Link State Routing
Link State Routing protocols provide greater flexibility and sophistication than their Distance Vector counterparts. They reduce overall broadcast traffic and make better decisions about routing by taking characteristics such as bandwidth, delay, reliability, and load into consideration (see Table 3.3), instead of basing their decisions solely on distance or hop count.
Examples of Link State Routing protocols are OSPF and IS-IS which only supports IP traffic, and Novell's NLSP (NetWare Link State Protocol), which only supports IPX. Other than mentioning NLSP here, it will not be discussed further. OSPF is covered in Chapter 6 and IS-IS is covered in Chapter 8.
Table 3.3 Link State Characteristics
Characteristic |
Routing Protocol |
|
|
OSPF |
IS-IS |
Route Updates: |
|
|
Multicasts |
X |
X |
Triggered Updates |
X |
X |
After initial route table exchange. Only sends changed route information |
X |
X |
Databases and Tables: |
|
|
Neighbor (Adjacency) |
X |
X |
Topology Map(Link State) |
X |
X |
Route (Forwarding) |
X |
X |
Metrics: |
|
|
Various. Link State protocols do share common values. OSPF uses Bandwidth only. Refer to Chapter 6. IS-IS may use Default, Delay, Expense, and/or Error (refer to Chapter 8). |
|
|
VLSM |
X |
X |
ToS |
X |
X |
Load balancing: |
|
|
Equal Cost |
X |
X |
Unequal Cost |
X |
X |
Authentication |
X |
X |