Tag Archives: datacenter

CCIE DC Written – 1.1.a Link Aggregation – vPC Components

virtual port channels

Virtual Port Channel master really does begin with a knowledge of the components that make them up. This post assumes you are familiar with the very basics of virtual port channels – knowledge you have gained through CCNA/CCNP Data Center.

Here are the components of the vPC:

  • vPC peers – two switches that act as a single logical switch to the downstream device.
  • vPC peer link – a link between the vPC peers that is used to synchronize state. Consider two physical links in a port channel. MAC address table synchronization, as well as other control plane, functions synchronize over this link.
  • Cisco Fabric Services – this protocol is responsible for synchronization between the peers. CFSoE is run. STP is modified to keep the peer link ports forwarding.
  • vPC peer keepalive link – Layer 3 communication link between the vPC peers to act as a secondary test of connectivity.
  • vPC – the virtual port channel depicts itself to the downstream device as a single logical switch. The downstream device does not need virtual port channel support. It forms its standard port channel configuration.
  • vPC member ports – a member of the vPC on the vPC peer switch.
  • vPC domain – a numeric identifier for the vPC domain.
  • Orphan device – a device that is connected to only one peer in the vPC.
  • Orphan port – the switchport that connects to an orphan device.
  • vPC VLANs – the VLANs permitted to use the vPC. They must be permitted on the peer link.
  • Non vPC VLANs – the VLANs not permitted on the vPC.

CCIE DC Written – 1.1.a Link Aggregation – LACP

NX-OS

Here are some Nexus facts to keep in mind:

  • With LACP, you can bundle up to 16 interfaces in a channel group. If the channel group has more than 8 interfaces, the remaining interfaces are in hot standby for the port channel associated with this channel group on the M-series modules.
  • From Cisco NX-OS Release 5.1, you can bundle up to 16 active links into a port channel on the F-series module.
  • When you delete the port channel, the software automatically deletes the associated channel group. All member interfaces revert to their original configuration.
  • You cannot disable LACP while any LACP configurations are present.
  • When you run static port channels with no aggregation protocol, the channel mode is always set to on.

Of course, you must globally enable LACP before you can use it on the Nexus device. There are two modes:

  • Passive – responds to negotiations, but does not initiate them – sounds like me at the High School dance
  • Active – initiates negotiations

Starting at 4.2(3) – Cisco introduced some LACP compatibility enhancements as follows:

  •  When a Cisco Nexus device is connected to a non-Nexus peer, its graceful failover defaults may delay the time taken for a disabled port to be brought down or cause traffic from the peer to be lost. To address these conditions, the lacp graceful-convergence command was added.
  • By default, LACP sets a port to the suspended state if it does not receive an LACP PDU from the peer. In some cases, although this feature helps in preventing loops created due to misconfigurations, it can cause servers to fail to boot up because they require LACP to logically bring up the port. You can put a port into an individual state by using the lacp suspend-individual command.

Starting with Release 5.1 Cisco introduced the Minimum Links feature as well as MaxBundle. The Minimum Links feature allows you to:

  • Configure the min number of links that must be in the bundle
  • Prevent low bandwidth LACP bundles from becoming available
  • Causes the port channel to go inactive if the required min bandwidth is not available

MaxBundle allows:

  • Upper limit on ports that are bundled
  • Allows the designation of ports as hot standby

Basic Configuration

  • Use feature lacp to enable the feature
  • Create the port channel interface with interface port-channel 10, use the switchport command in the interface
  • Add a Layer 2 interface to the port channel with switchport followed by channel-group 10 mode passive

 

CCIE DC Written – 1.1.a Link Aggregation – Overview

Port Channels

A port channel is an aggregation of multiple physical interfaces that create a logical interface. You can bundle up to 8 individual active links into a port channel to provide increased bandwidth and redundancy. If a member port within a port channel fails, the traffic previously carried over the failed link switches to the remaining member ports within the port channel.

On the Nexus 7Ks, port channeling also load-balances traffic on the M series module and across these physical interfaces The port channel stays operational as long as at least one physical interface within the port channel is operational.

Starting with the Cisco NX-OS Release 5.1, you can bundle up to 16 active links into a port channel on the F-series module with a Nexus 7K.

NOTE: You cannot configure a shared interface to be part of a port channel.

Like many later Cisco devices, the Nexus devices do not support PAgP, and instead, offer LACP for a dynamic protocol to assist with port channel creation.

Each port can be in only one port channel. All the ports in a port channel must be compatible; they must use the same speed and duplex mode.

You can create port channels directly by creating the port-channel interface, or you can create a channel group that acts to aggregate individual ports into a bundle. When you associate an interface with a channel group, the software creates a matching port channel automatically if the port channel does not already exist. In this instance, the port channel assumes the Layer 2 or Layer 3 configuration of the first interface.

You can also create the port channel first. In this instance, the Cisco NX-OS software creates an empty channel group with the same channel number as the port channel and takes the default Layer 2 or Layer 3 configuration, as well as the compatibility configuration.

Your port channel is operationally up when at least one of the member ports is up and that port’s status is channeling. The port channel is operationally down when all member ports are operationally down.

NOTE: You can create a Layer 2 port channel by bundling compatible Layer 2 interfaces, or you can create Layer 3 port channels by bundling compatible Layer 3 interfaces. After you create a Layer 3 port channel, you can add an IP address to the port-channel interface and create subinterfaces on the Layer 3 port channel. Of course, you cannot combine Layer 2 and Layer 3 interfaces in the same port channel. You can also change the port channel from Layer 3 to Layer 2.

Also as you would expect, all ports in the port channel must be in the same virtual device context (VDC).

Any configuration changes that you apply to the port channel are applied to each member interface of that port channel. For example, if you configure Spanning Tree Protocol (STP) parameters on the port channel, the Cisco NX-OS software applies those parameters to each interface in the port channel.

After a Layer 2 port becomes part of a port channel, all switchport configurations must be done on the port channel; you can no longer apply switchport configurations to individual port-channel members. You cannot apply Layer 3 configurations to an individual port-channel member either; you must apply the configuration to the entire port channel.

You can create subinterfaces on a Layer 3 port channel, even though a subinterface is part of the logical port-channel interface.

You can configure Layer 2 port channels in either access or trunk mode. Layer 3 port-channel interfaces have routed ports as channel members and might have subinterfaces.

From Cisco NX-OS Release 4.2(1), you can configure a Layer 3 port channel with a static MAC address. If you do not configure this value, the Layer 3 port channel uses the router MAC of the first channel member to come up.