Cisco IOS

Static Route Generator

Build Cisco IPv4/IPv6 static, default, floating, and Null0 routes with show commands and troubleshooting

What is a Static Route?

A static route is a manually configured route that tells the router exactly how to reach a destination network via a specified next-hop IP or exit interface. Unlike dynamic routing protocols (OSPF, EIGRP, BGP), static routes do not adapt automatically when the network changes.

Predictable — traffic always follows the path you define.
Lightweight — zero routing protocol overhead.
Secure — no routing updates to spoof or hijack.
Manual — must be updated by hand when topology changes.

Static Route Types

Type	Command Format	Use Case
Standard	ip route <net> <mask> <next-hop or intf>	Route to a specific network via next-hop IP or exit interface
Default Route	ip route 0.0.0.0 0.0.0.0 <next-hop>	Gateway of last resort — matches all traffic not matched by a more specific route
Floating Static	ip route <net> <mask> <next-hop> <AD>	Backup route with higher Administrative Distance; only used if primary route fails
Summary Static	ip route <supernet> <mask> <next-hop>	One route covering a block of contiguous networks to reduce routing table size
Null0 (Black Hole)	ip route <net> <mask> Null0	Discard traffic matching the route; prevents routing loops and blocks unwanted traffic
IPv6 Static	ipv6 route <prefix/len> <next-hop>	Same as IPv4 but for IPv6 address space

Administrative Distance (AD)

AD is a trustworthiness score for route sources. Lower AD wins. A floating static route uses a higher AD than the primary dynamic protocol so it only becomes active when the preferred route disappears.

Route Source	Default AD
Connected	0
Static Route	1
eBGP	20
EIGRP (internal)	90
OSPF	110
IS-IS	115
RIP	120
EIGRP (external)	170
iBGP	200
Unreachable / Floating	255

Next-Hop vs. Exit Interface

Method	Example	Notes
Next-hop IP	ip route 10.0.0.0 255.0.0.0 192.168.1.1	Most common. Router performs recursive lookup to find exit interface.
Exit Interface only	ip route 10.0.0.0 255.0.0.0 GigabitEthernet0/1	Avoid on multi-access (Ethernet) — causes ARP for every destination. OK on P2P serial.
Both (Recommended)	ip route 10.0.0.0 255.0.0.0 Gi0/1 192.168.1.1	No recursion + ARP for only the next-hop IP. Best practice for Ethernet.

Best Practice: On multi-access (Ethernet) interfaces, always specify both the exit interface and next-hop IP to avoid proxy-ARP issues and recursive lookup overhead.

Caution: Static routes require manual updates when network topology changes. Use dynamic routing protocols for larger environments and static routes only at the edge or for specific policy needs.

Route Entry Builder

Route Type

Destination Network

Subnet Mask

Next-Hop IP

Exit Interface (optional, recommended with next-hop)

+ Bulk Routes (one per line: network mask nexthop)

Description / Remark (optional)

conf t
ip route 10.10.10.0 255.255.255.0 192.168.1.1
!
end
copy running-config startup-config

Static Route Show & Verification Commands

Command	Purpose
show ip route	Full IPv4 routing table — `S` = static, `S*` = default static
show ip route static	Show only static routes in the routing table
show ip route 10.10.10.0	Lookup a specific network — shows best path, AD, and metric
show ip route 0.0.0.0	Verify default route (gateway of last resort) is installed
show running-config \| include ip route	View all configured static routes from running config
show running-config \| section ip route	Full static route section of running config
show ip route summary	Route count by type: connected, static, OSPF, etc.
show ip cef <dest>	CEF forwarding lookup — shows actual forwarding path in hardware
show ip cef exact-route <src> <dst>	CEF path for a specific source/destination pair
show ip interface brief	Verify exit interfaces are up/up before adding static routes
ping <destination> source <intf>	Test reachability to a static route destination from a specific source
traceroute <destination>	Trace hop-by-hop path to verify routing
show ipv6 route	Full IPv6 routing table
show ipv6 route static	Show only IPv6 static routes
show running-config \| include ipv6 route	All configured IPv6 static routes
debug ip routing	Live debug when routes are added/removed from RIB (use with caution in production)

Reading the Route Table: S = Static | S* = Static default route | [1/0] = [AD/metric] | via = next-hop IP or interface.

Route Table Code Legend

Code	Meaning
S	Static route
S*	Static default route / gateway of last resort
C	Connected (directly attached)
L	Local (router's own interface IP, /32)
O	OSPF
D	EIGRP
B	BGP
R	RIP
i	IS-IS

Static Route Not Working — Checklist

Route not in the table? Run show ip route static. If missing, the exit interface may be down or the next-hop is unreachable.
Check exit interface state — show ip interface brief. A route pointing to a down interface is not installed in the RIB (unless next-hop IP is also specified).
Verify next-hop reachability — ping <next-hop-IP>. The next-hop must be directly reachable via a connected subnet.
More-specific route overriding? — show ip route <dest>. A /28 always beats a /24 regardless of AD.
Confirm correct subnet mask — a /24 entered as /25 will silently miss half the range.
Floating static not appearing? — The primary route is still active. Remove it temporarily to test: no ip route <net> <mask> <primary-nexthop>.
Null0 route causing unexpected drops? — Verify with show ip route null0 that it is not matching traffic it should not.
Recursive lookup failure — If the next-hop IP is not reachable via a connected route, the static route will not be installed.
IPv6 routes not working? — Confirm ipv6 unicast-routing is enabled globally, then check show ipv6 route.
Use CEF for forwarding verification — show ip cef <dest> confirms what the forwarding plane actually uses.

Common Mistakes

Mistake	Symptom	Fix
Wrong subnet mask	Route installed but some hosts unreachable	Recalculate mask; use `show ip route <host-ip>` to check the matching route
Next-hop not reachable	Route absent from routing table	Ensure next-hop is on a directly connected subnet; ping it first
Exit interface only on Ethernet	Massive ARP table, intermittent drops	Specify both exit interface and next-hop IP
Floating AD too low	Floating route wins over dynamic protocol	Set AD higher than primary (e.g., 210 for OSPF backup)
Missing reverse route	One-way reachability; ping works one direction only	Add a static route on the remote router pointing back
Typo in destination	Traffic goes to wrong network or drops	`show run \| include ip route` and review carefully
Forgetting to save	Routes disappear after reboot	`copy running-config startup-config`

Routing Loop Risk: Never configure a static route where the next-hop is reachable only via that same static route — this creates a recursive lookup loop and black-holes traffic.