What is uplinkfast?

 

Spanning tree UplinkFast is a Cisco-specific enhancement to the Spanning Tree Protocol (STP). It's designed to improve the convergence time in the event of a direct link failure, especially in access-layer switches with redundant links to the distribution layer.

Here's how it works:

Quick Recovery: When the primary uplink fails, UplinkFast allows the switch to quickly transition the blocked port to forwarding, bypassing the usual listening and learning states.

Preventing Loops: It modifies the Bridge Protocol Data Units (BPDUs) to prevent loops by increasing the path cost and setting the local bridge priority.

Immediate Restoration: This feature ensures that connectivity is restored almost immediately, reducing downtime significantly.

UplinkFast is typically used in access-layer switches and should be deployed carefully to avoid potential issues with MAC address tables. 

Key points:-

• legacy/cisco proprietary feature
• uplinkfast is for speeding convergence when a direct link to an upstream switch fails. 
• when uplinkfast is enabled, it is enabled for the entire switch and all VLANs.

• this feature is not allowed on the root bridge switch. 
• when uplinkfast is configured, the bridge priority is changed to 49,152 so that this switch will not be selected as root.

We have three switches. Switch-1 is our Root, and two others are non-root switches. Switch-1's ports are Desg FWD because it's a root. Switch-2's gig0/0 port is a Root FWD, and gig 0/1 is a Desg FWD. Switch-3's gig0/0 is Root FWD, and gig1/0 is an Altn BLK state port. so that's what we have, now switch-3 uses gig0/0 to reach the root bridge, what if the port shuts down? how long does it take for switch-3 to make a transition? let's see. 

switch-1#show spanning-tree vlan 1
VLAN0001
  Spanning tree enabled protocol ieee
  Root ID    Priority    24577
             Address     0c58.a85e.0000
             This bridge is the root
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
  Bridge ID  Priority    24577  (priority 24576 sys-id-ext 1)
             Address     0c58.a85e.0000
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time  300 sec
Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi0/0               Desg FWD 4         128.1    Shr
Gi0/1               Desg FWD 4         128.2    Shr

switch-2#show spanning-tree vlan 1
VLAN0001
  Spanning tree enabled protocol ieee
  Root ID    Priority    24577
             Address     0c58.a85e.0000
             Cost        4
             Port        1 (GigabitEthernet0/0)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
             Address     0c2e.adf7.0000
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time  300 sec
Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi0/0               Root FWD 4         128.1    Shr
Gi0/1               Desg FWD 4         128.2    Shr

switch-3#show spanning-tree vlan 1
VLAN0001
  Spanning tree enabled protocol ieee
  Root ID    Priority    24577
             Address     0c58.a85e.0000
             Cost        4
             Port        1 (GigabitEthernet0/0)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
             Address     0c33.c353.0000
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time  300 sec
Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi0/0               Root FWD 4         128.1    Shr
Gi0/1               Altn BLK 4         128.2    Shr

switch-3#debug spanning-tree events

Spanning Tree event debugging is on

switch-3(config)#interface gigabitEthernet 0/0

switch-3(config-if)#shutdown

*Jan  5 08:15:36.684: STP: VLAN0001 new root port Gi0/1, cost 8

*Jan  5 08:15:36.684: STP: VLAN0001 Gi0/1 -> listening

*Jan  5 08:15:36.684: STP[1]: Generating TC trap for port GigabitEthernet0/0

*Jan  5 08:15:36.685: STP: VLAN0100 we are the spanning tree root

*Jan  5 08:15:38.685: STP: VLAN0001 sent Topology Change Notice on Gi0/1

*Jan  5 08:15:51.686: STP: VLAN0001 Gi0/1 -> learning

*Jan  5 08:16:06.686: STP[1]: Generating TC trap for port GigabitEthernet0/1

*Jan  5 08:16:06.686: STP: VLAN0001 Gi0/1 -> forwarding

switch-3#show spanning-tree vlan 1
VLAN0001
  Spanning tree enabled protocol ieee
  Root ID    Priority    24577
             Address     0c58.a85e.0000
             Cost        8
             Port        2 (GigabitEthernet0/1)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
             Address     0c33.c353.0000
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time  300 sec
Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi0/1               Root FWD 4         128.2    Shr

after a long time of listening and learning forwarding. our previous  Gig0/1 Altn BLK port is now Root FWD. This process takes time. now we have configure the Cisco Uplinkfast feature.  

switch-3(config)#interface gigabitEthernet 0/0

switch-3(config-if)#no shutdown

switch-3(config-if)#exit

switch-3(config)#do show spanning-tree vlan 1
VLAN0001
  Spanning tree enabled protocol ieee
  Root ID    Priority    24577
             Address     0c58.a85e.0000
             Cost        4
             Port        1 (GigabitEthernet0/0)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
             Address     0c33.c353.0000
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time  15  sec
Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi0/0               Root FWD 4         128.1    Shr
Gi0/1               Altn BLK 4         128.2    Shr

switch-3(config)#spanning-tree uplinkfast

switch-3(config)#end

switch-3#debug spanning-tree events

Spanning Tree event debugging is on

*Jan  5 08:22:15.071: STP: VLAN0001 new root port Gi0/1, cost 3008

*Jan  5 08:22:15.071: %SPANTREE_FAST-7-PORT_FWD_UPLINK: VLAN0001 GigabitEthernet0/1 moved to Forwarding (UplinkFast).

wooo no listening no learning direct forwarding) this is Uplinkfast....

switch-3#show spanning-tree vlan 1
VLAN0001
  Spanning tree enabled protocol ieee
  Root ID    Priority    24577
             Address     0c58.a85e.0000
             Cost        3008
             Port        2 (GigabitEthernet0/1)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
  Bridge ID  Priority    49153  (priority 49152 sys-id-ext 1)
             Address     0c33.c353.0000
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time  300 sec
  Uplinkfast enabled
Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi0/1               Root FWD 3004      128.2    Shr

you see after we configure the Uplinkfast feature this switch means switch-3 bridge ID priority is changed. now this switch will never be a root bridge. unless we disable uplink fast. so never configure Uplink fast on the root switch. 

What is ARP (Address Resolution Protocol)? How ARP works?

 What is ARP (Address Resolution Protocol)?

ARP (Address Resolution Protocol) it’s a communication protocol. Networking devices used for discovering MAC (media access control) addresses, associate with an IPv4 address (internet layer address), and map the MAC addresses to IPv4 addresses this mapping is done dynamically and stored in the ARP cache. ARP works between layer 2 and layer 3 of the OSI because the MAC address exists on the data link layer and the IP address exists on the network layer.

How does ARP work?

Whenever a fresh PC (computer) connects to LAN, it will assign an IP address statically or dynamically to use for identity and for communication. When an incoming packet destined for a host machine on a particular LAN arrives at a gateway, the gateway is going to ask ARP for a MAC address that matches the IP address. There is a table called ARP cache in this table ARP mapping record.  Whenever a host asks for a MAC address in order to send a packet to another host in the LAN, ARP looks it the cache to see if their IP to MAC mapping translation is already stored. If it’s already stored then no need for ARP broadcast but if there is no translation stored then ARP sends a request for the network address (does anybody knows this IP address)

 

ARP sends broadcast a request packet to all the hosts on the LAN network and asks is there any host using this particular IP address please let me know. When a host recognizes oh it’s my IP address it will immediately send a unicast reply so ARP can update and store it in the cache table and now communication can proceed.

 

 

What happens if the host (machine) doesn’t know its own IP address?

In this situation, RARP (Reverse ARP) protocol is used for discovery. next chapter we are going to see proxy ARP and RARP.

 

What is ARP cache?

ARP cache is a table where mapping or translation is stored. The size of the ARP cache is limited and from time to time cleansed its entire entries to free its space. Mappings are stored for a few minutes. ARP frequently updates when a host changes their requested IP address.

 

 

ARP Commands

we used arp -a command to display the ARP table. It shows all the entries of the ARP cache or table.

arp -g: This command works the same as the arp -a command.

we use arp -d command when we want to delete an entry from the ARP table for a particular interface.

 

YouTube channel https://www.youtube.com/watch?v=s8dclvAax48&t=24s

 

 

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What are the classes of IP Routing?

Routing protocol classes

   There are three classes of routing protocols:

·          Distance vector
·         Link state
·         Hybrid

Distance vector 

the distance vector protocol is used to find the best path to a remote network by judging distance. In RIP routing, each instance where a packet goes through a router is called a hop, and the route with the least number of hops to the network will be considered the best one. The vector indicates the direction of the remote network. RIP is a true distance-vector routing protocol and periodically sends out the entire routing table to directly connected neighbors.

Link state

Link-state protocols also called shortest-path first protocols, each router creates three separate tables. One of their tables keeps track of directly attached neighbors, one determines the topology of the entire internetwork, and one is used as the routing table. Link-state routers know more about internetwork than any distance-vector routing protocol ever could. OSPF is a true link-state routing protocol. Link-state protocols send updates containing the state of their own links to all other directly connected routers on the network. And this is then propagated to their neighbors.  

              

 Hybrid 

 Hybrid protocols use aspects of both distance-vector and link-state protocols, and EIGRP is a   great example- it is typically just called EIGRP an advanced distance-vector protocol.               

What is IP Routing? What is routing and routed protocol?

 IP Routing

IP routing is basically the process of moving packets from one network to another network using routers.

Here is the list of all the default routing labs and theories

1.       

2.       EIGRP Default route (CCIE)

3.       OSPF default routing (CCIE)

4.       Default Routing and configuration (CCNP)

5.     Default route EIGRP, RIP, and OSPF (CCNP)

Routing protocols

Router use routing protocol to dynamically find all the networks within the great internetwork and to ensure that all router have the same routing table, routing protocols are also employed to determine the best path a packet should through an internetwork to get its destination most effectively. RIP, RIPv2, OSPF, and EIGRP are the most common routing protocols.

Routed protocols

Routed protocols can be used to send user data (packets) through the established enterprise. Routed protocols are assigned to an interface and determine the method of packet delivery. E.g. IP and IPv6.

The three type of routing method.

Ø  Static routing

Ø  Default routing

Ø  Dynamic routing

Static Routing

Static routing is the process that ensure when you manually add routes in each router’s routing table. There are the advantages and disadvantages of Static Routing.

Here the advantages:

·         There is no overhead on the router CPU.

·         There is no bandwidth usage between routers.

·         It adds security because of you, the administrator, can be very exclusive and choose to allow routing access to certain networks only.

And here are the disadvantages:

·         The administrator is must have a vault-tight knowledge of the internetwork and how each router is connected in order to configure routes correctly. If you don’t have a good, accurate map of your internetwork, things will get very messy.

·         If you add a network to the internetwork, you have to tediously add a route to it on all routers by hand.

·         It’s just not feasible to use it in most large networks because maintaining it would be a full-time job in itself.

Here’s the command syntax you use to add a static route to a routing table from global

 ip route    [destination network] [mask] [next-hop address or exit interface­] [administrative distance] [permanent]

ip route- the command used to change the static route.

Destination network- the network you’re placing in the routing table

Mask-   the subnet mask being used on the network

Next-hop address- this is ip address o the next-hop router that will receive packets and forward them to the remote network.

Exit interface- used in place o the next-hop address if you want, and show up as a directly connected route.

Administrative- distance by default, static routes have an administrative distance o 1 or 0. Next-hop AD is 1, and exit interface AD is 0.

Permanent-  if the interface is shut down or the router can’t communicate to the next-hop router, the route will automatically discarded from the  routing table by default. Choosing the permanent option keeps the entry in the routing table no matter what happens.

Static routing config:

 Topology

                                            

    

GOAL:

·         Design topology and assign IP addresses as per the diagram.

·         Configure static routing on Router Luke, mark, and john. And ensure that all the LAN interfaces can ping to each other.

LUKE#show ip interface brief

Interface              IP-Address         OK? Method Status                Protocol

Serial3/0              10.1.1.1              YES manual up                           up

Loopback0          192.168.100.50  YES manual up                           up

 MARK#show ip interface brief

Interface              IP-Address           OK? Method Status                Protocol

Serial3/0              10.1.1.2                YES manual up                           up

Serial3/1              11.1.1.2                 YES manual up                           up

Loopback0          192.168.150.75     YES manual up                           up

JOHN#show ip interface brief

Interface              IP-Address            OK? Method Status                Protocol

Serial3/1              11.1.1.1                  YES manual up                         up

Loopback0           192.168.200.100    YES manual up                        up

LUKE(config)#ip route 192.168.150.0 255.255.255.0 10.1.1.2

LUKE(config)#ip route 192.168.200.0 255.255.255.0 10.1.1.2

LUKE(config)#ip route 11.0.0.0 255.0.0.0  10.1.1.2

MARK(config)#ip route 192.168.100.0 255.255.255.0 10.1.1.1

MARK(config)#ip route 192.168.200.0 255.255.255.0 11.1.1.1

JOHN(config)#ip route 192.168.100.0 255.255.255.0 11.1.1.2

JOHN(config)#ip route 192.168.150.0 255.255.255.0 11.1.1.2

JOHN(config)#ip route 10.0.0.0 255.0.0.0 11.1.1.2

LUKE#show ip route static

Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP

       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area

       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2

       E1 - OSPF external type 1, E2 - OSPF external type 2

       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2

       ia - IS-IS inter area, * - candidate default, U - per-user static route

       o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP

       + - replicated route, % - next hop override

Gateway of last resort is not set

S     11.0.0.0/8 [1/0] via 10.1.1.2

S     192.168.150.0/24 [1/0] via 10.1.1.2

S     192.168.200.0/24 [1/0] via 10.1.1.2

MARK#show ip route static

Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP

       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area

       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2

       E1 - OSPF external type 1, E2 - OSPF external type 2

       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2

       ia - IS-IS inter area, * - candidate default, U - per-user static route

       o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP

       + - replicated route, % - next hop override

Gateway of last resort is not set

S     192.168.100.0/24 [1/0] via 10.1.1.1

S     192.168.200.0/24 [1/0] via 11.1.1.1

JOHN#show ip route static

Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP

       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area

       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2

       E1 - OSPF external type 1, E2 - OSPF external type 2

       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2

       ia - IS-IS inter area, * - candidate default, U - per-user static route

       o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP

       + - replicated route, % - next hop override

Gateway of last resort is not set

S     10.0.0.0/8 [1/0] via 11.1.1.2

S     192.168.100.0/24 [1/0] via 11.1.1.2

S     192.168.150.0/24 [1/0] via 11.1.1.2

LUKE#ping 192.168.200.100

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 192.168.200.100, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 44/48/64 ms

LUKE#ping 192.168.150.75

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 192.168.150.75, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 20/24/28 ms

LUKE#ping 11.1.1.1

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 11.1.1.1, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 20/25/36 ms

MARK#ping 192.168.100.50

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 192.168.100.50, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 4/14/24 ms

MARK#ping 192.168.200.100

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 192.168.200.100, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 8/12/28 ms

JOHN#ping 192.168.100.50

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 192.168.100.50, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 24/32/40 ms

JOHN#ping 192.168.150.75

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 192.168.150.75, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 20/20/20 ms

JOHN#ping 10.1.1.1

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 10.1.1.1, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 40/45/60 ms

Default Routing

Default route is used by IP to forward any packet with a destination not found in the routing table, which is why it is also called a gateway of last resort. Also can be used at end location where is only one exit path for any destination (internet).

Default routes help in reducing the size of your routing table. It’s a last preferred route in the routing table.

Dynamic routing

Dynamic routing is used to find networks and update routing tables on routers dynamically. Its easier than using static or default routing, but it will cost you in term o router CPU processing and bandwidth on network link.

Advantages of dynamic over static:

·         There is no need to know the destination networks.

·         Need to advertise the directly connected networks.

·         Update the topology change dynamically

·         Administrative work is reduce.

·         Used for large organization.

·         This is easier than using static or default routing.

 Administrative distance

The administrative distance (AD) is used to rate the trustworthiness of routing information received on a router from a neighbor routers. An administrative distance is an integer from 0 to 255, where 0 is the most trusted and 255 means no traffic will be passed via this route.

Default administrative distance

Connected interface   = 0

Static route                 =1

EIGRP                        =90

OSPF                          =110

RIP                              =120

External EIGRP          =170

Unknown                     = 255 (this route will never used).

The OSI Model

The OSI Model Advantages of the reference model

It divided the network communication process into smaller and simpler components, thus aiding component development, design and troubleshooting.

It allows multiple-vendor development through standardization of network components.

It encourages industry standardization by defining what functions occur at each layer of the model.

It allows various types of network hardware and software to communicate.

It prevent changes in one layer from affective others, so it doesn’t hamper development.

The OSI Reference model

The OSI has seven different layers, divided into two groups. The top three upper layers define how the applications within the end station will communicate with each other and with users. The bottom four layers define how data is transmitted end to end.

 The application layer

Application layer provides a user interface, this layer of the OSI model mark the spot where users actually communicate to the computer.

The application layer is also responsible for identifying and establishing the availability of the intended communication partner and determines whether sufficient resources for the intended communication exist. It’s important to remember to remember that the application layer is acting as an interface between the actual application programs.

Here are a few good examples of these kinds of events:

  File transfers

 Email

Enabling remote access

 Network management activates

Client/server processes

 Information location

Many network applications provide service for communication over enterprise network.

  Presentation layer

Presentation layer gets its name from its purpose: it presents data to the application layer and in responsible for data compression, decompression, encryption, decryption and code formatting. It’s an OSI model’s translator, one very effective way of ensuring a successful data transfer is to convert the data into a standard format before transmission. Presentation layer ensure that data transferred from the application layer of one system can be read by the application layer of another one.

The session layer

The session layer is responsible for setting up, managing, and dismantling sessions between presentation layer entities and keeping user data separate. It coordinates communication between systems and serves to organize their communication via three different modes: simplex, half-duplex and full-duplex.

Simplex:  is simple one-way communication, kind of like saying something and not getting a reply.

Half-duplex: is actual two-way communication, but is can take place in only one direction at a time. It’s like walkie-talkie.

Full duplex: is exactly like a real conversation where device can transmit and receive at the same time. Like a telephone conversation.

 Transport layer

The transport layer segment and reassemble data into a data stream. They provide end-to-end data transport services and can establish a logical connection between the sending host and destination host on an internetwork. Transport layer is responsible for providing mechanism for multiplexing upper-layer application, establishing session, and tearing down virtual circuits. The transport layer can either be connectionless or connection-oriented. Transport layer use two types of protocol TCP and UDP.

Feature of TCP.

         

flow control

  Flowing control prevent a sending host on one side of the connection from overflowing the                  buffer in the receiving host.

The segments delivered are acknowledged back to the sender upon their reception.

 Any segments not acknowledge are retransmitted.

 Segments are sequenced back into their proper order upon arrival at their destination.

A manageable data flow is maintained in order to avoid congestion, overloading and data loss.

Connection-oriented connection

 In reliable transport operation, a device that wants to transmit sets up a connection-                       oriented communication with a remote device by creating a session is called a setup or three-way handshake.

The first “connection agreement” segment is a request for synchronization.

The second and third segments acknowledge the request and establish  connection parameters.

The final segment is also an acknowledgment. It notifies the destination host that the connection agreement has been accepted and the actual connection has been established.

A service is considered connection-oriented if it has the following characteristics:

A virtual circuit is set up(e.g., call setup   or three-way handshake).

Its uses sequencing.

Its use acknowledgements.

Its use flow control. The types of flow control are buffering, windowing and  congestion avoidance.

Windowing

The quantity of data segments measured in bytes that the transmitting machine is allowed to send without receiving an acknowledgement for them is called a windowing.

Acknowledgment

Reliable data delivery ensures the integrity of the stream of data sent from one machine to the other through s fully functional data link. It guarantees that the data won’t be lost or duplicated. This is achieved through something called positive acknowledgment with Retransmission.

Network layer

The network layer also called layer 3 manages device addressing, tracking the location of devices on the network, and determines the best way to move data. Two types of packets are used at the network layer: data packets and route packets.

 Data packets

It’s used to transport user data through the internetwork. Protocols used to support data traffic are called routed protocols; examples ipv4 and ipv6.

 Routed updates packets

Used to update neighboring routers about the networks connected to all routers within the internetwork, protocols that send route update packets are called routing protocols ; (e.g. RIP, RIPv2, ISIS , EIGRP and OSPF).

The Data link layer

The data link layer provides the physical transmission of the data and handles error notification; this means that the data link layer will ensure that message is delivered to the proper device on a LAN using hardware address. The IEEE Data link layer has two sub layers:

 Media access control (MAC) 802.3

Define how packets are placed on the media. Contention media access is “first come/first served”

 Logical link control (LLC) 802.2

Responsible for identifying networks layer protocols and then encapsulating them.

 Physical layer

Physical layer does two things: it send bits and received bits. The physical layer specifies the electrical, mechanical, procedural and functional requirement for activating, maintain, deactivating a physical link between end system. This layer is also where you indentify the interface between the data terminal equipment (DTE) and the data communication equipment (DCE)

 Data circuit-terminating equipment.

The DCE is usually located at the service provider. While the DTE is attached device.

 Data terminal equipment

The service available to the DTE is most often accessed via a modern or channel service unit (CSU/DSU)..