Network monitoring is the use of a system that constantly monitors a computer network for slow or failing components and that notifies the network administrator (via email, SMS or other alarms) in case of outages. It is part of network management
IP routing is the process of moving data packets between different networks. By default two different IP networks cannot communicate with each other. They need a mediator device that can switch packet between them. Router takes this responsibility. Routers interfaces are associated with different networks. This association is kept in routing table. Routers use it to take switching decision.
Example: IP Routing
- 10.0.0.0/8 Network is connected on router’s F0/1 interface.
- 18.104.22.168/8 Network is connected with router’s F0/2 interface.
- Laptop sends a packet to PC.
- Router receives this packet in F0/1 interface.
- Router checks destination address field in packet.
- Packet has 22.214.171.124/8 address in destination address field.
- IP address 126.96.36.199/8 belongs to 188.8.131.52/8 network.
- Router checks routing table for matching network.
- Routing table has an entry for 184.108.40.206/8 network.
- 220.127.116.11/8 Network is associated with F0/2 interface of router.
- Based on this information router moves this packet from F0/1 to F0/2.
- F0/2 interface sends this packet to its destination.Advertisements
It is the easiest example of IP routing. In above example we used only one router to explain the process. In real life there could be several routers in the way of destination address. These routers may create certain path to the destination. Routing protocols insure that packet takes the best path from these paths.
When routers learn from an administrator, it is called static routing. In static routing we have to add all network locations manually. If any change occurs in network, administrator is responsible to update it by hand in all routers.
When routers learn from neighboring router through the routing protocols, it is called dynamic routing. In dynamic routing routers add network locations automatically form the routing information. If any change occurs in network, affected routers update others via routing information.
Interior Gateway Protocols
Interior gateway protocols (IGPs) are used to share routing updates between routers in same AS. Some examples of IGPs are RIPv1, RIPv2, EIGRP, IGRP, and OSPF.
Exterior Gateway Protocols
Exterior gateway protocols (EGPs) are used to share routing updates between different AS. Example of EGPs is Border Gateway Protocol (BGP).
Administrative distance (AD) is the trustworthiness of routing update received from a neighbor router. If a router receives two routing updates for same path from two different routing protocols then router will check the AD value to choose the best path. AD is a numeric value from 0 to 255. If one update has lower AD value than other, then the route with the lowest AD will be placed in the routing tableRoute source Default AD valueDirect connected interface 0Static route 1EIGRP 90IGRP 100OSPF 110RIP 120External EIGRP 170Unknown 255
Lower AD value is more believable by router. 0 is considered as the most trustworthiness network while 255 is considered as invalid route and it will be never used.
If two routing updates for same network have same AD value then metric will use to choose the best path. Metric is a measurement to calculate best path. Route with the lowest metric will be chosen. Different routing protocols use different metrics. It may use single metric or multiple metrics. For example EIGRP uses bandwidth, delay, load, MTU and reliability while RIP only uses hop count as metric.
Three types of routing Protocols:
- Distance Vector
- Link State
Distance vector routing protocol uses distance (metric value) and direction (vector) to find the best path to destination network. Router receives routing update from neighboring router and these neighboring routers receive updates from their neighboring routers until the destination network. Every router in the way of destination network called hop. Each time a packet goes through a router, it add one in hop count value. Route with the least hop count value will be chosen as best path and will be placed in routing table. RIP is the example of distance vector routing protocol. These protocol shares entire routing table to the directly connected neighbors.
Link state routing protocols use more composite metric to locate the best path for destination network. It maintains three separate tables. First table keeps track of directly connected neighbors. Second table determines the entire network topology. Third is the routing table that keeps actual path. OSPF is the example of link state protocol. Link state protocols share their own links to all other routers in network.
Hybrid routing protocols are the mix of distance vector and link state protocol. To locate more accurate path, it uses aspect from both distance vector and link state. EIGRP is the example of hybrid routing protocols.
All three types of protocol have their own advantage and disadvantage. They take different approach in sharing routing updates and in choosing the best path. In next articles of this section we will explain these protocols in details with examples.