About this interactive
OSPF hellos double as keepalives:
- **Hello interval**: how often a router sends hellos. 10 seconds on broadcast (Ethernet) and point-to-point links; 30 seconds on NBMA (such as frame relay) and point-to-multipoint networks.
- **Dead interval**: how long a router waits without a hello before declaring the neighbor down, by default four times the hello: 40 or 120 seconds. On a Cisco router, changing only the hello moves the dead interval to four times the new value.
- The timers are set per interface and must match on both ends, or the routers never become neighbors.
The video calls the lab's Ethernet links non-broadcast multi-access with a 30-second hello. Ethernet is broadcast multi-access, with a 10-second hello.
What you'll learn
- State OSPF's default hello and dead intervals for broadcast and point-to-point links (10 and 40 seconds) and for NBMA and point-to-multipoint links (30 and 120 seconds)
- Work out when a silent neighbor is declared down, and explain why mismatched timers stop an adjacency forming
Aligned to
Cisco CCNA
3.4
Configure and verify single area OSPFv2
Key terms
- Hello Interval
- The configurable timer that defines how frequently an OSPF router sends hello packets out of an interface to maintain neighbor adjacencies.
- Dead Interval
- The configurable timer that defines how long an OSPF router waits without receiving a hello packet before declaring a neighbor down; defaults to four times the hello interval.
- OSPF Hello Packet
- A message sent by an OSPF-enabled interface to discover and maintain adjacencies with neighboring OSPF routers.
- Neighbor Adjacency
- A relationship formed between OSPF routers that have exchanged Hello packets and agreed on key parameters, enabling them to share routing information.
Topics
Ospf
Ospf Timers
Hello Interval
Dead Interval
Keepalive
Interactive
Calculation
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