Dell Configuration Guide for the S4048–ON System 9.14.2.5

RDMA is a technology that a virtual machine (VM) uses to directly transfer information to the memory of another VM, thus enabling VMs to be connected to storage networks. With RoCE, RDMA enables data to be forwarded without passing through the CPU and the main memory path of TCP/IP. In a deployment that contains both the RoCE network and the normal IP network on two different networks, RRoCE combines the RoCE and the IP networks and sends the RoCE frames over the IP network. This method of transmission, called RRoCE, results in the encapsulation of RoCE packets to IP packets. RRoCE sends Infini Band (IB) packets over IP. IB supports input and output connectivity for the internet infrastructure. Infini Band enables the expansion of network topologies over large geographical boundaries and the creation of next-generation I/O interconnect standards in servers.

When a storage area network (SAN) is connected over an IP network, the following conditions must be satisfied:

• Faster Connectivity: QoS for RRoCE enables faster and lossless nature of disk input and output services.

• Lossless connectivity: VMs require the connectivity to the storage network to be lossless always. When a planned upgrade of the network nodes happens, especially with top-of-rack (ToR) nodes where there is a single point of failure for the VMs, disk I/O operations are expected to occur in 20 seconds. If disk in not accessible in 20 seconds, unexpected and undefined behavior of the VMs occurs. You can optimize the booting time of the ToR nodes that experience a single point of failure to reduce the outage in traffic-handling operations.

RRoCE is bursty and uses the entire 10-Gigabit Ethernet interface. Although RRoCE and normal data traffic are propagated in separate network portions, it may be necessary in certain topologies to combine both the RRoCE and the data traffic in a single network structure. RRoCE traffic is marked with dot1p priorities 3 and 4 (code points 011 and 100, respectively) and these queues are strict and lossless. DSCP code points are not tagged for RRoCE. Both ECN and PFC are enabled for RRoCE traffic. For normal IP or data traffic that is not RRoCE-enabled, the packets comprise TCP and UDP packets and they can be marked with DSCP code points. Multicast is not supported in that network.

RRoCE packets are received and transmitted on specific interfaces called lite-subinterfaces. These interfaces are similar to the normal Layer 3 physical interfaces except for the extra provisioning that they offer to enable the VLAN ID for encapsulation.

You can configure a physical interface or a Layer 3 Port Channel interface as a lite subinterface. When you configure a lite subinterface, only tagged IP packets with VLAN encapsulation are processed and routed. All other data packets are discarded.

A normal Layer 3 physical interface processes only untagged packets and makes routing decisions based on the default Layer 3 VLAN ID (4095).

To enable routing of RRoCE packets, the VLAN ID is mapped to the default VLAN ID of 4095 using VLAN translation. After the VLAN translation, the RRoCE packets are processed in the same way as normal IP packets that a Layer 3 interface receives and routes in the egress direction. At the egress interface, the VLAN ID is appended to the packet and transmitted out of the interface as a tagged packet with the dot1Q value preserved.

To provide lossless service for RRoCE, the QoS service policy must be configured in the ingress and egress directions on lite sub interfaces.