Administrator Guide

information is communicated to the peer VLT node regardless of whether the VLAN configured is a VLT or a non-VLT interface. If the
VLAN operational state (OSTATE) is up, dynamically learned ND entry in VLT node1 synchronizes to VLT node2.
Tunneling IPv6 ND in a VLT Domain
Tunneling an NA packet from one VLT node to its peer is required because an NA may reach the wrong VLT node instead of arriving at
the destined VLT node. This may occur because of LAG hashing at the ToR switch. The tunneled NA carries some control information
along with it so that the appropriate VLT node can mimic the ingress port as the VLT interface rather than pointing to VLT node’s
interconnecting link (ICL link).
The overall tunneling process involves the VLT nodes that are connected from the ToR through a LAG. The following illustration is a basic
VLT setup, which describes the communication between VLT nodes to tunnel the NA from one VLT node to its peer.
NA messages can be sent in two scenarios:
• NA messages are almost always sent in response to an NS message from a node. In this case, the solicited NA has the destination
address field set to the unicast MAC address of the initial NS sender. This solicited NA must be tunneled when they reach the wrong
peer.
• Sometimes NA messages are sent by a node when its link-layer address changes. This NA message is sent as an unsolicited NA to
advertise its new address and the destination address field is set to the link-local scope of all-nodes multicast address. This unsolicited
NA packet does not have to be tunneled.
Consider a sample scenario in which two VLT nodes, Unit1 and Unit2, are connected in a VLT domain using an ICL or VLTi link. To the
south of the VLT domain, Unit1 and Unit2 are connected to a ToR switch named Node B. Also, Unit1 is connected to another node, Node
A, and Unit2 is linked to a node, Node C. When an NS traverses from Unit2 to Node B(ToR) and a corresponding NA reaches Unit1
because of LAG hashing, this NA is tunneled to Unit 2 along with some control information. The control information present in the
tunneled NA packet is processed in such a way so that the ingress port is marked as the link from Node B to Unit 2 rather than pointing to
ICL link through which tunneled NA arrived.
Figure 138. Sample Configuration of IPv6 Peer Routing in a VLT Domain
Sample Configuration of IPv6 Peer Routing in a VLT
Domain
Consider a sample scenario as shown in the following figure in which two VLT nodes, Unit1 and Unit2, are connected in a VLT domain
using an ICL or VLTi link. To the south of the VLT domain, Unit1 and Unit2 are connected to a ToR switch named Node B. Also, Unit1 is
connected to another node, Node A, and Unit2 is linked to a node, Node C. The network between the ToR and the VLT nodes is Layer 2.
Servers or hosts that are connected to the ToR (Node B) generate Layer 3 control/data traffic from the South or lower-end of the
vertically-aligned network.
Virtual Link Trunking (VLT)
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