Cisco Switch Frame Forwarding

We have different Frame Forwarding Option, another words When Frame comes in one of those Ethernet switches port. Switch begin to forward the frame out of the egress or the outgoing port.There is Different approach to do this

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Cut-Through Switching: -   

   Does not use FCS (frame Check Sequence)

   Start to forward the frame after examine the frame’s Destination mac address 

                   Basic Cut-Through Switching what we responsible for understanding CCNA exam is that with Cut-Through switching, as soon as switch sees those first 6 Bytes (48 bits), as soon as sees destination mac address, it can start forwarding that frame.

                  Therefore, upside is decreasing latency and the downside is we might forward the frame that’s corrupted frame

                   Ether Type: - This is an example, IPv4 Frame, may be ACL for blocking this frame, may be a Qos.

Store-and-Forward Switching

                     With Store and forward switching switch once to make sure that a frame is valid and that’s not corrupt, before it starts to forwarded it out. Switch wait until it receives the entire frame not just the first 48 bits or destination mac address, it waits until receives the entire frame and looks at the frame Check sequence embedded in frame, and switch is going to calculate using an algorithm, its gonna calculate its own Frame Check Sequence (FCS). So the Switch creates FCS of its own, and if the FCS in the frame equals the FCS calculates with the switch. 

                     The switch can conclude with reasonable certainty that this is a valid frame it is not being corrupted in transmission. Therefore I feel comfortable forwarding an out for the destination.Store and Forward Switching upside is that we were not going to waste bandwidth by beginning forward a frame that’s invalid anyway.

                        The Downside is that it might be little bit slower than Cut-Through Switching because we are waiting until we receiving the entire frame before we begin forwarding that frame.

Fragment-Free Switching  

                       Starts to forward the frame after the first 64 Byte are received, since most collision occur within the 64 Bytes                            

                      We could almost consider Fragment Free Switching as a compromise between Cut-Through Switching and Store and Forward Switching. One of big benefits of Cut-Through Switching was that switch didn’t have to see the entire frame before it started to forward it out towards its destination. However, it didn’t check to see if it valid or not, maybe collision had occurred may be FCS didn’t match up. With Store and Forward switching we would get the entire frame stored in the switch make sure it good then start forwarding it but it introducing some delay by having to receive the entire frame before we start to forward the frame.

                   With Fragment-Free Switching stats that most collisions that going to occurred within a frame, are going to occurred within first 64 Byte. Fragment switching does, it looks beyond the just destination mac address, and beyond the ether type, it will actually look 64 Bytes into our frame, because most of the collisions occurred in the first 64 Bytes, if it doesn’t see the collision has occurred in first 64 bytes, it has some assurance that this is probably an OK frame. We didn’t go to trouble for wait for FCS arrive and do calculation, as we would with in Store and Forward Switching. But at least we have some assurance that frame is valid as supposed to Cut-Through Switching

                     To Some Up Fragment Free Switching is going to examine the first 64 Bytes of a frame, if it doesn’t seem that a collision has occurred, it is then going to forward that frame based on destination mac address 


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Router Packet Forwarding

The Term packet switching is use to describe the routing of a packet from incoming interface on router to outgoing interface

                                                      Let’s now consider what’s going on inside of router architecturally as say, packet flows in the input, the ingress interface on a router and get routed to output or egress interface on a router.

We have different frame forwarding option: -

We wanna look at 3 major one in this topic: -

Process Switching: - With Process switching is we going to see, the router processor the CPU (Central Processing unit) gets involved with every packet forwarding decision. It gets quite a bit more efficient with fast switching. In Process switching router architecture dividing into two Plane “Control Plane and Data Plane”

The Data Plane is where our traffic is actually flowing through the router

The Control Plan is gonna be handling behind the seems tasks and we have a CPU the router processor that can do working both of these planes.

                                                      However, if the CPU became involved in every single packet forwarding decision. That’s not terribly efficient. We could overwhelm CPU with too much traffic. However, that’s exactly what processing switch does. This is the oldest approach to forwarding packet to router.

                                                         Let’s imagine that we have a packet coming in to this router incoming interface or the ingress interface. With Process Switching every single packet has to go up to CPU.

And we ask the CPU “how do we route this packet” and CPU has to take a look the routing table and say “that packet is gonna go out of this particular interface” So the CPU is gonna direct the packet to leave via the outgoing interface.

That’s Process switching and because of CPU is involved in every single packet, routing, packet switching, decision. It is not very efficient

Let’s look at much more efficient approach that’s called “Fast Switching”

With Fast Switching we have another architecture component. The “Route Cache”.

That can learn how we have previously routed a packet to a specific network.

                                            For example, let’s say “A packet comes into the router and its destined for a network that, we have not yet routed the packet too. Since we never done it before, we go ask CPU “how we route to his network”

The CPU is gonna do lookup its IP Routing Table and says” To go out this egress interface”. But here what happened. The CPU is going to cause that entry that says” to go to this network go out of this interface”. That information is gonna be written into the Route Cache.

And that first packet it is gonna be routed out to the destination network.

But now that information has been stored in to Route Cache. What happened, if second packet comes in and destined for that network. Since we done it before, since we learned, since we cache the information. That say’s” packet going to this network go out of this interface”. We don’t need to ask CPU, we can simply query the Route Cache and says “how do we route traffic”, going to this network”.

And Route Cache says” Oh! Yaw, I seen that before we gonna go out of this interface”.

That’s the concept of “Fast Switching”

Interestingly There is more efficient approach: - 

With CEF (Cisco Express Forwarding), we don’t have to ask the CPU for first time we trying to route a packet to a specific destination network, because with CEF, the CPU is going to proactively populate the FIB (that’s the Forwarding Information Base, that’s the Layer 3 information).

It essentially got the IP Routing table information in memory in this FIB, and very efficient table structure, where lookup information very very rapidly. That’s Layer 3 information but we also need some Layer 2 information, that will allow us to quickly foam a frame header. So for example, the FIB says “to go to this network, go to this next-hop ip address”. Well the Adjacency Table can say “To get to that next-hop ip address” we need to go out this interface, we gonna be using this “encapsulation type”, and here is destination mac-address.

So Adjacency Table and FIB Table, they provide all of the information we need to route a packet. The Packet comes in incoming interface even, if we never routed to this network before. We don’t ask the CPU how to get there, we just go to ask the FIB and Adjacency Table.

We ask CEF, and CEF has learned all this information, and CEF is gonna be directly out this appropriate egress interface.

                                                              This is gonna be most efficient approach to doing Packet Switching, because we never had to ask the CPU how I had get to the destination network. By the way There is change in network, if there is change in ip routing table then CEF it gonna be updated through reflect that

So CEF is a very CPU friendly approach to Packet Switching 

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Cisco iOS

Ø  Cisco iOS Use IFS (Integrated file System) To keep track of files and Folders

Ø  IFS give us Differnet Places where we Store and Retrive the Files 

Load the iOS from TFTP Server to Router

First Check the Connectivity with TFTP Server

TFTP Server is nothing But a PC which we install the TFTP software to Copy the Files from the Router}

Ø  Router# ping 192.168.1.50 (tftp Server ip address)

Ø  Router# copy tftp: flash:

Ø  Address or name of remote host []? 192.168.1.50                               {tftp server ip address}

Ø  Source filename []? c2900-universalk9-mz.SPA.151-4.M4.bin           {iOS file name}

Ø  Destination filename [c2900-universalk9-mz.SPA.151-4.M4.bin]             {enter}

  {iOS file name same as above}

{This will take some time}

Ø  Router# show flash:                                      (to check the iOS}

To Boot from this iOS image

Ø  Router(config)#boot system flash c2900-universalk9-mz.SPA.151-4.M4.bin            {new iOS}

Ø  Router(config)#no boot system flash c2600-universalk9-mz.SPA.151-4.M4.bin  

{To Train the router to Boot the system with newly iOS instead of Previous}

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Telnet and SSH Configuration in Cisco Router

Enable Telnet Access

Ø  Router (config)#enable secret Cisco      (configuring password for enter in Enable and Configuration mode)      

Ø  Router (config)#line vty 0 4                  (5 User Simultaneously access the Switch} Vty: - Virtual Terminal

Ø  Router (config-line)#password Cisco                    {password}

Ø  Router (config-line))#login                            {Ask of user Credentials}

Ø  Router (config-line))#exit

 {To Verify}

ü  Enable “Telnet client” Feature in”)

ü  Add or remove Program

ü  Turn on or off window feature

ü  Check the Telnet Client)

Window Terminal

Ø  C:\Users> telnet 192.168.2.10      (Switch IP)

Cisco Recommended Use SSH Instead Telnet because telnet is not Secure it will Send data in Clear text

    
Enable SSH {Secure Shell}

ü  It Securely Send and Receive data over the network

ü  When we Login It Prompt us for Username and Password

 Configuration

Ø  Router (config)#username admin secret Cisco                   (creating username and password for ssh)

Ø  Router (config)#ip domain-name ccna.local                      (domain-name mandatory for SSH)

Creating Self-signed Digital Certificate

Ø  Router (config)#crypto key generate rsa

: 1024                             {ask for choose the size of key}

Ø  Router(config)#ip ssh version 2                                            (enabling SSHv2) 

Now implement these Credentials in vty line

Ø  Router (config)#line vty 0 4

Ø  Router (config-line))##login local                  (Local username and password we created earlier)

Ø  Router (config-line))##transport input ssh            {this will allow only ssh to Communicate across the Network}

Ø  Router(config-line))##exit

Now Verify using Putty install on your Pc

ü  Host Name: - Router ip address

Ø  Port: - SSH Default Port number 22 

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RIP Configuration in IPv6 {CCNP Part2}

RIPng Configuration

Ø  R1(config)#ipv6 unicast-routing         {enable IPv6 on Router}

Ø  R1 (config)#ipv6 cef                                {enable cisco express forwarding (CEF) for IPv6.

CEF is a highly-efficient packet switching technology supported by Cisco router.}

v  Router1 interfaces Configuration

Ø  R1(config)#interface serial 2/0

Ø  R1(config-if)#description CONNECTED WITH R2

Ø  R1(config-if)#ipv6 address 2001:1::1/64

Ø  R1(config-if)#clock rate 64000

Ø  R1(config-if)#no shut

Ø  R1(config-if)#exit

Ø  R1(config)#interface fastEthernet 0/0

Ø  R1(config-if)#description CONNECTED WITH SW1

Ø  R1(config-if)#ipv6 address 2001:4::1/64              

Ø  R1(config-if)#no shut

Ø  R1(config-if)#exit

v  Router2 Enable IPv6

Ø  R2(config)#ipv6 unicast-routing

Ø  R2(config)#ipv6 cef

v  Router2 interfaces Configuration

Ø  R2(config)#interface serial 2/0

Ø  R2(config-if)#description CONNECTED WITH R1

Ø  R2(config-if)#ipv6 address 2001:1::2/64

Ø  R2(config-if)#no shut

Ø  R2(config-if)#exit

Ø  R2(config)#interface serial 2/1

Ø  R2(config-if)#description CONNECTED WITH R3

Ø  R2(config-if)#ipv6 address 2001:2::1/64

Ø  R2(config-if)#clock rate 64000

Ø  R2(config-if)#no shut

Ø  R2(config-if)#exit

v  Router3 Enable IPv6

Ø  R3(config)#ipv6 unicast-routing

Ø  R3(config)#ipv6 cef

v  Router2 interfaces Configuration

Ø  R3(config)#interface serial 2/1

Ø  R3(config-if)#description CONNECTED WITH R2

Ø  R3(config-if)#ipv6 address 2001:2::2/64

Ø  R3(config-if)#no shut

Ø  R3(config-if)#exit

Ø  R3(config)#interface fastEthernet 0/0

Ø  R3(config-if)#description CONNECTED WITH SW2

Ø  R3(config-if)#ipv6 address 2001:3::1/64

Ø  R3(config-if)#no shut

Ø  R3(config-if)#exit

v  RIPng Protocol Configuration in R1 under the interface:-

Ø  R1(config)#interface serial 2/0

Ø  R1(config-if)#ipv6 rip DEMO-RIP enable   {DEMO-RIP:- name to identify the RIP Process}

Ø  R1(config-if)#exit

Ø  R1(config)#interface fastEthernet 0/0

Ø  R1(config-if)#ipv6 rip DEMO-RIP enable

Ø  R1(config-if)#exit

v  RIPng Protocol Configuration in R2 :-

Ø  R2(config)#interface serial2/0

Ø  R2(config-if)#ipv6 rip DEMO-RIP enable

Ø  R2(config-if)#exit

Ø  R2(config)#interface serial 2/1

Ø  R2(config-if)#ipv6 rip DEMO-RIP enable

Ø  R2(config-if)#exit

v  RIPng Protocol Configuration in R3 :-

Ø  R3(config)#interface serial 2/1

Ø  R3(config-if)#ipv6 rip DEMO-RIP enable

Ø  R3(config-if)#exit

Ø  R3(config)#interface fastEthernet 0/0

Ø  R3(config-if)#ipv6 rip DEMO-RIP enable

Ø  R3(config-if)#exit

{Configuration is done}

v  Troubleshooting & Verification Commands

Ø  Show ipv6 route

Ø  Show ipv6 interface brief

Ø  Show ipv6 protocols

Ø  Show ipv6 rip {option}

Ø  Debug ipv6 rip {option}

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