jeudi 22 décembre 2011

Using the static route

Static routing operations are organized into three parts:
  • The network administrator configures the road
  •  The router inserts the route in the routing table
  •  The packets are routed using the static route

Since a static route is configured manually, the administrator must configure the routerusing the ip route command. The correct syntax of the command ip route is shown 
click the picture to enlarge

The administrative distance is an optional parameter which gives a measure of the reliability of the road. The higher the value of the administrative distance is low and the road is more reliable. So a road whose administrative distance is low will be inserted before a route identical with administrative distance is high. The default administrative distance is 1 when using a static route. When output interface is configured as a gateway into a static route, the static route appears to be directly connected. This can sometimes be confusing because a directly connected route really has an administrative distance of 0. To check the administrative distance of a route. Use the command show ip route address, the option is the IP address of this road. If we want an administrative distance other than the default, enter a value between 0 and 255 after the next hop or outgoing interface:
Waycross (config) # ip route 130
If the router can not reach the outgoing interface is taken on the road, the road is not installed in the routing table. This means that if the interface is down, the road is not inserted in the routing table.
Static routes are sometimes used for backup. It is possible to configure a router on a static route that will be used in case of failure of the road acquired dynamically. To use a static route in this way, simply assign an administrative distance value greater than the dynamic routing protocol used.

Introduction to Routing

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Introduction to Routing

Routing is the process that a router uses to transmit packets to a destination network. A router makes decisions based on the destination IP address of a packet. Along the way, use the various facilities of the destination IP address to direct the packet in the right direction so that it reaches its destination. To make the right decisions, routers must know the direction to take to the remote networks. When routers use dynamic routing, this information is provided by other routers. When static routing is used, a network administrator manually configures information about remote networks.Since the static routes must be configured manually, any change in the network topology requires the administrator to add and remove static routes to reflect the changes. In a large network, this manual maintenance of routing tables can generate a significant administrative burden. On small networks where few changes are possible, static routes require very little maintenance. Due to administrative requirements, static routing does not offer the same scalability as dynamic routing. Even in large networks, static routes are planned to achieve a specific purpose are often configured in conjunction with a dynamic routing protocol.

mardi 20 décembre 2011

Compare and contrast routing distance vector and link-state routing

All distance vector protocols are made aware of the roads and sending those routes to directly connected neighbors. However, the link-state routers advertise the states of their links to all other routers in the area so that each router can build a database of complete link-state. These ads are called updates link-state routing (LSA). Unlike distance vector routers, the link-state routers can form special relationships with their neighbors and other routers link-state. This ensures that the information of LSA is exchanged appropriately and effectively.

The initial release of the LSA provides routers with the information they need to build a database of link state. The routing updates occur only when changes in the network.Without change, the routing updates occur after a specific interval. If a change occurs on the network, a partial update is sent immediately. The latter contains only information about the links that have changed, and not a complete routing table. Any director concerned about the use of WAN links contained in these partial updates and sporadic an effective alternative to distance vector routing, which sends a complete routing table every thirty seconds. When a change occurs, the link-state routers are simultaneously notified by the partial update. The distance vector routers waiting their neighbors take note of the change, implement change, and then pass it in turn to their neighbors.The link-state protocols provide faster convergence and better use of bandwidth. They support the CIDR (classless interdomain routing) and VLSM (variable-length subnet mask). They are well suited for complex and evolving networks. In fact, the link-state protocols generally provide superior performance to those of distance vector protocols, and this regardless of the size of the network. The link-state protocols are not implemented on all networks, because they require more memory and processing power than distance vector protocols and can exceed the capacity of equipment slow. Their relative complexity is also an obstacle to their widespread adoption. Only adequately trained administrators can configure and manage them properly

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