1. Introduction
Routers learn
about remote networks either dynamically, using routing protocols, or manually,
or using static routes. In many cases, routers use a combination of both
dynamic routing protocols and static routes.
Static routes do
not require the same amount of processing and overhead as dynamic routing
protocols.
CCNA: methods: Classless
Inter-Domain Routing (CIDR) and the variable-length subnet mask (VLSM).
1 1.1 Static Routing Implementation
A router can
learn about remote networks in one of two ways:
·
Manually - Remote networks are
manually entered into the route table using static routes.
·
Dynamically - Remote routes are
automatically learned using a dynamic routing protocol.
Static route =
Reach specific networks and manually configured
1 1.2 Why Use Static Routing?
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Administrative distance (AD) of a static
route is 1.
Static for small network and with only
one path to an outside network.
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1.3 When to Use Static Routes
Static routing
has three primary uses:
·
Providing ease of routing table
maintenance in smaller networks that are not expected to grow significantly.
·
Routing to and from stub
networks. A stub network is a network accessed by a single route, and the
router has only one neighbor.
·
Using a single default route to
represent a path to any network that does not have a more specific match with
another route in the routing table. Default routes are used to send traffic to
any destination beyond the next upstream router.
2 2.
Types of Static Routes
2 2.1 Static Route Applications
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Static route
are used to:
-
Connect stub networks.
-
Connect to a specific network
-
Summarize routing table entry
-
Create backup route
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CCNA: IPv4 and
IPv6 static routes:
- Standard
static
- route
Default
- static route
- Summary
static route
- Floating
static route
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2 2.2 Standard Static Route
A static route
can be used to connect to any network.
2 2.3 Default Static Route
Static route is
a route that matches all packets. A default route identifies the gateway IP
address to which the router sends all IP packets that it does not have a
learned or static route. A default static route is simply a static route with
0.0.0.0/0 as the destination IPv4 address. Configuring a default static route
creates a Gateway of Last Resort.
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Note: route for larger subnets takes preference over default static
route
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Default static
routes are used:
-
Only one other router to which
it is connected. This condition is known as a stub router.
-
Default exit: routerß--àISP (An edge router to a service provider network)
2 2.4 Summary Static Route
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To reduce the number of routing table entries,
multiple static routes can be summarized into a
single static route if:
-
Destination networks are
contiguous and can be summarized into a single network address.
-
The multiple static routes
all use the same exit interface or next-hop IP address.
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2 2.5 Floating Static Route
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Floating
static routes are static routes that are used to provide a backup path to a
primary static or dynamic route, in the event of a link failure. The floating
static route is only used when the primary route is not available.
Example:
AD:95 Static route entry
AD: 90 EIGRP static route entry.
If learned route fails static route is
the backup.
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3 3. Configure Static and Default
Routes
3 3.1 ip route Command
R1(config)#ip
route network-address network-mask {ip-address | exit-interface}
3 3.2 Next-Hop Options
The next hop can
be identified by an IP address, exit interface, or both. How the destination is
specified creates one of the three following route types:
-
Next-hop route - Only the
next-hop IP address is specified.
-
Directly connected static route
- Only the router exit interface is specified.
-
Fully specified static route -
The next-hop IP address and exit interface are specified.
3 3.3 Configure a Next-Hop Static Route
Before any
packet is forwarded by a router, the routing table process must determine the
exit interface to use to forward the packet. This is known as route
resolvability. The route resolvability process will vary depending upon the
type of forwarding mechanism being used by the router. CEF (Cisco Express
Forwarding) is the default behavior on most platforms running IOS 12.0 or
later.
R1(config)#ip
route network-address network-mask ip-address
AD=1
3 3.4 Configure a Directly Connected Static Route
This method is
used to avoid the recursive lookup problem.
R1(config)#ip
route network-address network-mask exit-interface
AD=0
3 3.5 Configure a Fully Specified Static Route
In a fully
specified static route, both the output interface and the next-hop IP address
are specified. This is another type of static route that is used in older IOSs,
prior to CEF
R1(config)# ip
route 192.168.2.0 255.255.255.0 GigabitEthernet 0/1
3 3.6 Verify a Static Route
Along with ping
and traceroute, useful commands to verify static routes include:
-
show ip route
-
show ip route static
-
show ip route network
4 4. Configure IPv4 Default
Routes
4 4.1 Default Static Route (code “S”)
A default route
is a static route that matches all packets
R1(config)# ip
route 0.0.0.0 0.0.0.0 { ip-address | exit-intf }
Default static
routes are commonly used when connecting:
-
An edge router to a service
provider network
-
A stub router (a router with
only one upstream neighbor router)
5 5. Configure IPv6 Static Routes
5 5.1 The ipv6 route Command
Static routes
for IPv6 are configured using the ipv6 route global configuration command.
Router(config)#
ipv6 route ipv6-prefix/prefix-length
{ ipv6-address | exit-intf }
Most of
parameters are identical to the IPv4 version of the command. IPv6 static routes
can also be implemented as:
-
Standard IPv6 static route
Default
-
IPv6 static route Summary
-
IPv6 static route Floating
-
IPv6 static route
-
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R1(config)#ipv6 unicast-routing command
enable the router to forward IPv6 packets
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5.2 Verify IPv6 Static Routes
verify static
routes include:
show ipv6 route
show ipv6 route
static
show ipv6 route
network
5 5.3 Default Static IPv6 Route
R1(Config)# ipv6
route ::/0 { ipv6-address | exit-intf }
6 6. CIDR
Will be developed soon.
7 7. VLSM
Will be developed soon.
