Six major points of Routers

There are six major points to remember or keep in mind when working with routers or layer 3 devices. You should probably commit these to memory.

Here are the six major points

1. Routers, by default, will not forward any broadcast or multi-task packets.
2. Routers use the logical address in the network layer header to determine the next hop router to forward the packet to.
3. Routers can use access list, created by an administrator to control security on the types of packets that are allowed to enter or exit an interface.
4. Routers can provide layer 2 bridging functions if needed, and can simultaneously route through the same interface.
5. Routers provide connections between virtual LANS (VLANS).
6. Routers provide Quality of Service (QoS) for specific types of network traffic.

A closer look at the Network Layer

The network layer manages devices addressing, tracks location of devices on the network, and determines the best way to move data, which means the Network layer must transport traffic between devices that aren’t locally attached.

Lets take a closer look at it’s function

1. Checks a packet when it is first received on a router interface.
2. If the packet isn’t destined for that particular router, it will look up the destination network address in the routing table.
3. Once the router chooses an exit interface, the packet will be sent to that interface to be framed and sent out on the local network.
4. If the router is unable to locate an interface; the packets will be dropped.

Key Terms

Router – a router is a network layer device (layer 3 device) and provides the routing services within an internetwork.

Data packets – are used at the network layer to transport data through the internetwork.

Routed Protocols – are used to support data traffic.

Route Update Packets – are used to update neighboring routers about the networks connected to all routers within the internetwork.

Routing Protocols – are used to send out route updates packets.

Network Address

1. A protocol specific network address.
2. A router must maintain a routing table for individual routing protocols because each routing protocols keep track of a network with a different addressing scheme (ex. IP, IPv6, and IPX).

Interface – is the exit interface a packet will take when destined for a specific network.

Metric – is the distance to the remote network.

Visual of Windowing

 

Windowing Diagram

Window size of 1 = sending machine waits for an acknowledgement for each data segment it transmit before transmitting another segment.

Window size of 3 = allowed to transmit three data segments before an acknowledgement is actually received.

Types of flow control and a closer look at Windowing

 

The three types of flow control consists of:

1. buffering
2. windowing
3. congestion avoidance

A closer look at what windowing is and it's function at the transport layer

Windowing

• Windowing is the quantity of data segments (measured in bytes) that the transmitting machine is allowed to send without receiving an acknowledgement for them.
• In other words, it's the break of time in between data segments of before and after.
• Windowing is used to control the amount of outstanding, unacknowledged data segments.

Note: if hosts fails to receive all segments that it should have acknowledged, the host can improve the communication session by decreasing window size.

Connection-oriented Communication

Note: Recall that connection-oriented communications takes place in conjunction with flow control. These communication sessions, in combination of the protocols involved, provide for reliable data transports at the transport layer.

Diagram:

This is what we call the "Three Way Handshake"

1. The 1st "connection agreement" segment is a request for synchronization.
2. At the 2nd and 3rd connection agreement, segments acknowledge the requests and establishes connection parameters (the rules) between hosts. These segments request that the receiver sequencing is synchronized here as well, resulting in a bidirectional connection.
3. The final segment is also an acknowledgement. It notifies the destination host that the connection has been established – Data transfer can now begin.

How to identify a connection-oriented communication when you see one

1. It has a virtual circuit set up. (i.e.. 3 way handshake)
2. Use sequencing
3. Use acknowledgements
4. Use flow control

Question: What happens when a device receives a flooding of datagram's (packets) too quickly for it to process?

Answer: They store them in a memory section called a buffer.