Google Adsense CTR

All using Google AdSense specially the newbie should keep eye on (CTR) Cut through rate as it can go higher by just clicking at Google adds by you or by someone else.

Clickthrough rate is a percentage of the clicks your AdSense ads receive versus the number of page impressions your blog or website receives. CTR between 0.5% to 5.0 is considered as normal. If the CTR goes high than that, it triggers an alert to Google to check your account. And if it appears continuously high, then your account run the risk of getting banned.

You should enhance you site with putting more pages/blogs and content, so that can get more lot of hits by natual visitors. You will also get visitors referring from Google Search engine once you have enhanced your site. This will increase natural page impressions, which will than translate into natural clickthrough of your AdSense ads. This is one thing which you should work hard to achieve. Once your page impressions reach a certain level, it is much harder for the clickthrough rate to appear abnormal.

Virtual Router Redundancy Protocol

Virtual Router Redundancy Protocol (VRRP) is so similar to HSRP that it can be basically thought of as the standards-based version of the protocol. Like HSRP, it lacks the inherent load-balancing capabilities that GLBP provides. Although there are many customization commands, the command to enable the protocol is just like that of the other redundancy protocols in structure:

vrrp group ip ip-address [secondary]

Gateway Load Balancing Protocol

Gateway Load Balancing Protocol (GLBP) takes HSRP even further. Instead of just providing backup for a failed router, it can also handle the load balancing between multiple routers. GLBP provides this functionality using a single virtual IP address and multiple virtual MAC addresses. Workstations are configured with the same virtual IP address, and all routers in the virtual router group participate in forwarding packets. GLBP members communicate with each other using hello messages sent every three seconds to the multicast address 224.0.0.102.

Members of a GLBP group elect one gateway to be the active virtual gateway (AVG) for that group. It is the job of other group members to back up for the AVG in the event that the AVG fails. The AVG assigns a virtual MAC address to each member of the GLBP group. The AVG is responsible for answering ARP requests for the virtual IP address. Load sharing is achieved by the AVG replying to the ARP requests with different virtual MAC addresses that the group members will respond to. Although you can use many optional commands with GLBP, the primary command to enable GLBP is as follows:

glbp group ip [ip-address [secondary]]

Hot Standby Router Protocol

The Hot Standby Router Protocol (HSRP) provides high network availability by routing IP traffic from hosts without relying on the availability of any single router. HSRP is used in a group of routers to select an active router and a standby router. The active router is the router of choice for routing packets; a standby router is a router that takes over the routing duties when an active router fails, or when other preset conditions are met.

HSRP is useful for hosts that do not support a router discovery protocol (such as Internet Control Message Protocol [ICMP] Router Discovery Protocol [IRDP]) and that cannot switch to a new router when their selected router reloads or loses power.
When the HSRP is configured on a network segment, it provides a virtual MAC address and an IP address that is shared among a group of routers running HSRP. The address of this HSRP group is referred to as the virtual IP address. One of these devices is selected by the protocol to be the active router.

HSRP detects when the designated active router fails, at which point a selected standby router assumes control of the MAC and IP addresses of the Hot Standby group. A new standby router is also selected at that time. Devices that are running HSRP send and receive multicast User Datagram Protocol (UDP)-based hello packets to detect router failure and to designate active and standby routers. Below is an example of an HSRP topology.

Devices that are running HSRP send and receive multicast UDP-based hello packets to detect router failure and to designate active and standby routers. You can configure multiple Hot Standby groups on an interface, thereby making fuller use of redundant routers and load sharing. To do so, specify a group number for each Hot Standby command you configure for the interface.

To enable the HSRP on an interface, we can use the following command:
Router(config-if)# standby [group-number] ip [ip-address
[secondary]]

To configure the time between hello packets and the hold time before other routers declare the active router to be down, use the following command:

Router(config-if)# standby [group-number] timers [msec]
hellotime [msec] holdtime

To set the Hot Standby priority used in choosing the active router. The priority value range is from 1 to 255, where 1 denotes the lowest priority and 255 denotes the highest priority:

Router(config-if)# standby [group-number] priority priority

Internet Control Message Protocol

Internet Control Message Protocol (ICMP) assists the operation of the IP network by delivering messages about the network’s functionality—or lack thereof. ICMP includes functions for the following:
...Communicating network errors—Such as host or network unreachable.
...Announcing network congestion—An example is the ICMP Source Quench messages used to cause a sender to slow down transmission because of a router buffering too many packets.
...Provide troubleshooting tools—The Echo function is used by the ping utility to test connectivity between two systems.
...Communicate timeouts in the network—If a packet’s TTL reaches 0, an ICMP message can be sent announcing this fact.

ICMP protocol unreachable messages

If the Cisco device receives a nonbroadcast packet destined for itself that uses an unknown protocol, it sends an ICMP protocol unreachable message back to the source. Similarly, if the device receives a packet that it is unable to deliver to the ultimate destination because it knows of no route to the destination address, it sends an ICMP host unreachable message to the source. This feature is enabled by default. To enable it if it’s disabled, use the following command:

Router(config-if)# ip unreachables


ICMP redirects
If the router resends a packet through the same interface on which it was received, the Cisco IOS Software sends an ICMP redirect message to the originator of the packet, telling the originator that the router is on a subnet directly connected to the receiving device and that it must forward the packet to another system on the same subnet. To enable the sending of ICMP redirect messages if this feature was disabled, use the following command:

Router(config-if)# ip redirects

Address Resolution Protocol

Address Resolution Protocol (ARP) is used to resolve IP addresses to MAC addresses in an Ethernet network. A host wanting to obtain a physical address broadcasts an ARP request onto the TCP/IP network. The host on the network that has the IP address in the request then replies with its physical hardware address. When a MAC address is determined, the IP address association is stored in an ARP cache for rapid retrieval. Then the IP datagram is encapsulated in a link-layer frame and sent over the network. Encapsulation of IP datagrams and ARP requests and replies on IEEE 802 networks other than Ethernet is specified by the Subnetwork Access Protocol (SNAP). Reverse Address Resolution Protocol (RARP) works the same way as ARP, except that the RARP request packet requests an IP address rather than a MAC address. Use of RARP requires a RARP server on the same network segment as the router interface. RARP often is used by diskless nodes that do not know their IP addresses when they boot. The Cisco IOS Software attempts to use RARP if it does not know the IP address of an interface at startup. Also, Cisco routers can act as RARP servers by responding to RARP requests that they can answer.

History of Tag Switching to MPLS

Reference:- MPLS Fundamentals
http://www.ciscopress.com/bookstore/product.asp?isbn=1587051974

Cisco Systems started off with putting labels on top of IP packets in what was then called tag switching. The first implementation was released in Cisco IOS 11.1(17)CT in 1998. A tag was the name for what is now known as a label. This implementation could assign tags to networks from the routing table and put those tags on top of the packet that was destined for that network. Tag switching built a Tag Forwarding Information Base (TFIB), which is, in essence, a table that stores input-to-output label mappings. Each tag-switching router had to match the tag on the incoming packet, swap it with the outgoing tag, and forward the packet.

Later on, the IETF standardized tag switching into MPLS. The IETF released the first RFC on MPLS—RFC 2547, “BGP/MPLS VPNs”—in 1999. The result of this was that much of the terminology changed. Below table shows an overview of the old and new terminology.



Old Terminology --- New Terminology
Tag switching --- MPLS
Tag --- Label
TDP (Tag Distribution Protocol) --- LDP (Label Distribution Protocol)
TFIB (tag forwarding information base) --- LFIB (label forwarding information base)
TSR (tag switching router) --- LSR (label switching router)
TSC (tag switch controller) --- LSC (label switch controller)
TSP (tag switched path) --- LSP (label switched path)

Redistribution

Route redistribution might be required in an internetwork because multiple routing protocols must coexist in the first place. Multiple routing protocols might be a necessity because of an interim period during conversion from one to another, application-specific protocol requirements, political reasons, or a lack of multivendor interoperability.

A major issue with redistribution is the seed metric to be used when the routes enter the new routing protocol. Normally, the seed metric is generated from the originating interface. For example, EIGRP would use the bandwidth and delay of the originating interface to seed the metric. With redistributed routes, however, these routes are not connected to the router. Some routing protocols feature a default seed metric for redistribution, whereas others do not. Here is a list of the defaults for the various protocols. Note that Infinity indicates a seed metric must be configured; otherwise, the route will not be used by the receiving protocol.

Protocol ------ Default Seed Metric
OSPF ------ 20; except BGP, which is 1
IS-IS ------ 0
RIP ------ Infinity
IGRP/EIGRP ------ Infinity

Link-state and distance vector protocols

Distance vector
1. Examples: Routing Information Protocol Version 1 (RIPv1), RIPv2, Interior Gateway Routing Protocol (IGRP).
2. Features periodic transmission of entire routing tables to directly connected neighbors
3. Mathematically compares routes using some measurement of distance Features hop-count limitation

Link State
1. Examples: Open Shortest Path First (OSPF), Intermediate Systemto-Intermediate System (IS-IS).
2. Sends local connection information to all nodes in the internetwork.
3. Forms adjacencies with neighboring routers that speak the same protocol; sends local link information to these devices.
4. Note that although this is flooding of information to all nodes, the router is sending only the portion of information that deals with the state of its own links.
5. Each router constructs its own complete “picture” or “map” of the network from all of the information received.

Hybrid
1. Example: Enhanced Interior Gateway Routing Protocol (EIGRP)
2. Features properties of both distance vector and link-state routing protocols

Path vector protocol
1. Example: Border Gateway Protocol (BGP).
2. Path vector protocols are a subset of distance vector protocols; BGP uses “path vectors” or a list of all the autonomous systems a prefix has crossed to make metric decisions and to ensure a loopfree environment.
3. In addition to the autonomous system path list, an administrator can use many other factors to affect the forwarding or receipt of traffic using BGP

IPv4 addresses

IPv4 addresses consist of 32 bits. These 32 bits are divided into four sections of 8 bits, each called an octet. Addresses are typically represented in dotted-decimal notation. For example: 10.200.34.201
Subnet masks identify which portion of the address identifies a particular network and which portion identifies a host on the network.

The address classes defined for public and private networks consist of the following subnet masks:
Class A 255.0.0.0 (8 bits)
Class B 255.255.0.0 (16 bits)
Class C 255.255.255.0 (24 bits)

Class A addresses begin with 0 and have a first octet in decimal of 1 to 127.
Class B addresses begin with 10 and range from 128 to 191.
Class C addresses begin with 110 and range from 192 to 223.

Class D and Class E addresses also are defined. The Class D address space has the first 4 bits set to 1110 and has a first octet of 224 to 247.These addresses are used for IP multicast.

Class E addresses have the first 4 bits set to 1111 and have a first octet of 248 to 255. These addresses are reserved for experimental use.

RIB & FIB

The routing and forwarding architecture in Cisco routers and multilayer switches used to be a centralized, cache-based system that combined what is called a control plane and a data plane. The control plane refers to the resources and technologies used to create and maintain the routing table. The data plane refers to those resources and technologies needed to actually move data from the ingress port to the egress port on the device. This centralized architecture has migrated so that the two planes can be separated to enhance scalability and availability in the routing environment.

The separation of routing and forwarding tasks has created the Routing Information Base (RIB) and the Forwarding Information Base (FIB). The RIB operates in software, and the control plane resources take the best routes from the RIB and place them in the FIB. The FIB resides in much faster hardware resources. The Cisco implementation of this enhanced routing and forwarding architecture is called Cisco Express Forwarding (CEF).

Classful and classless routing protocols

Classful routing protocols are considered legacy and do not include subnet mask information with routing updates. Examples of classful routing protocols are RIPv1 and IGRP. Because subnet mask information is not included in updates, consistency of the mask is assumed throughout the network. Classful routing protocols also feature automatic summarization of routing updates when sent across a major classful network boundary. For example, the 10.16.0.0/16 network would be advertised as 10.0.0.0/8 when sent into a 172.16.0.0 domain.

BGP and EIGRP are not classful routing protocols, both engage in automatic summarization behavior by default, and in that sense they act classful. The no auto-summary command is used to disable this behavior. Classful routing protocols feature a fixed-length subnet mask (FLSM) as a result of their inherent limitations. The FLSM leads to inefficient use of addresses and limits the network’s overall routing efficiency. By default, classful routing protocols discard traffic bound for any unknown subnet of the major classful network. For example, if your classful routing protocol receives traffic destined for 10.16.0.0 and it knows of only the 10.8.0.0 and 10.4.0.0 subnets in its routing table, it discards the traffic—even if a default route is present! The ip classless command was introduced to change this behavior. The ip classless command allows the protocol to use the default route in this case. This command is on by default with Cisco IOS Release 12.0 and later routers.

As a classic example of a classless routing protocol, OSPF carries subnet mask information in updates. Wireless LAN Services Module (WLSM) is possible with such protocols.

Split horizon

Split horizon is a technique used by routing protocols to help prevent routing loops. The split-horizon rule states that an interface will not send routing information out an interface from which the routing information was originally received. Split horizon can cause problems in some topologies, such as hub-and-spoke Frame Relay configurations.

Administrative distance

If a router learns of a network from multiple sources (routing protocols or static configurations), it uses the administrative distance value to determine which route to install in the routing (forwarding) table. The default administrative distance values are listed here.

Source Administrative Distance

Connected interface - 0
Static route - 1
EIGRP summary route - 5
External BGP - 20
Internal EIGRP - 90
IGRP - 100
OSPF - 110
IS-IS - 115
RIP - 120
Exterior Gateway Protocol - 140
On-Demand Routing - 160
External EIGRP - 170
Internal BGP - 200
Unknown - 255

Administrators can create static routes that “float.” A floating static route means the administrator increases the administrative distance of the static route to be greater than the administrative distance of the dynamic routing protocol in use. This means the static route is relied on only when the dynamic route does not exist.

Routing decision criteria

Routers must determine the best route to send traffic on toward itsdestination. This is accomplished as follows (note that the order of operations is critical and fixed):

1. Valid next-hop IP address—when updates are received, the router first verifies that the next-hop IP address to reach the potential destination is valid.

2. Metric—the router then examines the metrics for the various routes that might exist from a particular protocol. For example, if OSPF has several routes to the destination, the router tries to install the route with the best metric (in this case, cost) into the routing table.

3. Administrative distance—if multiple routing protocols are running on the device, and multiple protocols are all presenting routes to the destination with valid next hops, the router examines administrative distance. The route sourced from the lowest administrative distance protocol or mechanism is installed in the routing table.

4. Prefix—the router examines the route’s prefix length. If no exact match exists in the routing table, the route is installed. Note that this might cause the routing table to be filled with the following entries: EIGRP 172.16.2.0/24 and RIP 172.16.2.0/19.

The subject of prefix length and the routing table, remember that when a router is looking for a match in the IP routing table for the destination address, it always looks for the longest possible prefix match. For example, if the routing table contains entries of 10.0.0.0/8, 10.2.0.0/16, and 10.2.1.0/24, and your traffic is destined for 10.2.1.0/24, the longest match prefix is selected.

Summarization

Summarization is the process in which the administrator collapses many routes with a long mask to form another route with a shorter mask. Route summarization reduces the size of routing tables and makes routing function more efficiently. Route summarization also helps make networks more stable by reducing the number of updates that are sent when subnets change state. Route summarization makes classless interdomain routing (CIDR) possible. Variable-length subnet masking (VLSM) promotes the use of route summarization. Some dynamic routing protocols engage in route summarization automatically for changes in a major classful network, whereas others do not.

For any routing protocol within the scope of the CCIE written exam, an administrator can disable any automatic summarization that might be occurring and configure “manual” summarization. To engage in route summarization, find all the leftmost bits that are in common and create a mask that encompasses them. An example follows:-

The following routes exist in the routing table—all routes use a 24-bit mask:

10.108.48.0 = 00001010 01101100 00110000 00000000
10.108.49.0 = 00001010 01101100 00110001 00000000
10.108.50.0 = 00001010 01101100 00110010 00000000
10.108.51.0 = 00001010 01101100 00110011 00000000
10.108.52.0 = 00001010 01101100 00110100 00000000
10.108.53.0 = 00001010 01101100 00110101 00000000
10.108.54.0 = 00001010 01101100 00110110 00000000
10.108.55.0 = 00001010 01101100 00110111 00000000

Notice that the first 21 bits of the subnetwork IDs are all common. These can be masked off. You can use the single route entry for all these subnetworks as follows:

10.108.48.0/21

EIGRP Authentication

By default, no authentication is used for any routing protocol. Some protocols, such as RIPv2, IS-IS, and OSPF, can be configured to do simple password authentication between neighboring routers. In this type of authentication, a clear-text password is used. EIGRP does not support simple authentication. However, it can be configured to authenticate each packet exchanged, using an MD5 hash. This is more secure than clear text, as only the message digest is exchanged, not the password.

EIGRP authenticates each of its packets by including the hash in eachone. This helps verify the source of each routing update.

To configure EIGRP authentication, follow these steps:

Step 1. Configure a key chain to group the keys.

Step 2. Configure a key within that key chain.

Step 3. Configure the password or authentication string for thatkey. Repeat Steps 2 and 3 to add more keys if desired.

Step 4. Optionally configure a lifetime for the keys within that key chain. If you do this, be sure that the time is synchronized between the two routers.

Step 5. Enable authentication and assign a key chain to an interface.

Step 6. Designate MD5 as the type of authentication.

EIGRP Bandwidth Configuration

Enhanced Interior Gateway Routing Protocol (EIGRP) is a Cisco proprietary classless routing protocol that uses a complex metric based on bandwidth and delay.

By default, EIGRP limits itself to bursting to half the link bandwidth.

This limit is configurable per interface using the ip bandwidth-percent command. The following example assumes EIGRP AS 7 and limits

EIGRP to one quarter of the link bandwidth:

Router(config)#int s0/0/0

Router(config-if)#ip bandwidth-percent eigrp 7 25

The real issue with WAN links is that the router assumes that each link has 1544 kbps bandwidth. If interface Serial0/0/0 is attached to a 128k fractional T1, EIGRP assumes it can burst to 768k and could overwhelm the line. This is rectified by correctly identifying link bandwidth.

Router (config)#int serial 0/0/0

Router (config-if)#bandwidth 128

The following shows a situation in which these techniques can be combined.

In this example, R1 has a 256 kbps connection to the Frame Relay network and two permanent virtual circuits (PVCs) with committed information rates (CIR) of 128 Kpbs and 64 Kbps. EIGRP divides the interface bandwidth evenly between the number of neighbors on that interface. What value should be used for the interface bandwidth in this case? The usual suggestion is to use the CIR, but the two PVCs have different CIRs. You could use the bandwidth-percent command to allow SNMP reporting of the true bandwidth value, while adjusting the interface burst rate to 25 percent, or 64 kbps.

R1(config)#int serial 0/0/0

R1 (config-if)#bandwidth 256

R1 (config-if)#ip bandwidth-percent eigrp 7 25

A better solution is to use sub-interfaces and identify bandwidth separately.

In the following example, s0/0/0.1 bursts to 64 k, and s0/0/0.2 bursts to 32 k, using EIGRP’s default value of half the bandwidth.

R1(config)#int serial 0/0/0.1

R1 (config-if)#bandwidth 128

!

R1(config)#int serial 0/0/0.2

R1 (config-if)#bandwidth 64

In cases where the hub interface bandwidth is oversubscribed, it may be necessary to set bandwidth for each sub-interface arbitrarily low, and then specify an EIGRP bandwidth percent value over 100 in order to allow EIGRP to use half the PVC bandwidth.