Allied Telesis AT-WR4500 manual Ospf Areas, Submenu level /routing ospf area

100	AT-WR4500 Series - IEEE 802.11abgh Outdoor Wireless Routers
	RouterOS v3 Configuration and User Guide

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Within one area, only the router that is connected to another area (i.e. Area border router) or to another AS (i.e. Autonomous System boundary router) should have the propagation of the default route enabled. OSPF protocol will try to use the shortest path (path with the smallest total cost) if available.

OSPF protocol supports two types of metrics:

•type1 - external metrics are expressed in the same units as OSPF interface cost. In other words the router expects the cost of a link to a network which is external to AS to be the same order of magnitude as the cost of the internal links.

•type2 - external metrics are an order of magnitude larger; any type2 metric is considered greater than the cost of any path internal to the AS. Use of type2 external metric assumes that routing between AS is the major cost of routing a packet, and climinates the need conversion of external costs to internal link state metrics.

Both Type 1 and Type 2 external metrics can be used in the AS at the same time. In that event, Type 1 external metrics always take precedence.

In /ip route you can see routes with Io status. Because router receives routers from itself.

The metric cost can be calculated from line speed by using the formula 10e+8/line speed. The table contains some examples:

Example

To enable the OSPF protocol redisrtibute routes to the connected networks as type1 metrics with the cost of 1, you need do the following:

[admin@AT-WR4562] routing ospf> set redistribute-connected=as-type-1 \ \... metric-connected=1

[admin@AT-WR4562] routing ospf> print router-id: 0.0.0.0

distribute-default: never redistribute-connected: no

redistribute-static: no redistribute-rip: no redistribute-bgp: no metric-default: 1 metric-connected: 20 metric-static: 20 metric-rip: 20 metric-bgp: 20

mpls-te-area: unspecified mpls-te-router-id: unspecified

[admin@AT-WR4562] routing ospf>

5.3.3 OSPF Areas

Submenu level: /routing ospf area

Description

OSPF allows collections of routers to be grouped together. Such group is called an area. Each area runs a separate copy of the basic link-state routing algorithm. This means that each area has its own link-state database and corresponding graph

The structure of an area is invisible from the outside of the area. This isolation of knowledge enables the protocol to effect a marked reduction in routing traffic as compared to treating the entire Autonomous System as a single link-state domain

60-80 routers have to be the maximum in one area

Property Description

area-id(IP address; default: 0.0.0.0) - OSPF area identifier. Default area-id=0.0.0.0is the backbone area. The OSPF backbone always contains all area border routers. The backbone is responsible for distributing routing information between non-backbone areas. The backbone must be contiguous.