Thursday, November 21, 2013

Distance Vector Routing Protocol

As we learn in previous subject, Distance Vector Routing protocol(DVRP) is Routing protocol that know about direction and distance to network destination.
The example of DVRP is RIP, IGRP, and EIGRP.
First we will discuss about RIP.
RIP (Routing Information Protocol)
In RIP, Routing update send by broadcast (RIPv1) and Multicast (RIPv2) every 30 second.
Information that sent by RIP is routing table.
IGRP (Interior Gateway Routing Protocol)
IGRP is protocol that only can run in cisco device (Cisco Proprietary). IGRP send periodic update every 90 second.
EIGRP (Enhanced Interior Gateway Routing Protocol)
EIGRP is the enhanced version for IGRP. It also cisco proprietary.
EIGRP had a feature unequal cost load balancing. It is also being called “hybrid” routing protocol because it had the benefit of DVRP and LSRP (fast convergence, low CPU processing, scalable, etc).
This protocol using DUAL (Diffusing Update ALgorithm) algorithm to count shortest path/metric.
In EIGRP there is no periodic update, routing update is being send if there are any changes in topology.
In DVRP, algorithm that being used is “Bellman-Ford Algorithm”
In RIP, There are 3 type of timer:
1. Invalid Timer (180s)
if information about the path is not being received in 180 second, the path will be marked invalid/unusable.
2. Flush Timer (240s)
If information about the path is not being received in 240 second, the path will be deleted in routing table.
3. Hold down Timer (180s)
One of the method to prevent routing loop.
Routing loop is a condition where a package still round without ever reach destination network.
EIGRP didn’t send periodic update but it send update when:
- Triggered update : send update if there are any changes in topology
- Bounded update : send update only to router that needed.
- Partial update : just send information routing that being needed.
RIP also had fitur triggered Update.
To prevent collision in sending periodic update in multi-access topology(hub-only), Random Jitter (RIP_JITTER) in RIP do randomize periodic update time between 25 until 30 second.
There are a few mechanism to prevent routing loop in DVDRP:
- Prevent Count to Infinity
Wrong Route wil being marked infinity / metric = 16
- Hold Down Timer
The dead route will being marked “down” and can only back if the interface is on or there are route to those network with a small metric.
- Split Horizon
Router will not send information about route to interface that it will received those information.


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