consul agent -retry-join "client-b-address:8303"`), or in the agent's
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configuration using the [retry-join option](/docs/agent/config/config-files#retry_join). This method
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is not compatible with [cloud auto-join](/docs/install/cloud-auto-join#auto-join-with-network-segments).
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2. **Specify an alternate Serf LAN port for the agent**. This can be done at the CLI when starting
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the agent (e.g., `consul agent -retry-join "client-b-address" -serf-lan-port 8303`), or in
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the agent's configuration using the [serf_lan](/docs/agent/config/config-files#serf_lan_port) option.
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When a Serf LAN port is not explicitly specified in the join address, the agent will attempt to
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join the target host at the Serf LAN port specified in CLI or agent configuration.
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3. **Use the default Serf LAN port (8301)**. The agent will attempt to join the target host
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on port 8301.
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-> Agents within a segment can use different port numbers for their Serf LAN port.
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For example, on the `<default>` segment, Server S can use port 8301, Client A
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can use 8303, and Client B can use 8304. However, if an agent wishes to join a
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segment via an agent that uses a different port number, the target agent's Serf LAN
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port must be specified in the join address (method 1 above).
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### Example Client Configuration
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The following client agent configuration will cause the agent to:
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- Open a Serf LAN listener port on 8303.
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- Attempt to join the cluster via servers on port 8303 (since an alternate port is not
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specified in the `retry_join` addresses).
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<CodeTabs heading="Example network segment configuration for client agents">
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```hcl
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node_name = "consul-client1"
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retry_join = ["consul-server1", "consul-server2", "consul-server3"]
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segment = "alpha"
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ports = {
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serf_lan = 8303
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}
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```
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```json
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{
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"node_name": "consul-client1",
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"retry_join": ["consul-server1", "consul-server2", "consul-server3"],
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"segment": "alpha",
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"ports": {
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"serf_lan": 8303
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}
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}
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```
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</CodeTabs>
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The client [agent configuration](/docs/agent/config/config-files) options relevant to network
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segments are:
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- [`segment`](/docs/agent/config/config-files#segment-2): The name of the network segment this
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client agent belongs to.
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- [`ports.serf_lan`](/docs/agent/config/config-files#serf_lan_port):
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Serf LAN port for the above segment on this client. This is not required
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to match the configured Serf LAN port for other agents on this segment.
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- [`retry_join`](/docs/agent/config/config-files#retry_join) or
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[`start_join`](/docs/agent/config/config-files#start_join): A list of agent addresses to join
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when starting. Ensure the correct Serf LAN port for this segment is used when joining
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the LAN gossip pool using one of the [available configuration methods](#join_a_client_to_a_segment).
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