| 1 | An Intermediate System is the ISO term for a router. |
| 2 | A Network Protocol Data Unit is the ISO term for a packet. |
| 3 | An L1 router has no direct connections to another area. An L2 router has no adjacencies with L1 routers. An L1/L2 router routes both inter-area and intra-area traffic and acts as an inter-area gateway for L1 routers. |
| 4 | Cisco routers by default are L1/L2. |
| 5 | The borders of IS-IS areas are between routers, on links. The borders of OSPF areas are defined by the routers themselves. |
| 6 | Two L1/L2 routers with the same AIDs will form both an L1 and an L2 adjacency. Two L1/L2 routers with different AIDs will form an L2 adjacency. |
| 7 | Two L2-only routers will form an L2 adjacency, whether the AIDs are the same or different. |
| 8 | The Network Entity Title is an address by which a router identifies both itself and the area in which it resides. |
| 9 | The NSAP Selector should be set to 0x00 in a NET. |
| 10 | The System ID uniquely identifies a router within an IS-IS domain. |
| 11 | The portion of the NET preceding the last seven octets is the area address. |
| 12 | IS-IS does not elect a BDR. |
| 13 | The Pseudonode ID is the last octet of a LAN ID. Its purpose is to distinguish LAN IDs that are originated by a single router that is the DR on multiple LANs. |
| 14 | The MaxAge of an IS-IS LSP is 1200 seconds (20 minutes). The MaxAge (or beginning Remaining Lifetime) can be configured up to 65,535 seconds. |
| 15 | OSPF increments the age up to MaxAge; IS-IS decrements the age down to 0. A new OSPF LSA has an age of 0, whereas a new IS-IS LSP has an age of MaxAge. |
| 16 | The refresh rate of an IS-IS router is 900 seconds (15 minutes). |
| 17 | A Complete Sequence Number Packet contains a full listing of all LSPs in a database. A CSNP is periodically sent by the Designated Router on a broadcast network to maintain database synchronization. |
| 18 | A Partial Sequence Number Packet contains a listing of one or more LSPs. It has two uses: On point-to-point networks, it is used to acknowledge the receipt of LSPs. On broadcast networks, it is used to request LSPs. |
| 19 | An IS-IS router uses the Overload bit to inform its neighbors that it is experiencing a memory overload and cannot store the entire link-state database. |
| 20 | The Attached bit is used by L1/L2 routers to inform L1 routers that it is attached to the L2 backbone. |
| 21 | The Up/down bit is used to distinguish between an address that originated within an area, or an address that was leaked into an area. |
| 22 | The ISO specifies four metrics: Default, Expense, Delay, and Error. Cisco supports only the Default metric. |
| 23 | The two metric styles are narrow and wide. The narrow metric has a maximum value of 63. The wide metric has a maximum value of 16777214. |
| 24 | The maximum metric value of an IS-IS route is 1023 for narrow metrics and 4261412864 for wide metrics. |
| 25 | L1 IS-IS metrics apply to intra-area routes, and L2 IS-IS metrics apply to inter-area routes. |
| 26 | Internal metrics apply to routes to destinations within the IS-IS domain. External metrics apply to routes to destinations external to the IS-IS domain. |
| 27 | A single adjacency is formed between two routers, even if both IPv4 and IPv6 are configured in multi-topology mode. |
| 28 | L1 areas may be configured on a router. One L2 area is configured. |
| 29 | The two active mesh group modes are Blocked and Set (Numbered). Blocked mode offers the most reduced flooding, but at the possible cost of the most reduced redundancy and increased convergence time. Set mode, or numbered mesh groups, do not reduce flooding load as much as Blocked mode, but also have less potential impact on redundancy and convergence time. |
