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Understanding the network.pdf - Back to Home

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C 192.168.191.0/24 is directly connected, E<strong>the</strong>rnet0/1<br />

192.168.0.0/30 is subnetted, 1 subnets<br />

The default administrative distance for all OSPF routes (which is 110) can be<br />

adjusted using <strong>the</strong> router subcommand . It is also possible <strong>to</strong><br />

adjust <strong>the</strong> distances of external, inter-area, and intra-area routes using <strong>the</strong> OSPF<br />

configuration subcommand .<br />

OSPF Route Types<br />

An "O" type route indicates that <strong>the</strong> route is directly connected <strong>to</strong> <strong>the</strong> backbone area.<br />

"IA" routers indicate that <strong>the</strong> route is an inter-area. <strong>Back</strong>bone and inter-area route<br />

costs reflect <strong>the</strong> cost of <strong>the</strong> entire route path. "E1" indicates that route is an external,<br />

type 1 route. Type 1 metrics show <strong>the</strong> <strong>to</strong>tal cost of route path between <strong>the</strong> source<br />

and destination. All directly connected external <strong>network</strong>s use type 1 metrics since<br />

<strong>the</strong> actual cost <strong>to</strong> reach <strong>the</strong> <strong>network</strong> is <strong>the</strong> cost of <strong>the</strong> internal path <strong>to</strong> <strong>the</strong> ASB router.<br />

The "E2" marker is used for type 2 routes. Redistributed routes are announced as<br />

type 2 metrics. The route cost associated with a type 2 metric only reflects <strong>the</strong> cost<br />

<strong>to</strong> <strong>the</strong> source of <strong>the</strong> external route.<br />

You should recall from Chapter 8, "TCP/IP Dynamic Routing Pro<strong>to</strong>cols," that OSPF<br />

uses a structured scale for establishing interface costs based on bandwidth, (see<br />

Table 10.4).<br />

Table 10.4. OSPF Interface Bit Value and Cost<br />

Network Bandwidth (in bits) Bandwidth (in KBit/s) Path Cost<br />

100,000,000 100,000 (Fast E<strong>the</strong>rnet) 1<br />

16,000,000 16,000 (16Mb Token Ring) 6<br />

10,000,000 10,000 (E<strong>the</strong>rnet) 10<br />

4,000,000 4,000 (4Mb Token Ring) 25<br />

1,544,000 1,544 (serial T1) 64<br />

64,000 640 (single B-ISDN) 1562<br />

56,000 560 (single T-channel) 1786<br />

33,600 33.6 (codex modem) 3354<br />

28,000 2.8 (28K baud modem) 2604<br />

14,400 1.4.4 (14.4 baud modem) 5208

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