Data link layer (Virtual local area networks)
Virtual local area networks
CCNA, Data link layer
Virtual local area networks(vlans) :-
Vlan: - is virtual switch inside of main switch (physical switch)
Vlan is layer 2 (data link layer) broad cast domain
The idea is when we have some PCs belong to a department (have its own IP addressing schema) and there are another PCs belong to another department also (have its own IP schema)
Benefits of creating Vlans :-
- Saving money by (using all ports of the switch).
- Can transverse different switches (distance constraints had gone)
No Need for physical separate by another switch, only need logical separate by creating vlans inside switch
Types of memory on cisco routers:-
- RAM(random access memory) :- holds the running configuration, when power off device configuration is gone.
- NV RAM(Non- volatile RAM):- holds your start up configuration
- Flash memory: - holds your operating system.
Two ways to logging into a router:-
- Throw console port on a router to the communication port of a computer
- Remote login using telnet or ssh.
There are two types of links (ports) can exist on switch:-
- Access links: - any link (port) on a switch that can carry one vlan, part of only one vlan
- Trunk links :- links (ports) that can carry more than one vlan at a time
The idea that we need to put vlan 10 and vlan 20 in port 1 so p1device on switch1 can talk to p2 device on switch 2, and p3 can talk to p4 on switch2.
so in this case port1 is a trunk link
How switch know which frame belong to which vlan?
By frame tagging or trunking protocol
Switch 1 will put identifier on the frame telling the frame your part of vlan 10
When switch 2 receive frame coming from switch 1 the frame have id in it says this frame belong to vlan 10 or vlan 20
The frame tagging is done by using one of two protocols:-
- Inter switch link (ISL) :- only for cisco devices
Encapsulate the original frame into new header frame, a new 26 byte frame (header) and 4 byte footer. Total 30 bytes
The new frame has a field (vlan id) that identifies the vlans the frame belongs to.
- IEEE 801q (dot 1q) open standards :-
Insert a 4 bytes field in the original frame, its tag identifying what vlan belong to.
Features when I make a vlan my native vlan there is no tag will be add to the frame.
IEEE 802.1q is better than inter switch link because inter switch link add 26 byte for over header that switch need to process for frame.
Performs automatic trunk negotiation between switches that connected together
There are three modes for dynamic trunking protocol:-
- Dynamic desirable :- it will send and respond dynamic truncking protocol (dtp) frames
- Dynamic auto mode :- the port will respond to dtp frame from the other end, but it will not send dtp frames
- Dynamic Mode on :- set my side unconditionally to a trunk, also will send and respond DTP frames.
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