Design Reference

RSMLT timer tuning
RSMLT enables a participating peer switch to act as a router for its peer by MAC address. This
doubles router capacity and enables fast failover in the event of a peer switch failure. RSMLT
provides hold-up and hold-down timer parameters to aid these functions.
The hold-up timer defines the length of time the RSMLT-peer switch routes for its peer after a peer
switch failure. Configure the hold-up timer to at least 1.5 times greater than the routing protocol
convergence time.
The RSMLT hold-down timer defines the length of time that the recovering switch remains in a non-
Layer 3 forwarding mode for the MAC address of its peer. Configure the hold-down timer to at least
1.5 times greater than the routing protocol convergence time. The configuration of the hold-down
timer gives RIP, OSPF or BGP time to build up the routing table before Layer 3 forwarding for the
peer router MAC address begins again.
Important:
When using a Layer 3 SMLT client switch without a routing protocol, configure two static routes
to point to both RSMLT switches or configure one static route. Configure the RSMLT hold-up
timer to 9999 (infinity). Also configure the RSMLT hold-up timer to 9999 (infinity) for RSMLT
Edge (Layer 2 RSMLT).
IPv6 differences
The following list identifies ways in which the IPv6 implementation of RSMLT differs from the IPv4
implementation of RSMLT.
• After the switch begins to forward traffic on behalf of the peer, duplicate address detection
(DAD) is not executed for the IPv6 address of the peer. The implementation assumes that the
peer IPv6 address is already known to be unique.
• An RSMLT switch installs a neighbor entry for the peer IPv6 address immediately after the peer
disappearance is detected, possibly while a route for the peer still exists. This action can result
in packets destined to the peer IPv6 address being delivered to the CP for a short period of
time.
• You can not configure a vIST with IPv6 peer address
• In a dual-stack VLAN, adding or deleting IPv4 or IPv6 does not affect the RSMLT functionality
of one another. If you add IPv4 or IPv6 to an existing IPv6 or IPv4 RSMLT VLAN, the RSMLT
state for the protocol you add second will be the same as the previous RSMLT state.
Example: RSMLT redundant network with bridged and routed edge VLANs
Many Enterprise networks require the support of VLANs that span multiple wiring closets. VLANs
are often local to wiring closets and routed towards the core. The following figure shows VLAN-10,
which has all IP Deskphones as members and resides everywhere, while at the same time VLANs
20 and 30 are user VLANs that are routed through VLAN-40.
A combination of SMLT and RSMLT provide sub-second failover for all VLANs bridged or routed.
VLAN-40 is RSMLT enabled that provides for the required redundancy. You can use unicast routing
protocols—such as RIP, OSPF, or BGP—and routing convergence times do not impact the network
convergence time provided by RSMLT.
Routed SMLT
June 2015 Network Design Reference for Avaya VSP 4000 Series 57
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