Cisco Certified Network Associate (CCNA) IP Connectivity Syllabus

What command verifies the IPv6 routing table?

show ipv6 route

What routing protocol type is OSPF (e.g., distance vector vs link state), and what algorithm does it use?

OSPF is a link-state interior gateway protocol (IGP) that uses the Dijkstra Shortest Path First (SPF) algorithm to compute loop-free shortest paths.

What is the default metric (cost) basis for OSPF, and what is the default reference bandwidth?

OSPF cost = reference bandwidth / interface bandwidth. The default reference bandwidth is 100 Mbps (10^8), so cost = 100,000,000 / interface-bandwidth-in-bps.

Using default settings, what is the OSPF cost of a 100 Mbps (FastEthernet) link and a 1 Gbps link?

100 Mbps link: 100/100 = 1. 1 Gbps link: 100/1000 = 0.1, rounded up to a minimum of 1. (Both are cost 1 by default, which is why reference bandwidth is often raised.)

What command changes the OSPF reference bandwidth and why is it adjusted?

auto-cost reference-bandwidth <Mbps> (under router ospf). It is raised (e.g., to 10000 for 10 Gbps) so links faster than 100 Mbps get distinct costs instead of all being cost 1.

What is the syntax to enable OSPF on networks in area 0 using the network command?

router ospf <process-id>, then network <address> <wildcard-mask> area 0 (e.g., network 10.0.0.0 0.0.0.255 area 0).

Is the OSPF process ID locally significant or must it match between neighbors?

The OSPF process ID is locally significant only; it does NOT need to match between neighboring routers for them to form an adjacency.

How is the OSPF Router ID selected, in order of preference?

1) Manually configured router-id command; 2) highest IP address on an up loopback interface; 3) highest IP address on any up physical interface. (Once chosen it persists until OSPF is reset.)

What command manually sets the OSPF Router ID, and what must be done for it to take effect?

router-id <A.B.C.D> under the OSPF process. You must then clear/reset the OSPF process (clear ip ospf process) or reload for the new ID to be used.

List the OSPF neighbor states in order from initial discovery to full adjacency.

Down → Init → 2-Way → ExStart → Exchange → Loading → Full.

What does the OSPF 2-Way state signify, and on which network types do some routers intentionally stop here?

2-Way means bidirectional communication is established (each router sees its own ID in the neighbor's Hello). On broadcast/multi-access networks, DROther routers stay 2-Way with each other and only go Full with the DR and BDR.

What does the OSPF FULL state indicate?

FULL means the two routers have fully synchronized their link-state databases and have a complete adjacency; this is the normal operational state for adjacent OSPF neighbors.

Which five values must match for two OSPF routers to form a neighbor adjacency?

They must agree on: same area ID, same subnet (matching IP/mask on the link), matching Hello and Dead timers, same authentication, and matching stub area flags / MTU. (RouterIDs must be unique, not matching.)

What are the default OSPF Hello and Dead intervals on broadcast and point-to-point networks?

Hello = 10 seconds, Dead = 40 seconds (Dead is 4x Hello) on broadcast and point-to-point network types.

What multicast addresses does OSPFv2 use for all-OSPF-routers and for DR/BDR?

224.0.0.5 = all OSPF routers (AllSPFRouters); 224.0.0.6 = all DR/BDR routers (AllDRouters).

On a broadcast (multi-access) OSPF network, what roles are elected and why?

A Designated Router (DR) and Backup DR (BDR) are elected to reduce the number of full adjacencies and LSA flooding; all other routers (DROthers) form full adjacencies only with the DR and BDR.

How does OSPF elect the DR and BDR on a broadcast segment?

Highest OSPF interface priority wins; if priorities tie, the highest Router ID wins. The highest becomes DR, the second-highest becomes BDR. (Election is non-preemptive.)

What OSPF interface priority value prevents a router from becoming DR or BDR, and what is the command?

A priority of 0 makes the router ineligible (always DROther). Command: ip ospf priority 0 on the interface.

Why does the OSPF point-to-point network type not elect a DR/BDR?

A point-to-point link has only two routers, so there is no benefit to electing a DR/BDR; both routers form a full adjacency directly with each other.

What command forces an Ethernet interface to behave as an OSPF point-to-point network, and what benefit does it give?

ip ospf network point-to-point on the interface. It skips DR/BDR election, speeding adjacency formation and simplifying the topology on a link with only two routers.

What is the difference between OSPF totally default behavior on point-to-point vs broadcast network types regarding Hello timers?

Both default to Hello 10 / Dead 40 seconds. The key difference is broadcast elects a DR/BDR and uses multicast to a DR, while point-to-point does not elect a DR/BDR.

Which command shows OSPF neighbor adjacencies and their states?

show ip ospf neighbor

What does the command show ip ospf interface (or 'brief') reveal that is useful for troubleshooting adjacencies?

It shows the interface's OSPF area, process ID, cost, network type, Router ID, DR/BDR, priority, and Hello/Dead timers — useful for spotting mismatched area, timers, or network type.

Name three common reasons two OSPF routers fail to become neighbors.

Mismatched area IDs, mismatched Hello/Dead timers, mismatched subnet/mask on the link, MTU mismatch, mismatched authentication, or one interface being passive.

What does the passive-interface command do in OSPF and when is it used?

It stops OSPF from sending/receiving Hellos (no adjacencies) on that interface while still advertising the interface's network. Used on interfaces facing end hosts/LANs with no OSPF neighbors.

What is the purpose of a First Hop Redundancy Protocol (FHRP)?

FHRPs provide default-gateway redundancy by letting multiple routers share a single virtual IP/MAC so hosts keep connectivity if their default gateway router fails — without reconfiguring hosts.

In HSRP, what roles do routers take and what does each do?

One router is Active (forwards traffic for the virtual IP/MAC), one is Standby (monitors and takes over if Active fails), and any others are in Listen state as backups.

How is the HSRP Active router elected?

The router with the highest HSRP priority becomes Active; if priorities tie (default 100), the highest interface IP address wins.

What is the HSRP version 2 virtual MAC address format and the multicast address it uses?

HSRPv2 virtual MAC = 0000.0C9F.FXXX (XXX = group number in hex), and it uses multicast 224.0.0.102 (HSRPv1 uses 0000.0C07.ACXX and 224.0.0.2).

What is HSRP preemption and how is it enabled?

Preemption lets a higher-priority router take over the Active role when it comes online (instead of waiting for the current Active to fail). Enabled with 'standby <group> preempt'. Without it, the election is non-preemptive.

Compare HSRP, VRRP, and GLBP in terms of standardization and load behavior.

HSRP = Cisco proprietary, one active router (no load balancing). VRRP = IETF open standard (RFC 5798), one master router. GLBP = Cisco proprietary, provides active/active load balancing across multiple routers via one virtual IP with multiple virtual MACs.

What is the key advantage of GLBP over HSRP and VRRP?

GLBP allows simultaneous load balancing: a single Active Virtual Gateway (AVG) assigns multiple virtual MAC addresses so several Active Virtual Forwarders (AVFs) forward traffic at once, using all routers rather than just one.