[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
>
>
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