Specifications

Ethernet Bridge Operation 9-11
Spanning Tree Operation
A similar case can be made for EVENIN, the bridge that spans LAN B and
LAN C shown in Figure 9-5.
Figure 9-5. BPDUs in from ANN to EVENIN
EVENIN would have also thought that it was root until it found out
otherwise. Let’s look at the progression of BPDUs from ANN. Here are
EVENIN’s BPDUs:
The BPDU coming in to port 1 on EVENIN indicates that SAM has a
higher priority than it does, so it also stops generating its own BPDUs and
forwards those of the higher priority. The BPDU coming out of port 2 of
EVENIN reflects SAM as the root (root ID). The incoming BPDU reflects
that ANN can get to the root from LAN B at a cost of 100. The outgoing
BPDU onto LAN C represents the fact to any Bridge on LAN C that
EVENIN can get to the root for a cost of 200 (root path cost).
BPDU IN (Port 1) BPDU OUT (Port 2)
Root ID 80-00-00-00-1d-23-56-a2 80-00-00-00-1d-23-56-a2
Path Cost 100 200
Bridge ID 80-00-00-00-1d-56-d4-f4 80-00-00-00-1d-4f-94-a1
Port ID 8002 8002
LAN A
LAN B
LAN C
ANN
JANET
SAM
EVENIN
Port 1
Port 2
BPDU in
from ANN
BPDU out
1913-35