Initialize the OSPF process router ospf process-id Enable OSPF on network interfaces matching a specified network range for a specific OSPF area network ip-address wildcard-mask area area-id Enable OSPF on an explicit specific network interface for a specific OSPF area ip ospf process-id area area-id Configure a specific interface as passive passive interface-id Configure all interfaces as passive passive interface default Advertise a default route into OSPF default-information originate [always] [metric metric-value] [metric-type type-value] Modify the OSPF reference bandwidth for dynamic interface metric costing auto-cost reference-bandwidth bandwidth-in-mbps Statically set the OSPF metric for an interface ip ospf cost 1–65535 Configure the OSPF priority for a DR/BDR election ip ospf priority 0–255 Statically configure an interface as a broadcast OSPF network type ip ospf network broadcast Statically configure an interface as a point-topoint OSPF network type ip ospf network point-to-point Restart the OSPF process clear ip ospf process Display the OSPF interfaces on a router show ip ospf interface [brief | interface-id] Display the OSPF neighbors and their current states show ip ospf neighbor [detail] Display the OSPF routes that are installed in the RIB show ip route ospf
Table 8-2 OSPF Packet Types Type Packet Name Functional Overview
1 Hello These packets are for discovering and maintaining neighbors. Packets are sent out periodically on all OSPF interfaces to discover new neighbors while ensuring that other adjacent neighbors are still online.
2 Database description (DBD) or (DDP)
These packets are for summarizing database contents. Packets are exchanged when an OSPF adjacency is first being formed. These packets are used to describe the contents of the LSDB.
3 Link-state request (LSR)
These packets are for database downloads. When a router thinks that part of its LSDB is stale, it may request a portion of a neighbor’s database by using this packet type.
4 Link-state update (LSU)
These packets are for database updates. This is an explicit LSA for a specific network link and normally is sent in direct response to an LSR.
5 Link-state ack These packets are for flooding acknowledgments. These packets are sent in response to the flooding of LSAs, thus making flooding a reliable transport feature.
OSPF hello packets are responsible for discovering and maintaining neighbors. In most instances, a router sends hello packets to the AllSPFRouters address (22.214.171.124). Table 8-3 lists some of the data contained within an OSPF hello packet.
Table 8-3 OSPF Hello Packet Fields Data Field Description
Router ID (RID) A unique 32-bit ID within an OSPF domain.
Authentication options A field that allows secure communication between OSPF routers to prevent malicious activity. Options are none, clear text, or Message Digest 5 (MD5) authentication.
Area ID The OSPF area that the OSPF interface belongs to. It is a 32-bit number that can be written in dotted-decimal format (0.0.1.0) or decimal (256).
Interface address mask The network mask for the primary IP address for the interface out which the hello is sent.
Interface priority The router interface priority for DR elections.
Hello interval The time span, in seconds, that a router sends out hello packets on the interface.
Dead interval The time span, in seconds, that a router waits to hear a hello from a neighbor router before it declares that router down.
Designated router and backup designated router
The IP address of the DR and backup DR (BDR) for the network link.
Active neighbor A list of OSPF neighbors seen on the network segment. A router must have received a hello from the neighbor within the dead interval.
Published @ November 21, 2021 3:16 am