Routed Split Multi-Link Trunking (RSMLT) is an enhancement to SMLT that enables the exchange of Layer 3 information between peer nodes in a switch cluster. RSMLT provides two main advantages over SMLT:
provides backup for the peer after the peer goes down
routes traffic on behalf of the peer to prevent Virtual Inter-Switch Trunk (vIST) overload
IPv6 RSMLT enables the subsecond failover for IPv6 forwarding.
The overall model for IPv6 RSMLT is essentially identical to that of IPv4 RSMLT. In short, RSMLT peers exchange their IPv6 configuration and track their states by using vIST messages. An RSMLT node always performs IPv6 forwarding on the IPv6 packets destined to the MAC addresses of the peer. If an RSMLT node detects that the RSMLT peer is down, the node forwards IPv6 traffic destined to the IPv6 addresses of the peer.
With RSMLT enabled, an SMLT switch performs IP forwarding on behalf of the SMLT peer, which prevents IP traffic from being sent over the vIST.
IPv6 RSMLT supports the full set of topologies and features supported by IPv4 RSMLT, including SMLT triangles, squares, and SMLT full-mesh topologies, with routing enabled on the core VLANs.
Because you configure RSMLT on a VLAN, not at the IP layer, the configuration applies to both IPv4 and IPv6. You cannot enable or disable RSMLT on a VLAN for IPv6 but not IPv4; or for IPv4 but not IPv6.
With IPv6, you must configure the RSMLT peers to use the same set of IPv6 prefixes.
Supported routing protocols include the following:
IPv6 static routes
OSPFv3
Note
IPv6 RSMLT is not virtualized, therefore it is not possible to enable IPv6 and RSMLT together on a VLAN which is associated with a VRF.
Create an IPv6 interface on a VLAN which is associated with a VRF and RSMLT is enabled on the VLAN.
Enable RSMLT on an IPv6 enabled VLAN which is associated with a VRF.
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 cannot 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.