Chapter 3. Configuring IPoIB By default, InfiniBand does not use the internet protocol (IP) for communication. However, IP over InfiniBand (IPoIB) provides an IP network emulation layer on top of InfiniBand remote direct memory access (RDMA) networks. This allows existing unmodified applications to transmit data over InfiniBand networks, but the performance is lower than if the application would use RDMA natively. Note The Mellanox devices, starting from ConnectX-4 and above, on RHEL 8 and later use Enhanced IPoIB mode by default (datagram only). Connected mode is not supported on these devices. 3.1. The IPoIB communication modes An IPoIB device is configurable in either Datagram or Connected mode. The difference is the type of queue pair the IPoIB layer attempts to open with the machine at the other end of the communication: In the Datagram mode, the system opens an unreliable, disconnected queue pair. This mode does not support packages larger than Maximum Transmission Unit (MTU) of the InfiniBand link layer. During transmission of data, the IPoIB layer adds a 4-byte IPoIB header on top of the IP packet. As a result, the IPoIB MTU is 4 bytes less than the InfiniBand link-layer MTU. As 2048 is a common InfiniBand link-layer MTU, the common IPoIB device MTU in Datagram mode is 2044 . In the Connected mode, the system opens a reliable, connected queue pair. This mode allows messages larger than the InfiniBand link-layer MTU. The host adapter handles packet segmentation and reassembly. As a result, in the Connected mode, the messages sent from Infiniband adapters have no size limits. However, there are limited IP packets due to the data field and TCP/IP header field. For this reason, the IPoIB MTU in the Connected mode is 65520 bytes. The Connected mode has a higher performance but consumes more kernel memory. Though a system is configured to use the Connected mode, a system still sends multicast traffic by using the Datagram mode because InfiniBand switches and fabric cannot pass multicast traffic in the Connected mode. Also, when the host is not configured to use the Connected mode, the system falls back to the Datagram mode. While running an application that sends multicast data up to the MTU on the interface, configure the interface in Datagram mode or configure the application to cap the send size of a packet that will fit in datagram-sized packets. 3.2. Understanding IPoIB hardware addresses IPoIB devices have a 20 byte hardware address that consists of the following parts: The first 4 bytes are flags and queue pair numbers The 8 bytes are the subnet prefix The default subnet prefix is 0xfe:80:00:00:00:00:00:00 . After the device connects to the subnet manager, the device changes this prefix to match with the configured subnet manager. The last 8 bytes are the Globally Unique Identifier (GUID) of the InfiniBand port that attaches to the IPoIB device Note As the first 12 bytes can change, do not use them in the udev device manager rules. 3.3. Renaming IPoIB devices By default, the kernel names Internet Protocol over InfiniBand (IPoIB) devices, for example, ib0 , ib1 , and so on. To avoid conflicts, Red Hat recommends creating a rule in the udev device manager to create persistent and meaningful names such as mlx4_ib0 . Prerequisites You have installed an InfiniBand device. Procedure Display the hardware address of the device ib0 : The last eight bytes of the address are required to create a udev rule in the step. To configure a rule that renames the device with the 00:02:c9:03:00:31:78:f2 hardware address to mlx4_ib0 , edit the /etc/udev/rules.d/70-persistent-ipoib.rules file and add an ACTION rule: Reboot the host: Additional resources udev(7) man page on your system Understanding IPoIB hardware addresses 3.4. Configuring an IPoIB connection by using nmcli You can use the nmcli utility to create an IP over InfiniBand connection on the command line. Prerequisites An InfiniBand device is installed on the server The corresponding kernel module is loaded Procedure Create the InfiniBand connection to use the mlx4_ib0 interface in the Connected transport mode and the maximum MTU of 65520 bytes: Set a P_Key , for example: Configure the IPv4 settings: To use DHCP, enter: Skip this step if ipv4.method is already set to auto (default). To set a static IPv4 address, network mask, default gateway, DNS servers, and search domain, enter: Configure the IPv6 settings: To use stateless address autoconfiguration (SLAAC), enter: Skip this step if ipv6.method is already set to auto (default). To set a static IPv6 address, network mask, default gateway, DNS servers, and search domain, enter: To customize other settings in the profile, use the following command: Enclose values with spaces or semicolons in quotes. Activate the profile: Verification Use the ping utility to send ICMP packets to the remote host's InfiniBand adapter, for example: 3.5. Configuring an IPoIB connection by using the network RHEL system role You can use IP over InfiniBand (IPoIB) to send IP packets over an InfiniBand interface. To configure IPoIB, create a NetworkManager connection profile. By using Ansible and the network system role, you can automate this process and remotely configure connection profiles on the hosts defined in a playbook. You can use the network RHEL system role to configure IPoIB and, if a connection profile for the InfiniBand's parent device does not exist, the role can create it as well. Prerequisites You have prepared the control node and the managed nodes You are logged in to the control node as a user who can run playbooks on the managed nodes. The account you use to connect to the managed nodes has sudo permissions on them. An InfiniBand device named mlx4_ib0 is installed in the managed nodes. The managed nodes use NetworkManager to configure the network. Procedure Create a playbook file, for example ~/playbook.yml , with the following content: --- - name: Configure the network hosts: managed-node-01.example.com tasks: - name: IPoIB connection profile with static IP address settings ansible.builtin.include_role: name: rhel-system-roles.network vars: network_connections: # InfiniBand connection mlx4_ib0 - name: mlx4_ib0 interface_name: mlx4_ib0 type: infiniband # IPoIB device mlx4_ib0.8002 on top of mlx4_ib0 - name: mlx4_ib0.8002 type: infiniband autoconnect: yes infiniband: p_key: 0x8002 transport_mode: datagram parent: mlx4_ib0 ip: address: - 192.0.2.1/24 - 2001:db8:1::1/64 state: up The settings specified in the example playbook include the following: type: <profile_type> Sets the type of the profile to create. The example playbook creates two connection profiles: One for the InfiniBand connection and one for the IPoIB device. parent: <parent_device> Sets the parent device of the IPoIB connection profile. p_key: <value> Sets the InfiniBand partition key. If you set this variable, do not set interface_name on the IPoIB device. transport_mode: <mode> Sets the IPoIB connection operation mode. You can set this variable to datagram (default) or connected . For details about all variables used in the playbook, see the /usr/share/ansible/roles/rhel-system-roles.network/README.md file on the control node. Validate the playbook syntax: Note that this command only validates the syntax and does not protect against a wrong but valid configuration. Run the playbook: Verification Display the IP settings of the mlx4_ib0.8002 device: Display the partition key (P_Key) of the mlx4_ib0.8002 device: Display the mode of the mlx4_ib0.8002 device: Additional resources /usr/share/ansible/roles/rhel-system-roles.network/README.md file /usr/share/doc/rhel-system-roles/network/ directory 3.6. Configuring an IPoIB connection by using nmstatectl You can use the nmstatectl utility to configure an IP over InfiniBand (IPoIB) connection through the Nmstate API. The Nmstate API ensures that, after setting the configuration, the result matches the configuration file. If anything fails, nmstatectl automatically rolls back the changes to avoid leaving the system in an incorrect state. Prerequisites An InfiniBand device is installed on the server. The kernel module for the InfiniBand device is loaded. Procedure Create a YAML file, for example ~/create-IPoIB-profile.yml , with the following content: interfaces: - name: mlx4_ib0.8002 type: infiniband state: up ipv4: enabled: true address: - ip: 192.0.2.1 prefix-length: 24 dhcp: false ipv6: enabled: true address: - ip: 2001:db8:1::1 prefix-length: 64 autoconf: false dhcp: false infiniband: base-iface: "mlx4_ib0" mode: datagram pkey: "0x8002" routes: config: - destination: 0.0.0.0/0 -hop-address: 192.0.2.254 -hop-interface: mlx4_ib0.8002 - destination: ::/0 -hop-address: 2001:db8:1::fffe -hop-interface: mlx4_ib0.8002 An IPoIB connection has now the following settings: IPOIB device name: mlx4_ib0.8002 Base interface (parent): mlx4_ib0 InfiniBand partition key: 0x8002 Transport mode: datagram Static IPv4 address: 192.0.2.1 with the /24 subnet mask Static IPv6 address: 2001:db8:1::1 with the /64 subnet mask IPv4 default gateway: 192.0.2.254 IPv6 default gateway: 2001:db8:1::fffe Apply the settings to the system: Verification Display the IP settings of the mlx4_ib0.8002 device: Display the partition key (P_Key) of the mlx4_ib0.8002 device: Display the mode of the mlx4_ib0.8002 device: Additional resources nmstatectl(8) man page on your system /usr/share/doc/nmstate/examples/ directory 3.7. Configuring an IPoIB connection by using nm-connection-editor The nmcli-connection-editor application configures and manages network connections stored by NetworkManager by using the management console. Prerequisites An InfiniBand device is installed on the server. The corresponding kernel module is loaded. The nm-connection-editor package is installed. Procedure Enter the command: Click the + button to add a new connection. Select the InfiniBand connection type and click Create . On the InfiniBand tab: Change the connection name if you want to. Select the transport mode. Select the device. Set an MTU if needed. On the IPv4 Settings tab, configure the IPv4 settings. For example, set a static IPv4 address, network mask, default gateway, and DNS server: On the IPv6 Settings tab, configure the IPv6 settings. For example, set a static IPv6 address, network mask, default gateway, and DNS server: Click Save to save the team connection. Close nm-connection-editor . You can set a P_Key interface. As this setting is not available in nm-connection-editor , you must set this parameter on the command line. For example, to set 0x8002 as P_Key interface of the mlx4_ib0 connection: 3.8. Testing an RDMA network by using qperf after IPoIB is configured The qperf utility measures RDMA and IP performance between two nodes in terms of bandwidth, latency, and CPU utilization. Prerequisites You have installed the qperf package on both hosts. IPoIB is configured on both hosts. Procedure Start qperf on one of the hosts without any options to act as a server: Use the following commands on the client. The commands use port 1 of the mlx4_0 host channel adapter in the client to connect to IP address 192.0.2.1 assigned to the InfiniBand adapter in the server. Display the configuration of the host channel adapter: Display the Reliable Connection (RC) streaming two-way bandwidth: Display the RC streaming one-way bandwidth: Additional resources qperf(1) man page on your system

Commands:
ip link show ib0 8: ib0: >BROADCAST,MULTICAST,UP,LOWER_UP< mtu 65520 qdisc pfifo_fast state UP mode DEFAULT qlen 256 link/infiniband 80:00:02:00:fe:80:00:00:00:00:00:00: 00:02:c9:03:00:31:78:f2 brd 00:ff:ff:ff:ff:12:40:1b:ff:ff:00:00:00:00:00:00:ff:ff:ff:ff
ACTION=="add", SUBSYSTEM=="net", DRIVERS=="?*", ATTR{type}=="32", ATTR{address}=="?* 00:02:c9:03:00:31:78:f2 ", NAME=" mlx4_ib0 "
reboot
nmcli connection add type infiniband con-name mlx4_ib0 ifname mlx4_ib0 transport-mode Connected mtu 65520
nmcli connection modify mlx4_ib0 infiniband.p-key 0x8002
nmcli connection modify mlx4_ib0 ipv4.method auto
nmcli connection modify mlx4_ib0 ipv4.method manual ipv4.addresses 192.0.2.1/24 ipv4.gateway 192.0.2.254 ipv4.dns 192.0.2.200 ipv4.dns-search example.com
nmcli connection modify mlx4_ib0 ipv6.method auto
nmcli connection modify mlx4_ib0 ipv6.method manual ipv6.addresses 2001:db8:1::fffe/64 ipv6.gateway 2001:db8:1::fffe ipv6.dns 2001:db8:1::ffbb ipv6.dns-search example.com
nmcli connection modify mlx4_ib0 <setting> <value>
nmcli connection up mlx4_ib0
ping -c5 192.0.2.2
--- - name: Configure the network hosts: managed-node-01.example.com tasks: - name: IPoIB connection profile with static IP address settings ansible.builtin.include_role: name: rhel-system-roles.network vars: network_connections: # InfiniBand connection mlx4_ib0 - name: mlx4_ib0 interface_name: mlx4_ib0 type: infiniband # IPoIB device mlx4_ib0.8002 on top of mlx4_ib0 - name: mlx4_ib0.8002 type: infiniband autoconnect: yes infiniband: p_key: 0x8002 transport_mode: datagram parent: mlx4_ib0 ip: address: - 192.0.2.1/24 - 2001:db8:1::1/64 state: up
ansible-playbook --syntax-check ~/playbook.yml
ansible-playbook ~/playbook.yml
ansible managed-node-01.example.com -m command -a 'ip address show mlx4_ib0.8002' managed-node-01.example.com | CHANGED | rc=0 >> inet 192.0.2.1/24 brd 192.0.2.255 scope global noprefixroute ib0.8002 valid_lft forever preferred_lft forever inet6 2001:db8:1::1/64 scope link tentative noprefixroute valid_lft forever preferred_lft forever
ansible managed-node-01.example.com -m command -a 'cat /sys/class/net/mlx4_ib0.8002/pkey' managed-node-01.example.com | CHANGED | rc=0 >> 0x8002
ansible managed-node-01.example.com -m command -a 'cat /sys/class/net/mlx4_ib0.8002/mode' managed-node-01.example.com | CHANGED | rc=0 >> datagram
interfaces: - name: mlx4_ib0.8002 type: infiniband state: up ipv4: enabled: true address: - ip: 192.0.2.1 prefix-length: 24 dhcp: false ipv6: enabled: true address: - ip: 2001:db8:1::1 prefix-length: 64 autoconf: false dhcp: false infiniband: base-iface: "mlx4_ib0" mode: datagram pkey: "0x8002" routes: config: - destination: 0.0.0.0/0 next-hop-address: 192.0.2.254 next-hop-interface: mlx4_ib0.8002 - destination: ::/0 next-hop-address: 2001:db8:1::fffe next-hop-interface: mlx4_ib0.8002
nmstatectl apply ~/create-IPoIB-profile.yml
ip address show mlx4_ib0.8002 inet 192.0.2.1/24 brd 192.0.2.255 scope global noprefixroute ib0.8002 valid_lft forever preferred_lft forever inet6 2001:db8:1::1/64 scope link tentative noprefixroute valid_lft forever preferred_lft forever
cat /sys/class/net/mlx4_ib0.8002/pkey 0x8002
cat /sys/class/net/mlx4_ib0.8002/mode datagram
nm-connection-editor
nmcli connection modify mlx4_ib0 infiniband.p-key 0x8002
qperf
qperf -v -i mlx4_0:1 192.0.2.1 conf conf: loc_node = rdma-dev-01.lab.bos.redhat.com loc_cpu = 12 Cores: Mixed CPUs loc_os = Linux 4.18.0-187.el8.x86_64 loc_qperf = 0.4.11 rem_node = rdma-dev-00.lab.bos.redhat.com rem_cpu = 12 Cores: Mixed CPUs rem_os = Linux 4.18.0-187.el8.x86_64 rem_qperf = 0.4.11
qperf -v -i mlx4_0:1 192.0.2.1 rc_bi_bw rc_bi_bw: bw = 10.7 GB/sec msg_rate = 163 K/sec loc_id = mlx4_0 rem_id = mlx4_0:1 loc_cpus_used = 65 % cpus rem_cpus_used = 62 % cpus
qperf -v -i mlx4_0:1 192.0.2.1 rc_bw rc_bw: bw = 6.19 GB/sec msg_rate = 94.4 K/sec loc_id = mlx4_0 rem_id = mlx4_0:1 send_cost = 63.5 ms/GB recv_cost = 63 ms/GB send_cpus_used = 39.5 % cpus recv_cpus_used = 39 % cpus