Intermediate System to Intermediate System | 509Multi-Topology IS-ISFTOS 7.8.1.0 and later support Multi-Topology Routing IS-IS.E-Series ExaScale platform ex supports Multi-Topology IS-IS with FTOS 8.2.1.0 and later.Multi-Topology IS-IS (MT IS-IS) allows you to create multiple IS-IS topologies on a single router withseparate databases. This feature is used to place a virtual physical topology into logical routing domains,which can each support different routing and security policies.All routers on a LAN or point-to-point must have at least one common supported topology when operatingin Multi-Topology IS-IS mode. If IPv4 is the common supported topology between those two routers,adjacency can be formed. All topologies must share the same set of L1-L2 boundaries.You must implement a wide metric-style globally on the Autonomous System to run Multi-Topology IS-ISfor IPv6 because the TLVs used to advertise IPv6 information in link-state packets (LSPs) are defined touse only extended metrics.The Multi-Topology ID is shown in the first octet of the IS-IS packet. Certain MT topologies are assignedto serve predetermined purposes:• MT ID #0: Equivalent to the "standard" topology.• MT ID #1: Reserved for IPv4 in-band management purposes.• MT ID #2: Reserved for IPv6 routing topology.• MT ID #3: Reserved for IPv4 multicast routing topology.• MT ID #4: Reserved for IPv6 multicast routing topology.• MT ID #5: Reserved for IPv6 in-band management purposes.Transition ModeAll routers in the area or domain must use the same type of IPv6 support, either single-topology ormulti-topology. A router operating in multi-topology mode will not recognize the ability of thesingle-topology mode router to support IPv6 traffic, which will lead to holes in the IPv6 topology.While in transition mode, both types of TLVs (single-topology and multi-topology) are sent in LSPs for allconfigured IPv6 addresses, but the router continues to operate in single-topology mode (that is, thetopological restrictions of the single-topology mode remain in effect). Transition mode stops after allrouters in the area or domain have been upgraded to support multi-topology IPv6. Once all routers in thearea or domain are operating in multi-topology IPv6 mode, the topological restrictions of single-topologymode are no longer in effect.Interface supportMT IS-IS is supported on physical Ethernet interfaces, physical Sonet interfaces, port-channel interfaces(static & dynamic using LACP), and VLAN interfaces.
