Static Routes · Default Routes · OSPFv2 · Admin Distance · HSRP/VRRP · IPv6 Routing
Study with Practice Tests →The largest exam domain at ~25% of the CCNA 200-301 exam (~30 questions). Covers how routers forward packets using static routes, OSPF, and first-hop redundancy protocols.
Domain Weight: ~25% · ~30 Questions| Domain | Topic | Weight |
|---|---|---|
| 1 | Network Fundamentals | 20% |
| 2 | Network Access | 20% |
| 3 | IP Connectivity (This Topic) | 25% |
| 4 | IP Services | 10% |
| 5 | Security Fundamentals | 15% |
| 6 | Automation & Programmability | 10% |
Manually configured routes with AD=1. Used for stub networks, default routes, and backup paths (floating static). Syntax: ip route NETWORK MASK {NEXT-HOP | INTERFACE}. Do not adapt automatically to topology changes.
Gateway of last resort — matches any destination when no more specific route exists. Configured as ip route 0.0.0.0 0.0.0.0 NEXT-HOP. Longest prefix match means /0 is chosen last. Critical for stub routers pointing to the ISP.
Link-state routing protocol using Dijkstra's SPF algorithm. Open standard (RFC 2328). Metric = cost (reference BW ÷ interface BW). Organizes routers into areas; Area 0 is the backbone. AD=110. Supports MD5 authentication.
Trustworthiness rating of a routing source. Lower = more trusted. Connected=0, Static=1, EIGRP=90, OSPF=110, RIP=120. When two protocols advertise the same prefix, the lower-AD source wins. Longest prefix match always evaluated first.
First Hop Redundancy Protocols eliminate the single-gateway failure point. HSRP (Cisco proprietary) uses Active/Standby model with virtual IP & MAC. VRRP (open standard, RFC 5798) uses Master/Backup. GLBP adds load balancing.
Requires ipv6 unicast-routing globally. Static routes via ipv6 route PREFIX/LEN NEXT-HOP. OSPFv3 for dynamic IPv6 routing. NDP Router Advertisements deliver prefix and default gateway info to hosts. Default route: ipv6 route ::/0 NEXT-HOP.
Static routes are the foundation of IP routing. Understanding syntax, administrative distance, and the routing table lookup process is essential for the exam.
Matches any destination when no more specific route exists:
Shown in show ip route as "Gateway of last resort is 10.0.0.1"
Backup route with higher AD than the primary dynamic route:
Route stays hidden while OSPF route is present. Appears when OSPF route is removed.
| Route Source | Administrative Distance | Notes |
|---|---|---|
| Directly Connected | 0 | Absolute trust — interface is directly attached |
| Static Route | 1 | Manually configured; highly trusted |
| EIGRP (internal) | 90 | Cisco proprietary; very efficient |
| OSPF | 110 | Open standard; most common IGP |
| IS-IS | 115 | Used in large ISP/SP networks |
| RIP | 120 | Legacy; max 15 hops |
| EIGRP (external) | 170 | Routes redistributed into EIGRP |
| BGP (external) | 20 | eBGP — used between autonomous systems |
| Unknown / Unreachable | 255 | Never installed in routing table |
Rule: The router always selects the most specific (longest) matching prefix. If two routes match, the one with lower AD wins. If AD ties, metric decides.
Example: destination 10.1.1.5 → matches both 10.1.1.0/28 and 10.1.0.0/16 — router picks /28 (longer prefix).
When a static route specifies a next-hop IP (not an interface), the router must look up that next-hop IP in its own routing table to find the actual exit interface. This is a "recursive" lookup. If the next-hop IP has no route, the static route is invalid and won't appear in the table.
show ip route — full routing tableshow ip route 10.1.1.5 — lookup specific addressshow ip route static — only static routesping 10.1.1.1 — test reachabilitytraceroute 10.1.1.1 — trace path hop by hopip default-gateway is for layer-2 switches, not routersOpen Shortest Path First version 2 — the primary IGP on the CCNA exam. Link-state protocol using Dijkstra's SPF algorithm. Open standard (RFC 2328). AD=110.
Cost = Reference Bandwidth ÷ Interface Bandwidth
Default reference bandwidth = 100 Mbps.
FastEthernet (100 Mbps) = 100/100 = cost 1
Serial (1.544 Mbps) = 100/1.544 ≈ cost 64
GigabitEthernet (1000 Mbps) = 100/1000 = cost 1 (same as FastEthernet!)
Fix: auto-cost reference-bandwidth 1000 under router ospf to distinguish GigE from FastEthernet.
| Type | Name | Purpose |
|---|---|---|
| 1 | Hello | Discover & maintain neighbors; sent to 224.0.0.5 (all OSPF routers) |
| 2 | DBD (Database Description) | Summary of LSDB; used during initial LSDB exchange (Exstart/Exchange) |
| 3 | LSR (Link-State Request) | Request specific LSAs that are missing from local LSDB |
| 4 | LSU (Link-State Update) | Contains actual LSAs; sent in response to LSR |
| 5 | LSAck (Link-State Acknowledgment) | Acknowledge receipt of LSAs |
Down → Init → 2-Way → Exstart → Exchange → Loading → Full
2-Way: Hello received from neighbor; DR/BDR election occurs here.
Exstart: Master/slave relationship established; determine starting sequence number.
Exchange: DBD packets exchanged — each router describes its LSDB.
Loading: LSR/LSU exchange — missing LSAs are requested and delivered.
Full: LSDBs are synchronized. DR/BDR form Full with all routers. DROthers form 2-Way with each other.
| Network Type | Hello Interval | Dead Interval |
|---|---|---|
| Broadcast (Ethernet) | 10 seconds | 40 seconds |
| NBMA (Frame Relay) | 30 seconds | 120 seconds |
| Point-to-Point | 10 seconds | 40 seconds |
Exam Trap: Hello and Dead timers MUST match between neighbors or adjacency will never reach Full state. Mismatched timers are a very common exam scenario.
router-id X.X.X.XLoopback interfaces are preferred because they're always up, providing a stable Router ID that prevents unnecessary OSPF reconvergence.
| LSA Type | Name | Generated By | Scope |
|---|---|---|---|
| Type 1 | Router LSA | Every OSPF router | Within originating area |
| Type 2 | Network LSA | Designated Router (DR) | Within originating area |
| Type 3 | Summary LSA | ABR (Area Border Router) | Between areas |
| Type 4 | ASBR Summary LSA | ABR | Describes how to reach ASBR |
| Type 5 | External LSA | ASBR | Entire OSPF domain |
Area 0 = Backbone. All non-backbone areas must connect to Area 0 (directly or via virtual link).
ABR (Area Border Router): connects two or more areas. Summarizes routes between areas.
ASBR (AS Boundary Router): connects OSPF domain to external routing domain (e.g., BGP, RIP, static redistribution).
0.0.0.255 wildcard0.0.0.3 wildcard0.0.0.0 wildcard (exact host)0.0.255.255 wildcardFirst Hop Redundancy Protocols solve the single-gateway problem. IPv6 routing requires specific global commands and protocols.
Hosts configure a single default gateway IP. If that router fails, hosts can't reach remote networks — even if another router is available. FHRPs solve this by presenting a virtual IP shared between multiple physical routers.
0000.0c07.acXX (XX = group number in hex)Group 1 example: Virtual MAC = 0000.0c07.ac01
| Feature | HSRP | VRRP | GLBP |
|---|---|---|---|
| Standard | Cisco proprietary | Open (RFC 5798) | Cisco proprietary |
| Roles | Active / Standby | Master / Backup | AVG / AVF |
| Default Priority | 100 | 100 | 100 |
| Virtual MAC | 0000.0c07.acXX | 0000.5e00.01XX | 0007.b4XX.XXYY |
| Load Balancing | No | No | Yes (multiple AVFs) |
| Preempt Default | Disabled | Enabled | Enabled |
| UDP Port | 1985 | Protocol 112 | 3222 |
GLBP uniquely provides load balancing — HSRP and VRRP do not. The AVG (Active Virtual Gateway) assigns different virtual MACs to AVF (Active Virtual Forwarder) routers. Hosts ARP for the virtual IP and receive different virtual MACs, distributing traffic across multiple routers simultaneously.
NDP (Neighbor Discovery Protocol) replaces ARP in IPv6.
Routers multicast Router Advertisements (RA) to FF02::1 (all IPv6 nodes) periodically.
Hosts use RA messages to learn: default gateway (link-local address of router), IPv6 prefix for SLAAC, and other configuration flags.
Note: ipv6 enable on an interface generates a link-local address (LLA) — this is separate from ipv6 unicast-routing, which enables the router to forward IPv6 packets.
10 questions covering static routes, OSPFv2, FHRP, and IPv6. Select your answer then submit to see results.
Visual mnemonics and mental models to make exam concepts stick. Review before your exam day.
auto-cost reference-bandwidth 1000 for GigE environments.ipv6 unicast-routing first, then ipv6 ospf PROCESS area AREA on each interface. Routing table shows link-local as next-hop — that's normal!Click any card to flip it. Use the advisor to get targeted exam tips by topic.
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