OSPF command

Allows to review current running router configuration.

• "running-config" – shows a current router’s configuration, available in any mode.
• "neighbor [A.B.C.D] [detail]" – displays the neighbors status. It is possible to specify IP address of a network interface, which state and neighbors list need to be shown. If this parameter is not specified the command shows a summary information for all interfaces. If the "detail" parameter is specified, then neighbors information is output in a detailed form, not just a summary table. For more information about the data displayed in the table, see the "Example" section.
• "show database" – shows a summary table with a database contents (LSA). The parameter has following arguments:
  • "[asbr-summary|external|network|router|summary|nssa-external|max-age|self-originate]" – specifies the link advertisement type to review.
  • "[A.B.C.D]" - link destination (in IP address form), which advertisements need to be reviewed.
  • "[adv-router A.B.C.D]" - router id (whole 32-bit number, can be set in the "OSPF config-router" mode), which link advertisements need to be reviewed.

• "access-list" – displays access lists content.

  • "[(<1-99>|<100-199>|<1300-1999>|<2000-2699>|WORD)]" - the list identifier, if not specified then a content of all lists is displayed.

• "prefix-list" – displays prefix-lists content (for more information about the prefix lists configuration see subsection "Filtration objects").

  • "WORD" – the prefix list identifier, if not specified, then a content of all lists are displayed.

  • "summary" и "detail" – used to output a summary and more detailed data.

• "route" – displays a routing table. For more information about table content see the "Example" subsection.

• "interface [INTERFACE]" – displays the information about network interfaces including virtual links states.

  • "[INTERFACE]" - an interface name, if not specified all interfaces information will be shown.

• "border-routers" – shows a table of paths to area boundary routers.
• "memory" – a memory statistic.
  • "all", "lib", "ospf" and "rip" – specify values types to be shown. If not specified, data will be displayed for all types, same as the "all" parameter.
• "ospf" – displays OSPF protocol summary information.
• "summary-address" – displays a possible aggregate networks list with number of network prefixes that can be replaced by a summary route.
  • “detail” – shows detailed information, can be used as a hint while network planning.
• "show thread cpu" – shows current cpu load. Filters can be used to display specific data (rwtex).
• "version" – shows ARDA version.

OSPF configure mode

Adds OSPF debug information to the system log.

• "N" – possible log levels are from "0" (no information logged) to "255" (the most verbose logging).

Stops the OSPF daemon:

• "daemon" – stops the OSPF router;
• "clear" –  the router will clear its part of system configuration before quitting OSPF CS.

OSPF config-router mode

Allows to assign an identifier to this OSPF router. Every OSPF router has a unique identifier. Identifier is a 32-bit integer. If identifier was not set by administrator, the router will automatically assign an identifier which equals to a maximal (by value) IP address from all router's IP addresses participating in OSPF system.

Allows to modify the "reference_bandwidth" value, "<1-4294967>" – Mbit/s parameter value in range 1-4294967.

Link metric is a cost of traffic delivery through the network interface. OSPF router automatically calculates an internal link cost taking physical interface’s capacity to which link belongs:

M = reference_bandwidth/bandwidth:

• "reference_bandwidth" – default capacity equals 100 Mbit/s,
• "bandwidth" – a capacity (bandwidth) of a physical network interface to which the link belongs.

This metric configuration method is used for all links for which interfaces a specific cost is not set.

The router automatically updates link-state information with its neighbors. Only an obsolete information is updated which age has exceeded a specific threshold. This parameter changes a threshold value, which by default is 1800 seconds (half an hour). The value is applied to the whole OSPF router.

Enables to log changes in the adjacency state.

• "detail" – logging every step neighboring routers take to establish the adjacency state.

OSPF areas

OSPF protocol has an ability to join adjacent networks and hosts into special groups. This group along with a router that has a link to one (any) of the networks included into the group is called an area. In each area an independent copy of OSPF is functioning. That means that each area has its own database and a corresponding graph.

• A router that is configured to advertise only internal links is called an internal router.
• A router connected to networks in more than one area is called an area border router (ABR).
• A router that advertises its link to external destinations ("redistribute" command) is called AS Boundary Router (ASBR).

Each area is assigned a unique identifier area-id. An area with area-id equal to zero is called a backbone of OSPF system. OSPF backbone area always includes all ABR. Backbone area is responsible for routing information distribution between other (non-backbone) areas. Backbone area should be contiguous but it does not always imply a physical adjacency – backbone connections can be organized using virtual connections.

This parameter allows to "shortcut" routes (non-backbone) for inter-area routes. There are three modes available for routes shortcutting:

• "default" –  this area will be used for shortcutting only if ABR does not have a link to the backbone area or this link was lost.
• "enable" – the area will be used for shortcutting every time the route that goes through it is cheaper.
• "disable" – this area is never used by ABR for routes shortcutting.

This parameter allows to configure a stub area. Some areas may be defined as stub areas. It is used for an area which has either a single ABR or several ABR but route selection does not depend on external destination address. The information about external link (to OSPF system) is not sent to stub areas by ABR. Instead, ABR advertises a default gateway to the stub area with a route coming through this ABR.

• "no-summary" – can be specified if it is not necessary to advertise a summary routes of other area’s to this area. This can save the internal routers database resources in this area. Keep in mind, all area routers should have same settings of this parameter, otherwise they will not be able to establish the adjacency relations, which will be discussed below.

Provides a backbone area coherence by virtual link establishment.

In general, OSPF protocol requires a backbone area (area 0) to be coherent and fully connected. I.e. any backbone area router must have a route to any other backbone area router. Moreover, every ABR must have a link to backbone area. However, it is not always possible to have a physical link to a backbone area. In this case between two ABR (one of them has a link to the backbone area) in the area (not stub area) a virtual link is organized.

• "(A.B.C.D|<0-4294967295>)" – area identifier through which a virtual link goes.
• "A.B.C.D" – ABR router-id with which a virtual link is established. Virtual link must be configured on both routers.

Formally, a virtual link looks like a point-to-point network connecting two ABR from one area one of which physically connected to a backbone area. This pseudo-network is considered to belong to a backbone area.

Provides link information filtering for the area. If the filter conditions match, the information will be discarded.

• "export-list|import-list" – summary information about area’s links which is advertised by ABR through backbone to other area (export) can be filtered. Moreover, the information from ABR (that came from other areas) can also be filtered (import).
  • "NAME" – name of a filtering list (access-list).
• "filter-list prefix" – filtering can be also provided using "prefix-list". Filters can be applied to any area to which ABR is connected, except for the backbone.
  • "(in|out)" – filtering direction ("in" – import, "out" – export).
    
  • "WORD" – filtering prefix-list name.

Allows you to configure the link aggregation and announcements suppression. For every area to which OSPF router is connected there is a list of address ranges for link aggregation before sending a summary LSA to a backbone area. Aggregated links are checked to belong to one of the address ranges. If several links belong to one address range, ABR makes an advertisement to the backbone (or to other areas) of only one single link with destination equal to the address range and a metric equal to the maximal metric of all links or equal to the specified for this range value. It is possible to announce that some range is a blocking one, and then advertising of links which belong to this range will be blocked. When advertising an aggregated backbone link to other (non-backbone) areas, the aggregation will not be performed if the area to which backbone links are advertised is a transit area (it has virtual links).

The list of addresses ranges for the area consists of the records with following fields:

• "range A.B.C.D/M" – addresses range (R);
• "not-advertise" – advertisement suppression flag;
• "cost <0-16777215>" – aggregated link metric (C);
• "substitute A.B.C.D/M" – advertised link (Rs).

If non-advertise flag is not specified, C and Rs parameters can be configured. If a destination for one or more links belongs to R, the router will advertise one link with R destination (or Rs, if specified) and with metric that is a maximal metric of links (or C, if specified).

Authentication type can be specified for the whole area to which a network belongs, and to a link by which OSPF packets are received. If authentication is turned on for both interface and the area, the interface authentication type will be used. So if an interface has a "null" authentication type, then no authentication is performed. This parameter sets the authentication type for the whole area to which network and link belong.

• "message-digest" – sets the MD5 authentication type, if not specified, simple password authentication will be enabled for the area.

As was mentioned before, area authentication type is applied only if interface’s authentication was totally disabled.

Allows to configure virtual links authentication.

• "A.B.C.D/<0-4294967295>" – area identifier through which a virtual link goes.
• "A.B.C.D" – ABR router-id with which a virtual link is established.
• "authentication-key AUTH_KEY" – sets simple password authentication. "AUTH_KEY" – password.

• "message-digest-key <1-255> md5 KEY" – sets MD5 digest key authentication.

  • "KEY" – private MD5 key.
  • "<1-255>" – private key sequence number. So, up to 255 private keys can be set for this channel or interface. The router will use the last installed key to transmit packets. When receiving packets, the router will use the key with the same sequence number used by the transmitting side.

Establishes neighboring relationship between two routers when virtual links are used.

• "A.B.C.D/<0-4294967295>" – area identifier through which a virtual link goes.
• "A.B.C.D" – ABR router-id with which a virtual link is established.
• "(hello-interval|retransmit-interval|transmit-delay|dead-interval)" – set interval values, for more information see "Config-if mode" subsection.
• "<1-65535>" – interval value in seconds.

Selects ABR model. OSPF router supports four ABR models:

• "cisco" – a router will be considered as ABR if it has several configured links to the networks in different areas one of which is a backbone area. Moreover, the link to the backbone area should be active (working).
• "ibm" – identical to "cisco" model but in this case a backbone area link may not be active.
• "standard" – router has several active links to different areas.
• "shortcut" – identical to "standard" but in this model a router is allowed to use a connected areas topology without involving a backbone area for inter-area connections.

Detailed information about "cisco" and "ibm" models differences can be found in RFC 3509. A "shortcut" model allows ABR to create routes between areas based on the topology of the areas connected to this router but not using a backbone area in case if non-backbone route will be "cheaper". For more information about "shortcut" model, see ospf-shortcut-abr-02.txt

Config-if mode

In order to prevent an unauthorized connection of routers to OSPF system, the system has an identity check for protocol’s packets. This parameter allows to set simple password authentication. Authentication can be configured individually for each interface’s link (or for the interface including virtual link) and/or individually for every area to which the router is connected. By default authentication is disabled.

• "AUTH_KEY" – key.
• "[A.B.C.D]" – link identifier (in IP address form), to configure selected channel authentication.

Allows to set digest key authentication.

• "KEY" – private MD5 key.
• "[A.B.C.D]" – link identifier, to configure selected channel authentication.
• "<1-255>" – private key sequence number. So, up to 255 private keys can be set for this channel or interface. The router will use the last installed key to transmit packets. When receiving packets, the router will use the key with the same sequence number used by the transmitting side.

Allows to enable one or another authentication mode after setting its parameters.

• "null" – no authentication (obligatory authentication suppression), if not set, simple password authentication is turned on.
• "message-digest" – digest key authentication.
• "A.B.C.D" – interface link IP address.

priority <0-255> [A.B.C.D]

Allows to control retransmits periodicity for each interface and/or interface’s links. OSPF protocol requires that Link-State databases of one area routers should be identical. To do that routers exchange LSA information. In particular, transit networks are used. In order to minimize network traffic, routers exchange their LSA not directly with each other but using DR and Backup DR (BDR). BDR is used for backing up DR in case of DR failure. BDR selection rules are identical to DR selection rules. While Link-state database synchronization routers exchange database descriptions using master-slave relationship and broadcast IP packets. Each packet reception should be acknowledged. If acknowledge is not received, initiating party makes a series of retransmits.

• "<3-65535>" – retransmits interval in seconds.
• "[A.B.C.D]" – link identifier.

Allows to set and adjust for each interface the delay interval before starting the synchronizing process of the router's database with all neighbors.

• "<3-65535>" – delay value in seconds.
• "[A.B.C.D]" – link identifier.

Sets links metric (cost) of the interface. 

• <1-65535> – metric value.
• "[A.B.C.D]" – subnetwork interface IP address (link destination). If not specified, for any link related to this physical interface the specified cost (metric) will be set.

OSPF config-route-map mode