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261 lines
9.4 KiB
Markdown
261 lines
9.4 KiB
Markdown
---
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layout: "docs"
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page_title: "Partial LAN Connectivity - Configuring Network Segments"
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sidebar_current: "docs-guides-segments"
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description: |-
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Many advanced Consul users have the need to run clusters with segmented networks, meaning that
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not all agents can be in a full mesh. This is usually the result of business policies enforced
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via network rules or firewalls. Prior to Consul 0.9.3 this was only possible through federation,
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which for some users is too heavyweight or expensive as it requires running multiple servers per
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segment.
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---
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# Network Segments [Enterprise Only]
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~> Note, the network segment functionality described here is available only in [Consul Enterprise](https://www.hashicorp.com/products/consul/) version 0.9.3 and later.
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Many advanced Consul users have the need to run clusters with segmented networks, meaning that
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not all agents can be in a full mesh. This is usually the result of business policies enforced
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via network rules or firewalls. Prior to Consul 0.9.3 this was only possible through federation,
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which for some users is too heavyweight or expensive as it requires running multiple servers per
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segment.
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This guide will cover the basic configuration for setting up multiple segments, as well as
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how to configure a prepared query to limit service discovery to the services in the local agent's
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network segment.
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To complete this guide you will need to complete the
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[Deployment Guide](https://learn.hashicorp.com/consul/advanced/day-1-operations/deployment-guide).
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## Partial LAN Connectivity with Network Segments
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By default, all Consul agents in one datacenter are part of a shared gossip pool over the LAN;
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this means that the partial connectivity caused by segmented networks would cause health flapping
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as nodes failed to communicate. In this guide we will cover the Network Segments feature, added
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in [Consul Enterprise](https://www.hashicorp.com/products/consul/) version 0.9.3, which allows users
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to configure Consul to support this kind of segmented network topology.
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### Network Segments Overview
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All Consul agents are part of the default network segment, unless a segment is specified in
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their configuration. In a standard cluster setup, all agents will normally be part of this default
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segment and as a result, part of one shared LAN gossip pool.
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Network segments can be used to break
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up the LAN gossip pool into multiple isolated smaller pools by specifying the configuration for segments
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on the servers. Each desired segment must be given a name and port, as well as optionally a custom
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bind and advertise address for that segment's gossip listener to bind to on the server.
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A few things to note:
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1. Servers will be a part of all segments they have been configured with. They are the common point
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linking the different segments together. The configured list of segments is specified by the
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[`segments`](/docs/agent/options.html#segments) option.
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2. Client agents can only be part of one segment at a given time, specified by the [`-segment`]
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(/docs/agent/options.html#_segment) option.
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3. Clients can only join agents in the same segment as them. If they attempt to join a client in
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another segment, or the listening port of another segment on a server, they will get a segment mismatch error.
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Once the servers have been configured with the correct segment info, the clients only need to specify
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their own segment in the [Agent Config](/docs/agent/options.html#_segment) and join by connecting to another
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agent within the same segment. If joining to a Consul server, client will need to provide the server's
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port for their segment along with the address of the server when performing the join (for example,
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`consul agent -retry-join "consul.domain.internal:1234"`).
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## Setup Network Segments
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### Configure Consul Servers
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To get started,
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start a server or group of servers, with the following section added to the configuration. Note, you may need to
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adjust the bind/advertise addresses for your setup.
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```json
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{
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"segments": [
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{"name": "alpha", "bind": "{{GetPrivateIP}}", "advertise": "{{GetPrivateIP}}", "port": 8303},
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{"name": "beta", "bind": "{{GetPrivateIP}}", "advertise": "{{GetPrivateIP}}", "port": 8304}
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]
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}
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```
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You should see a log message on the servers for each segment's listener as the agent starts up.
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```sh
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2017/08/30 19:05:13 [INFO] serf: EventMemberJoin: server1.dc1 192.168.0.4
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2017/08/30 19:05:13 [INFO] serf: EventMemberJoin: server1 192.168.0.4
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2017/08/30 19:05:13 [INFO] consul: Started listener for LAN segment "alpha" on 192.168.0.4:8303
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2017/08/30 19:05:13 [INFO] serf: EventMemberJoin: server1 192.168.0.4
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2017/08/30 19:05:13 [INFO] consul: Started listener for LAN segment "beta" on 192.168.0.4:8304
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2017/08/30 19:05:13 [INFO] serf: EventMemberJoin: server1 192.168.0.4
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```
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Running `consul members` should show the server as being part of all segments.
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```sh
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(server1) $ consul members
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Node Address Status Type Build Protocol DC Segment
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server1 192.168.0.4:8301 alive server 0.9.3+ent 2 dc1 <all>
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```
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### Configure Consul Clients in Different Network Segments
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Next, start a client agent in the 'alpha' segment, with `-join` set to the server's segment
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address/port for that segment.
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```sh
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(client1) $ consul agent ... -join 192.168.0.4:8303 -node client1 -segment alpha
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```
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After the join is successful, we should see the client show up by running the `consul members` command
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on the server again.
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```sh
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(server1) $ consul members
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Node Address Status Type Build Protocol DC Segment
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server1 192.168.0.4:8301 alive server 0.9.3+ent 2 dc1 <all>
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client1 192.168.0.5:8301 alive client 0.9.3+ent 2 dc1 alpha
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```
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Now join another client in segment 'beta' and run the `consul members` command another time.
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```sh
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(client2) $ consul agent ... -join 192.168.0.4:8304 -node client2 -segment beta
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```
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```sh
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(server1) $ consul members
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Node Address Status Type Build Protocol DC Segment
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server1 192.168.0.4:8301 alive server 0.9.3+ent 2 dc1 <all>
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client1 192.168.0.5:8301 alive client 0.9.3+ent 2 dc1 alpha
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client2 192.168.0.6:8301 alive client 0.9.3+ent 2 dc1 beta
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```
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### Filter Segmented Nodes
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If we pass the `-segment` flag when running `consul members`, we can limit the view to agents
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in a specific segment.
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```sh
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(server1) $ consul members -segment alpha
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Node Address Status Type Build Protocol DC Segment
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client1 192.168.0.5:8301 alive client 0.9.3+ent 2 dc1 alpha
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server1 192.168.0.4:8303 alive server 0.9.3+ent 2 dc1 alpha
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```
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Using the `consul catalog nodes` command, we can filter on an internal metadata key,
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`consul-network-segment`, which stores the network segment of the node.
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```sh
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(server1) $ consul catalog nodes -node-meta consul-network-segment=alpha
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Node ID Address DC
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client1 4c29819c 192.168.0.5 dc1
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```
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With this metadata key, we can construct a [Prepared Query](/api/query.html) that can be used
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for DNS to return only services within the same network segment as the local agent.
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## Configure a Prepared Query to Limit Service Discovery
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### Create Services
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First, register a service on each of the client nodes.
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```sh
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(client1) $ curl \
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--request PUT \
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--data '{"Name": "redis", "Port": 8000}' \
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localhost:8500/v1/agent/service/register
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```
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```sh
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(client2) $ curl \
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--request PUT \
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--data '{"Name": "redis", "Port": 9000}' \
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localhost:8500/v1/agent/service/register
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```
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### Create the Prepared Query
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Next, write the following to `query.json` and create the query using the HTTP endpoint.
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```sh
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(server1) $ curl \
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--request POST \
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--data \
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'{
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"Name": "",
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"Template": {
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"Type": "name_prefix_match"
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},
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"Service": {
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"Service": "${name.full}",
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"NodeMeta": {"consul-network-segment": "${agent.segment}"}
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}
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}' localhost:8500/v1/query
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{"ID":"6f49dd24-de9b-0b6c-fd29-525eca069419"}
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```
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### Test the Segments with DNS Lookups
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Now, we can replace any dns lookups of the form `<service>.service.consul` with
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`<service>.query.consul` to look up only services within the same network segment.
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**Client 1:**
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```sh
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(client1) $ dig @127.0.0.1 -p 8600 redis.query.consul SRV
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; <<>> DiG 9.8.3-P1 <<>> @127.0.0.1 -p 8600 redis.query.consul SRV
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; (1 server found)
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;; global options: +cmd
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;; Got answer:
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;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 3149
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;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
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;; WARNING: recursion requested but not available
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;; QUESTION SECTION:
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;redis.query.consul. IN SRV
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;; ANSWER SECTION:
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redis.query.consul. 0 IN SRV 1 1 8000 client1.node.dc1.consul.
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;; ADDITIONAL SECTION:
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client1.node.dc1.consul. 0 IN A 192.168.0.5
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```
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**Client 2:**
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```sh
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(client2) $ dig @127.0.0.1 -p 8600 redis.query.consul SRV
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; <<>> DiG 9.8.3-P1 <<>> @127.0.0.1 -p 8600 redis.query.consul SRV
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; (1 server found)
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;; global options: +cmd
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;; Got answer:
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;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 3149
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;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
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;; WARNING: recursion requested but not available
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;; QUESTION SECTION:
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;redis.query.consul. IN SRV
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;; ANSWER SECTION:
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redis.query.consul. 0 IN SRV 1 1 9000 client2.node.dc1.consul.
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;; ADDITIONAL SECTION:
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client2.node.dc1.consul. 0 IN A 192.168.0.6
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```
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## Summary
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In this guide you configured the Consul agents to participate in partial
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LAN gossip based on network segments. You then set up a couple services and
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a prepared query to test the segments.
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