02-27-2011 03:19 AM - edited 03-06-2019 03:47 PM
Hi,
I don't see the ethertype for STP in the file:
standards.ieee.org/regauth/ethertype/eth.txt
Would it be similar to the protocol identifier in 802.1D, that is 00-00?
Thanks for your opinion,
best regards,
Michelot
Solved! Go to Solution.
02-27-2011 06:46 AM
Hello Ian,
Good work!
Just a brief additional comment: neither IEEE STP nor Cisco PVST+/RPVST+ are encapsulated into Ethernet_II frames, that is why there is no information about the assigned EtherType. An Ethernet frame carrying these protocols carries the length of the frame in the respective field, and the actual payload type is determined by additional headers.
The IEEE STP/RSTP/MSTP uses LLC encapsulation with the DSAP=SSAP=0x42. The Cisco's PVST+ uses SNAP encapsulation where, because of SNAP, DSAP=SSAP=0xAA and the Protocol=0x010B.
Best regards,
Peter
02-27-2011 03:37 AM
After digging around I found this:
1. LSAP 0x4242 -> IEEE STP and PVST (ISL trunks, access ports)
2. ether 0x010B -> PVST+ (802.1q trunks)
3. LSAP 0xAAAA -> All SNAP encaps, including PVST+, CDP, VTP, etc, which can all be matched with ethertype (even though is protocol ID).
HTH,
Ian
02-27-2011 06:46 AM
Hello Ian,
Good work!
Just a brief additional comment: neither IEEE STP nor Cisco PVST+/RPVST+ are encapsulated into Ethernet_II frames, that is why there is no information about the assigned EtherType. An Ethernet frame carrying these protocols carries the length of the frame in the respective field, and the actual payload type is determined by additional headers.
The IEEE STP/RSTP/MSTP uses LLC encapsulation with the DSAP=SSAP=0x42. The Cisco's PVST+ uses SNAP encapsulation where, because of SNAP, DSAP=SSAP=0xAA and the Protocol=0x010B.
Best regards,
Peter
02-27-2011 06:49 AM
Thanks Peter for the clarification.
02-27-2011 10:04 AM
Thanks Peter,
for these very interresting comments.
Best regards,
Michelot
02-27-2011 10:11 AM
Thanks Ian,
for your digging, and your introduction to peter comments.
Best regards,
Michelot
Find answers to your questions by entering keywords or phrases in the Search bar above. New here? Use these resources to familiarize yourself with the community: