The list has filtered every message I have sent since yesterday afternoon,
but hopefully this will get to you Chris.
A BPDU resides inside a Logical Link Control (LLC) header. The LLC Service
Access Point (SAP) to identify BPDU is 42.
BPDUs are sent to a multicast address. It appears that you were using a
Token Ring document as your bits in your response are all reversed. ;-) On
Ethernet, the frame goes to 01:80:C2:00:00:00.
For a frame to be a broadcast or multicast, the first bit transmitted must
be a one. Notice that Ethernet transmits the least-significant bit first,
which is a one in 01:80:C2:00:00:00.
Your information about the source address doesn't quite make sense because
a source address has no concept of multicast. On Token Ring, the first bit
transmitted of the source address indicates whether source routing
information is present, that is, whether the Routing Information Field
(RIF) is present. I didn't know that this bit was set for BPDUs in a Token
Ring environment. It doesn't seem like it would need to be??
Priscilla
At 04:35 AM 8/29/01, Burnham, Chris wrote:
>I diasagree,
> I understood that the BPDU has it's own frame format ..the
>frame format depends on what type of spanning tree is configured.There is no
>concept of a SAP field.
>
>Destination Address
>The Destination Address field indicates the destination address as specified
>in the Bridge Group Address table. For IEEE Spanning-Tree Protocol BPDU
>frames, the address is 0x800143000000. For IBM Spanning-Tree Protocol BPDU
>frames, the address is 0xC00000000100. For Cisco Spanning-Tree Protocol BPDU
>frames, the address is 0x800778020200.
>
>Source Address
>The Source Address field indicates the base MAC address used by the switch.
>For Cisco Spanning-Tree Protocol BPDU frames, the multicast bit is set to
>indicate the presence of a RIF in the header.
>
>
>
>-----Original Message-----
>From: Michael Snyder [mailto:[EMAIL PROTECTED]]
>Sent: 29 August 2001 04:59
>To: [EMAIL PROTECTED]
>Subject: Re: BPDUs [7:17607]
>
>
>Layer two broadcast.
>
>What Sap does it use?
>
>
>""Christopher Supino"" wrote in message
>[EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
> > All ,
> >
> > I came across this question while studying: How are BPDU's propagated
> > amongst switches? Broadcast, multicast, or unicast? Anyone have an
> > explanation?
> >
> > Christopher Supino
> > CCNP, CCDP, MCSE, CNA5, ASE
> > Senior System Engineer
________________________
Priscilla Oppenheimer
http://www.priscilla.com
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=17747&t=17607
--------------------------------------------------
FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html
Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
