VTP does stand for VLAN Trunking Protocol but note that it is not a trunking protocol. There are only two trunking/tagging protocols as discussed earlier. The Cisco proprietary ISL protocol, that is now getting obsolete and the industry-standard IEEE 802.1Q protocol.
(1) Verify current vtp status [Covered as part of CCNA Rev]
(2) Configure vtp domain/password [Covered as part of CCNA Rev]
(3) Configure vtp mode [Covered as part of CCNA Rev]
(4) Configure vtp version [CCNP]
(5) Verify vtp configuration [Covered as part of CCNA Rev]
Configure VTP version:
The way to do that is by going under global-config mode and typing in the command:
S1(config)#vtp version 2
VTP: Difference between version 1 and version 2
The difference between version 1 and version 2 is that vtp v.2 adds support for token ring but more importantly also gives transparent switches the capability to forward vtp information through them. If you're running vtp version 1, which all switches are running by default (even though it says 'VTP Version: 2' when you do a 'show vtp status' you'll notice 'VTP V2 Mode: Disabled'.) If you're running vtp version 1 the transparent mode switches will stop vtp broadcasts, they absorb them rather then pass them on.
Some conflicting information here, a second source tells me that VTP version 1 devices functioning in transparent mode doesn't stop broadcasts but will forward advertisements to downstream switches only if the forwarding device and d0wnstream devices domain name and version number match. Version 2 devices functioning in transparent mode will forward information across a trunk port even if the domain names do not match.
VTP: VTP Advertisements
VTP advertisements are multicast packets sent out through trunk ports only. There are 3 kinds of VTP advertisements:
(1) Summary
(2) Subset
(3) Client
(1) Summary Advertisements:
Summary advertisements are transmitted by vtp servers every 5 minutes or upon a change in VLAN database. Information included in the summary advertisement is as follows:
-VTP domain name and version.
-Configuration revison number
-MD5 Hash
-Timestamp
-Number of subset advertisements that will follow this advertisement
-Configuration revison number
-MD5 Hash
-Timestamp
-Number of subset advertisements that will follow this advertisement
(2) Subset Advertisements
Subset advertisements tell whether a LAN has beeen created, deleted, activated or suspended and will give the name, MTU and type of VLAN.
(3) Client Advertisements
Client advertisements are actually clients requesting vlan information. A server will respond to this request with a summary and subset advertisement.
Subset advertisements tell whether a LAN has beeen created, deleted, activated or suspended and will give the name, MTU and type of VLAN.
(3) Client Advertisements
Client advertisements are actually clients requesting vlan information. A server will respond to this request with a summary and subset advertisement.
VTP: Further reading (Optional)
http://www.cisco.com/univercd/cc/td/doc/product/lan/cat5000/rel_4_2/config/vlans.htm#xtocid79807
http://www.javvin.com/protocolVTP.html
ISL and 802.1Q: Difference between the two tagging protocols
As promised somewhere in one of the earlier posts, here's the breakdown between the two tagging protocols:
-Inter-Switch Link (ISL)
(1) Cisco proprietary
(2) Encapsulates the entire frame before it goes out the trunk. Adds a brand-new 26-byte header (containing a 15-bit VLAN identifier) which is put right in front of the packet and a brand-new 4 byte CRC trailer put at the end of the packet.
(3) Being phased out
-802.1Q
(1) Open Standard / Industry Standard
(2) Inserts tag into frame rather than encapsulating it (like it's done with ISL and increasing the overhead significantly). A shim (4 byte tag) is inserted right behind the source mac-address field in the header and then simply recalculates the CRC on the end ofthe packet to reflect that new tag that is put in there. Thus a much better method than ISL and because of that Cisco is phasing the latter out.
ISL:
Right before the packet is sent across the trunk, the switch slaps on the 26 byte header off which the VLAN header is only 16 bits (i.e: really small, 2 bytes). The rest is just 'junk' (cdb stuff, bpdu stuff, etc) as Cisco had a lot of intentions for ISL. It follows up with an additional 4 byte CRC (to the normal CRC)
802.1Q
802.1Q just slides in a 4 byte shim (tag) into the existing header. Inside of there is the 2 byte VLAN header. There is also a 3 bit PRI field (very valuable field - Priority for QOS markings) along with some other stuff.
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