ICND2 – Chapter 10 – Routing Protocol Theory

We finally get to routing in Chapter 10 which covers a lot of concepts about Distance Vector Protocols and Link State Protocols. It is definitely a good read. I knew a good bit about this so I did not highlight as much as some others might. No commands in this chapter. (only theory) Here are my notes:

Routing protocols perform 4 basic functions:

1. Learn routes from neighbor routers
2. Advertise routes to neighbors
3. If more than one route exists, pick the nest route, and populate it in the routing table
4. If anything changes, react, and pick new best routes

Distance Vector Routing Protocols:

RIPv1: Classful, No VLSM, Broadcasts instead of Multicasts, No Manual Summarization, No Authentication, Uses Hop Count as Metric

RIPv2: Classless, VLSM, Uses Hop Count as Metric

Link State Routing Protocols:

OSPF: Classless, VLSM, No Auto-Summarization, Uses Cost as Metric

IS-IS: Classless, VLSM

Hybrid (Balanced) Routing Protocols:

EIGRP: Classless, VLSM, Proprietary, Used Bandwidth and Delay as Metric

RIP sends full routing table every 30 seconds. All others send partial updates when changes occur.

Administrative Distance for ICND2 Routing Protocols:

0 Connected
1 Static
110 OSPF
120 RIP

Distance Vector Concepts:

Route poisoning refers to advertising a route with an infinity metric.

Split Horizon: Do not advertise a route out the same interface you learned it on. Cisco IOS defaults to use split horizon on most interfaces.

Hold down timer: As soon as a route is down, keep it down until the hold time timer expires.

Link State Concepts:

Link State protocols advertise information about every detail of the network to their neighbors. After all the flooding is complete each router has the same information and store it in a Link State Database (LSDB).

Two main LSA types: Router LSA and Link LSA.

To prevent loops the router asks if its neighbor already knows about an LSA before sending it.

OSPF re-floods each LSA based on its aging timer. (Default 30 minutes)

Each router looks independent at the LSDB and determines which routes to place in its routing table.

Link State protocols have very fast convergence times.


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