Dell PowerSwitch S4820T Configuration Guide for the S4820T System 9.100.0 - Page 446

• area address - within your routing domain or area, each area must have a unique area value. The first byte is called the authority and format indicator (AFI). • system address - the router's MAC address. • N-selector - this is always 0. The following illustration is an example of the ISO-style address to show the address format IS-IS uses. In this example, the first five bytes (47.0005.0001) are the area address. The system portion is 000c.000a.4321 and the last byte is always 0. Figure 57. ISO Address Format Multi-Topology IS-IS Multi-topology IS-IS (MT IS-IS) allows you to create multiple IS-IS topologies on a single router with separate databases. Use this feature 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 operating in 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 (AS) to run multi-topology IS-IS for IPv6 because the Type, Length, Value (TLVs) used to advertise IPv6 information in link-state packets (LSPs) are defined to use only extended metrics. The multi-topology ID is shown in the first octet of the IS-IS packet. Certain MT topologies are assigned to 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 Mode All routers in the area or domain must use the same type of IPv6 support, either single-topology or multi-topology. A router operating in multi-topology mode does not recognize the ability of the single-topology mode router to support IPv6 traffic, which leads to holes in the IPv6 topology. While in Transition mode, both types of TLVs (single-topology and multi-topology) are sent in LSPs for all configured IPv6 addresses, but the router continues to operate in single-topology mode (that is, the topological restrictions of the single-topology mode remain in effect). Transition mode stops after all routers in the area or domain have been upgraded to support multi-topology IPv6. After all routers in the area or domain are operating in multi-topology IPv6 mode, the topological restrictions of single-topology mode are no longer in effect. Interface Support MT IS-IS is supported on physical Ethernet interfaces, physical synchronous optical network technologies (SONET) interfaces, portchannel interfaces (static and dynamic using LACP), and virtual local area network (VLAN) interfaces. 446 Intermediate System to Intermediate System