A static routing table is created, maintained, and updated by a
network administrator, manually. A
static route to every network must be configured on every router for full
connectivity. This provides a greater control
for administrator over routing,but its impratical over larger networks.
Static routes provide greater security because network administrator
only know the complete routes.Routers will not share static routes with each
other.This reduce CPU/RAM overhead and save bandwidth.
static routing is not fault-tolerant , as any change to the routing
infrastructure (such as a link going
down, or a new network added) must be done manually corrected by admininstrator. Static routes have an
Administrative Distance (AD) of 1, and thus are always preferred over
dynamic routes, unless the default AD is changed. A static route with an
adjusted AD is called a floating static route
For complete list of Administrative distance of static and dynamic
routing protocols Click here
Mainly Static routes are used
•
where there is only a
single path to a network (stub network)
•
When connecting to an ISP
and configuring it as a default (static) route
•
No bandwidth overhead
(updates are not shared between routers)
•
More control on how traffic
is routed
Disadvantages of Static routing
•
No “dynamic” fault
tolerance if a link goes down ,Means Administrator need to do it
•
Impractical on large
network
•
Infrastructure changes must
be manually adjusted
To configure a static route:
R1(config)#
ip route [destination_network] [subnet_mask] [next
hope IP / exit interface
]
R1(config)#
ip route 172.16.0.0 255.255.0.0 172.18.10.2
In above example
172.16.0.0 is the destination network
255.255.0.0 is the subnet mask
172.18.10.2 is the next hop IP
R1(config)#
ip route 172.16.0.0 255.255.0.0 172.18.10.2 S0/0
Here instead of next hop IP ,exit interface is used
NOTE
:
•
Next hope IP is the IP address of the
neigbouring router which the packet will go,After it leaves the R1.
•
Exit interface is the interface of R1 which the packet leaving
To remove a static route, simply type no in front of it:
R1(config)# no ip route 172.16.0.0 255.255.0.0
172.18.10.2
Default
Routes
Normally, if a specific route to a particular network does not exist, a
router will drop all traffic destined to that network. A default route, or
gateway of last resort, allows traffic to be forwarded, even without a specific
route to a particular network.
The default route is identified by all zeros in both the network and
subnet mask (0.0.0.0 0.0.0.0). It is the least
specific route possible, and thus will only be used if a more specific route
does not exist (hence “gateway of last resort”).
To configure a default route:
R1(config)# ip route 0.0.0.0 0.0.0.0 [address | interface ]
R1(config)# ip route 0.0.0.0 0.0.0.0
172.18.10.2
Floating
Static Routes
There are some circumstances to use a static route as a backup to a
dynamic routing protocol.But we know the default administrative distance ofstatic
route is less dynamic routing protocols.So inorder to use static routes as back
up we need to increase the AD value of static value than dynamic routing
protocol used.
To change the Administrative Distance of a static route to 200
R1(config)# ip route 172.16.0.0 255.255.0.0
172.18.10.2 200
Static routes will only remain in the routing table as long as the
interface connecting to the next-hop router is up. To ensure a static route
remains permantly in the routing table, even if the next-hop interface is down:
R1(config)# ip route 172.16.0.0 255.255.0.0 172.18.10.2 permanent
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