Static Routing and Recursive Lookups Basics

Static Routes and Recursive Lookups:

A static route that uses a next-hop address (intermediate address) causes the router to look at the routing table twice: once when a packet first enters the router and router looks up the entry in the routing table, and In second time when the router has to resolve the location of the intermediate address.
For point to point link, always use an exit interface in static route statements.
Router1(config)#ip route 192.168.1.0 255.255.255.0 serial 2/0

                          


The Permanent Keyword:
Without the permanent keyword in a static route statement, a static route is removed if an interface goes down. A downed interface causes the directly connected network and any associated static routes to be removed from the routing table. If the interface comes back up, the routes of the router are returned.
Adding the permanent keyword to a static route statement keeps the static routes in the routing table even if the interface goes down and the directly connected networks are removed. We cannot get to these routes the interface is down but the routes remain in the Routing table.When a static route is added or deleted, this route, along with all static routes, is processed in 1 second. Before Cisco IOS Release 12.0, this processing time was 5 seconds. 
The routing table processes the static routes in every minute to install or remove static routes according to the changing routing table.
          To specify that the route will not be removed, even if the interface shuts down, we will enter the following command. 

For example:
Router1(config)#ip route 172.16.1.0 255.255.255.0 172.16.10.2 permanent

Floating Static Routes and Administrative Distance:

To specify that an administrative distance (AD) of 200 has been assigned to a given  route,enter the following command, for example:

                   Router1(config)#ip route 172.16.1.0 255.255.255.0  172.16.10.2 200

By default, The Administrative distance of Static route is 1. AD rates the “trustworthiness” of a route. AD is a number start from 0 to 255 (254 for IPv6),where 0  is trusted and 255 cannot be trusted at all. So an AD of 1 is an extremely reliable rating. An Administrative Distance (AD) of 0 is assigned to a directly connected route.

Table of AD with Route type:

Route Type
AD IPv4
AD IPv6
Directly Connected
0
0
Static Route
1
1
Enhanced Interior Gateway Routing Protocol (EIGRP) summary route
5
5
External Border Gateway Protocol (eBGP)
20
20
Enhanced Interior Gateway Routing Protocol (EIGRP)  (internal)
90
90
Open Shortest Path First Protocol (OSPF)
110
110
Intermediate System-to-Intermediate System Protocol (IS-IS)
115
115
RIP ( Routing Information Protocol)
120
120
External Gateway Protocol (EGP)
140
140
Enhanced Interior Gateway Routing Protocol (EIGRP)   (external)
170
170
Internal Border Gateway Protocol (iBGP) (external)
200
200
Unknown or unbelievable
255 (Does not pass traffic)
254 (Does not pass traffic)






No comments