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Chapter 2. Network Configuration Reference

Network configuration is critical for building a high performance Red Hat Ceph Storage cluster. The Ceph storage cluster does not perform request routing or dispatching on behalf of the Ceph client. Instead, Ceph clients make requests directly to Ceph OSD daemons. Ceph OSDs perform data replication on behalf of Ceph clients, which means replication and other factors impose additional loads on the networks of Ceph storage clusters.

All Ceph clusters must use a public network. However, unless you specify a cluster (internal) network, Ceph assumes a single public network. Ceph can function with a public network only, but you will see significant performance improvement with a second "cluster" network in a large cluster.

Red Hat recommends running a Ceph storage cluster with two networks:

  • a public network
  • and a cluster network.

To support two networks, each Ceph Node will need to have more than one network interface card (NIC).

Network Architecture

There are several reasons to consider operating two separate networks:

  • Performance: Ceph OSDs handle data replication for the Ceph clients. When Ceph OSDs replicate data more than once, the network load between Ceph OSDs easily dwarfs the network load between Ceph clients and the Ceph storage cluster. This can introduce latency and create a performance problem. Recovery and rebalancing can also introduce significant latency on the public network.
  • Security: While most people are generally civil, some actors will engage in what is known as a Denial of Service (DoS) attack. When traffic between Ceph OSDs gets disrupted, peering may fail and placement groups may no longer reflect an active + clean state, which may prevent users from reading and writing data. A great way to defeat this type of attack is to maintain a completely separate cluster network that does not connect directly to the internet.

2.1. Network Configuration Settings

Network configuration settings are not required. Ceph can function with a public network only, assuming a public network is configured on all hosts running a Ceph daemon. However, Ceph allows you to establish much more specific criteria, including multiple IP networks and subnet masks for your public network. You can also establish a separate cluster network to handle OSD heartbeat, object replication, and recovery traffic.

Do not confuse the IP addresses you set in the configuration with the public-facing IP addresses network clients might use to access your service. Typical internal IP networks are often 192.168.0.0 or 10.0.0.0.

Tip

If you specify more than one IP address and subnet mask for either the public or the cluster network, the subnets within the network must be capable of routing to each other. Additionally, make sure you include each IP address/subnet in your IP tables and open ports for them as necessary.

Note

Ceph uses CIDR notation for subnets (for example, 10.0.0.0/24).

When you configured the networks, you can restart the cluster or restart each daemon. Ceph daemons bind dynamically, so you do not have to restart the entire cluster at once if you change the network configuration.

2.1.1. Public Network

To configure a public network, add the following option to the [global] section of the Ceph configuration file. 

[global]
    ...
    public_network = <public-network/netmask>

The public network configuration allows you specifically define IP addresses and subnets for the public network. You may specifically assign static IP addresses or override public network settings using the public addr setting for a specific daemon.

public_network
Description
The IP address and netmask of the public (front-side) network (for example, 192.168.0.0/24). Set in [global]. You can specify comma-delimited subnets.
Type
<ip-address>/<netmask> [, <ip-address>/<netmask>]
Required
No
Default
N/A
public_addr
Description
The IP address for the public (front-side) network. Set for each daemon.
Type
IP Address
Required
No
Default
N/A

2.1.2. Cluster Network

If you declare a cluster network, OSDs will route heartbeat, object replication, and recovery traffic over the cluster network. This can improve performance compared to using a single network. To configure a cluster network, add the following option to the [global] section of the Ceph configuration file. 

[global]
    ...
    cluster_network = <cluster-network/netmask>

It is preferable, that the cluster network is not reachable from the public network or the Internet for added security.

The cluster network configuration allows you to declare a cluster network, and specifically define IP addresses and subnets for the cluster network. You can specifically assign static IP addresses or override cluster network settings using the cluster addr setting for specific OSD daemons.

cluster_network
Description
The IP address and netmask of the cluster network (for example, 10.0.0.0/24). Set in [global]. You can specify comma-delimited subnets.
Type
<ip-address>/<netmask> [, <ip-address>/<netmask>]
Required
No
Default
N/A
cluster_addr
Description
The IP address for the cluster network. Set for each daemon.
Type
Address
Required
No
Default
N/A

2.1.3. Verifying and configuring the MTU value

The maximum transmission unit (MTU) value is the size, in bytes, of the largest packet sent on the link layer. The default MTU value is 1500 bytes. Red Hat recommends using jumbo frames, a MTU value of 9000 bytes, for a Red Hat Ceph Storage cluster.

Important

Red Hat Ceph Storage requires the same MTU value throughout all networking devices in the communication path, end-to-end for both public and cluster networks. Verify that the MTU value is the same on all nodes and networking equipment in the environment before using a Red Hat Ceph Storage cluster in production.

Note

When bonding network interfaces together, the MTU value only needs to be set on the bonded interface. The new MTU value propagates from the bonding device to the underlying network devices.

Prerequisites

  • Root-level access to the node.

Procedure

  1. Verify the current MTU value:

    Example

    [root@mon ~]# ip link list
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: enp22s0f0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP mode DEFAULT group default qlen 1000

    For this example, the network interface is enp22s0f0 and it has a MTU value of 1500.

  2. To temporarily change the MTU value online:

    Syntax

    ip link set dev NET_INTERFACE mtu NEW_MTU_VALUE

    Example

    [root@mon ~]# ip link set dev enp22s0f0 mtu 9000

  3. To permanently change the MTU value.

    1. Open for editing the network configuration file for that particular network interface:

      Syntax

      vim /etc/sysconfig/network-scripts/ifcfg-NET_INTERFACE

      Example

      [root@mon ~]# vim /etc/sysconfig/network-scripts/ifcfg-enp22s0f0

    2. On a new line, add the MTU=9000 option:

      Example

      NAME="enp22s0f0"
DEVICE="enp22s0f0"
MTU=9000 1
ONBOOT=yes
NETBOOT=yes
UUID="a8c1f1e5-bd62-48ef-9f29-416a102581b2"
IPV6INIT=yes
BOOTPROTO=dhcp
TYPE=Ethernet

    3. Restart the network service:

      Example

      [root@mon ~]# systemctl restart network

Additional Resources

2.1.4. Messaging

Messenger is the Ceph network layer implementation. Red Hat supports two messenger types:

  • simple
  • async

In RHCS 2 and earlier releases, simple is the default messenger type. In RHCS 3, async is the default messenger type. To change the messenger type, specify the ms_type configuration setting in the [global] section of the Ceph configuration file.

Note

For the async messenger, Red Hat supports the posix transport type, but does not currently support rdma or dpdk. By default, the ms_type setting in RHCS 3 should reflect async+posix, where async is the messenger type and posix is the transport type.

About SimpleMessenger

The SimpleMessenger implementation uses TCP sockets with two threads per socket. Ceph associates each logical session with a connection. A pipe handles the connection, including the input and output of each message. While SimpleMessenger is effective for the posix transport type, it is not effective for other transport types such as rdma or dpdk. Consequently, AsyncMessenger is the default messenger type for RHCS 3 and later releases.

About AsyncMessenger

For RHCS 3, the AsyncMessenger implementation uses TCP sockets with a fixed-size thread pool for connections, which should be equal to the highest number of replicas or erasure-code chunks. The thread count can be set to a lower value if performance degrades due to a low CPU count or a high number of OSDs per server.

Note

Red Hat does not support other transport types such as rdma or dpdk at this time.

Messenger Type Settings

ms_type
Description
The messenger type for the network transport layer. Red Hat supports the simple and the async messenger type using posix semantics.
Type
String.
Required
No.
Default
async+posix
ms_public_type
Description
The messenger type for the network transport layer of the public network. It operates identically to ms_type, but is applicable only to the public or front-side network. This setting enables Ceph to use a different messenger type for the public or front-side and cluster or back-side networks.
Type
String.
Required
No.
Default
None.
ms_cluster_type
Description
The messenger type for the network transport layer of the cluster network. It operates identically to ms_type, but is applicable only to the cluster or back-side network. This setting enables Ceph to use a different messenger type for the public or front-side and cluster or back-side networks.
Type
String.
Required
No.
Default
None.

2.1.5. AsyncMessenger Settings

ms_async_transport_type
Description
Transport type used by the AsyncMessenger. Red Hat supports the posix setting, but does not support the dpdk or rdma settings at this time. POSIX uses standard TCP/IP networking and is the default value. Other transport types are experimental and are NOT supported.
Type
String
Required
No
Default
posix
ms_async_op_threads
Description
Initial number of worker threads used by each AsyncMessenger instance. This configuration setting SHOULD equal the number of replicas or erasure code chunks. but it may be set lower if the CPU core count is low or the number of OSDs on a single server is high.
Type
64-bit Unsigned Integer
Required
No
Default
3
ms_async_max_op_threads
Description
The maximum number of worker threads used by each AsyncMessenger instance. Set to lower values if the OSD host has limited CPU count, and increase if Ceph is underutilizing CPUs are underutilized.
Type
64-bit Unsigned Integer
Required
No
Default
5
ms_async_set_affinity
Description
Set to true to bind AsyncMessenger workers to particular CPU cores.
Type
Boolean
Required
No
Default
true
ms_async_affinity_cores
Description
When ms_async_set_affinity is true, this string specifies how AsyncMessenger workers are bound to CPU cores. For example, 0,2 will bind workers #1 and #2 to CPU cores #0 and #2, respectively. NOTE: When manually setting affinity, make sure to not assign workers to virtual CPUs created as an effect of hyper threading or similar technology, because they are slower than physical CPU cores.
Type
String
Required
No
Default
(empty)
ms_async_send_inline
Description
Send messages directly from the thread that generated them instead of queuing and sending from the AsyncMessenger thread. This option is known to decrease performance on systems with a lot of CPU cores, so it’s disabled by default.
Type
Boolean
Required
No
Default
false

2.1.6. Bind

Bind settings set the default port ranges Ceph OSD daemons use. The default range is 6800:7100. Ensure that the firewall configuration allows you to use the configured port range.

You can also enable Ceph daemons to bind to IPv6 addresses.

ms_bind_port_min
Description
The minimum port number to which an OSD daemon will bind.
Type
32-bit Integer
Default
6800
Required
No
ms_bind_port_max
Description
The maximum port number to which an OSD daemon will bind.
Type
32-bit Integer
Default
7300
Required
No.
ms_bind_ipv6
Description
Enables Ceph daemons to bind to IPv6 addresses.
Type
Boolean
Default
false
Required
No

2.1.7. Hosts

Ceph expects at least one monitor declared in the Ceph configuration file, with a mon addr setting under each declared monitor. Ceph expects a host setting under each declared monitor, metadata server and OSD in the Ceph configuration file.

mon_addr
Description
A list of <hostname>:<port> entries that clients can use to connect to a Ceph monitor. If not set, Ceph searches [mon.*] sections.
Type
String
Required
No
Default
N/A
host
Description
The host name. Use this setting for specific daemon instances (for example, [osd.0]).
Type
String
Required
Yes, for daemon instances.
Default
localhost
Tip

Do not use localhost. To get your host name, execute the hostname -s command and use the name of your host to the first period, not the fully-qualified domain name.

Important

Do not specify any value for host when using a third party deployment system that retrieves the host name for you.

2.1.8. TCP

Ceph disables TCP buffering by default.

ms_tcp_nodelay
Description
Ceph enables ms_tcp_nodelay so that each request is sent immediately (no buffering). Disabling Nagle’s algorithm increases network traffic, which can introduce congestion. If you experience large numbers of small packets, you may try disabling ms_tcp_nodelay, but be aware that disabling it will generally increase latency.
Type
Boolean
Required
No
Default
true
ms_tcp_rcvbuf
Description
The size of the socket buffer on the receiving end of a network connection. Disable by default.
Type
32-bit Integer
Required
No
Default
0
ms_tcp_read_timeout
Description
If a client or daemon makes a request to another Ceph daemon and does not drop an unused connection, the tcp read timeout defines the connection as idle after the specified number of seconds.
Type
Unsigned 64-bit Integer
Required
No
Default
900 15 minutes.

2.1.9. Firewall

By default, daemons bind to ports within the 6800:7100 range. You can configure this range at your discretion. Before configuring the firewall, check the default firewall configuration. You can configure this range at your discretion. 

sudo iptables -L

For the firewalld daemon, execute the following command as root: 

# firewall-cmd --list-all-zones

Some Linux distributions include rules that reject all inbound requests except SSH from all network interfaces. For example: 

REJECT all -- anywhere anywhere reject-with icmp-host-prohibited

2.1.9.1. Monitor Firewall

Ceph monitors listen on port 6789 by default. Additionally, Ceph monitors always operate on the public network. When you add the rule using the example below, make sure you replace <iface> with the public network interface (for example, eth0, eth1, and so on), <ip-address> with the IP address of the public network and <netmask> with the netmask for the public network. 

sudo iptables -A INPUT -i <iface> -p tcp -s <ip-address>/<netmask> --dport 6789 -j ACCEPT

For the firewalld daemon, execute the following commands as root: 

# firewall-cmd --zone=public --add-port=6789/tcp
# firewall-cmd --zone=public --add-port=6789/tcp --permanent

2.1.9.2. OSD Firewall

By default, Ceph OSDs bind to the first available ports on a Ceph node beginning at port 6800. Ensure to open at least three ports beginning at port 6800 for each OSD that runs on the host:

  1. One for talking to clients and monitors (public network).
  2. One for sending data to other OSDs (cluster network).
  3. One for sending heartbeat packets (cluster network).
OSD Firewall

Ports are node-specific. However, you might need to open more ports than the number of ports needed by Ceph daemons running on that Ceph node in the event that processes get restarted and the bound ports do not get released. Consider to open a few additional ports in case a daemon fails and restarts without releasing the port such that the restarted daemon binds to a new port. Also, consider opening the port range of 6800:7300 on each OSD host.

If you set separate public and cluster networks, you must add rules for both the public network and the cluster network, because clients will connect using the public network and other Ceph OSD Daemons will connect using the cluster network.

When you add the rule using the example below, make sure you replace <iface> with the network interface (for example, eth0 or eth1), `<ip-address> with the IP address and <netmask> with the netmask of the public or cluster network. For example: 

sudo iptables -A INPUT -i <iface>  -m multiport -p tcp -s <ip-address>/<netmask> --dports 6800:6810 -j ACCEPT

For the firewalld daemon, execute the following commands as root: 

# firewall-cmd --zone=public --add-port=6800-6810/tcp
# firewall-cmd --zone=public --add-port=6800-6810/tcp --permanent

If you put the cluster network into another zone, open the ports within that zone as appropriate.

2.2. Ceph Daemons

Ceph has one network configuration requirement that applies to all daemons. The Ceph configuration file must specify the host for each daemon. Ceph no longer requires that a Ceph configuration file specify the monitor IP address and its port.

Important

Some deployment utilities might create a configuration file for you. Do not set these values if the deployment utility does it for you.

Tip

The host setting is the short name of the host (that is, not an FQDN). It is not an IP address either. Use the hostname -s command to retrieve the name of the host. 

[mon.a]

    host = <hostname>
    mon addr = <ip-address>:6789

[osd.0]
    host = <hostname>

You do not have to set the host IP address for a daemon. If you have a static IP configuration and both public and cluster networks running, the Ceph configuration file might specify the IP address of the host for each daemon. To set a static IP address for a daemon, the following option(s) should appear in the daemon instance sections of the Ceph configuration file. 

[osd.0]
    public_addr = <host-public-ip-address>
    cluster_addr = <host-cluster-ip-address>

One NIC OSD in a Two Network Cluster

Generally, Red Hat does not recommend deploying an OSD host with a single NIC in a cluster with two networks. However, you cam accomplish this by forcing the OSD host to operate on the public network by adding a public addr entry to the [osd.n] section of the Ceph configuration file, where n refers to the number of the OSD with one NIC. Additionally, the public network and cluster network must be able to route traffic to each other, which Red Hat does not recommend for security reasons.