VLANs (Logically divides the broadcast domain)are broadcast domains defined within switches to allow control of broadcast, multicast, unicast, and unknown unicast within a Layer 2 device. VLANs are created by number, and there are two ranges of usable VLAN numbers (normal range 1–1000 and extended range 1025–4096). We cannot currently use VTP to manage VLANs in the extended range, and these VLANs cannot be passed over an Inter-Switch Link (ISL) trunk link. The vlan-id would be a number from 1025 to 4096. Numbers 1001 to 1024 are reserved by Cisco and cannot be configured.
We can create VLANs in either VLAN database mode or global configuration mode. We must create VLANs that are numbered higher than 1005 in global configuration mode. The VTP mode must be set to transparent in order to create these VLANs. VLANs that are numbered higher than 1005 are not advertised by VTP. Furthermore, VLANs that are numbered higher than 1005 are stored in the switch configuration file and not in the VLAN .dat file.
the VLAN information is on a separate file named vlan.dat. If the vlan.dat file is deleted accidently and the switch gets reloaded, all the VLANs that were available on the switch are lost. Until the switch is reloaded, the VLAN information is present in the switch. in this case we have to just create or delete or modify the vlan to get back the vlan.dat file.
There are three mode of VTP
- Server: This is the default mode of VTP. It will add, delete, rename vlans also these vlan are propagated to other switch. We must configure the VTP domain.
- Client: If we don’t configure the VTP domain on client switch then also it will receive information from the server domain and learn the domain name and revision number. Can not create delete, add, rename VLAN.
- Transparent: Revision number is always ZERO. This switch will relayed all the VTP messages.
Different VTP domain won’t communicate with each other.so if we add switch which has different domain(Say AAA) in between the two switch which are running same VTP domain(say CISCO) then the new switch will not transfer the CISCO domain messages to other switch as transient switch is in AAA domain when it receives the CISCO VTP domain name packet it just Drop those packets. We must have a trunk link in between the two switch to pass the VTP messages. VTP messages contain the tag value.
We can configure Password in VTP
Normal-range VLANs are VLANs 1–1005, and can be advertised via VTP versions 1 and 2. These
VLANs can be configured in VLAN database mode, with the details being stored in the vlan.dat file in
Extended-range VLANs range from 1006–4094, inclusive. However, these additional VLANs
cannot be configured in VLAN database mode, nor stored in the vlan.dat file, nor advertised via
VTP. In fact, to configure them, the switch must be in VTP transparent mode
Take care while adding switch
If we want to add the switch in the network then we will check revision number of switch if revision number of switch is more then we will make this switch as TRANSPARENT mode so that revision value becomes ZERO then we will configured what ever way we want. Another way is to configured that switch in different domain so that there revision number will start from ZERO. but when the revision number is higher(for both sever/client mode switch) than the already running network the adding switch will defiantly harm whole network even though that switch is running in CLIENT mode or SERVER mode because client switch also share the VTP with the server and other clients.
VTP Version 1,2,3
Version 1 is by default. Version 2 is used when we want to use the token ring. I have to read about version 3.
It is used when in order to eliminate or prune this unnecessary traffic which broadcast to all the switch in the domain. VLAN 1 and VLANs 1002 to 1005 are always pruning-ineligible; traffic from these VLANs cannot be pruned. Extended-range VLANs (VLAN IDs greater than 1005) are also pruning-ineligible.
Dynamic Trunking Protocol (DTP)
Access: Don’t send DTP packet. Dynamic desirable: Actively send DTP packet. Auto: Not send DTP packet. but if receive packet from other end then only it become trunk port. It never become trunk when other end is auto. Trunk: Send DTP packet. Non-negotiate: Not send DTP packet
ISL, 802.1Q, QinQ
ISL: complete frame is encapsulated and additional header is added after it has been send. Then at receiver the header is removed and frame is de-encapsulated.
802.1Q: 4 byte is added in the frame. The 802.1Q tag is 4 bytes. Therefore, the resulting Ethernet frame can be as large as 1522 bytes. The minimum size of the Ethernet frame with 802.1Q tagging is 68 bytes.
diffrence between ISL and 802.1Q : 802.1Q support native vlan but ISL doesn’t support native vlan concept.
QinQ:The recommended minimum MTU is 1504 bytes for QinQ because 4 byte extra is added in the frame. The QinQ frame contains the modified tag protocol identifier (TPID) value of VLAN Tags. By default, the VLAN tag uses the TPID field to identify the protocol type of the tag.
The value of this field, as defined in IEEE 802.1Q, is 0x8100.
The device determines whether a received frame carries a service provider VLAN tag or a customer VLAN tag by checking the corresponding TPID value. After receiving a frame, the device compares the compares the configured TPID value with the value of the TPID field in the frame. If the two match, the frame carries the corresponding VLAN tag. For example, if a frame carries VLAN tags with the TPID values of 0x9100 and 0x8100, respectively, while the configured TPID value of the service provider VLAN tag is 0x9100 and that of the VLAN tag for a customer network is 0x8200, the device considers that the frame carries only the service provider VLAN tag but not the customer VLAN tag