Cisco Cisco Nexus 5010 Switch Guida Alla Progettazione
Design Guide
© 2010 Cisco Systems, Inc. All rights reserved. This document is Cisco Public Information.
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Spanning Tree
vPC modifies the way in which spanning tree works on the switch in two ways:
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It makes sure that the peer link is always forwarding. In fact, even if the switch has a direct path to the root,
the secondary vPC peer always sees the peer link as the root port towards the primary vPC device.
the secondary vPC peer always sees the peer link as the root port towards the primary vPC device.
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It ensures that only the primary switch forwards BPDUs on vPCs, so that the other switches connected to the
vPC system perceive the two peers as a single entity from a spanning tree perspective. This modification is
strictly limited to vPC-member ports.
vPC system perceive the two peers as a single entity from a spanning tree perspective. This modification is
strictly limited to vPC-member ports.
As a result, the BPDUs that may be received by the secondary vPC peer on a vPC port are forwarded to the primary
vPC peer through the peer link for processing.
vPC peer through the peer link for processing.
Note: Non-vPC ports operate like regular ports. The special behavior of the primary vPC member applies uniquely
to ports that are part of a vPC.
CDP
From a Cisco Discovery Protocol perspective, the presence of vPC doesn’t hide the fact that the two Cisco Nexus
7000 Series systems are two distinct devices, as illustrated by the following output:
7000 Series systems are two distinct devices, as illustrated by the following output:
tc-nexus5k01# show cdp neigh
Capability Codes: R - Router, T - Trans-Bridge, B - Source-Route-Bridge
S - Switch, H - Host, I - IGMP, r - Repeater,
V - VoIP-Phone, D - Remotely-Managed-Device,
s - Supports-STP-Dispute
Device-ID Local Intrfce Hldtme Capability Platform Port ID
tc-nexus7k01-vdc2(TBM12162254)Eth2/1 158 R S I s N7K-C7010 Eth2/9
tc-nexus7k02-vdc2(TBM12193229)Eth2/2 158 R S I s N7K-C7010 Eth2/9
Cisco Fabric Services over Ethernet Synchronization Protocol
The vPC peers use the Cisco Fabric Services protocol to synchronize forwarding-plane information and implement
necessary configuration checks or both.
necessary configuration checks or both.
vPC peers must be synchronized because the Layer 2 forwarding table — that is, the MAC address information
between the vPC peers—must be synchronized. This way, if one vPC peer learns a new MAC address, that MAC
address is also programmed on the Layer 2 forwarding table of the other peer device.
between the vPC peers—must be synchronized. This way, if one vPC peer learns a new MAC address, that MAC
address is also programmed on the Layer 2 forwarding table of the other peer device.
The Cisco Fabric Services protocol travels on the peer link and does not require any configuration from the user.
In order to ensure that the peer link communication for the Cisco Fabric Services over Ethernet protocol is always
available, spanning tree has been modified to keep the peer link ports always forwarding.
available, spanning tree has been modified to keep the peer link ports always forwarding.
As described in the next section, the Cisco Fabric Services over Ethernet protocol is also used to perform the
compatibility checks to validate vPC member ports compatibility to form the channel, to synchronize the IGMP
snooping status, and to monitor the status of the vPC member ports.
compatibility checks to validate vPC member ports compatibility to form the channel, to synchronize the IGMP
snooping status, and to monitor the status of the vPC member ports.
COMPAT Checks
COMPAT check stands for compatibility check. During a compatibility check, one vPC peer conveys configuration
information to the other vPC peer in order to verify that vPC member ports can actually form a PortChannel. As an
example, if two ports that are going to join the channel carry a different set of VLANs, this is a misconfiguration.
information to the other vPC peer in order to verify that vPC member ports can actually form a PortChannel. As an
example, if two ports that are going to join the channel carry a different set of VLANs, this is a misconfiguration.