EIGRP Metric And K Values

EIGRP Metric And K Values

EIGRP Metric And K Values are important concepts for configuration of EIGRP on Cisco Router. This post also explains how neighbor adjacencies are formed and the purpose of the metrics in EIGRP. The objective of any dynamic routing protocol is to discover remote networks of other routers and achieve convergence in the routing domain. Before any EIGRP update package can be exchanged between routers, EIGRP must discover its neighbors. Neighboring EIGRP are other routers that run EIGRP on directly connected networks.

How EIGRP NEIGHBORS and ADJACENCY Form

EIGRP uses greeting packages to establish and maintain neighbor adjacencies. For two EIGRP routers to become neighbors, several parameters must match between them. For example, two EIGRP routers must use the same EIGRP metric parameters and both must be configured with the same autonomous system number. Each EIGRP router maintains a neighbor table, which contains a list of the routers in the shared links that have an EIGRP adjacency with that router. The neighbor table is used to track the status of these EIGRP neighbors.
The illustration shows two EIGRP routers that exchange initial EIGRP hello packets. When a router with EIGRP enabled receives a hello packet in an interface, it adds that router to its neighbor table.

1. A new router (R1) appears on the link and sends an EIGRP hello packet through all its configured EIGRP interfaces.
2. Router R2 receives the hello packet on an interface with EIGRP enabled. R2 responds with an EIGRP update package that contains all the routes included in its routing table, except those discovered through that interface (split horizon). However, neighbor adjacency is not established until R2 also sends an EIGRP hello packet to R1.
3. Once both routers exchange greetings, neighbor adjacency is established. R1 and R2 update their EIGRP neighbor tables and add the adjacent router as a neighbor.

EIGRP TOPOLOGY TABLE

EIGRP updates contain networks that can be reached from the router that sends the update. As EIGRP updates are exchanged between neighbors, the receiving router adds those entries to its EIGRP topology table.
Each EIGRP router maintains a topology table for each configured routing protocol, such as IPv4 and IPv6. The topology table includes the route entries for each destination that the router discovers from its directly connected EIGRP neighbors.
The illustration shows the continuation of the initial route discovery process on the previous page. Now, the topology table update is displayed.

When a router receives an EIGRP routing update, it adds the routing information to its EIGRP topology table and responds with an EIGRP acknowledgment.

1. R1 receives the EIGRP update from neighbor R2 and includes information about the routes announced by the neighbor, including the metric to each destination. R1 adds all update entries to its topology table. The topology table includes all destinations announced by neighboring (adjacent) routers and the cost (metric) to reach each network.
2. EIGRP update packages use reliable delivery; therefore, R1 responds with an EIGRP acknowledgment packet that informs R2 that it received the update.
3. The R1 sends an EIGRP update to the R2 in which it announces the networks it knows, except those discovered from the R2 (split horizon).
4. R2 receives the EIGRP update from neighbor R1 and adds this information to its own topology table.
5. The R2 responds to the EIGRP update package of R1 with an EIGRP acknowledgment.

EIGRP CONVERGENCE

In the illustration, the last steps of the initial route discovery process are shown.

After receiving the EIGRP update packets from R2, R1 uses the information in the topology table to update its IP routing table with the best route to each destination, including the metric and router of the next hop.
In the same way as R1, R2 updates its IP routing table with the best routes to each network.
At this point, EIGRP is considered to be in convergent state on both routers.

EIGRP K Values & Metrics

By default, EIGRP uses the following values ​​in its composite metric to calculate the preferred route to a network:

• Bandwidth : the slowest bandwidth between all output interfaces, along the route from origin to destination.
• Delay : the accumulation (sum) of all interface delays along the route (in tens of microseconds).

The following values ​​can be used, but not recommended, because they usually result in frequent recalculations of the topology table:

• Reliability : represents the worst reliability between origin and destination, which is based on keepalives.
• Load : represents the worst load on a link between origin and destination, which is calculated based on the packet speed and the configured bandwidth of the interface.

While the MTU is included in the routing table updates, it is not a routing metric used by EIGRP.

EIGRP COMPOSITE METRIC

In Image 4, the compound metric formula that EIGRP uses is shown.

The formula consists of the values ​​K1 to K5, known as " EIGRP metric weights ". K1 and K3 represent bandwidth and delay, respectively. K2 represents load, and K4 and K5 represent reliability.
By default, K1 and K3 are set to 1, and K2, K4 and K5 are set to 0. As a result, only the bandwidth and delay values ​​are used in the calculation of the default composite metric. In EIGRP for IPv4 and EIGRP for IPv6 the same formula is used for the composite metric.
The method to calculate the metric (k values) and the EIGRP autonomous system number must match between EIGRP neighbors. If they do not match, the routers do not form an adjacency.
The default k values ​​can be changed with the metric weights command of the router configuration mode:
Router (config-router) # metric weights tos k1 k2 k3 k4 k5
Note : the modification of the value of metric weights is generally not recommended and exceeds the scope of this course. However, its importance is relevant to the establishment of neighborhood adjacencies. If one router modified the weights of the metric and another router did not, an adjacency is not formed.

VERIFICATION OF THE EIGRP K VALUES

The show ip protocols command is used to verify the k values. In Image 5, the result of the command for R1 is shown. Note that the k values ​​in R1 are set to the default setting.

INTERFACE VALUE ANALYSIS

The show interfaces command displays information about the interfaces, including the parameters used to calculate the EIGRP metric. The illustration shows the command show interfaces for the Serial 0/0/0 interface on R1.

• BW : interface bandwidth (in kilobits per second | kb / s = Kbit / sec ).
• DLY : interface delay (in microseconds | usec ).
• Reliability : interface reliability expressed as a fraction of 255 (255/255 is a 100% reliability), calculated as an exponential average for five minutes.

By default, EIGRP does not include its value when calculating the metric.

• Txload, Rxload : load transmitted and received through the interface expressed as a fraction of 255 (255/255 is completely saturated), calculated as an exponential average for five minutes. By default, EIGRP does not include its value when calculating the metric.

EIGRP BANDWIDTH METRIC

The bandwidth metric is a static value that some routing protocols, such as EIGRP and OSPF, use to calculate the routing metric .
The bandwidth is shown in kilobits per second (kb / s). Most serial interfaces use the default bandwidth value of 1544 kb / s or 1,544,000 b / s (1,544 Mb / s). This is the bandwidth of a T1 connection.

However, some serial interfaces use another default bandwidth value. In Image 7, the topology used in this section is shown. The types of serial interfaces and their associated bandwidths may not necessarily reflect the most frequent types of connections found in networks today.
Always verify bandwidth with the show interfaces command . (EIGRP Verification Commands Cisco)
The default bandwidth value may or may not reflect the actual physical bandwidth of the interface. If the actual bandwidth of the link differs from the default bandwidth value, the bandwidth value must be modified.
BANDWIDTH PARAMETER SETTING
On most serial links, the default bandwidth metric is 1544 kb / s. Because EIGRP and OSPF use bandwidth in default metric calculations, a correct value for bandwidth is very important for the accuracy of routing information.
Use the following interface configuration mode command to modify the bandwidth metric:
Router (config-if) # bandwidth  kilobits-bandwidth-value
Use the no bandwidth command to restore the default value.
The configuration used in the three routers to modify the bandwidth in the appropriate serial interfaces is shown below.
R1 (config) # interface s 0/0/0
R1 (config-if) # bandwidth 64
R2 (config) # interface s 0/0/0
R2 (config-if) # bandwidth 64
R2 (config-if) # exit
R2 (config) # interface s 0/0/1
R2 (config-if) # bandwidth 1024
R3 (config) # interface s 0/0/1
R3 (config-if) # bandwidth 1024

BANDWIDTH PARAMETER VERIFICATION

Use the show interfaces command to verify the new bandwidth parameters, as shown in Image. It is important to modify the bandwidth metric on both sides of the link to ensure proper routing in both directions.

Modifying the bandwidth value does not change the actual bandwidth of the link. The bandwidth command only modifies the bandwidth metric that routing protocols use, such as EIGRP and OSPF.

EIGRP DELAY METRIC

The delay is the measure of the time it takes for a package to cross the route.
The delay metric (DLY) is a static value determined based on the type of link to which the interface is connected and is expressed in microseconds.
Delay is not measured dynamically. In other words, the router does not really track the time it takes for packets to reach the destination. The delay value, like the bandwidth value, is a default value that the network administrator can modify.
When used to determine the EIGRP metric, the delay is the accumulation (sum) of all interface delays along the route (measured in tens of microseconds).

In the table in Image, the default delay values ​​for various interfaces are shown. Note that the default value is 20,000 microseconds for serial interfaces and 10 microseconds for GigabitEthernet interfaces.

Use the show interfaces command to verify the delay value on an interface, as shown in Image 10.

While an interface with multiple bandwidths may have the same default delay value, Cisco recommends not changing the delay parameter, unless the network administrator has a specific reason for doing so.

HOW TO CALCULATE THE EIGRP METRIC

While EIGRP automatically calculates the routing table metric used to choose the best route, it is important that the network administrator understand how these metrics were determined.
The figure shows the composite metric used by EIGRP. By using the default values ​​for K1 and K3, the calculation can be simplified to the slowest bandwidth (or minimum bandwidth), plus the sum of all delays.

In other words, by analyzing the bandwidth and delay values ​​for all output interfaces on the route, we can determine the EIGRP metric as follows:

• Step 1 . Determine the link with the slowest bandwidth. Use that value to calculate the bandwidth (10 000 000 / bandwidth).
• Step 2 . Determine the delay value for each exit interface on the way to the destination. Add the delay values ​​and divide by 10 (sum of the delays / 10).
• Step 3 . Add the calculated bandwidth and delay values ​​and multiply the sum by 256 to obtain the EIGRP metric.

The result of the routing table for R2 shows that the route to 192.168.1.0/24 has an EIGRP metric of 3,012,096.

2.6. EIGRP METRIC CALCULATION
In Image , the topology of the three routers is shown. This example illustrates how EIGRP determines the metric shown in the R2 routing table for the 192.168.1.0/24 network.

EIGRP BANDWIDTH

EIGRP uses the slowest bandwidth in the calculation of its metric. The slowest bandwidth can be determined by analyzing each interface between R2 and the destination network 192.168.1.0.
The Serial 0/0/1 interface on R2 has a bandwidth of 1024 kb / s. The GigabitEthernet 0/0 interface on R3 has a bandwidth of 1 000 000 kb / s. Therefore, the slowest bandwidth is 1024 kb / s and is used in the calculation of the metric.
EIGRP divides a reference bandwidth value of 10,000,000 by the value in kb / s of the interface bandwidth. As a result, higher bandwidth values ​​receive a lower metric, and lower bandwidth values ​​receive a higher metric. 10 000 000 is divided by 1024.
If the result is not an integer, the value is rounded down. In this case, 10 000 000 divided by 1024 is equal to 9765.625. Decimals (625) are discarded, and the result is 9765 for the bandwidth portion of the composite metric, as shown in Image.

EIGRP TIME DELAY

As shown in Image, the same output interfaces are used to determine the delay value.

EIGRP uses the sum of all delays to the destination. The Serial 0/0/1 interface on R2 has a delay of 20,000 microseconds. The Gigabit 0/0 interface on R3 has a delay of 10 microseconds. The sum of these delays is divided by 10.
In the example, (20,000 + 10) / 10, results in a value of 2001 for the delay portion of the composite metric.

METRIC CALCULATION

Finally, use the calculated values ​​for the bandwidth and the delay in the metric formula. The result is a metric of 3,012,096, as shown in Image.

This value matches the value shown in the routing table for R2.

EIGRP Verification Commands & Troubleshooting

EIGRP Verification Commands & Troubleshooting

This article describe how to verify the implementation of EIGRP for IPv4 in a small routed network and you will learn EIGRP Verification Commands & Troubleshooting. If you want to learn how to configure EIGRP on Cisco Router you can visit here.

show ip eigrp neighbors

Before EIGRP can send or receive updates, routers must establish adjacencies with their neighbors, and do so by exchanging EIGRP hello packets.Use the show ip eigrp neighbors command to view the neighbors table and verify that EIGRP has established an adjacency with its neighbors. For each router, you should be able to see the IPv4 address of the adjacent router and the interface that router uses to reach that neighboring EIGRP. With this topology, each router has two neighbors included in the neighbors table.

The result of the show ip eigrp neighbors command includes the following:

• Column H : lists the neighbors in the order in which they were discovered.
• Address : IPv4 address of the neighbor.
• Interface : the local interface on which this greeting packet was received.
• Hold : the current wait time. When a greeting packet is received, this value is reset to the maximum timeout for that interface and then a countdown to zero is performed. If it reaches zero, the neighbor is considered inactive.
• Uptime : the amount of time since this neighbor was added to the neighbors table.
• SRTT and RTO (average round trip time and retransmission timeout): used by RTP to manage reliable EIGRP packets.
• Q Cnt (tail count): must always be zero. If it is more than zero, there are EIGRP packets waiting to be sent.
• Seq Num (sequence number): used to track update, query and response packets.

The show ip eigrp neighbors command is very useful for checking and solving EIGRP problems.

SHOW IP PROTOCOLS COMMAND

The show ip protocols command shows the parameters and other information about the current status of any active IPv4 routing protocol process configured on the router.
The show ip protocols command shows different types of results specific to each routing protocol.

The result in Image indicates several EIGRP parameters, including the following:

1. EIGRP is an active dynamic routing protocol on R1, configured with autonomous system number 1.
2. The EIGRP router ID of R1 is 1.1.1.1.
3. The administrative distances of EIGRP on R1 are internal AD of 90 and external AD of 170 (default values).
4. By default, EIGRP does not automatically summarize networks. Subnets are included in routing updates.
5. The adjacencies of EIGRP neighbors that R1 has with other routers used to receive EIGRP routing updates.

Note : Prior to IOS 15, automatic EIGRP summarization was enabled by default.

The information in the Routing Information Sources field can help identify a router suspected of delivering defective routing information. The Routing Information Sources field lists all the EIGRP routing sources that Cisco IOS software uses to build its IPv4 routing table. For each origin, observe the following:

• IPv4 address
• Administrative distance
• Time when the last update of this origin was received

ADMINISTRATIVE DISTANCE

As shown in the figure, EIGRP has a default AD of 90 for internal routes and 170 for routes imported from an external source, such as default routes. Compared to other IGPs, EIGRP is preferred by Cisco IOS, because it has the lowest administrative distance. EIGRP has a third AD value of 5, for summary routes.

ANALYSIS OF THE IPV4 ROUTING TABLE

Another way to verify that EIGRP and other router functions are configured correctly is to examine the IPv4 routing tables with the show ip route command .
As with any dynamic routing protocol, the network administrator must verify the information in the routing table to ensure that it is completed as expected, based on the settings entered.
For this reason, it is important to have a good level of knowledge of the routing protocol configuration commands , as well as the routing protocol operations and the processes used by said protocol to arm the IP routing table.
The state of automatic summarization can make a difference in the information shown in the IPv4 routing table. If an earlier version of IOS is used, automatic summarization can be disabled using the no auto-summary command of the router configuration mode:
Router (config-router) # no auto-summary
The following figure shows the topology of R1, R2 and R3.

IPV4 ROUTING TABLE ANALYSIS EXAMPLE

In Image, the IPv4 routing table is examined by the show ip route command . EIGRP routes are indicated in the routing table with a D.
The letter "D" represents EIGRP because the protocol is based on the DUAL algorithm.

The show ip route command shows the complete routing table, including dynamically discovered remote networks, directly connected routes and static routes. For this reason, it is usually the first command used to verify convergence .
Note that on R1 routes to three remote IPv4 networks were installed in your IPv4 routing table:

• 172.16.2.0/24, received from router R2 on the Serial interface0 / 0/0
• 192.168.1.0/24, received from router R2 on the Serial interface 0/0/1
• 192.168.10.8/30, received from R2 on the Serial0 / 0/0 interface and from R3 on the Serial0 / 0/1 interface

The R1 has two routes to the 192.168.10.8/30 network, because its cost or metric to reach that network is the same when using both routers. These are known as " routes of the same cost ." R1 uses both routes to reach this network, what is known as “ load balancing ”.

In Image, the routing table of R2 is shown. Note that similar results are shown, including a route of the same cost for the 192.168.10.4/30 network.

In Image, the R3 routing table is shown. Remote networks are discovered through EIGRP, including a route of the same cost for the 172.16.3.0/30 network.

OSPF Multi-Area Configuration & Summary Routes

Cisco OSPF Multi-Area Configuration & Summary Routes

This article is a complete step by step guide for OSPF Multi-Area Configuration & Summary Routes on Cisco Router. Also topology examples of multi-area OSPF v2 and OSPF v3 configuration are explained here. Following are some OSPF related articles:

• OSPF Area 
• OSPF Authentication Types
• OSPF DR BDR Election 
• Advanced Single-Area OSPF Configurations On Cisco Router 

Configuration of OSPF Multi-Area 

The OSPF implementation can be single or multi-area. The type of OSPF implementation chosen depends on the specific requirements and the existing topology.
To implement multi-area OSPF, four steps must be followed.
Steps 1 and 2 are part of the planning process.

• Step 1. Collect network parameters and requirements : this includes determining the number of host and network devices, the IP addressing scheme (if already implemented), the size of the domain and routing tables, the risk of changes in the topology and other characteristics of the network.
• Step 2. Define the OSPF parameters : Based on the information you collected in step 1, the network administrator must determine if the preferred implementation is single-area or multi-area OSPF. If multi-area OSPF is selected, the network administrator must consider the following:
•  IP addressing plan : this governs the way in which OSPF can be implemented and how well the OSPF implementation could be scaled.
•  OSPF Areas : The division of an OSPF network into areas decreases the size of the LSDB and limits the propagation of link state updates when the topology is modified. The routers that are going to fulfill the function of ABR and ASBR must be identified, as well as those that will carry out the summarization or redistribution.
•  Network topology: this consists of links that connect the network equipment and that belong to different OSPF areas in a multi-area OSPF design. The network topology is important to determine the main and backup links.
• Step 3 . Configure the multi-area OSPF implementation according to the parameters.
• Step 4 . Verify the implementation of multi-area OSPF according to the parameters.

OSPF Configuration of Different Areas

In Figure 1, the multi-area OSPF reference topology is shown. In this example:

• R1 is an ABR because it has interfaces in area 1 and an interface in area 0.
• R2 is an internal backup router because all its interfaces are in area 0.
• R3 is an ABR because it has interfaces in area 2 and an interface in area 0.

No special commands are required to implement this OSPF network from various areas. A router simply becomes ABR when it has two network instructions in different areas .

OSPF v2 Multi-Area Configuration Example

As shown below, router ID 1.1.1.1 was assigned to R1. This example activates OSPF on the two LAN interfaces in area 1.
The serial interface is configured as part of OSPF area 0. Since R2 has interfaces connected to two different areas, it is an ABR.

R1 (config) # router ospf 10
R1 (config-router) # router-id 1.1.1.1
R1 (config-router) # network 10.1.1.1 0.0.0.0 area 1
R1 (config-router) # network 10.1.2.1 0.0.0.0 area 1
R1 (config-router) # network 192.168.10.1 0.0.0.0 area 0
R1 (config-router) # end
R1 #

Multi-area OSPF is configured on R2 and the wildcard mask of the interface network address is used:

R2 (config) # router ospf 10
R2 (config-router) # router-id 2.2.2.2
R2 (config-router) # network 192.168.10.0 0.0.0.3 area 0
R2 (config-router) # network 192.168.10.4 0.0.0.3 area 0
R2 (config-router) # network 10.2.1.0 0.0.0.255 area 0
R2 (config-router) # end
R2 #
* Apr 19 18: 11: 04.029:% ​​OSPF-5-ADJCHG: Process 10, Nbr 1.1.1.1 on 
Serial0 / 0/0 from LOADING to FULL, Loading Done
R2 #

Then multi-area OSPF is configured on R3. Here the wildcard mask 0.0.0.0 is used for all networks.

R3 (config) # router ospf 10
R3 (config-router) # router-id 3.3.3.3
R3 (config-router) # network 192.168.10.6 0.0.0.0 area 0
R3 (config-router) # network 192.168.1.1 0.0.0.0 area 2
R3 (config-router) # network 192.168.2.1 0.0.0.0 area 2
R3 (config-router) # end
Apr 19 18: 12: 55,881:% OSPF-5-ADJCHG: Process 10, Nbr 2.2.2.2 on 
Serial0 / 0/1 from LOADING to FULL, Loading Done

OSPFv3 Configuration of various areas

As in OSPFv2, the implementation of the multi-area OSPFv3 topology of Image 2 is simple.

No special commands are required. A router becomes ABR when it has two interfaces in two different areas.

OSPFv3 Multi-Area Configuration Example

For example, in the scheme below, router ID 1.1.1.1 was assigned to R1. The example also enables OSPF on the two LAN interfaces in area 1 and on the serial interface in area 0. Since R1 has interfaces connected to two different areas, it is an ABR.

R1 (config) # ipv6 router ospf 10
R1 (config-rtr) # router-id 1.1.1.1
R1 (config-rtr) # exit
R1 (config) # 
R1 (config) # interface GigabitEthernet 0/0
R1 (config-if) # ipv6 ospf 10 area 1
R1 (config-if) # 
R1 (config-if) # interface Serial0 / 0/0
R1 (config-if) # ipv6 ospf 10 area 0
R1 (config-if) # end
R1 #

For R2, we enter the OSPFv3 router configuration mode with process ID 10 and configure router ID 2.2.2.2.

R2 (config) # ipv6 router ospf 10
* Apr 24 14: 18: 10,463:% OSPFv3-4-NORTRID: Process OSPFv3-10-IPv6 
could not pick a router-id, please configure manually
R2 (config-rtr) # router-id 2.2.2.2
R2 (config-rtr) # exit

Now, OSPFv3 is configured for process ID 10 on each of the interfaces:

R2 (config) # interface g0 / 0
R2 (config-if) # ipv6 ospf 10 area 0
R2 (config-if) # interface S0 / 0/0
R2 (config-if) # ipv6 ospf 10 area 0
R2 (config-if) # interface S0 / 0/1
R2 (config-if) # ipv6 ospf 10 area 0
R2 (config-if) # end
* Apr 24 14: 18: 35.135:% OSPFv3-5-ADJCHG: Process 10, Nbr 1.1.1.1 on 
Serial0 / 0/0 from LOADING to FULL, Loading Done

For R3, we enter the OSPFv3 router configuration mode with process ID 10 and configure router ID 3.3.3.3.

R3 (config) # ipv6 router ospf 10
* Apr 24 14: 20: 42.463:% OSPFv3-4-NORTRID: Process OSPFv3-10-IPv6 
could not pick a router-id, please configure manually
R3 (config-rtr) # router-id 3.3.3.3
R3 (config-rtr) # exit

And finally, OSPFv3 is configured for process ID 10 in each of the interfaces:

R3 (config) # interface g0 / 0
R3 (config-if) # ipv6 ospf 10 area 2
R3 (config-if) # interface S0 / 0/1
R3 (config-if) # ipv6 ospf 10 area 0
R3 (config-if) # end
* Apr 24 14: 21: 01.439:% OSPFv3-5-ADJCHG: Process 10, Nbr 2.2.2.2 on 
Serial0 / 0/1 from LOADING to FULL, Loading Done
R3 #

OSPF Summary Routes

The summary helps to make the routing tables shorter. It involves consolidating several routes into a single ad, which then spreads to the backbone area.
Typically, type 1 and type 2 LSAs are generated within each area , translated into type 3 LSAs and sent to other areas. If area 1 had thirty networks to announce, thirty Type 3 LSAs would be forwarded to the backbone network. With the route summary, the ABR consolidates the 30 networks into one of two advertisements.
In Image 3, R1 consolidates all network announcements in a summary LSA.

Instead of resending LSA individually for each route in area 1, R1 forwards a summary LSA to core router C1. C1, in turn, forwards the summary LSA to R2 and R3. R2 and R3 then forward it to their respective internal routers.
The summary also helps increase network stability, because it reduces unnecessary flooding of LSA.
This situation directly affects the amount of memory, CPU and bandwidth resources used by the OSPF routing process. Without a route summary, all specific link LSAs propagate on the OSPF backbone network and beyond, which generates unnecessary network traffic and router reload.
In Image, a network link on R1 fails. R1a sends an LSA to R1. However, R1 does not propagate the update, since it has a summary route configured. The saturation of specific links outside the area with LSA does not occur.

Summarization of external and inter-area routes

In OSPF, summarization can be configured only in ABRs or ASBRs. Instead of announcing many specific networks, ABR and ASBR routers announce a summary route. The ABR summary LSA type 3 routers and the ASBR summary LSA type 5 routers.
By default, summary LSAs (type 3 LSAs) and external LSAs (type 5) do not contain summary (aggregate) routes; that is, by default, summary LSAs are not summarized.

As shown in above Images , route summarization can be configured as follows:

• Inter-area route summarization : inter-area route summarization occurs in the ABRs and is applied to routes within each area. It does not apply to external routes introduced in OSPF through redistribution.

To effectively summarize inter-area routes, network addresses must be assigned contiguously, so that these addresses can be summarized in a minimum number of summary addresses.

• Summarization of external routes : the summarization of external routes is specific to the external routes that are introduced in OSPF through the redistribution of routes. Again, it is important to ensure the contiguity of the external address ranges that are summarized.

Usually, only ASBRs summarize external routes. As shown in Image 6, ASBR R2 summarizes the external EIGRP routes in a single LSA and sends them to R1 and R3.
Note : In ASBRs, the summarization of external routes is configured using the summary-address address mask command of the router configuration mode.

 Inter-area route summarization

OSPF does not perform automatic summarization. The inter-area summarization must be manually configured in the ABRs.
Only ABRs can summarize internal routes. When summarization is enabled in an ABR, a single type 3 LSA describing the summary route is introduced into the backbone. This unique LSA summarizes several routes within the area.
A summary route is generated if at least one subnet within the area is within the range of summary addresses. The summary route metric equals the lowest cost of all subnets within the range of summary addresses.

In Image, a multi-area OSPF topology is shown. The routing tables of R1 and R3 are analyzed to see the effect of summarization.

In Image below, the routing table of R1 is shown before summarization is configured, while in next Image , the routing table of R3 is shown.

Calculation of the summary route

The figure shows that the summary of networks in a single address and mask can be done in three steps:

• Step 1 . List the networks in binary format. In the example, the two networks in area 1 (10.1.1.0/24 and 10.1.2.0/24) are indicated in binary format.
• Step 2 . Count the number of bits that match on the far left to determine the summary path mask. As highlighted, the first 22 digits of the far left match. This produces the prefix / 22 or subnet mask 255.255.252.0.
• Step 3 . Copy the matching bits and then add the zero bits to determine the summarized network address. In this example, the bits coinciding with leading zeros show us as a result the network address 10.1.0.0/22. This summary address brings together four networks: 10.1.0.0/24, 10.1.1.0/24, 10.1.2.0/24 and 10.1.3.0/24.

In the example, the summary address matches four networks although there are only two networks.

Inter-route summary configuration

In Image, to demonstrate the effect of route summarization, R1 is configured to summarize the internal routes of area 1.
To manually configure inter-route route summarization in an ABR, use the area area-id range address mask command in router configuration mode. This instructs the ABR to summarize the routes for a specific area before introducing them into another area in the form of LSA type 3 summary through the backbone.
Note : In OSPFv3, the command is identical, except for the IPv6 network address. The command syntax for OSPFv3 is area area id range prefix / prefix-length .
The two internal routes of area 1 are summarized below in an OSPF inter-area summary route on R1. The summary route 10.1.0.0/22 ​​summarizes four network addresses: from 10.1.0.0/24 to 10.1.3.0/24.
R1 (config) # router ospf 10
R1 (config-router) # area 1 range 10.1.0.0 255.255.252.0
R1 (config-router) #

Link Aggregation with EtherChannel

Link Aggregation with EtherChannel

This article describes Link Aggregation with EtherChannel on Cisco Router and the methods used to create an EtherChannel. An EtherChannel can be configured manually or can be negotiated using the Cisco aggregation protocol (PAgP), exclusive to Cisco, or the link aggregation control protocol (LACP), defined in IEEE 802.3ad.

What is Link Aggregation ?

In Image 1, traffic coming from several links (normally, 100 Mb / s or 1000 Mb / s) is added to the access switch and must be sent to the distribution switches. Due to the aggregation of traffic, there must be links with a higher bandwidth between the access and distribution switches.

It may be possible to use faster links (for example, 10 Gb / s) in the aggregate link between the access and distribution layer switches. However, adding faster links is expensive. In addition, as the speed increases in the access links, not even the fastest possible port in the aggregate link is fast enough to add the traffic coming from all the access links.
It is also possible to multiply the amount of physical links between switches to increase the overall speed of switch-to-switch communication. However, STP is enabled by default on switch devices. STP blocks redundant links to avoid routing loops.
For these reasons, the best solution is to implement an EtherChannel configuration .

Cisco EtherChannel

In the beginning, Cisco developed EtherChannel technology as a switch-to-switch LAN technique to group several Fast Ethernet or Gigabit Ethernet ports into a single logical channel . When an EtherChannel is configured, the resulting virtual interface is called the " port channel ". The physical interfaces are grouped into a port channel interface.

EtherChannel advantages

EtherChannel technology has many advantages:

• Most configuration tasks can be performed on the EtherChannel interface instead of on each individual port, which ensures configuration consistency across all links.
• The EtherChannel depends on the existing switch ports . It is not necessary to update the link to a faster and more expensive connection to have more bandwidth.
• Load balancing occurs between the links that are part of the EtherChannel itself . Depending on the hardware platform, one or more load balancing methods can be implemented. These methods include load balancing from the source MAC to the destination MAC or load balancing from the source IP to the destination IP, through physical links.
• EtherChannel creates an aggregation that looks like a single logical link . When there are several EtherChannel groups between two switches, STP can block one of the groups to avoid switching loops. When STP blocks one of the redundant links, it blocks the entire EtherChannel. This blocks all ports that belong to that EtherChannel link. Where there is only a single EtherChannel link, all physical links in the EtherChannel are active, since STP only sees a single (logical) link.
• EtherChannel provides redundancy, since the general link is seen as a single logical connection. In addition, the loss of a physical link within the channel does not create any change in the topology, so it is not necessary to recalculate the expansion tree. Assuming there is at least one physical link present, the EtherChannel remains operational, even if its overall performance decreases due to the loss of a link within the EtherChannel.

EtherChannel Operation

EtherChannel can be implemented by grouping several physical ports into one or more logical EtherChannel links.
The EtherChannel provides a full-duplex bandwidth of up to 800 Mb / s (Fast EtherChannel) or 8 Gb / s (Gigabit EtherChannel) between a switch and another switch or host. At present, each EtherChannel can consist of up to eight Ethernet ports configured in a compatible way.

Implementation Restrictions

The Cisco IOS switch can currently support six EtherChannels . However, as new IOSs develop and platforms change, some cards and platforms can support a greater number of ports within an EtherChannel link, as well as a larger amount of Gigabit EtherChannels.
The concept is the same, regardless of the speeds or the number of links that are involved. When configuring EtherChannel on the switches, consider the limits and specifications of the hardware platform.
The original purpose of EtherChannel is to increase the speed capacity in the aggregate links between the switches. However, the concept spread as EtherChannel technology gained more popularity, and now many servers also support link aggregation with EtherChannel.
EtherChannel creates a one-to-one relationship, that is, an EtherChannel link connects only two devices. An EtherChannel link can be created between two switches or between a server with EtherChannel enabled and a switch. However, traffic cannot be sent to two different switches through the same EtherChannel link .

The configuration of the individual ports that are part of the EtherChannel group must be consistent on both devices. If the physical ports on one side are configured as trunk links, the physical ports on the other side must also be configured as trunk links within the same native VLAN. In addition, all ports on each EtherChannel link must be configured as Layer 2 ports .
Each EtherChannel has a logical port channel interface, as shown in Image 3. The configuration applied to the port channel interface affects all physical interfaces that are assigned to that interface.

Port Aggregation Protocol (PAgP)

EtherChannels can be formed through negotiation with one of two protocols: PAgP or LACP . These protocols allow ports with similar characteristics to form a channel through dynamic negotiation with adjacent switches.

• It is also possible to configure a static or unconditional EtherChannel without PAgP or LACP.

PAgP (Port Aggregation Protocol) is an exclusive Cisco protocol that helps in the automatic creation of EtherChannel links . When an EtherChannel link is configured through PAgP, PAgP packets are sent between ports suitable for EtherChannel to negotiate the formation of a channel. When PAgP identifies compatible Ethernet links, it groups the links into an EtherChannel. The EtherChannel is then added to the expansion tree as a single port.
When enabled, PAgP also manages the EtherChannel. PAgP packets are sent every 30 seconds . PAgP checks the consistency of the configuration and manages the links that are added, as well as the failures between two switches. When an EtherChannel is created, it ensures that all ports have the same type of configuration.

PAgP modes

PAgP helps create the EtherChannel link by detecting the settings on each side and making sure the links are compatible, so that the EtherChannel link can be enabled when necessary. In Image 4, the modes for PAgP are shown.

• On : this mode forces the interface to provide a channel without PAgP. The interfaces configured in the on mode do not exchange PAgP packets.
• Desired PAgP : This PAgP mode places an interface in an active negotiation state in which the interface initiates negotiations with other interfaces when sending PAgP packets.
• Automatic PAgP : This PAgP mode places an interface in a passive negotiation state in which the interface responds to the PAgP packets it receives, but does not initiate PAgP negotiation.

The modes must be compatible on each side. If one side is configured in automatic mode, it is placed in a passive state, waiting for the other side to start the EtherChannel negotiation. Also, if the other side is set to automatic mode, the negotiation never starts and the EtherChannel channel is not formed. If all modes are disabled using the no command or if no mode is configured, then the EtherChannel is disabled.
On mode manually places the interface in an EtherChannel, without any negotiation. It works only if the other side is also set to on mode. If the other side is set to negotiate the parameters through PAgP, no EtherChannel is formed, since the side that is set to on mode does not negotiate.

Link Aggregation Control Protocol (LACP)

LACP (Link Aggregation Control Protocol) is part of an IEEE (802.3ad) specification that allows grouping several physical ports to form a single logical channel . LACP allows a switch to negotiate an automatic group by sending LACP packets to the peer. Performs a function similar to PAgP with Cisco EtherChannel. Because LACP is an IEEE standard, it can be used to facilitate EtherChannels in multi-vendor environments. On Cisco devices, both protocols are supported.
Note : In the beginning, LACP was defined as IEEE 802.3ad. However, LACP is now defined in the most modern IEEE 802.1AX standard for local and metropolitan area networks.

LACP modes

LACP provides the same negotiation benefits as PAgP. LACP helps create the EtherChannel link by detecting the settings on each side and ensuring they are compatible, so that the EtherChannel link can be enabled when necessary. In Image 5, the modes for LACP are shown.

•  On : this mode forces the interface to provide a channel without LACP. The interfaces configured in the on mode do not exchange LACP packets.
• LACP active : This LACP mode places a port in active negotiation state. In this state, the port starts negotiations with other ports by sending LACP packets.
• Passive LACP : This LACP mode places a port in passive negotiation state. In this state, the port responds to the LACP packets it receives, but does not initiate the negotiation of LACP packets.

As with PAgP, the modes must be compatible on both sides for the EtherChannel link to form. The on mode is repeated, as it creates the EtherChannel configuration unconditionally, without dynamic negotiation of PAgP or LACP.

How to Choose a Good Router for your Business Network

How to Choose a Good Router for your Business Network

The article describe How to Choose a Good Router that can meet the requirements of an enterprise network. If you want to about How to Choose a Good Switch for your Business Network you can visit here. The routing is needed in the distribution layer of an enterprise network. Without the routing process, packets cannot leave the local network.

Router Requirements

Routers play a very important role in the network, as they interconnect multiple sites within the business network, which provides redundant routes and connects ISPs on the Internet. Routers can also act as translators between different types of media and protocols. For example, a router can accept packets from an Ethernet network and re-encapsulate them for transport over a serial network.
Routers use the network part of the destination IP address to route packets to the correct destination. They select an alternative route if the link stops working or if there is a lot of traffic. All hosts on a local network specify the IP address of the local router interface in the IP configuration. This router interface is the default gateway .
Routers also fulfill other useful functions:

• They offer broadcast contention
• Connect remote locations
• Logically group users according to the application or department
• Provide enhanced security
  

With the company and the ISP, the ability to route efficiently and recover a network link failure is essential for the delivery of packets to their destination.

Cisco routers

As the network grows, it is important to select the appropriate routers to meet the requirements. As shown in the illustration, there are three categories of routers:

Branch Routers

Branch routers optimize branch services on a single platform, while providing an optimal application experience across all branch and WAN infrastructures. Maximizing service availability at the branch requires that the network be designed to be active every day, 24 hours a day (365 days a year).
High-availability branch networks must ensure rapid recovery of typical failures and, at the same time, minimize or eliminate the impact on the service and provide simple network configuration and administration.

Network perimeter routers

Network perimeter routers allow that perimeter to provide reliable high-performance, high-security services that link campus, data center and branch networks. Customers expect a high quality media experience and more types of content than ever. Customers seek interactivity, personalization, mobility and control for all that content. They also want to be able to access the content at any time and place of their choice, and with any device, either from home, from the office or when they go from one place to another. Network perimeter routers must provide improved quality of service and uninterrupted video and mobile technology capabilities.

Routers of service providers

These routers differentiate the service portfolio and increase profits by providing end-to-end scalable solutions and services that recognize subscribers. Operators must optimize operations, reduce costs and improve scalability and flexibility in order to provide state-of-the-art Internet experiences across all devices and locations.
These systems are designed to simplify and improve the operation and implementation of service delivery networks.

Router hardware

In addition, routers come in many form factors, as shown in the illustration. Network administrators in a business environment must be able to support a variety of routers, from a small desktop router to a rack-mounted or a blade model.

Routers can also be categorized as fixed or modular configuration . With the fixed configuration, the desired router interfaces are incorporated. Modular routers have several slots that allow the network administrator to modify the interfaces on the router. For example, the Cisco 1841 router has two built-in Fast Ethernet RJ-45 interfaces and two slots that can accommodate various network interface modules. Routers have a variety of different interfaces, such as Fast and Gigabit Ethernet, Serial and fiber optic.
In summary, the network designer must specify a router of the appropriate category, be it a branch router, a network perimeter router or a service provider router. It is also important to implement the appropriate switch type for a set of specific switch requirements, features and specifications and the expected traffic flow.