Wednesday, March 31, 2010

OSPF elections

1. Router ID election
The router ID is used to specify a particular router in a area, which is in ip address format.. the parameter used for router ID election are
a. Manual ID - Statically assigned id.
b. Loopback Address - Dynamically assumed from configuration.
c. Highest Interface
Address - Dynamically assumed from configuration.

In these three parameter's first preference is given to Manual id(if any) else it will check for loopback address(if any) this is second preference else it'll go for last option of choosing highest interface address.

2. Master/slave or DR/BDR election.

OSPF tables

Routing table : Basic table, it holds routing information.

Neighbor table : Maintains information of its neighbor routers.

Database table : Maintains the entire protocol's database information.

Sunday, March 28, 2010

Redistribution:

Redistribution is a process used to make communication between two different routing protocols and also two different Autonomous Systems in IGRP and EIGRP protocol.

Redistribution can be performed in intermediate router only. Intermediate router means "it is a router where two different protocols or two different AS is enabled".

Example for redistribution with different protocols and commands:
Assume RIP and EIGRP is enabled in this router.

router(config)#router rip
router(config-router)#redistribute eigrp 10 metric 5

(The range of metric is 0-16, it is RIP metric). Do you know why metric is specified? we are redistributing EIGRP in RIP, does RIP knows how EIGRP calculates metric? no. that's y metric is specified, whatever metric it receives with EIGRP update will be converted into the metric what is specified.

router(config-router)#exit
router(config)#router eigrp 10
router(config-router)#redistribute rip

(The range of metric is 1- 4294967295, it is EIGRP metric).Do you know why metric is specified? we are redistributing RIP in EIGRP, does EIGRP knows how RIP calculates metric? no. that's y metric is specified, whatever metric it receives with RIP update will be converted into the metric what is specified.

Example for redistribution with different AS and commands:
Assume IGRP 20 and 30 is enabled in this router.
router(config)#router igrp 20
router(config-router)#redistribute igrp 30

Here, it is not necessary to specify the metric, y because both are igrp(same protocol).

router(config-router)#exi
router(config)#router igrp 30
router(config-router)#redistribute igrp 20

Here, it is not necessary to specify the metric, y because both are igrp(same protocol).

What is Autonomous System number?

Autonomous System number is numeric value with the range from 1 to 65535 is used to express a network or a group of network comes under single administration with same routing policy.

IGRP and EIGRP uses AS number, OSPF also uses AS number in the form of Process ID.

In IGRP and EIGRP different AS number will not communicate(exchange update) by default, to make them communicate we need to go for redistribution process.
whereas in OSPF no such issues different AS will communicate by default.

commands:
router(config)#router igrp 10

router(config)#router eigrp 100

router(config)#router ospf 20

Sunday, March 21, 2010

Protocol and standards.

Protocol

Standard

Developer

RIP

Open.

RFC (Request For Comment), 1988.

IGRP

Only for CISCO routers.

CISCO, Mid-1980’s.

EIGRP

Only for CISCO routers

CISCO.

OSPF

Open.

RFC 2328, 1998.

IS-IS

Only for defense department.

OSI.

BGP

Open.

CISCO, RFC, 1990’s.

Sunday, March 7, 2010

What is ICMP Protocol?

ICMP - Internet Control Message Protocol

ICMP is a control protocol, meaning that it does not carry application data, but rather information about the status of the network itself. ICMP can be used to report.

· errors in the underlying communications of network applications.

· availability of remote hosts.

· network congestion.

What is RARP?

RARP – Reverse Address Resolution Protocol.

The RARP protocol is used to find the unknown IP address for the Known MAC(Media Access Control)address.

What is ARP?

ARP – Address Resolution Protocol.

The ARP protocol is used to find the unknown MAC(Media Access Control) address for the Known IP address.

Protocol and Port Number:

TCP

UDP

FTP 20, 21

DNS 53

TELNET 23

TFTP 69

SMTP 25

SNMP 161

HTTP 80

HTTPS 443

Saturday, March 6, 2010

What is Classless and Class full Routing?

While sending routing update packet, if it sends subnet mask information also with that packet it is called as classless routing. If it sends packet without subnet mask information then it is called class full routing.

Define Passive Interface?

The router will receive the routing information through that interface but it wont send the routing information through that interface this concept is called Passive Interface. By default it is disabled.

To enable

router#config ter
router(config)#router rip
router(config-router)#passive interface serial 0

Now the routing information is received via serial 0 interface but no routing information is send via it.

Define Split Horizon?








image2






image 3



The Router will not resend the same routing information from which interface it learnt that information is called Split-Horizon. The use of this concept is to avoid the routing loops in Network.

Explanation with Example:

LOOK AT SECOND IMAGE

Here in RA router the 30.0.0.0 information was received via RIP protocol on s0 interface but it wasn’t resend on same interface, it sending only 10.0.0.0 information. Here Split-horizon was enabled.

Lets see what happens when disabled

LOOK AT THIRD IMAGE

Now RA Router is resending the 30.0.0.0 information via s0 interface. It creates routing loops.

This is Split-horizon concept.

Route Propagation:

RIPv1 - Broadcast - 255.255.255.255.

RIPv2 - Multicast - 224.0.0.9.

EIGRP - Multicast - 224.0.0.10.

OSPF - Multicast - 224.0.0.5 - Hello packet 224.0.0.6 - Routing Update.

Protocol Special Properties:

Parameter/Protocol

RIPv1

RIPv2

IGRP/EIGRP

summarization

Auto

Auto

Auto and Manual

VLSM support

No

Yes

Yes

Classless Support

No (Class full)

Yes

Yes

Discontiguous support

No

Yes

Yes

Convergence

Slow

Slow

Fast/Very Fast

Authentication

No

Yes(clear text and MD5)

yes(MD5 only)

Route computation

Bellman-Ford

Bellman-Ford

DUAL

Parameter/Protocol

OSPF

summarization

Manual

VLSM support

Yes

Classless Support

Yes

Discontiguous support

Yes

Convergence

Fast

Authentication

Yes( clear text and MD5)

Route computation

Dijkstra algorithm






Protocol Timers:

Parameter/protocol

RIP

IGRP

Update

30 sec

90 sec

Invalid

180 sec

270 sec

Hold Down

180 sec

280 sec

Flush

240 sec

630 sec



Parameter/Protocol

OSPF

Hello

10 sec

Wait

40 sec

Dead

40 sec

Parameter/protocol

EIGRP

Hello

5 sec

Hold down

15 sec

Active

Manually assigned

Metric Calculation Formula:

RIP

Hop count- To Reach Destination how many router it has to pass.

IGRP

107/Least Bandwidth + ∑ Delay

EIGRP

256*[107/Least Bandwidth + ∑ Delay]

OSPF

108/Bandwidth

Friday, March 5, 2010

Protocols and their Metric Parameters:

RIP
1. Hop count.

IGRP & EIGRP
2. Bandwidth.
3. Reliability.
4. delay.
5. Load.
6. MTU(Maximum Transmission Unit).

OSPF
7. Cost.

What is Metric?

Metric is numeric value used to calculate the best path to the destination. The lowest metric value is considered as best route to the destination. The metric calculation varies based on the type of protocol.

lets take RIP protocol for example,

The RIP protocol calculates metric based on hop count(0-15). To reach a destination one route has metric value 3 and one more route has metric value 5, The route with metric 3 is choosed as best path to reach destination.

What is Administrative Distance?

The Administrative Distance(AD) is the Numerical value that ranges between 0 -255. AD shows the Trust-worthiness of the Protocol.

If AD is high, Trust-worthiness is Less.
If AD is Less, Trust-worthiness is High.

Example and explaination:
You are advertising the same network using RIP and EIGRP Protocol, but the router will take the routes advertised by EIGRP. Why because the AD of EIGRP is 90 and the AD of RIP is 120, the router will prefer the route with low AD(high trust-worthiness) only. thus it takes EIGRP routes.

Protocols and its Administrative Distance

1. Directly Connected - 0.
2. Static Route - 1.
3. External BGP(Border Gateway Protocol) - 20.
4. Internal EIGRP - 90.
5. IGRP - 100.
6. OSPF - 110.
7. IS-IS(Intermediate sys- Intermediate sys)- 115.
8. RIP - 120.
9. ODR(On Demand Routing) - 160.
10.External EIGRP - 170.
11.Internal BGP - 200.
12.Unknown - 255.

Thursday, March 4, 2010

What is Hybrid Protocol?

This Protocol has both Distance Vector and Link State protocols characteristics, thus it is called as Hybrid Protocol.

EIGRP belongs Hybrid Protocol.

What is Link State Protocol?

The Link State Protocol is also called as Shortest path Protocol. Here it maintains three tables neighbor table, LSA (Link State adjacency) table, routing table. Link state protocol send updates containing the state of their own links to all routers on the network.

OSPF is a Link State protocol.

What is Distance Vector protocol?

The Distance vector Protocol finds the path to remote network by judging the distance. The vector indicates the direction to the remote network. They send the entire routing table as a periodic update to its directly connected neighbors.

RIP and IGRP belongs to Distance Vector protocol.

What are Protocols used for Dynamic Routing?

There are 3 such Protocols.

1. Distance vector.

2. Link State.

3. Hybrid.

Types of Dynamic Routing Protocol?

There are 4 types dynamic routing protocol.

1.RIP - Routing Information protocol.

2.IGRP - Interior Gateway Routing Protocol.

3.EIGRP - Enhanced Interior Gateway Routing Protocol.

4.OSPF - Open Shortest Path First.

Types of Routing?

There are two types
1.Static Routing.
2.Dynamic Routing.

Static Routing: Manually assigning route to destination by adding information in routing table.
The command for creating static route is
vasanth1406(config)#ip route(network)(subnetmask)(gateway)

Example:

vasanth1406(config)#ip route 10.0.0.0 255.0.0.0 20.0.0.2

Dynamic routing: A routing system that automatically adapts to network topology or traffic changes by advertising its directly connected networks.

What is Routing?

Ans 1: Routing (or routeing) is the process of selecting paths in a network along which to send network traffic.

Ans 2: Routing is a method of finding paths from origins to destinations in a network such as the Internet, along which information can be passed