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Thursday 23 June 2011

Network Security Notes: Network Protocols: OSPF Protocol on CISCO Routing Protocols and Concepts

This blog is created for network security review, study and understanding about network related issues only! The blog is mainly focus on Network Security Notes about Network, Network Security, Network Technology, Network Labs review related Cisco and Microsoft technology ,Network Threats, Types of Network Threats, Network Alerts, Enterprise Security Policy and Audits, Security Policy and Audits,Logical Security, Physical and Logical Security, Physical Security,Cisco Products Review, Microsoft Products review, Cisco Routers, Routers Security, Console Access, Telnet Access, Network Attack, Network Attack report, Network management, Anti-virus, Network Security with Anti-virus, and All About Network Security... Thanks for your visit!

I have already posted about Understanding OSPF Protocol. And here this post, you can find out more about OSPF on CISCO Routing Protocols and Concepts Chapter 13...

Let me quote some:

Exploration Routing Protocols and ConceptsChapter 11 - Presentation Transcript

1. OSPF Routing Protocols and Concepts – Chapter 11
2. Objectives
* Describe the background and basic features of OSPF.
* Identify and apply the basic OSPF configuration commands.
* Describe, modify and calculate the metric used by OSPF.
* Describe the Designated Router/Backup Designated Router (DR/BDR) election process in multiaccess networks.
* Describe the uses of additional configuration commands in OSPF.
3. Introduction
4. Introduction to OSPF
* Background of OSPF
o Began in 1987
o 1989 OSPFv1 released in RFC 1131
o This version was experimental & never deployed
o 1991 OSPFv2 released in RFC 1247
o 1998 OSPFv2 updated in RFC 2328
o 1999 OSPFv3 published in RFC 2740
5. Introduction to OSPF
* OSPF Message Encapsulation
o OSPF packet type
+ There exist 5 types
o OSPF packet header
+ Contains - Router ID and area ID and Type code for OSPF packet type
o IP packet header
+ Contains - Source IP address, Destination IP address, & Protocol field set to 89
6. Introduction to OSPF
* OSPF Message Encapsulation
o Data link frame header
o Contains - Source MAC address and Destination MAC address
7. Introduction to OSPF
* OSPF Packet Types
8. Introduction to OSPF
* Hello Protocol
* OSPF Hello Packet
o Purpose of Hello Packet
+ Discover OSPF neighbors & establish adjacencies
+ Advertise guidelines on which routers must agree to become neighbors
+ Used by multi-access networks to elect a d esignated r outer and a b ackup d esignated r outer
9. Introduction to OSPF
* Hello Packets continued
o Contents of a Hello Packet router ID of transmitting router
* OSPF Hello Intervals
o Usually multicast (224.0.0.5)
o Sent every 30 seconds for NBMA segments
* OSPF Dead Intervals
o This is the time that must transpire before the neighbor is considered down
o Default time is 4 times the hello interval
10. Introduction to OSPF
* Hello protocol packets contain information that is used in electing
o Designated Router (DR)
+ DR is responsible for updating all other OSPF routers
o Backup Designated Router (BDR)
+ This router takes over DR’s responsibilities if DR fails
11. Introduction to OSPF
* OSPF Link-state Updates
o Purpose of a Link State Update (LSU)
+ Used to deliver link state advertisements
o Purpose of a Link State Advertisement (LSA)
+ Contains information about neighbors & path costs
12. Introduction to OSPF
* OSPF Algorithm
* OSPF routers build & maintain link-state database containing LSA received from other routers
o Information found in database is utilized upon execution of Dijkstra SPF algorithm
o SPF algorithm used to create SPF tree
o SPF tree used to populate routing table
13. Introduction to OSPF
* Administrative Distance
o Default Administrative Distance for OSPF is 110
14. Introduction to OSPF
* OSPF Authentication
o Purpose is to encrypt & authenticate routing information
o This is an interface specific configuration
o Routers will only accept routing information from other routers that have been configured with the same password or authentication information
15. Basic OSPF Configuration
* Lab Topology
* Topology used for this chapter
o Discontiguous IP addressing scheme
o Since OSPF is a classless routing protocol the subnet mask is configured in
16. Basic OSPF Configuration
* The router ospf command
* To enable OSPF on a router use the following command
o R1(config)# router ospf process-id
o Process id
+ A locally significant number between 1 and 65535
+ This means it does not have to match other OSPF routers
17. Basic OSPF Configuration
* OSPF network command
o Requires entering:
+ network address
+ wildcard mask - the inverse of the subnet mask
+ area-id - area-id refers to the OSPF area – OSPF area is a group of routers that share link state information
o Example: Router(config-router)# network network-address wildcard-ask area area-id
18. Basic OSPF Configuration
* Router ID
o This is an IP address used to identify a router
o 3 criteria for deriving the router ID
+ Use IP address configured with OSPF router-id command
# Takes precedence over loopback and physical interface addresses
+ If router-id command not used then router chooses highest IP address of any loopback interfaces
+ If no loopback interfaces are configured then the highest IP address on any active interface is used
19. Basic OSPF Configuration
* OSPF Router ID
* Commands used to verify current router ID
o Show ip protocols
o Show ip ospf
o Show ip ospf interface
20. Basic OSPF Configuration
* OSPF Router ID
* Router ID & Loopback addresses
o Highest loopback address will be used as router ID if router-id command isn’t used
o Advantage of using loopback address
+ The loopback interface cannot fail  OSPF stability
* The OSPF router-id command
o Introduced in IOS 12.0
o Command syntax
+ Router(config)#router ospfprocess-id
+ Router(config-router)#router-idip-address
* Modifying the Router ID
o Use the command Router #clear ip ospf process
21. Basic OSPF Configuration
* Verifying OSPF
* Use the show ip ospf command to verify & trouble shoot OSPF networks
* Command will display the following:
o Neighbor adjacency
+ No adjacency indicated by
# Neighboring router’s Router ID is not displayed
# A state of full is not displayed
+ Consequence of no adjacency
# No link state information exchanged
# Inaccurate SPF trees & routing tables
22. Basic OSPF Configuration
* Verifying OSPF - Additional Commands
Displays hello interval and dead interval Show ip ospf interface Displays OSPF process ID, router ID , OSPF area information & the last time SPF algorithm calculated Show ip ospf Displays OSPF process ID, router ID , networks router is advertising & administrative distance Show ip protocols Description Command
23. Basic OSPF Configuration
* Examining the routing table
* Use the show ip route command to display the routing table
o An “O’ at the beginning of a route indicates that the router source is OSPF
o Note OSPF does not automatically summarize at major network boundaries
24. OSPF Metric
* OSPF uses cost as the metric for determining the best route
o The best route will have the lowest cost
o Cost is based on bandwidth of an interface
+ Cost is calculated using the formula
# 10 8 / bandwidth
o Reference bandwidth
+ Defaults to 100Mbps
+ Can be modified using
+ Auto-cost reference-bandwidth command
25. OSPF Metric
* COST of an OSPF route
o Is the accumulated value from one router to the next
26. OSPF Metric
* Usually the actual speed of a link is different than the default bandwidth
o This makes it imperative that the bandwidth value reflects link’s actual speed
+ Reason: so routing table has best path information
* The show interface command will display interface’s bandwidth
o Most serial link default to 1.544Mbps
27. Basic OSPF Configuration
* Modifying the Cost of a link
* Both sides of a serial link should be configured with the same bandwidth
o Commands used to modify bandwidth value
+ Bandwidth command
# Example: Router(config-if)# bandwidth bandwidth-kbp s
+ ip ospf cost command – allows you to directly specify interface cost
# Example: R1(config)#interface serial 0/0/0
# R1(config-if)#ip ospf cost 1562
28. Basic OSPF Configuration
* Modifying the Cost of the link
* Difference between bandwidth command & the ip ospf cost command
o Ip ospf cost command
+ Sets cost to a specific value
o Bandwidth command
+ Link cost is calculated
29. OSPF and Multiaccess Networks
* Challenges in Multiaccess Networks
* OSPF defines five network types:
o Point-to-point
o Broadcast Multiaccess
o Nonbroadcast Multiaccess (NBMA)
o Point-to-multipoint
o Virtual links
30. OSPF in Multiaccess Networks
* 2 challenges presented by multiaccess networks
o Multiple adjacencies
o Extensive LSA flooding
31. OSPF in Multiaccess Networks
* Extensive flooding of LSAs
o For every LSA sent out there must be an acknowledgement of receipt sent back to transmitting router
o Consequence: lots of bandwidth consumed and chaotic traffic
32. OSPF in Multiaccess Networks
* Solution to LSA flooding issue is the use of
o Designated router (DR)
o Backup designated router (BDR)
* DR & BDR selection
o Routers are elected to send & receive LSA
* Sending & Receiving LSA
o DR others send LSAs via multicast 224.0.0.6 to DR & BDR
o DR forward LSA via multicast address 224.0.0.5 to all other routers
33. OSPF in Multiaccess Networks
* DR/BDR Election Process
o DR/BDR elections DO NOT occur in point to point networks
34. OSPF in Multiaccess Networks
* DR/BDR elections will take place on multiaccess networks as shown below
35. OSPF in Multiaccess Networks
* Criteria for getting elected DR/BDR
o DR: Router with the highest OSPF interface priority
o BDR : Router with the second highest OSPF interface priority
o If OSPF interface priorities are equal , the highest router ID is used to break the tie
36. OSPF in Multiaccess Networks
* Timing of DR/BDR Election
o Occurs as soon as 1 st router has its interface enabled on multiaccess network
+ When a DR is elected it remains as the DR until one of the following occurs
# The DR fails
# The OSPF process on the DR fails
# The multiaccess interface on the DR fails
37. OSPF in Multiaccess Networks
* Manipulating the election process
o If you want to influence the election of DR & BDR then do one of the following:
+ Boot up the DR first, followed by the BDR, and then boot all other routers
+ OR
+ Shut down the interface on all routers, followed by a no shutdown on the DR, then the BDR, and then all other routers
38. OSPF in Multiaccess Networks
* OSPF Interface Priority
* Manipulating the DR/BDR election process continued
o Use the ip ospf priority interface command.
o Example:Router(config-if)# ip ospf priority { 0 - 255 }
+ Priority number range 0 to 255
# 0 means the router cannot become the DR or BDR
# 1 is the default priority value
39. More OSPF Configuration
* Redistributing an OSPF Default Route
* Topology includes a link to ISP
o Router connected to ISP
+ Called an autonomous system border router
+ Used to propagate a default route
# Example of static default route:
# R1(config)# ip route 0.0.0.0 0.0.0.0 loopback 1
# Requires the use of the default-information originate command
# Example of default-information originate command:
# R1(config-router)# default-information originate
40. More OSPF Configuration
* Fine-Tuning OSPF
* Since link speeds are getting faster it may be necessary to change reference bandwidth values
o Do this using the auto-cost reference-bandwidth command
o Example:
+ R1(config-router)# auto-cost reference-bandwidth 10000
41. More OSPF Configuration
* Fine-Tuning OSPF
* Modifying OSPF timers
o Reason to modify timers
+ Faster detection of network failures
o Manually modifying Hello & Dead intervals
+ Router(config-if)# ip ospf hello-interval seconds
+ Router(config-if)# ip ospf dead-interval seconds
o Point to be made
+ Hello & Dead intervals must be the same between neighbors
42. Summary
* RFC 2328 describes OSPF link state concepts and operations
* OSPF Characteristics
o A commonly deployed link state routing protocol
o Employs DR s & BDR s on multi-access networks
+ DRs & BDRs are elected
+ DR & BDRs are used to transmit and receive LSAs
o Uses 5 packet types:
+ 1: HELLO
+ 2: D ATA B ASE D ESCRIPTION
+ 3: L INK S TATE R EQUEST
+ 4: L INK S TATE U PDATE
+ 5: L INK S TATE A CKNOWLEDGEMENT
43. Summary
* OSPF Characteristics
o Metric = cost
+ Lowest cost = best path
* Configuration
o Enable OSPF on a router using the following command
+ R1(config)# router ospf process-id
o Use the network command to define which interfaces will participate in a given OSPF process
+ Router(config-router)# network network-address wildcard-mask area area-id
44. Summary
* Verifying OSPF configuration
o Use the following commands:
+ show ip protocol
+ show ip route
+ show ip ospf interface
+ show ip ospf neighbor


More details about OSPF Protocol on CISCO Routing Protocols and Concepts...Please visit directly here...




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Tuesday 14 June 2011

Network Security Notes: Network Protocols: Understanding OSPF Protocol

This blog is created for network security review, study and understanding about network related issues only! The blog is mainly focus on Network Security Notes about Network, Network Security, Network Technology, Network Labs review related Cisco and Microsoft technology ,Network Threats, Types of Network Threats, Network Alerts, Enterprise Security Policy and Audits, Security Policy and Audits,Logical Security, Physical and Logical Security, Physical Security,Cisco Products Review, Microsoft Products review, Cisco Routers, Routers Security, Console Access, Telnet Access, Network Attack, Network Attack report, Network management, Anti-virus, Network Security with Anti-virus, and All About Network Security... Thanks for your visit!

As my previous post about Understanding EIGRP and IGRP Protocols. This post I want to learn about OSPF protocol.

Open Shortest Path First (OSPF) is an adaptive routing protocol for Internet Protocol (IP) networks. It uses a link state routing algorithm and falls into the group of interior routing protocols, operating within a single autonomous system (AS). It is defined as OSPF Version 2 in RFC 2328 (1998) for IPv4. The updates for IPv6 are specified as OSPF Version 3 in RFC 5340 (2008). Research into the convergence time of OSPF can be found in Stability Issues in OSPF Routing (2001).

OSPF is perhaps the most widely-used interior gateway protocol (IGP) in large enterprise networks. IS-IS, another link-state routing protocol, is more common in large service provider networks. The most widely-used exterior gateway protocol is the Border Gateway Protocol (BGP), the principal routing protocol between autonomous systems on the Internet.

OSPF is an interior gateway protocol that routes Internet Protocol (IP) packets solely within a single routing domain (autonomous system). It gathers link state information from available routers and constructs a topology map of the network. The topology determines the routing table presented to the Internet Layer which makes routing decisions based solely on the destination IP address found in IP packets. OSPF was designed to support variable-length subnet masking (VLSM) or Classless Inter-Domain Routing (CIDR) addressing models.

OSPF detects changes in the topology, such as link failures, very quickly and converges on a new loop-free routing structure within seconds. It computes the shortest path tree for each route using a method based on Dijkstra's algorithm, a shortest path first algorithm.

The link-state information is maintained on each router as a link-state database (LSDB) which is a tree-image of the entire network topology. Identical copies of the LSDB are periodically updated through flooding on all OSPF routers.

The OSPF routing policies to construct a route table are governed by link cost factors (external metrics) associated with each routing interface. Cost factors may be the distance of a router (round-trip time), network throughput of a link, or link availability and reliability, expressed as simple unitless numbers. This provides a dynamic process of traffic load balancing between routes of equal cost.

An OSPF network may be structured, or subdivided, into routing areas to simplify administration and optimize traffic and resource utilization. Areas are identified by 32-bit numbers, expressed either simply in decimal, or often in octet-based dot-decimal notation, familiar from IPv4 address notation.

By convention, area 0 (zero) or 0.0.0.0 represents the core or backbone region of an OSPF network. The identifications of other areas may be chosen at will; often, administrators select the IP address of a main router in an area as the area's identification. Each additional area must have a direct or virtual connection to the backbone OSPF area. Such connections are maintained by an interconnecting router, known as area border router (ABR). An ABR maintains separate link state databases for each area it serves and maintains summarized routes for all areas in the network.

OSPF does not use a TCP/IP transport protocol (UDP, TCP), but is encapsulated directly in IP datagrams with protocol number 89. This is in contrast to other routing protocols, such as the Routing Information Protocol (RIP), or the Border Gateway Protocol (BGP). OSPF handles its own error detection and correction functions.

OSPF uses multicast addressing for route flooding on a broadcast network link. For non-broadcast networks special provisions for configuration facilitate neighbor discovery. OSPF multicast IP packets never traverse IP routers, they never travel more than one hop. OSPF reserves the multicast addresses 224.0.0.5 for IPv4 or FF02::5 for IPv6 (all SPF/link state routers, also known as AllSPFRouters) and 224.0.0.6 for IPv4 or FF02::6 for IPv6 (all Designated Routers, AllDRouters), as specified in RFC 2328 and RFC 5340.

For routing multicast IP traffic, OSPF supports the Multicast Open Shortest Path First protocol (MOSPF) as defined in RFC 1584. Neither Cisco nor Juniper Networks include MOSPF in their OSPF implementations. PIM (Protocol Independent Multicast) in conjunction with OSPF or other IGPs, (Interior Gateway Protocol), is widely deployed.

The OSPF protocol, when running on IPv4, can operate securely between routers, optionally using a variety of authentication methods to allow only trusted routers to participate in routing. OSPFv3, running on IPv6, no longer supports protocol-internal authentication. Instead, it relies on IPv6 protocol security (IPsec).

OSPF version 3 introduces modifications to the IPv4 implementation of the protocol. Except for virtual links, all neighbor exchanges use IPv6 link-local addressing exclusively. The IPv6 protocol runs per link, rather than based on the subnet. All IP prefix information has been removed from the link-state advertisements and from the Hello discovery packet making OSPFv3 essentially protocol-independent. Despite the expanded IP addressing to 128-bits in IPv6, area and router identifications are still based on 32-bit values.

What is Link-state routing protocol?

A link-state routing protocol is one of the two main classes of routing protocols used in packet switching networks for computer communications (the other is the distance-vector routing protocol). Examples of link-state routing protocols include OSPF and IS-IS.

The link-state protocol is performed by every switching node in the network (i.e. nodes that are prepared to forward packets; in the Internet, these are called routers). The basic concept of link-state routing is that every node constructs a map of the connectivity to the network, in the form of a graph, showing which nodes are connected to which other nodes. Each node then independently calculates the next best logical path from it to every possible destination in the network. The collection of best paths will then form the node's routing table.

This contrasts with distance-vector routing protocols, which work by having each node share its routing table with its neighbors. In a link-state protocol the only information passed between nodes is connectivity related.

Link state algorithms are sometimes characterized informally as each router 'telling the world about its neighbors'.

Learn about Shortest Path First Algorithm:

OSPF uses a shorted path first algorithm in order to build and calculate the shortest path to all known destinations.The shortest path is calculated with the use of the Dijkstra algorithm. The algorithm by itself is quite complicated. This is a very high level, simplified way of looking at the various steps of the algorithm:

1. Upon initialization or due to any change in routing information, a router generates a link-state advertisement. This advertisement represents the collection of all link-states on that router.

2. All routers exchange link-states by means of flooding. Each router that receives a link-state update should store a copy in its link-state database and then propagate the update to other routers.

3. After the database of each router is completed, the router calculates a Shortest Path Tree to all destinations. The router uses the Dijkstra algorithm in order to calculate the shortest path tree. The destinations, the associated cost and the next hop to reach those destinations form the IP routing table.

4. In case no changes in the OSPF network occur, such as cost of a link or a network being added or deleted, OSPF should be very quiet. Any changes that occur are communicated through link-state packets, and the Dijkstra algorithm is recalculated in order to find the shortest path.

The algorithm places each router at the root of a tree and calculates the shortest path to each destination based on the cumulative cost required to reach that destination. Each router will have its own view of the topology even though all the routers will build a shortest path tree using the same link-state database. The following sections indicate what is involved in building a shortest path tree.

What about OSPF Cost?

The cost (also called metric) of an interface in OSPF is an indication of the overhead required to send packets across a certain interface. The cost of an interface is inversely proportional to the bandwidth of that interface. A higher bandwidth indicates a lower cost. There is more overhead (higher cost) and time delays involved in crossing a 56k serial line than crossing a 10M ethernet line. The formula used to calculate the cost is:

*cost= 10000 0000/bandwith in bps

For example, it will cost 10 EXP8/10 EXP7 = 10 to cross a 10M Ethernet line and will cost 10 EXP8/1544000 = 64 to cross a T1 line.

By default, the cost of an interface is calculated based on the bandwidth; you can force the cost of an interface with the ip ospf cost interface subconfiguration mode command.

How about Shortest Path Tree?

Assume we have the following network diagram with the indicated interface costs. In order to build the shortest path tree for RTA, we would have to make RTA the root of the tree and calculate the smallest cost for each destination.

Now Let's Compare OSPF and RIP protocols:

The rapid growth and expansion of today's networks has pushed RIP to its limits. RIP has certain limitations that can cause problems in large networks:

* RIP has a limit of 15 hops. A RIP network that spans more than 15 hops (15 routers) is considered unreachable.

* RIP cannot handle Variable Length Subnet Masks (VLSM). Given the shortage of IP addresses and the flexibility VLSM gives in the efficient assignment of IP addresses, this is considered a major flaw.

* Periodic broadcasts of the full routing table consume a large amount of bandwidth. This is a major problem with large networks especially on slow links and WAN clouds.

* RIP converges slower than OSPF. In large networks convergence gets to be in the order of minutes. RIP routers go through a period of a hold-down and garbage collection and slowly time-out information that has not been received recently. This is inappropriate in large environments and could cause routing inconsistencies.

* RIP has no concept of network delays and link costs. Routing decisions are based on hop counts. The path with the lowest hop count to the destination is always preferred even if the longer path has a better aggregate link bandwidth and less delays.

* RIP networks are flat networks. There is no concept of areas or boundaries. With the introduction of classless routing and the intelligent use of aggregation and summarization, RIP networks seem to have fallen behind.

Some enhancements were introduced in a new version of RIP called RIP2. RIP2 addresses the issues of VLSM, authentication, and multicast routing updates. RIP2 is not a big improvement over RIP (now called RIP 1) because it still has the limitations of hop counts and slow convergence which are essential in todays large networks.

OSPF, on the other hand, addresses most of the issues previously presented:

* With OSPF, there is no limitation on the hop count.

* The intelligent use of VLSM is very useful in IP address allocation.

* OSPF uses IP multicast to send link-state updates. This ensures less processing on routers that are not listening to OSPF packets. Also, updates are only sent in case routing changes occur instead of periodically. This ensures a better use of bandwidth.

* OSPF has better convergence than RIP. This is because routing changes are propagated instantaneously and not periodically.

* OSPF allows for better load balancing.

* OSPF allows for a logical definition of networks where routers can be divided into areas. This limits the explosion of link state updates over the whole network. This also provides a mechanism for aggregating routes and cutting down on the unnecessary propagation of subnet information.

* OSPF allows for routing authentication by using different methods of password authentication.

* OSPF allows for the transfer and tagging of external routes injected into an Autonomous System. This keeps track of external routes injected by exterior protocols such as BGP.

For more other details about OSPF protocol, you can find document at IETF.Org


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Daily Blogging: http://visablogging.blogspot.com/
Love Sharing: http://visa-love.blogspot.com/
NetworkSecurity: http://networksecuritynotes.blogspot.com/
About Insurance:http://visa-insurance.blogspot.com
All about Love: http://visa-love.blogspot.com/
Learning English Online: http://visa-elb.blogspot.com/
Discovery Internet: http://visa-isp.blogspot.com/

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Wednesday 8 June 2011

Network Security Notes: Top 100 Network Security Tools

This blog is created for network security review, study and understanding about network related issues only! The blog is mainly focus on Network Security Notes about Network, Network Security, Network Technology, Network Labs review related Cisco and Microsoft technology ,Network Threats, Types of Network Threats, Network Alerts, Enterprise Security Policy and Audits, Security Policy and Audits,Logical Security, Physical and Logical Security, Physical Security,Cisco Products Review, Microsoft Products review, Cisco Routers, Routers Security, Console Access, Telnet Access, Network Attack, Network Attack report, Network management, Anti-virus, Network Security with Anti-virus, and All About Network Security... Thanks for your visit!

My previous post: Cisco Network Security Certification Training

This post, related to network security, I would like to share you a great video that shows you Top 100 Network Security Tools...Please check and learn from the video...

***Top 100 Network Security Tools:

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