Overview of Topology

Topology shows all the physical nodes and clusters that are discoverable.

The GigaVUE H Series and TA Series nodes are capable of snooping Link Layer Discovery Protocol (LLDP) packets and Cisco Discovery Protocol (CDP) packets. Starting in GigaVUE‑FM 5.2, they are also capable of sending Gigamon Discovery packets.

GigaVUE nodes receive LLDP and CDP packets from non Gigamon devices. They receive Gigamon Discovery packets from GigaVUE nodes managed by GigaVUE‑FM.

If the nodes in your network use either of these protocols, they can identify its immediate neighbors and their capabilities. The LLDP, CDP, and Gigamon discovery information includes the remote port and chassis IDs, as well as other selected information, if it is included by the sender. This information can be used to determine the origin of traffic flows.

All these protocols are physical topology discovery protocols (Layer 2). LLDP and CDP are unidirectional. Devices send their identity and capabilities in a packet. The node receives the packet and extracts information from it, such as the chassis ID and port ID of a neighbor. The information from the neighbors varies depending on what is sent in the packet.

Gigamon discovery is bidirectional. GigaVUE nodes transmit the LLDP packets with a unique type-length-value (TLV) structure that is identifiable by another GigaVUE node. When a GigaVUE node receives these packets, it detects the TLV structure and identifies the discovered node as a GigaVUE node. These Gigamon discovery packets also include the management IP4 and IP6 address of the node in the unique TLV structure. Using the management IP address, the neighbor information of the discovered nodes is collected to build the entire physical topology.

The Gigamon discovery packets can be transmitted out of tool, stack, network, and hybrid port types. For stack port types, Gigamon Discovery works only when both ends of the link are of type stack.

The hybrid ports and ports configured with force link up are operated in loopback mode. So, when Gigamon discovery is enabled, these ports show themselves as neighbors.

The Gigamon discovery packets are transmitted as soon as the link is up on the relevant port. They are retransmitted when changes are made to the port or chassis configuration such as the host name on the box, port type, IP address of the management interface, and so on. When the transmission or retransmission of Gigamon discovery packets begins, the interpacket time intervals per port is 1, 2, 4, 8, 16, 30, 30, 30, .... seconds. The packets are transmitted every 30 seconds so that the nodes are discovered as soon as possible. Discovery packets are terminated on the receiving GigaVUE node.

GigaVUE‑FM constructs the topology by doing the following:

■   Groups discovered nodes into clusters by combining nodes with the same cluster ID.
■   Queries the leader for the existing stack links.
■   Extracts the box IDs from the connected nodes.
o   For port-based stack links, the box ID is extracted from the interconnected stack port IDs.
o   For GigaStream-based stack links, the box ID is extracted from the first port member of each GigaStream.

Topology construction has the following limitations:

■   GigaVUE‑FM relies on the cluster configuration to construct the topology.
o   Cascading nodes interconnected over network or tool ports or over Port Groups or GigaStream (other than stack links) are not discovered.
o   GigaVUE‑FM does not detect miswired cluster cabling.
o   If GigaVUE H and TA Series nodes connected over tool ports are not managed by GigaVUE‑FM, then they are not automatically discovered.
■   GigaVUE‑FM constructs H Series cluster topology by querying nodes for the relevant connectivity information. The topology is constructed based on information from the GigaVUE nodes.
■   Gigamon discovery is not supported on inline-tool and inline-network port type.
■   For stack ports, Gigamon discovery will work only if both ends of the link are of type stack.
■   If a pass-all map is configured for Gigamon discovery enabled ports, the show map statistics will show an increment in the map rule counter for Gigamon discovery packets although the Gigamon discovery packets are not sent to the tool ports.
■   If Gigamon discovery is enabled on a port, for example port 9/3/x1, and the port type is changed to an unsupported port types such as inline-network, Gigamon discovery is immediately disabled and an error message is displayed.


■   Prior to GigaVUE‑OS version 4.7, GigaVUE TA Series Traffic Aggregator nodes did not support tool ports. Instead, they supported gateway ports. Starting in GigaVUE‑OS version 4.7, all gateway ports on GigaVUE TA Series nodes are tool ports. However, GigaVUE‑FM may be managing nodes running a software version lower than version 4.7.
■   G-Series nodes are not supported in Topology Visualization.