5.8.1. OSPF

OSPF (Open Shortest Path First) is a dynamic routing protocol that is based on the link state tracking technology and Dijkstra's algorithm for finding the shortest paths between nodes. The OSPF protocol redistributes information about the available routes among routers within the same autonomous system (AS). For more details on OSPF, please refer to the corresponding technical documentation.

To set up OSPF in UserGate, perform the following steps:

Name

Description

Step 1. Enable an OSPF router.

In the UserGate console, go to Network-->OSPF-->OSPF router, click Configure and configure parameters of the OSPF router.

Step 2. Select the interfaces through which the OSPF router will be receiving/redistributing information from other routers.

In the UserGate console, go to Network-->OSPF-->Interfaces, click Add and configure parameters of the interface. Add as many interfaces as necessary for proper operation of OSPF in your organization.

Step 3. Define an OSPF area.

In the UserGate console, go to Network-->OSPF-->Areas, click Add and configure parameters of the OSPF area. Make sure to provide the interfaces (created in the previous step) through which the area will be available to other routers.

Add as many areas as necessary for proper operation of OSPF in your organization.

When setting up an OSPF router, make sure to provide the following parameters:

Name

Description

Enabled

Enables or disables a given OSPF router.

Router ID

IP address of the router. Must be the same as one of IP addresses assigned to network interfaces of UserGate.

Redistribute

Redistributes routes directly connected to the UserGate network or kernel routes added by administrators in the Routes section among other OSPF routers.

Metric

Set the metric for the redistributed routes.

Default originate

Notify other routers that a given router has a default route.

When setting up OSPF interfaces, make sure to provide the following parameters:

Name

Description

Enabled

Enables or disables a given interface.

Interface

Select an existing interface that will be used for OSPF.

Cost

Cost of the channel in a given interface. This value is sent by LSA (link state advertisement) for the adjacent routers and then is used by these routers when they calculate the shortest route. The default value is 1.

Priority

An integer from 0 to 255. A larger value means higher chances for a router to become the designated router in the network for sending LSAs. Set this value to 0 if you do not want to make this router the designated router. The default value is 1.

Hello interval

Time period in seconds after which a router sends 'hello' packets. This value must be the same across all routes within the autonomous system. The default value is 10 seconds.

Dead interval

Time period in seconds after which the adjacent router will be considered unavailable. This time period is counted since the moment when the last 'hello' packet is received from the adjacent router. The default value is 40 seconds.

Retransmit interval

Sets the time interval before repeated sending of an LSA packet. The default value is 5 seconds.

Transmit delay

Sets an approximate time period required for delivering the updated link state to the adjacent routers. The default value is 1 second.

Authentication Enabled

Enables mandatory authentication for each incoming OSPF message on the router. Authentication is mostly used for prevention of injected false routes from unauthorized routers.

Auth type

Possible values:

  • Plain -- an open key is transferred for authentication of routers. Make sure to fill out the Key field.

  • Digest -- an MD5 hash is used as a key for authentication of OSPF packets. Make sure to provide the Key and MD5 key ID. For proper operation, these parameters must be the same across all routers.

When setting up an OSPF area, make sure to provide the following parameters:

Name

Description

Enabled

Enables or disables a given area.

Name

Name of a given area.

Cost

Cost of LSA announced in the stub zone

Area ID

Area identifier. An identifier can be specified in a decimal format or as an IP address. However, area identifiers are not IP addresses and thus can coincide with any assigned IP address.

Auth type

Possible values:

  • None - no authentication for OSPF packets is required

  • Plain - an open key is transferred for authentication of OSPF packets. The key specified in the interface settings is used

  • Digest - an MD5 hash is used as a key for authentication of OSPF packets. The key specified in the interface settings is used

Identification at the interface level has primacy over authentication at the area level.

Area type

Sets the area type. The following area types are supported:

  • Normal - a standard area created by default. This area obtains channel updates, summary routes, and external routes.

  • Stub - a stub area does not obtain information about external routes for a standalone system, but obtains routes from other areas. When routers from a stub area are required to send information outside the standalone area, they can use the default route. No ASBRs can be within a stub area.

  • NSSA - Not-so-stubby. An NSSA area defines an additional type of LSA --- LSA type 7. An NSSA area can contain an edge router (ASBR).

Do not sum up

Prohibits injection of summary routes to stub areas.

Interfaces

Selection of OSPF interfaces in which this area will be accessible.

Virtual links

A special connection for merging a disrupted area or joining an area to a backbone through another area. It can be configured between two ABRs.

This option allows a router sending OSPF packets through virtual links by encapsulating these packets in IP packets. This mechanism can be used as a temporary solution or as a backup when the core connections go down.

You can specify IDs of routers that should be accessible through a given area.