What is routing? Routing

What is routing?-Routing is the act of moving information across an internetwork from a source to a destination.

What is difference between routing and bridging?-bridging occurs at Layer 2 (the link layer) of the OSI reference model.-whereas routing occurs at Layer 3 (the network layer).

What are routing components?-Routing involves two basic activities:

1. determining optimal routing paths .2. transporting information (packets) through an internetwork.

What is packet switching?-In the context of the routing process, the latter on,routing is referred to as packet

switching.-It is relatively straightforward.-path determination can be very complex.

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What is path determination?-What things routing protocols use?-metrics

For what?-to evaluate what path will be the best for a packet to travel.

What is metrics?-A metric is a standard of measurement.e.g bandwidth.

Why it use metrics?-to determine the optimal path to a destination.Then what?-routing algorithms initialize and maintain routing tables

What is in routing table?-contain route information.-Route information varies depending on the routing algorithm used.




What routing algorithm?-fill routing tables with a variety of information.

Which h/w device do routing?-router

How router comes to know he path?-Destination/next hop associations tell a router about a particular destination.

How it reach to that destination?-by sending the packet to a next router

What is other information in routing tables?-such as data about the desirability of a path-Routers compare metrics to determine optimal routes.




Destination/Next Hop Associations Determine the Data's Optimal Path




What happens when two routers communicates with each other?-maintain their routing tables .

How they maintain routing tables?-by transmission of a variety of messages.

What are routing algorithms?-for calculation of optimal route.

What are design goals of RA?- • Optimality • Simplicity and low overhead • Robustness and stability • Rapid convergence • Flexibility

What is optimality?- selecting the best route-How to select best route?-depends on the metrics .




What is simplicity and low overhead?-RA must offer its functionality efficiently with a minimum of software and utilization

overhead.

What is Robustness?-RA should perform correctly in the face of unusual or unforeseen circumstances.

Which are these circumstances?-such as hardware failures, high load conditions, and incorrect implementations.

What is convergence?-is the process of agreement by all routers on optimal routes.

What is flexibility?-means RA should quickly and accurately adapt to a variety of network circumstances.

What are n/w circumstances?-e.g. a network segment has gone down.




What are the types of RA?-Static versus dynamic • Single-path versus multipath • Flat versus hierarchical • Host-intelligent versus router-intelligent • Intradomain versus interdomain• Link-state versus distance vector

Intradomain and interdomain routing and their algorithmsIntradomain:-Routing works only within domains.

Interdomain:-Routing work within and between domains.

What are Intradomain and Interdomain Routing algorithms?




Unicats Routing Protocols:-

What is Multicast?-communication between a single sender and a group of selected receivers.

What is anycast?-communication between any sender and a group of receivers near the sender in a network.

What is unicast?-is the process of forwarding unicasted traffic from a source to a destination on network.-same as point to point network.

What is unicasted traffic?-is destined for a unique address.-means just one sender, and one receiver.

Who supports Unicast transmission?-All LANs (e.g. Ethernet) and IP networks




Unicast and Unicast Routing




Which are standard Unicast applications?-such as http, smtp, ftp and telnet.

Which protocol supports unicast as well as anycast and multicast?-new Internet Protocol version 6 (IPv6)

Which protocols supports Unicast on internet?-Routing Information Protocol (RIP) -Open Shortest Path First (OSPF)




Routing Information Protocol (RIP)

What its background?-dynamic routing protocol used in local and wide area networks.

On which algorithm it is based/-Distance vector routing algorithm

For what?-to mathematically compare routes Then what?-identify the best path to any given destination address.




Features of Routing Information Protocol (RIP) 1.Routing updates

What is routing updates?-RIP sends routing-update messages at regular intervals .

When it sends the message?-when the network topology changes.

Where that message goes?-router

What then router do?-it updates its routing table to reflect the new route.

2.RIP Routing Metric-RIP uses a single routing metric

-What is that metric?-hop count.




What is the use of that metric?-to measure the distance between the source and a destination .-Each hop in a path from source to destination is assigned a hop count value.

What happens when a router receives a update message ( contains a new or changed destination network entry)?-the router adds 1 to the metric value which indicated in the update message.-makes entry in routing table.

3. RIP stability featuresDo RIP prevents continuous routing loop?-yes

How?-By implementing a limit on the number of hops allowed in a path from the source to a destination.

What that limit?-keeping maximum number of hops in a path i.e.15




What happens when router gets updates message to make new entry?-increases the metric value by 1.-causes the metric to be infinity (that is, 16).-then the network destination is considered unreachable.-This is RIP stability.

4. RIP Timers-RIP uses numerous timers to regulate its performance.

1. a routing-update timer2.a route-timeout timer3.a route-flush timer

What routing –update timer do?-clocks the interval between periodic routing updates.-Generally, it is set to 30 seconds.-A small random amount of time added whenever the timer is reset.

Why time is added?-to prevent congestion.

What happens then?-all routers simultaneously attempting will update their neighbors.




What route-timeout timer do?-route-timeout timer’s entry in routing table.- When the route-timeout timer expires, the route is marked

invalid .-but is retained in the table until the route-flush timer expires.




RIP Packet Formats-two packet formats

IP RIP IP RIP 2

IP RIP Packet Format




1.Command field-Indicates whether the packet is a request or a response.-What request packet do?-asks to a router send all or part of its routing table.

What response packet do?-a reply to a request.

What it contains?-contain routing table entries.

2.Version Number-Specifies the RIP version used.

3. Zero field-not actually used -provide backward compatibility with prestandard varieties of RIP.(helping to new version by giving older version interface.)




4.Address family Identifier(AFI)-Specifies the address family used.Each RT entry has an address-family identifier .

Why?-to indicate the type of address being specifiede.g. AFI for IP is 2.

5. Address-Specifies the IP address for the entry.

MetricWhat it does?-indicates how many internetwork hops (routers) have been traversed in the trip to the destination. -this value is between 1 and 15 for a valid route, or 16 for an unreachable route.




IP RIP 2 Packet




1.Command-same as above

2.Version Number-same as above

3. Unused-Has a value set to zero

4. Address-family identifier (AFI)-same as above.

5. Route tag-Provides a method for distinguishing between internal routes (learned by RIP) and external routes (learned from other protocols).

6. IP address--Specifies the IP address for the entry.

7. Subnet mask-Contains the subnet mask for the entry.- If this field is zero, no subnet mask has been specified for the entry




8. Next hop-Indicates the IP address of the next hop to which packets for the entry should be forwarded.

9. Metric- same as above.




Open Shortest Path First (OSPF) protocol

Why it is developed?-due to a need in the internet community.

What is that need?-to introduce a high functionality non-proprietary Internal Gateway Protocol (IGP) for the TCP/IP protocol family.

On which algorithm it is based?-link state algorithm.

What new concepts are introduced in OSPF?-such as authentication of routing updates- Variable Length Subnet Masks (VLSM)-route summarization




Differentiate between RIP and OSPF

RIP OSPF

has a limit of 15 hops no limitation on the hop count

cannot handle Variable Length Subnet Masks (VLSM).

VLSM is very useful in IP address allocation




What are limits in RIP?1.What is limit on hop count?-15A RIP network that spans more than 15 hops (15 routers) is considered unreachable.2.Can RIP handle Variable Length Subnet Masks (VLSM)?-NO, cannot.

Then what happen when it doesn’t handle VLSM?-the shortage of IP addresses and the flexibility VLSM gives in the efficient

assignment of IP addresses.-There is Periodic broadcasts of the full routing table.

Then what happen when there is periodic broadcasts of full RT?-consume a large amount of bandwidth.

-RIP converges slower than OSPF.

What about the convergence in large network?-It is in minutes.

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What are advantages of OSPF?-is no limitation on the hop count.-intelligent use of VLSM is very useful in IP address allocation.-OSPF uses IP multicast to send link-state updates.- Then what is advantage?

- This ensures less processing on routers.Which routers?- which are not listening to OSPF packets

-updates are only sent.When?-in case routing changes occur instead of periodically.

What is its advanatge?-better use of bandwidth.

-OSPF has better convergence than RIP.why?- because routing changes are propagated instantaneously and not periodically.

- OSPF allows for better load balancing.

-OSPF allows for a logical definition of networks What is logical definition?- where routers can be divided into areas.




What is routing? Routing

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