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nx.os.and.cisco.nexus.switching.2nd.edition.1587143046

Nexus Switching 2nd Edition

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precedence<br />

protocol<br />

Precedence in IP(v4) <strong>and</strong> IPv6 packets<br />

Protocol<br />

N5K-1(config-cmap-q<strong>os</strong>)#<br />

Note<br />

The Nexus 7000 supports additional classification match options such as MPLS<br />

experimental bits <strong>and</strong> matching on packet length. This is due to different hardware<br />

<strong>and</strong> software capabilities between the platforms.<br />

The network-q<strong>os</strong> policy is used to define global queuing <strong>and</strong> scheduling parameters for the<br />

entire switch. Configuration parameters such as a no-drop class <strong>and</strong> default queuing policies<br />

are defined in the network-q<strong>os</strong> policy. The network-q<strong>os</strong> policy should be consistent acr<strong>os</strong>s<br />

the entire network, especially in cases where no-drop traffic classes are used, such as for<br />

Fibre Channel over Ethernet (FCoE). Platform-specific network-q<strong>os</strong> settings are discussed<br />

under each platform.<br />

Note<br />

In Nexus 7000 devices the network-q<strong>os</strong> policy is defined in the default Virtual<br />

Device Context (VDC) or Admin VDC, <strong>and</strong> the policy applies to all ports in all<br />

VDCs.<br />

The queuing policies define platform-specific CoS-to-queue mappings. Platform-specific<br />

queuing settings are discussed under each platform.<br />

QoS on Nexus 7000<br />

The Nexus 7000 series of modular switches provide a full set of QoS mechanisms for<br />

network administrators to deploy. The QoS implementation follows the MQC described<br />

earlier in this chapter. QoS capabilities between Nexus devices can vary based on<br />

hardware <strong>and</strong> software capabilities. This section focuses on Nexus 7000-specific<br />

configuration.<br />

Forwarding Architecture<br />

The forwarding architecture of the Nexus 7000 uses the concept of virtual output queues<br />

managed by centralized arbitration to forward traffic acr<strong>os</strong>s the internal components of the<br />

switch. The I/O modules installed in a chassis connect into the fabric modules to create a<br />

three-stage switching fabric. This architecture enables the switch to manage traffic acr<strong>os</strong>s<br />

the switch in a granular fashion <strong>and</strong> avoids a situation referred to as head-of-line blocking<br />

(HOLB). HOLB can occur in a fabric when congestion on an egress port prevents (blocks)<br />

ingress traffic bound for other destinations. One of the goals of the Nexus family of switches<br />

was to engineer a platform that would avoid head-of-line blocking. In addition, the ability to<br />

have an arbitrated fabric enables guaranteed traffic within the switch. This enables the

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