Advanced OSPF Design Concepts

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Command Mode: Interface configuration.

Usage Guidelines: The password created by this command is used as a “key” that is inserted directly into the OSPF header when the Cisco IOS software originates routing protocol packets. A separate password can be assigned to each network on a per- interface basis. All neighboring routers on the same network must have the same password to be able to exchange OSPF information.


Notes:  
The Cisco IOS software will use this key only when authentication is enabled for an area with the area authentication router configuration command.

Example: In the following example, the authentication key is enabled with the string yourpass:

    ip ospf authentication-key yourpass 

Related commands: area authentication

ip ospf cost

To explicitly specify the cost of sending a packet on an interface, use the ip ospf cost interface configuration command. To reset the path cost to the default value, use the no form of this command. The syntax for this command (and the no form) is as follows:

    ip ospf cost cost    no ip ospf cost 

Syntax Description:

cost. Unsigned integer value expressed as the link-state metric. It can be a value in the range 1 to 65535.

Default: The default cost is 10^8/bandwidth.

Command Mode: Interface configuration.

Usage Guidelines: Unlike IGRP, you must set this metric manually using this command, if you need to change the default. Changing the bandwidth will change the link cost.

The link-state metric is advertised as the link cost in the router link advertisement. Cisco does not support type of service (TOS), so you can assign only one cost per interface.

In general, the path cost is calculated using the following formula:

    108 √ Bandwidth 

The default of reference-bandwidth is 10^8.

Using the preceding formula, the default path costs were calculated as noted in Table 6-2. If these values do not suit your network, you can use your own method of calculating path costs as demonstrated in Table 6-2.

Table 6-2 Calculating path costs based on network type
Network type Default cost

56kbps serial link 1,785
64kbps serial link 1,562
T1 (1.544Mbps serial link) 65
E1 (2.048Mbps serial link) 48
4Mbps Token Ring 25
Ethernet 10
16Mbps Token Ring 6
FDDI 1

Example: The following example sets the interface cost value to 65:

    ip ospf cost 65 

ip ospf dead-interval

To set how long hello packets must not have been seen before its neighbors declare the router down, use the ip ospf dead-interval interface configuration command. To return to the default time, use the no form of this command. The syntax for this command (and the no form) is as follows:

    ip ospf dead-interval seconds    no ip ospf dead-interval 

Syntax Description:

seconds. Unsigned integer that specifies the interval in seconds; the value must be the same for all nodes on the network.

Default: Four times the interval set by the ip ospf hello-interval command.

Command Mode: Interface configuration.

Usage Guidelines: The interval is advertised in the router’s hello packets. This value must be the same for all routers and access servers on a specific network.

Example: The following example sets the OSPF dead interval to 60 seconds:

    interface ethernet 1    ip ospf dead-interval 60 

Related commands: ip ospf hello-interval

ip ospf demand circuit

To configure OSPF to treat the interface as an OSPF demand circuit, use the ip ospf demand-circuit interface configuration command. To remove the demand circuit designation from the interface, use the no form of this command. The syntax for this command (and the no form) is as follows:

    ip ospf demand-circuit    no ip ospf demand-circuit 

ip ospf hello-interval

To specify the interval between hello packets that the Cisco IOS software sends on the interface, use the ip ospf hello-interval interface configuration command. To return to the default time, use the no form of this command. The syntax for this command (and the no form) is as follows:

    ip ospf hello-interval seconds    no ip ospf hello-interval 

Syntax Description:

seconds. Unsigned integer that specifies the interval in seconds. The value must be the same for all nodes on a specific network.

Default: 10 seconds.

Command Mode: Interface configuration.

Usage Guidelines: This value is advertised in the hello packets. The smaller the hello interval, the faster topological changes will be detected, but more routing traffic will ensue. This value must be the same for all routers and access servers on a specific network.

Example: The following example sets the interval between hello packets to 15 seconds:

    interface ethernet 1    ip ospf hello-interval 15 

Related Commands: ip ospf dead-interval

ip ospf message-digest-key

To enable OSPF MD5 authentication, use the ip ospf message-digest-key interface configuration command. To remove an old MD5 key, use the no form of this command. The syntax for this command (and the no form) is as follows:

    ip ospf message-digest-key keyid md5 key    no ip ospf message-digest-key keyid 

Syntax Description:

keyid. An identifier in the range 1 through 255.
key. An alphanumeric password of up to 16 bytes.

Default: OSPF MD5 authentication is disabled.

Command Mode: Interface configuration.

Usage Guidelines: Usually there is one key per interface, which is used to generate authentication information when sending packets and to authenticate incoming packets. The same key identifier on the neighbor router must have the same key value.


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OSPF Network Design Solutions
OSPF Network Design Solutions
ISBN: 1578700469
EAN: 2147483647
Year: 1998
Pages: 200
Authors: Tom Thomas

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