Dell C9000 Series Networking Configuration Manual page 446

To provide lossless service for RRoCE, the QoS service policy must be configured in the ingress and egress
directions on lite subinterfaces.
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.
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 has IP headers. 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.
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