DTP uses protocol type 2004 too, just like DISL. I guess it's just an update to DISL for use with 802.1Q rather than ISL?
And, I figured out why you might want to tell DTP not to autonegotiate or be desirable and why in that case no VTP domain name is exchanged and the VTP domain names don't have to match. The main reason is that the other end might not be Cisco and might not care about VTP anyway. Does that make sense? Priscilla Priscilla Oppenheimer wrote: > > [EMAIL PROTECTED] wrote: > > > > Is VTP dependent of DTP or is DTP dependent of VTP?. > > > > From the following statement I think DTP can still form a > trunk > > even if VTP > > domain is different on both switches. > > I doubt that DTP can form a trunk if the VTP domains are > different, though Cisco's documentation is rather unclear about > this: > > "To autonegotiate trunking, the interfaces must be in the same > VTP domain. Use the trunk or nonegotiate keywords to force > interfaces in different domains to trunk. For more information > on VTP domains, see "Configuring VTP. Trunk negotiation is > managed by the Dynamic Trunking Protocol (DTP). DTP supports > autonegotiation of both ISL and 802.1Q trunks." > > The URL is: > > cisco.com/univercd/cc/td/doc/product/lan/cat6000/ios127xe/config/layer2.htm > > I think it's saying that DTP won't trunk if the VTP domains > differ, but if you don't negotiate with DTP, and instead use > the "trunk" or "nonegotiate" keywords, you can get the switches > to trunk even if they are in different domains. (I've never > heard of that, but that's what they seem to be saying.) > > I haven't ever sniffed a DTP frame. I have sniffed DISL frames > and they have the VTP domain name in them. I bet DTP does too? > And if they disagreed, I think the trunking would fail. > > > But I have read opposite > > statements. > > Unfortunatelly I can not test it now. Any thoughts? > > > > "The VTP protocol communicates between switches using an > > Ethernet destination multicast > > MAC address (01-00-0c-cc-cc-cc) and SNAP HDLC protocol type > > Ox2003. > > Oh, isn't that awful they would call this HDLC. Ouch. The > original HDLC protocol architecture didn't even have a method > for defining the encapsulated protocol! That was added by many > of the derivatives of HDLC, including PPP, Cisco HDLC, and > Logical Link Control (LLC), used on LANs. > > Obviously this is a LAN, so they could have easily said LLC > and/or SNAP instead of HDLC. VTP uses an LLC Source Service > Access Point (SSAP) and Destination Service Access Point (DSAP) > of 0xAA, meaning that the frame has an additional header, > called a Subnetwork Access Protocol (SNAP) header. SNAP has a > vendor code and two-byte protocol type. For VTP the protocol > type is indeed 2003. DISL is 2004. I don't know for DTP? Anyone > know? Could we guess 2005? > > A VTP frame is a difficult frame to sniff, but I have caught > one in the wild. The ISL was stripped before the frame was > given to my analyzer port. But here's what the rest of the VTP > frame looks like: > > DLC: ----- DLC Header ----- > DLC: > DLC: Destination = Multicast 01000CCCCCCC > DLC: Source = Station 00B06426795B > DLC: 802.3 length = 284 > DLC: > LLC: ----- LLC Header ----- > LLC: > LLC: DSAP Address = AA, DSAP IG Bit = 00 (Individual > Address) > LLC: SSAP Address = AA, SSAP CR Bit = 00 (Command) > LLC: Unnumbered frame: UI > LLC: > SNAP: ----- SNAP Header ----- > SNAP: > SNAP: Vendor ID = Cisco1 > SNAP: Type = 2003 (VTP) > SNAP: > VTP: ----- Cisco Virtual Trunk Protocol (VTP) Packet ----- > VTP: > VTP: Version = 1 > VTP: Message type = 0x02 > (Subset-Advert) > VTP: Sequence number = 1 > VTP: Management Domain Name length = 3 > VTP: Management Domain Name = "Lab" > VTP: Number of Padding bytes = 29 > VTP: Configuration revision number = 0x00000002 > VTP: > VTP: VLAN Information Field # 1: > VTP: VLAN information field length = 28 > VTP: VLAN Status = 00 (Operational) > VTP: VLAN type = 1 (Ethernet) > VTP: Length of VLAN name = 7 > VTP: ISL VLAN-id = 1 > VTP: MTU size = 1500 > VTP: 802.10 SAID field = 100001 > VTP: VLAN Name = "default" > VTP: # padding bytes in VLAN Name = 1 > VTP: Reserved 8 bytes > VTP: > VTP: VLAN Information Field # 2: > VTP: VLAN information field length = 24 > VTP: VLAN Status = 00 (Operational) > VTP: VLAN type = 1 (Ethernet) > VTP: Length of VLAN name = 11 > VTP: ISL VLAN-id = 10 > VTP: MTU size = 1500 > VTP: 802.10 SAID field = 100010 > VTP: VLAN Name = "Engineering" > VTP: # padding bytes in VLAN Name = 1 > VTP: > VTP: VLAN Information Field # 3: > VTP: VLAN information field length = 24 > VTP: VLAN Status = 00 (Operational) > VTP: VLAN type = 1 (Ethernet) > VTP: Length of VLAN name = 10 > VTP: ISL VLAN-id = 50 > VTP: MTU size = 1500 > VTP: 802.10 SAID field = 100050 > VTP: VLAN Name = "Accounting" > VTP: # padding bytes in VLAN Name = 2 > > > _______________________________ > > Priscilla Oppenheimer > www.troubleshootingnetworks.com > www.priscilla.com > > > > > It does not work over non-trunk ports (VTP is a payload of > > ISL or 802.1Q), > > so messages cannot be sent until DTP has brought the trunk > > online." > > > > > > > http://www.cisco.com/en/US/products/hw/switches/ps663/products_tech_note09186a0080094713.shtml > > > > > > Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=64956&t=64892 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
