10-29-2014 09:27 AM
On the EdgeRouter Lite, when STP is enabled on a bridge interface, the default bridge priority is 0.
Please consider changing the default STP Bridge priority from 0 to 32768 to match the defaults of other major switch manufacturers.
The STP bridge priority is used to determine which bridge (switch) will win an election to become the STP Root bridge. The switch running STP with the lowest priority value will become the Root Bridge.
Having the ERL use a default STP priority of 0 may cause unexpected behaviour for users accustomed to the defaults used by other manufacturers. Changing the default priority from 0 to 32768 will address these concerns.
I can not immedately think of an environment where an ERL would be the preferred STP Root over another switch so having the default be 0 seems aggressive. Typically a "core" switch is manually configured to become the STP Root by lowering its configured priority but it is hard to go lower then 0 in order to beat the default of the ERL.
HOW TO REPRODUCE
( below behaviour confirmed on ERL versions "v1.5.0" and "v1.6.0rc2" )
Create a bridge, enable STP, and assign it to a physical interface. (do not specify a priority value)
ubnt@ubnt:~$ configure ubnt@ubnt# set interfaces bridge br0 stp true ubnt@ubnt# set interfaces ethernet eth0 bridge-group bridge br0 ubnt@ubnt# commit ubnt@ubnt# save ubnt@ubnt# exit
Running "show bridge" displays the priority value (in hex) as the first part of the "bridge id"
ubnt@ubnt:~$ show bridge bridge name bridge id STP enabled interfaces br0 0000.dc9fxxxxb9de yes eth0
A packet capture confirms that EdgeMax is using the above bridge-id in its BPDU frames.
ubnt@ubnt:~$ sudo tcpdump -vvv -p -n -i eth0 stp tcpdump: WARNING: eth0: no IPv4 address assigned tcpdump: listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes 10:49:49.177091 STP 802.1d, Config, Flags [none], bridge-id 0000.dc:9f:xx:xx:b9:de.8001, length 35 message-age 0.00s, max-age 20.00s, hello-time 2.00s, forwarding-delay 15.00s root-id 0000.dc:9f:xx:xx:b9:de, root-pathcost 0
Info from the connected Cisco switch confirms the priority value of 0 of the ERL Root Bridge:
VLAN0001 Spanning tree enabled protocol rstp Root ID Priority 0 Address dc9f.xxxx.b9de Cost 4 Port 35 (GigabitEthernet0/35) Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Bridge ID Priority 24577 (priority 24576 sys-id-ext 1) Address 0019.xxxx.9880 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Aging Time 300 sec Interface Role Sts Cost Prio.Nbr Type ------------------- ---- --- --------- -------- -------------------------------- Gi0/35 Root FWD 4 128.35 P2p Peer(STP)
Juniper default priority is 32,768
Cisco default priority is 32,768
"...switch priority of all the switches is set to the default (32768)"
HP ProCurve default is 32,768
- [PDF page 27] http://www.hp.com/rnd/pdfs/CLI_reference.pdf
"priority <0..65535> - Switch (or bridge) priority used along with the switch MAC address to determine which device is the root. The default is 32768. "
Mikrotik default is 32,768
Wikipedia states default is 32,768
"...The bridge priority default is 32768"