Tag - Bandwidth

Routing Protocol Characteristics

Packets originating from a nonrouting device destined for another network are sent to their default gateway (Layer 3 device on segment). The router consults its routing table to dvcer-mine if the destination network can be reached. If not, the ICMP Destination Unreachable message is sent to the source. If so, packet is forwarded out interface associated with the des­tination network in routing table.

Routing Sources

Default Administrative Distances

Maximum Hop Counts
Routed Source
Default Distance
Static route
EIGRP (internal)
RIPv1 and v2
EIGRP (external)

Static and Default Routes

Static routes are useful in stub networks in which we want to control the routing behavior by manually configuring destination networks into the routing table:

Router(config)#ip route

A floating static route can be configured when redundant connections exist and you want to use the redundant link if the primary fails. This is configured by adding a higher administra­tive distance at the end of a static route:

Router(config)#ip route 2

A default route is a gateway of last resort for a router when there isn’t a specific match for an IP destination network in the routing table (such as packets destined for the Internet):

Router(config)#ip route 0/0

With routing protocols, you can specify a default network, which is a network in the routingtable that routing devices consider to be the gateway of last resort. Using their routing proto­cols, they dvcermine the best path to the default network:

Router(config)#ip default-network

Dynamic Routing Protocols

In complex networks with multiple pathways to destinations, dynamic routing protocols enable routers to advertise their networks to each other and dynamically react to topology changes.

Routing protocols dvcermine the best path based on the lowest metric.

 Routing Metrics

Because one of the core responsibilities of routing protocols is to build routing tables to dvcermineoptimal routing paths, we need to have some means of measuring which routes are preferred whenthere are multiple pathways to a destination. Routing protocols use some measure of metrics toidentify which routes are optimal to reach a destination network. The lowest cumulative metric toa destination is the preferred path and the one that ultimately enters the routing table. Different routing protocols use one or several of the following metrics to calculate the best path.

Routing Metrics

Hop count
The number of routing devices that the packet must travel to reach a destination network
The cumulative bandwidth of the links to the destination in kilobits per second
The length of time (measured in microseconds) a packet takes from source to destination
The consistency of the links and paths toward the destination based on error rates of the interfaces
The cumulative amount of congestion or saturation of the links toward the destination
The maximum frame size that is allowed to traverse the links to the destination
Cost   An arbitrary number typically based on the link’s bandwidth

Interior and Exterior Gateway Routing Protocols

  1. Interior gateway routing protocols: IG routing protocols advertise networks and metrics within an autonomous system.
  2. Exterior gateway routing protocols: EG routing protocols advertise networks in between autonomous systems.

Classful and Classless Routing Updates

  1. Classful routing: The routing updates only contain the classful networks without any subnet mask. Summarization is automatically done when a router advertises a network out an interface that is not within the same major subnet. Classful routing protocols must have a FLSM design and do not operate correctly with discontiguous networks.
  2. Classless routing: The routing updates can contain subnetted networks because the subnet mask is advertised in the updates. Route summarization can be manually config­ured at any bit boundary. Classless routing protocols support VLSM designs and dis­contiguous networks.

all routing protocol

Routing Protocol Classes

  1. Distance vector: The entire routing table is periodically sent to directly connected neighbors regardless of a topology change. These routing protocols manipulate the routing table updates before sending that information to their neighbors and are slow to converge when a topology change occurs.
  2. Link state: All possible link states are stored in an independent topology table in which the best routes are calculated and put into the routing table. The topology table is ini­tially synchronized with discovered neighbors followed by frequent hello messages. These routing protocols are faster to converge than distance vector routing protocols.
  3. Hybrid: By using the best characteristics from link-state and routing protocols, these advanced routing protocols efficiently and quickly build their routing information and converge when topology changes occur.


Redistribution is the method of configuring routing protocols to advertise networks from other routing protocols:

  1. One-way redistribution: Networks from an edge protocol are injected into a more robust core routing protocol, but not the other way around. This method is the safest way to perform redistribution.
  2. Two-way redistribution: Networks from each routing protocol are injected into the other. This is the least preferred method because it is possible that suboptimal routing or routing loops might occur because of the network design or the difference in con­vergence times when a topology change occurs.

Distance Vector Routing Loop Mitigation

Distance vector routing protocols contain several measures to prevent routing loops:

Maximum hop counts: To ensure that routing metrics do not increment until infinity in a routing loop, distance vector routing protocols have a maximum hop count.

Distance Vector/Link State/Hybrid
Maximum Hop Count
RI Pv1
Distance vector
RI Pv2
Distance vector
Link state

Split horizon:

Subnets learned from neighbor routers should not be sent back out the same interface from which the original update came.

Route poisoning with poison reverse:

When a route to a subnet fails, the subnet is advertised with an infinite metric. Routers receiving the poisoned route override the split horizon rule and send a poison reverse back to the source.

Hold-down timers:

The amount of time a router ignores any information about an alternative route with a higher metric to a poisoned subnet.

Flash updates/triggered updates:

When a route fails, the router immediately shoots out an update as opposed to waiting for a normal update interval.

Cabling, Lines, and Services


The total amount of information that can traverse a communications medium measured in millions of bits per second. Bandwidth is helpful for network per¬formance analysis. Also, availability is increasing but limited.


An electrical or magnetic field that is a result of one communications signal that can affect the signal in a nearby circuit.

Near-end Crosstalk (NEXT)

Crosstalk measured at the transmitting end of a cable.

Far-end Crosstalk (FEXT)

Crosstalk measured at the far end of the cable from where the transmission was sent.

Unshielded twisted-pair (UTP) cables are vulnerable to Electromagnetic Interference (EMI) and use an RJ-45 connector. Fiber-optic cables are not susceptible to EMI.

data cabling work

Use a straight-through cable to connect the following devices:

.      Terminated directly into a dedicated hub or switch port

.      From a PC to a switch or a hub

.      From a router to a switch or a hub

Use a cross-over cable to connect the following devices:

.      From switch to switch

.      From router to router

.      From PC to PC

.      From a PC to a router

.      From a hub to a hub

.      From a hub to a switch

Spread Spectrum Wireless LANs allow for high-speed transmissions over short distances.

Wireless Fidelity (Wi-Fi) is defined by IEEE 802.11.

Standard Speed Media Type Connector Used
10BASE-2 10Mbps RG-58 coaxial BNC
10BASE-5 10Mbps RG-58 coaxial BNC
1 0BASE-T 10Mbps Category 3, 4, or 5 UTP or STP RJ-45
1 0BASE-FL 10Mbps Fiber-optic SC or ST
TABLE FF.10 Comparison of Fast Ethernet 802.3u Characteristics
Standard Speed Media Type Connector Used
1 00BASE-T4 100Mbps Category 3, 4, or 5 UTP or STP RJ-45
1 00 BASE-TX 100Mbps Category 5 UTP or STP RJ-45
100BASE-FX 100Mbps Fiber-optic SC or ST
Standard Speed Media Type Connector Used
1 000BASE-T or 1 000BASE-TX 1000Mbps or 1Gbps Category 5 UTP or higher RJ-45
TABLE FF.12 Comparison of Gigabit Ethernet 802.3z Characteristics
Standard Speed Media Type Connector Used
1 000BASE-CX 1000Mbps or 1Gbps Shielded copper wire Nine-pin shielded connector
1 000BASE-SX 1000Mbps or 1Gbps MM fiber-optic SC or ST
1 000BASE-LX 1000Mbps or 1Gbps MM or SM fiber-optic SC or ST

What is Frame Relay

Frame Relay is a WAN technology, it is used for communication. Frame relay is an industry standard, shared across, best effort, switch Data Link layer encapsulation that services multiple virtual circuits and protocols between connected mechanisms.


Frame Relay Terminologies:

1. Local-Access-Rate: 

Form 64- 2MB. It is a required bandwidth

2. Virtual Circuit

It is used for connection to a station

Types of VC:

  • PVC (Permanent Virtual Circuit)

           It is a dedicated line, which is used permanently

  • SVC (Switch Virtual Circuit)

           It is used when data is flowing.

3. Committed information Rate:

      Frame relay works by providing a portion of dedicated bandwidth to each user, and it also allows the user to exceed their guaranteed bandwidth if resources on the Telco network happen to be available. Frame Relay providers allow customers to buy a lower amount of bandwidth than what they really use.

 4. Data Link Connection Identifier:

It is a value which is used in virtual circuit.

5. Local Management Interface:

It is used to establish connection between Frame Relay switch and client router.

 Configuration of a Router in a Frame Relay environment:

  • Router(config)# int so
  • Router(config_if)# ip address
  • Router(cofnig_if)# encapsulation frame-relay
  • Router(config_if)# frame-relay lmi-type ansi
  • Router(config_if)# no shut
  • Router(config_if)# exit

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