IS-IS Discovery

IS-IS Links are found in the isisISAdjTable that is defined in ISIS-MIB (mib-rfc4444.txt). In this table is found the information needed to find the Adjacency Intermediate System. The information about IS-IS is stored into two tables: isisElement and isisLink. isisElement contains the ISISSysID, a unique identifier of the "Intermediate System" (the name for the Router in ISO protocols). Each entry in this SNMP MIB table represents a unidirectional link from the Intermediate System that is queried to the Adjacent Intermediate Systems running IS-IS and "peering" with the source router. If two routers IS-A and IS-B support ISIS-MIB, then EnLinkd will create two link entries in Horizon: one from IS-A to IS-B (from the adjtable of IS-A) the complementary link back from IS-B to IS-A (from the adjTable of IS-B). IS-IS links are represented in the ISIS-MIB as follows:

The following OIDs are supported to discover and build the ISIS network topology and are collected by the ISIS Discovery Collector.

Table 1. Supported OIDs from ISIS-MIB
Name	OID	Description
isisSysID	`.1.3.6.1.2.1.138.1.1.1.3.0`	The ID for this Intermediate System. This value is appended to each of the area addresses to form the Network Entity Titles. The derivation of a value for this object is implementation specific. Some implementations may automatically assign values and not permit an SNMP write, while others may require the value to be set manually. Configured values must survive an agent reboot.
isisSysAdminState	`.1.3.6.1.2.1.138.1.1.1.8.0`	The administrative state of this Intermediate System. Setting this object to the value `on` when its current value is `off` enables the Intermediate System. Configured values must survive an agent reboot.
isisSysObject	`.1.3.6.1.2.1.138.1.1.1`	isisSysObject
isisCircIfIndex	`.1.3.6.1.2.1.138.1.3.2.1.2`	The value of ifIndex for the interface to which this circuit corresponds. This object cannot be modified after creation.
isisCircAdminState	`.1.3.6.1.2.1.138.1.3.2.1.3`	The administrative state of the circuit.
isisISAdjState	`.1.3.6.1.2.1.138.1.6.1.1.2`	The state of the adjacency.
isisISAdjNeighSNPAAddress	`.1.3.6.1.2.1.138.1.6.1.1.4`	The SNPA address of the neighboring system.
isisISAdjNeighSysType	`.1.3.6.1.2.1.138.1.6.1.1.5`	The type of the neighboring system.
isisISAdjNeighSysID	`.1.3.6.1.2.1.138.1.6.1.1.6`	The system ID of the neighboring Intermediate System.
isisISAdjNbrExtendedCircID	`.1.3.6.1.2.1.138.1.6.1.1.7`	The 4-byte Extended Circuit ID learned from the Neighbor during 3-way handshake, or 0.

Generic information about the IS-IS link discovery process can be found in the IS-IS Information box on the Node Detail Page of the device. Information gathered from this OIDs will be stored in the following database table:

Figure 1. Database tables related to IS-IS discovery

ISIS Topology Updater provides ISIS OnmsTopology consolidating IS-IS data collected by ISIS Collector only full bidirectional connections between two ISIS supported devices become edges. Node A and Node B are connected by an ISIS edge if and only if there is a ISIS link in Node A to Node B and vice versa.