RE: BPDUs [7:17607]
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 0x80014300. For IBM Spanning-Tree Protocol BPDU frames, the address is 0xC100. 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 Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=17644t=17607 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: BPDUs [7:17607]
multicast At 09:03 PM 8/28/01, Christopher Supino wrote: 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=7i=17748t=17607 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: BPDUs [7:17607]
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 0x80014300. For IBM Spanning-Tree Protocol BPDU frames, the address is 0xC100. 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=7i=17747t=17607 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: BPDUs [7:17607]
Layer 2 multicast, Destination: 01:80:C2:00:00:00 Multicast 802.1d Bridge group. It uses the meaning of life for its SAP: 42. Prisiclla At 11:59 PM 8/28/01, Michael Snyder wrote: 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=7i=17750t=17607 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: BPDUs [7:17607]
BPDUs are sent out multicasted using an Ethernet multicast address of 01-80-C2-XX-XX-XX and a SAP of 42 (bridging SAP). They are sourced from what ever private mac address pool the vendor chooses. e.g. (Ethernet SAP) Dest Source Ln DSAP SSAP CNTL INFOPAD FCS 0180C200 0010E7123456 26 42 42 03[BPDU] Since BPDUs (both TCN and Configs) are always 35 Bytes long add 3 for the SAP Header to get a total length of 38 (hex 0x26) for Length 40 for SNAP, although I do not believe there is a SNAP formation for BPDUs. Perhaps Frame Relay bridging? By simply looking at the destination address you should be able to determine that it is in fact a multicast address by looking at the the second nibble in the first octet. If it is odd (1,3,5,7,9,B,D,F) it is a multicast address. Interconnections: Routers, Bridges, and Switches by Radia Perlman is suggested reading. Ref: RFC 1700 Wayne -Original Message- From: Christopher Supino [mailto:[EMAIL PROTECTED]] Sent: Wednesday, August 29, 2001 10:04 AM To: [EMAIL PROTECTED] Subject: BPDUs [7:17607] 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 Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=17804t=17607 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
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 Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=17620t=17607 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
