Smlt And Vrrp Backup Master - Nortel 8300 User Manual

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SMLT and VRRP backup master

When configuring routing on SMLT aggregation switches, Nortel
recommends that you use VRRP for default gateway redundancy. With
the standard implementation in a VRRP environment, you can have one
active primary router per IP subnet, with all other network VRRP interfaces
in backup mode.
A deficiency occurs when VRRP-enabled switches use SMLT. If VRRP
switches are aggregated into two SMLT switches, the end host traffic is
load-shared on all uplinks to the aggregation switches (based on the MLT
traffic distribution algorithm).
VRRP normally has only one active routing interface enabled. All other
VRRP routers are in backup (standby) mode. Therefore, all traffic that
reaches the backup VRRP router is forwarded over the Inter Switch Trunk
(IST) link towards the master VRRP router. In this case, the IST link does
not have enough bandwidth to carry all the aggregated traffic.
You can overcome this issue by assigning the backup router as the Backup
Master router. The Backup Master router is a backup router permitted to
actively load-share the routing traffic with a master router.
When enabled, the VRRP Backup Master acts as an IP router for packets
destined for the logical VRRP IP address. With the Backup Master router
enabled, the incoming host traffic is forwarded over the SMLT links as
normal. The Backup Master routes traffic received on the SMLT VLAN,
thus avoiding traffic flow across the IST trunk. This eliminates the potential
limitation in the available IST bandwidth and provides true load-sharing
capabilities.
To avoid potential frame duplication problems, the VRRP Backup Master feature
for SMLT can be used only on interfaces defined for SMLT. It cannot be used in
conjunction with HUBs to avoid frame duplication.
Configuration — VLANs, Spanning Tree, and Static Link Aggregation using Device Manager
Copyright © 2005-2007, Nortel Networks
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config ethernet <slot/port> perform-tagging enable
Enable dropping of untagged frames on IST trunk links:
config ethernet <slot/port> untagged-frames-
discard enable
Nortel Ethernet Routing Switch 8300
NN46200-510 03.01 Standard
4.0 27 August 2007
Split MultiLink Trunking 51
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ATTENTION