CCNA Routing
Layer 3 devices are generically referred to as routers. The router has two basic functions:
1. To find a path to a level 3 destination network
2. In order to get packets from one interface to another of a packet to its destination
To achieve the first function, a router, you should:
- The experience is more connected through the network router to know that they know
- Find places of destination network numbers
- Select abest route to each destination
- Maintain contact with the most updated routing information to destination networks
Types of routes
static and dynamic: A router can be a way to meet one of two methods. A static route is a route that is manually configured on the router. Dynamic routes are routes that a router learns a routing protocol. routing protocols are run over distances from other adjacent routers to learn the same routingProtocol.
Administrative distance
Remote Administration classifies IP routing protocols, assign a value or weight of any protocol. Distances, 0-255 range. A smaller gap is more credible by a router is the best and the worst position 0, 255
Static route configuration
Router (config) # ip route destination_network_ # [subnet_mask] IP_address_of_next_hop_neighbor
[Administrative_distance]
or
Router (config) # ip routedestination_network_ # [subnet_mask] interface_to_exit [administrative_distance]
Default Route Configuration
A default route is a special type of static route.Where a static route is a route using a router to reach a goal should be, there is a default route using a route for the router if you do not know how to reach the goal should .
Router (config) # ip route 0.0.0.0 0.0.0.0 IP_address_of_next_hop_neighbor [administrative distance]
O
Router (config) # ipinterface_to_exit route 0.0.0.0 0.0.0.0 [administrative_distance]
Dynamic routing protocols
networks to learn dynamic routing protocols in use from neighboring routers. The dynamic routing protocols in one of three categories: distance vector, link state and hybrid. Because of the differences between different types of routing protocol has advantages and disadvantages of each.
Distance Vector Protocols
distance vector protocols are the simplest. Distance Vector Protocolsrouting protocols use distance and direction (vector) to find the paths to the destinations. Most distance vector protocols use the Bellman-Ford algorithm for finding ways to network destinations. Some examples of IP routing protocols RIPv1 and IGRP are distance vector. distance vector protocols periodically broadcasts a local destination IP address of 255.255.255.255 to share routing information.
Processing Updates
If a protocol receives a distance vectorRouting update before it:
1. Improve the metrics of incoming routes in advertising (for the IP
RIP, add between 1 and the number of hops).
2. Compare the line numbers in the next routing update from
to what the router has in its routing table.
3. If the information on the next best is to put in the routing table, and remove the old entry.
4. If the information on the next is worse to ignore.
5. If the neighbor is exactly the informationthe same element in the table, the timer for the entry in the routing table (in other words, the router already learned in this way from near the same).
6. If the information on the next is another way to a destination network unknown, but with the same metric as the existing network in the routing table, routing table of the router with the old. This means that did not exceed the maximum number of equal-cost paths to this destinationNetwork number.
The six points are commonly known as the Bellman-Ford algorithm.
Link state protocols
Link state protocols use an algorithm called the Shortest Path First (SPF) algorithm invented by Dijkstra, to determine the best way to find a target. Examples of link-state protocols include IP OSPF. While the distance vector protocols use local broadcasts to disseminate information routing, link state protocols use multicast. A routing protocol sends its distanceTable religiously their regular intervals, whether or not change. link state protocols are more intelligent. They called a multicast Link State Advertisement (LSA), a piece of routing information that originates contains advertising and what is the network number. LSAs are usually generated only when there are changes in the network. link-state router sends only incremental updates. Advantage of link-state protocols are distance vector protocolsthat support classless routing path [VLSM].
Hybrid protocols
A hybrid protocol takes the advantages of both protocols distance vector and link-state and combines them into a new protocol. In general, protocols based on a hybrid distance vector protocol, but they contain many of the features and benefits of link-state protocols. Examples of protocols include hybrid RIPv2, EIGRP.
Problems with distance vector protocols
Problem: Convergence
The concept of convergence,Routing conditions, refers to the time to understand all the routers on the current network topology. Link state protocols tend to converge very rapidly, while the distance vector protocols converge curtain slowly.
Solution: Update On
In reality there are two solutions that is used to accelerate the convergence can: on the periodic interval timer and / or use of updates.
Problem: routing loop
A routing loop is a loop of 3 Layer on the network.Basically, there is a difference of opinion on how to achieve a target network. Packet loops in the network.
Solution: The maximum number of hops: set the default IP RIP, a hop count limit of 15, and provides a hop count of IGRP 100
Solution: Split Horizon
Split Horizon is used with small rings of routing. The States Split horizon that, if a neighbor sends a path to a router, the router does not propagate in this way already in the router advertisements on the sameInterface.
Solution: Route Poisoning
While Split Horizon is used to solve small problems loop distance vector routing protocols use two mechanisms to deal with major problems of routing loops in conflict: the timers and route poisoning hold. Route poisoning is a derivative of split-horizon. When a router detects that a failed in its related services, poison the router on a path by assigning infinite metric. In IP-RIP, the route is assigned a hop count of 16 (15 is theMaximum), which makes a network unreachable.
When a router announces a balanced path for its neighbors, its neighbors, the rule of split horizon and poisoned break his back to the sender of the same route, called poison reverse. This will ensure that everyone has received the poisoned route update the original.
Hold-down Timer
For the router enough time to spread the poison and the route to ensure that no routing loops occurring during replication takes place, theRouters implement a mechanism for hold-down. During this time, the router will block the path poisoned in their routing tables for the period of the hold-down timer to update the typically three times the length of the routing program. 180 sec's
RIP (Routing Information Protocol)
IP RIP (Routing Information Protocol), available in two versions: 1 and 2 Version 1 is a distance vector protocol. Version 2 is a hybrid protocol. RIPv1 broadcasts used to share local routingInformation. These updates are regularly found in nature, which by default every 30 seconds with a hold-down period of 180 seconds. Both versions of RIP hops as a metric to use, it is not always the best metric. RIPv1 is a classful protocol. Another interesting feature is that RIP supports up to six equal cost paths to a single target. The default value is actually four ways, but this can be increased up to a maximum of six.
RIPv2
A significant improvement is RIPv2As in the case of routing updates. Instead of programs, RIPv2 uses multicast. And speed up the convergence RIPv2 supports triggered updates when a change occurs, a RIPv2 router immediately propagate routing information to its neighbors connected. A second important extension, RIPv2 is that he is a classless protocol. RIPv2 supports variable length subnet masking (VLSM), which you can use more than one subnet mask for a certain class of networkNumber.
Configuring IP RIP
Router (config) # router rip
Router (config-router) # network IP_network_
Specify RIP version 1 and 2
Router (config) # router rip
Router (config-router) # version 1 | 2
Troubleshooting IP RIP
Show IP Protocols
show ip route
debug ip rip
debug ip rip
IGRP (Interior Gateway Routing Protocol)
The Interior Gateway Routing Protocol (IGRP) is a proprietary Cisco routing protocol for IP. As IP RIPv1 is aDistance Vector Protocol. However, it is best to scale from RIP because these benefits:
- It uses a sophisticated metric based on bandwidth and delay.
- It uses triggered updates to speed convergence.
- Supports load balancing of a difference in cost for a single objective. IGRP uses a composite metric of bandwidth,, delay, reliability, load, MTU, and includes the selection of routes to a destination. By default, the algorithm uses only the bandwidth and delay
IP ConfigurationIGRP
Router (config) # router IGRP autonomous_system_ #
Router (config-router) # network IP_network_
Unlike RIP, IGRP understand the concept of an autonomous system, and requires that you configure the routing process in autonomous system. For routers to share routing information must be in the same AS.
Load Balancing
With RIP, you do not need something to allow equal-cost load balancing and configuring RIP does not support unequal cost load balancing.IGRP supports both equal and unequal cost paths for load balancing a single destination. equal cost paths by default, where IGRP supports up to six equal-cost paths (four standard) to a single destination in the IP routing table. IGRP, but also supports equal-cost paths, but this feature is disabled by default.
The function allows equal variance and unequal cost routes IGRP routing tables.
Router (config-router) # varianceMultiplier
Troubleshooting IP IGRP
Show IP Protocols
show ip route
IGRP debug ip events
IGRP debugging ip
OSPF (Open Shortest Path First)
The Open Shortest Path First (OSPF) protocol is a treatment protocol for link-state routing of IP traffic. Because it is based on an open standard, OSPF is very popular in many enterprise networks today, and has many benefits, including:
- Will run on most routers, as it has an open baseStandard.
- You use the SPF algorithm developed by Dijkstra, provide a ring topology.
- Provides fast convergence triggered by incremental updates via Link State Advertisements (LSA).
- It 's a classless protocol, allowing a hierarchical design with VLSM and route summarization.
Taking into account the benefits, OSPF does not have its share of disadvantages:
- OSPF operates three types of tables. So you need more memory, holding close to the (list of OSPFNeighbors), topology (a link-state database of all routers and their routes), and the routing tables.
- The development of additional CPU to the SPF algorithm, which therefore requires especially when for the first time since the router and that is before starting the construction of the tables in the neighborhood and the topology is performed.
- For large networks, it requires careful planning to break the network into a hierarchical adequate conception of the separation of the routers in different areas.
- It 's too complexconfigure and difficult to resolve.
Hierarchical Design: Areas
The surfaces are used to provide hierarchical routing. Basically spaces to control when and how the routing information to be shared on the network. In the flat network designs, such as IP RIP, if a change occurs on a router, maybe a path problem flapping, each router across the network. To be with a hierarchical network properly designed, these changes in a single room contents.OSPF implements a two-level hierarchy: the backbone (area 0) and the areas of the spine. With proper designs IP addressing, you should be able to summarize the routing information between areas. The implementation of this synthesis, the routers have (taken together, have only links in a separate area and routes) has a smaller topology database and routing tables are smaller (who know only their skills, courses Travel and summaries).
metrical structure
UnlikeRIP, the hop count is used as a metric that OSPF uses cost. The cost is actually the inverse of the bandwidth of a connection: The faster the connection, the lower the cost. The most favorite is the lowest cost. Through the use of cost as a metric OSPF will choose a more intelligent RIP. OSPF load balancing up to six equal cost paths to support a single target. The standard size that Cisco uses to calculate the cost metric: cost = 10 ^ 8 / (interfaceBandwidth).
Router ID
Each router in an OSPF network must have a unique ID. The ID is used to provide a unique identity, the router OSPF. This is included in each OSPF messages generated by the router. The router ID is selected from one of the following criteria:
- The highest IP address on its loop back interfaces (This is a logical interface on a router)
- The highest IP address on its active interfaces
It is strongly recommended to use a cyclethis interface, because it is always active, and the router can get a router ID.
Find Neighbors
OSPF learns its neighbors and is expanding its neighborhood and topology through the exchange of LSAs tables. There are different types of LSA. If learning about the neighbors that a router, and neighbors intentions known is connected OSPF router LSAs hi every 10 seconds. If a neighbor is discovered, and formed a neighborhood with neighbors, waiting for a routerHello to see messages from the neighboring country. If a neighbor within the dead time interval, the default values for 40 seconds, the neighbor is declared dead. If this happens, the router LSA this information through a message, advertise to other routers OSPF neighbors. A two routers become neighbors, the router next to each game:
- The number and type of area
- The hello and dead interval timers
We say that is enabled on all routerssimultaneously on a segment. In this case, through the OSPF router is called the process of exchange of three states:
1. Down was the new router has exchanged information with any other OSPF router.
2. Init state has received a new router A destination router Hello and adds them to its neighbor list (on the assumption that certain values are the same). Note that only one-sided communication, at this point.
3. State two ways of the new router will have a one-way response to hishello first package and adds the destination router for the next database. Once the router is a two-way typed as they are considered neighbors. At this point there is a local election process to elect the designated router (DR) and Backup Designated Router (BDR).
Designated and backup designated routers
An OSPF router will not form adjacencies on any router. Instead, client / server design OSPF is implemented. For each network, multi-access segment,there is a DR and BDR as well as other routers. When an OSPF router may arise form adjacencies with the DR and the BDR on each multi-access segment, which is attached. Any exchange of routing information between routers / DR and BDR other OSPF neighbors on a segment (and vice versa). An OSPF router talking to a DR with the multicast IP address of 224.0.0.6. The DR and BDR is all routers to the multicast IP address 224.0.0.5.
The router with the OSPFhighest priority is the DR for the segment. If there is a tie, the router with the highest router ID will be the DR. By default, all routers have a priority of 1 (priority 0-255). If the DR fails, the BDR is promoted to DR and select another router as BDR. OSPF use incremental updates. This means that when a change is taking place, the only change to the DR, which share this information is then shared with other routers along the path. OSPF routers shareInformation on routes connected to the DR, the type of link-state includes the ID of the router advertisement, the advertised link cost and the serial number of the link.
Configuring OSPF
Router (config) # router OSPF process_ID
Router (config-router) # network ip_address area wildcard_mask area_ #
Note that you do not have the process ID of different routers and who agree to do anything with numbers, autonomous system.
A wildcard32 bits long. A 0 in a bit position means that there must be a game, and a 1 in position a little 'do not care about the router. In reality, a wildcard mask an inverted subnet mask, turned on the 1 and 0.
Class A: 0,255,255,255,255
Class B: 0.0.255.255
Class C: 0.0.0.255
Loopback
A loopback interface is a logical, virtual interface on a router. By default, the router no loopback interface, but can be easily created. Here are someReasons why you might want to create a loopback interface:
- To make a router ID for an OSPF router
- To use for testing purposes, since this interface is always
To create a loopback interface, use the following command:
Router (config) # interface loopback # Port_
Router (config-if) # ip address IP_address subnet_mask
Troubleshooting OSPF
• show ip protocols
• show ip route
• show ip interface OSPF
• show ip OSPF neighbor
•debug ip ospf adj
• debug ip OSPF events
• debug ip packet OSPF
EIGRP (Enhanced Interior Gateway Routing Protocol)
The Enhanced Interior Gateway Routing Protocol (EIGRP) is a proprietary Cisco routing protocol for IP. It's actually based on IGRP, built with many improvements in it. Some of these features:
- Fast convergence
- Loop-free topology
- VLSM and route summarization
- Multicast and incremental updates
- Pathways tomost routing protocols (supports IP, IPX, Apple Talk)
Features of EIGRP
Both provide load balancing across six lanes (equal or unequal).
- They have similar structures metrics.
- EIGRP has led to a faster convergence (updates and storing a neighbor
Routing table on the spot).
- EIGRP network has less overhead because it uses incremental updates.
EIGRP and IGRP in the same metrical structure. Both can be bandwidth, delay, reliability, and MTU, ifCalculating a way better metric to a destination. By default, only bandwidth and delay in the metric calculation can be used. An interesting point of these protocols is that if you do some networking and router running EIGRP, IGRP, and both have the same number of autonomous system, routing information is automatically shared between the two.
EIGRP uses the Distribution Update Algorithm (DUAL) to update the routing table. This algorithm is very fastConvergence of storing routing information of a neighbor in a local topology table. If a primary path in the routing table, take a backup of the dual path topology and routing table to table without necessarily linked to other neighboring EIGRP routers discussion of an alternative route to your destination.
Interaction with other EIGRP router
EIGRP use hello packets to discover and maintain neighbor relationships, like OSPF does. EIGRP createshello packets every 5 seconds on the LAN, point to point and multipoint on a speed T1/E1 speeds. Otherwise, greetings are generated every 60 seconds. The range of deaths is three times the hello interval. EIGRP uses multicast address 224.0.0.10 to the destination in the Hello packets.
For routers to become EIGRP neighbors must meet the following:
- The number of AS
- The value of K (the activation and deactivation of various metricsComponents)
If two routers to decide whether to become neighbors, they go through the following steps:
1. The first router generates a hello with configuration information.
2. If the match of the configuration data, the second router responds with an update message with topology information.
3. The first router responds with an ACK message acknowledging the receipt of the ACK of the second.
4. The first router sends its topology router on a second oneUpdate message.
5. The second router responds with an ACK back.
At this point, the two routers are converging.
The types of messages for which a router waits for an EIGRP ACK:
- Update contains a routing update
- Query asks a neighbor to validate the routing information
- Responding to an inquiry response message
If there is an EIGRP router receiving an ACK from these three types of packets, the router will process 16 timesInformation. Thereafter, the router declares dead the next. When a router sends a hello packet, the corresponding ACK is not expected.
Configuring EIGRP
Setting EIGRP is almost as easy as configuring IGRP:
Router (config) # router EIGRP autonomous_system_ #
Router (config-router) # network IP_network_
You need the number as when configuring EIGRP. Although EIGRP is classless, it is necessary
Configuration protocol as classful in the indication of its networkNumbers with the command network.
Troubleshooting EIGRP
- Show IP Protocols
- Show ip route
- Show IP EIGRP neighbors
- Show IP EIGRP Topology
- Show IP EIGRP Traffic
- Debug IP EIGRP
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