beautypg.com

Dell PowerEdge FX2/FX2s User Manual

Page 239

background image

– When you change the default VLAN ID on a VLT peer switch, the VLT interconnect may flap.
– In a VLT domain, the following software features are supported on VLTi: link layer discovery

protocol (LLDP), flow control, port monitoring, jumbo frames, and data center bridging (DCB).

– When you enable the VLTi link, the link between the VLT peer switches is established if the

following configured information is true on both peer switches:

* the VLT system MAC address matches.
* the VLT unit-id is not identical.

NOTE: If you configure the VLT system MAC address or VLT unit-id on only one of the VLT

peer switches, the link between the VLT peer switches is not established. Each VLT peer

switch must be correctly configured to establish the link between the peers.

– If the link between the VLT peer switches is established, changing the VLT system MAC address or

the VLT unit-id causes the link between the VLT peer switches to become disabled. However,

removing the VLT system MAC address or the VLT unit-id may disable the VLT ports if you happen

to configure the unit ID or system MAC address on only one VLT peer at any time.

– If the link between VLT peer switches is established, any change to the VLT system MAC address or

unit-id fails if the changes made create a mismatch by causing the VLT unit-ID to be the same on

both peers and/or the VLT system MAC address does not match on both peers.

– If you replace a VLT peer node, preconfigure the switch with the VLT system MAC address, unit-id,

and other VLT parameters before connecting it to the existing VLT peer switch using the VLTi

connection.

• VLT backup link

– In the backup link between peer switches, heartbeat messages are exchanged between the two

chassis for health checks. The default time interval between heartbeat messages over the backup

link is 1 second. You can configure this interval. The range is from 1 to 5 seconds. DSCP marking

on heartbeat messages is CS6.

– In order that the chassis backup link does not share the same physical path as the interconnect

trunk, Dell Networking recommends using the management ports on the chassis and traverse an

out-of-band management network. The backup link can use user ports, but not the same ports

the interconnect trunk uses.

– The chassis backup link does not carry control plane information or data traffic. Its use is restricted

to health checks only.

• Virtual link trunks (VLTs) between access devices and VLT peer switches

– To connect servers and access switches with VLT peer switches, you use a VLT port channel, as

shown in

Overview

. Up to 48 port-channels are supported; up to eight member links are

supported in each port channel between the VLT domain and an access device.

– The discovery protocol running between VLT peers automatically generates the ID number of the

port channel that connects an access device and a VLT switch. The discovery protocol uses LACP

properties to identify connectivity to a common client device and automatically generates a VLT

number for port channels on VLT peers that connects to the device. The discovery protocol

requires that an attached device always runs LACP over the port-channel interface.

– VLT provides a loop-free topology for port channels with endpoints on different chassis in the VLT

domain.

– VLT uses shortest path routing so that traffic destined to hosts via directly attached links on a

chassis does not traverse the chassis-interconnect link.

– VLT allows multiple active parallel paths from access switches to VLT chassis.
– VLT supports port-channel links with LACP between access switches and VLT peer switches. Dell

Networking recommends using static port channels on VLTi.

– If VLTi connectivity with a peer is lost but the VLT backup connectivity indicates that the peer is

still alive, the VLT ports on the Secondary peer are orphaned and are shut down.

PMUX Mode of the IO Aggregator

239