Nortel 8300 用户指南
52
VLANs, Spanning Tree, and Static Link Aggregation
The Backup Master feature provides an additional benefit. Under normal
VRRP operation, a hello packet is sent every second. When three hellos are
not received, all switches automatically revert to master mode. This results
in a 3 second outage. When you are using VRRP in an SMLT environment,
and a link goes down, traffic is automatically forwarded to the remaining
ports configured for SMLT VRRP Backup Master. Because both switches
are processing traffic, the node immediately recognizes the VRRP state
change, so there is faster failure recovery (less than 1 second).
VRRP operation, a hello packet is sent every second. When three hellos are
not received, all switches automatically revert to master mode. This results
in a 3 second outage. When you are using VRRP in an SMLT environment,
and a link goes down, traffic is automatically forwarded to the remaining
ports configured for SMLT VRRP Backup Master. Because both switches
are processing traffic, the node immediately recognizes the VRRP state
change, so there is faster failure recovery (less than 1 second).
Network design considerations for SMLT with VRRP
When you enable the VRRP BackupMaster with SMLT, refer to the following
guidelines:
guidelines:
•
The VRRP virtual IP address and the VLAN IP address cannot be the
same.
same.
•
Configure the hold-down timer for VRRP to a value approximately 150
percent of the IGP (Interior Gateway Protocol, such as RIP or OSPF)
convergence time to allow the IGP enough time to reconverge following
a failure. That is, if OSPF takes 40 seconds to reconverge, set the
holddown timer to 60 seconds.
percent of the IGP (Interior Gateway Protocol, such as RIP or OSPF)
convergence time to allow the IGP enough time to reconverge following
a failure. That is, if OSPF takes 40 seconds to reconverge, set the
holddown timer to 60 seconds.
•
Stagger the hold-down timers with ARP requests. This means that the
Ethernet Routing Switch 8300 does not have to run ARP at the same
time, causing excess CPU load. For example, if one node has the
hold-down timer set for 60 seconds, you can set the other to 65 seconds.
Ethernet Routing Switch 8300 does not have to run ARP at the same
time, causing excess CPU load. For example, if one node has the
hold-down timer set for 60 seconds, you can set the other to 65 seconds.
•
Enable hold-down times on both VRRP sides (Master and
BackupMaster).
BackupMaster).
Simple Loop Prevention Protocol
Simple Loop Prevention Protocol (SLPP) is used at the edge of a network to
prevent loops in an SMLT network if Spanning Tree is not used. Although
SLPP is focused on SMLT networks, it also works with other configurations.
Logical loops can occur in SMLT networks for the following reasons:
prevent loops in an SMLT network if Spanning Tree is not used. Although
SLPP is focused on SMLT networks, it also works with other configurations.
Logical loops can occur in SMLT networks for the following reasons:
•
Misconfigurations occur (for example, when SMLT client devices are
erroneously directly connected together).
erroneously directly connected together).
•
MLT is not operating correctly (for example, when a switch is connected
to the network using the default configuration without any MLT settings).
to the network using the default configuration without any MLT settings).
•
Problems occur with the edge switch (for example, when MLT or some
other form of link aggregation is not working).
other form of link aggregation is not working).
You can detect loops with SLPP and the 8000 Series switch Loop Detection
feature.
feature.
If an SLPP test packet—called an SLPP-packet data unit (SLPP-PDU)— is
received by the originating switch SMLT port or by a peer aggregation switch
on the same VLAN, a loop exists and the port is disabled.
received by the originating switch SMLT port or by a peer aggregation switch
on the same VLAN, a loop exists and the port is disabled.
Nortel Ethernet Routing Switch 8300
Configuration — VLANs, Spanning Tree, and Static Link Aggregation using Device Manager
NN46200-510
03.01
Standard
4.0
27 August 2007
Copyright © 2005-2007, Nortel Networks
.