3Com 5500 SI - Switch - Stackable, Configuration Manual

Page: 277 / 686

Introduction to Gratuitous ARP 277
Resilient ARP
Configuration
This section contains configuration information for Resilient ARP.
Overview of Resilient ARP
To support resilient networking in XRN applications, redundant links are required
between the XRN fabric and other devices. But if intra-fabric connections are broken
and the original fabric is split, these redundant links may cause a situation where the
network connects to two or more layer 3 devices of the same configuration and they
run the same routing function. To eliminate this situation, you can resort to resilient
ARP mechanism, which can immediately detect if there are layer 3 devices of the
same configuration existing in the network. If yes, it will keep only one as a Layer 3
device and turn the others in to Layer 2 devices.
A resilient ARP state machine may be in one of six states: Initialize, LisentForL3Master,
L3Master, L3Slave, L2Master and L2Slave. An L3Master state machine regularly sends
resilient ARP messages to notify other XRN fabrics that its home fabric is in Layer 3
state.
The resilient ARP mechanism can implement state transition by sending/receiving
resilient ARP messages regularly, so as to determine if a device serves as a Layer 3 or
Layer 2 device.
Resilient ARP configuration is described in the following sections:
■
Enabling/Disabling Resilient ARP Function
■
Configuring Resilient ARP Packet-sending VLAN Interface
Enabling/Disabling Resilient ARP Function
After resilient ARP is enabled, the system can ensure there is only one Layer 3 device,
and that others are Layer 2 devices.
Perform the following configuration in System View.
By default, resilient ARP function is enabled.
If you are attempting to stop the Switch from transmitting packets, you need to
disable all features which may generate packets. By default these are:
■
DHCP
■
Resilient ARP
■
Spanning Tree
Configuring Resilient ARP Packet-sending VLAN Interface
You must configure the VLAN interface corresponding to the redundant links which
connect the XRN fabric with other devices, to make resilient ARP operate normally.
Then if intra-fabric connections are broken, resilient ARP packets can be sent through
these VLAN interfaces corresponding to the redundant links, to determine if the
system works as a layer 3 or layer 2 device.
Table 274 Enabling/Disabling Resilient ARP Function
Operation Command
Enable resilient ARP function
resilient-arp enable
Disable resilient ARP function
undo resilient-arp enable