Okay, here's the jist of things.
The Catalyst 2924XL is the root bridge:
> C2924XL#sh span
>
> Spanning tree 1 is executing the IEEE compatible Spanning Tree protocol
> Bridge Identifier has priority 32768, address 0050.3ef0.3580
> Configured hello time 2, max age 20, forward delay 15
> We are the root of the spanning tree
Port 0/26 on the Catalyst 1912 is identifying "Port 22" as the "designated
port":
> Port FastEthernet 0/26 of VLAN1 is Forwarding
> Port path cost 10, Port priority 128
> Designated root has priority 32768, address 0050.3EF0.3580
> Designated bridge has priority 32768, address 0050.3EF0.3580
> Designated port is 22, path cost 0
> Timers: message age 20, forward delay 15, hold 1
Port 22 is, port 0/20 on the Catalyst 2924XL switch:
> Interface Fa0/20 (port 22) in Spanning tree 1 is FORWARDING
> Port path cost 19, Port priority 128
> Designated root has priority 32768, address 0050.3ef0.3580
> Designated bridge has priority 32768, address 0050.3ef0.3580
> Designated port is 22, path cost 0
> Timers: message age 0, forward delay 0, hold 0
> BPDU: sent 46897, received 5
We can deduce that FastEthernet 0/26 on the 1912 switch is directly
connected to FastEthernet 0/20 on the 2924XL switch.
Note that FastEthernet 0/26 on the Catalyst 1912 is identified as the root
port as seen below:
> C1912#sh span
>
> VLAN1 is executing the IEEE compatible Spanning Tree Protocol
> Bridge Identifier has priority 32768, address 0050.50E2.42C0
> Configured hello time 2, max age 20, forward delay 15
> Current root has priority 32768, address 0050.3EF0.3580
> Root port is FastEthernet 0/26, cost of root path is 10
> Topology change flag not set, detected flag not set
> Topology changes 5, last topology change occured 0d02h42m54s ago
> Times: hold 1, topology change 8960
> hello 2, max age 20, forward delay 15
> Timers: hello 2, topology change 35, notification 2
So what we have is a LAN segment connection where one end of the connection
is identified as the root port while the other is identified as the root
port for the non-root-bridge Catalyst 1912 switch. Everything seems to be
"kosher".
All ports on the root bridge are designated ports by default. During the
execution of the Spanning Tree Algorithm, a root port (the port with the
lowest cost path to the root bridge) is identified, and each LAN segment
must identify one port as a designated port. If the LAN segment contains
one or more ports not identified as the root port for the switch or a
designated port, the port is identified as non-designated and is placed in
the blocking state.
If spanning tree was working properly in this topology, and if a looped
topology actually existed, another port on the Catalyst 1912 should show a
port on the Catalyst 2924XL as its designated port with that port on the
Catalyst 1912 as set in the blocking state -- but we don't see that. What
MAY be the case, because on the Catalyst 1912 FastEthernet port 0/27 is set
to trunking but hasn't established a physical connection, is that the port
is operating normally as a member of VLAN 1. If the port in which it is
connected to on the 2924XL is a member of a VLAN other than VLAN 1,
communication shouldn't occur properly -- and a looped topology wouldn't
actually exist. Only port 0/21 on the 2924XL is operating at 100 Mbps in
Full-Duplex mode - so I suspect the 1912 0/27 port IS in fact connected to
the 0/21 port. HOWEVER... if you do a "show interface fastethernet 0/21,
you will see that last input was 3:49:16 - which means it's been quite some
time since this port received anything from what it's connected to... It's
not receiving BPDU's every 2 seconds from 0/27 if it is in fact connected to
0/27...
> C2924XL#sh int f 0/21
> FastEthernet0/21 is up, line protocol is up
> Hardware is Fast Ethernet, address is 0050.3ef0.3597 (bia
0050.3ef0.3597)
> MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec, rely 255/255, load 1/255
> Encapsulation ARPA, loopback not set, keepalive not set
> Full-duplex, 100Mb/s, 100BaseTX/FX
> ARP type: ARPA, ARP Timeout 04:00:00
> Last input 03:49:16, output 00:00:01, output hang never
So... do we have an active looped topology? I doubt it. Likely, Spanning
Tree's working just fine. Check the LED's on both of your switches to see
if you see a solid orange glow...
-- Leigh Anne
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of
Leigh Anne Chisholm
Sent: February 13, 2001 10:22 PM
To: Cisco@Groupstudy. Com
Subject: RE: DISTURBING: Spanning Tree Protocol Does not Work.
Which ports on the 2924XL are trunking? The only port I can see configured
for trunking is FA0/20. I'm not clear on exactly where you've connected the
1912's 0/26 and 0/27 ports on the 2924XL...
Also, you indicate that you've set up the 2924XL to be the root bridge --
you might want to check what criteria it is that you use when ensuring a
device is deemed to be the root bridge. I suspect you've played with the
wrong parameters to ensure that the 2924XL is the root bridge. Yes, the
2924XL IS the root bridge--but not because of anything you've configured.
-- Leigh Anne
(My apologies if this appears twice in GroupStudy -- I originally sent this
four hours ago, but have yet to see it appear on the list...)
-----Original Message-----
From: Pierre-Alex [mailto:[EMAIL PROTECTED]]
Sent: February 13, 2001 5:22 PM
To: Rik Guyler; Cisco Groupstudy (E-mail)
Cc: Lachisho; [EMAIL PROTECTED]; Dale Cunningham
Subject: RE: DISTURBING: Spanning Tree Protocol Does not Work.
<snip>
C2924XL# sh run
Building configuration...
Current configuration:
!
version 11.2
no service pad
no service udp-small-servers
no service tcp-small-servers
!
hostname C2924XL
!
enable secret 5 $1$OixX$sb.r.W9jrZfT7VfMQdtgF/
!
!
no ip domain-lookup
!
interface VLAN1
ip address 192.168.0.10 255.255.255.0
no ip route-cache
!
interface FastEthernet0/1
switchport access vlan 3
!
interface FastEthernet0/2
!
interface FastEthernet0/3
!
interface FastEthernet0/4
!
interface FastEthernet0/5
!
interface FastEthernet0/6
!
interface FastEthernet0/7
!
interface FastEthernet0/8
switchport access vlan 3
!
interface FastEthernet0/9
switchport access vlan 2
!
interface FastEthernet0/10
!
interface FastEthernet0/11
!
interface FastEthernet0/12
!
interface FastEthernet0/13
!
interface FastEthernet0/14
!
interface FastEthernet0/15
!
interface FastEthernet0/16
switchport access vlan 2
!
interface FastEthernet0/17
!
interface FastEthernet0/18
!
interface FastEthernet0/19
!
interface FastEthernet0/20
switchport mode trunk
!
interface FastEthernet0/21
!
interface FastEthernet0/22
!
interface FastEthernet0/23
!
interface FastEthernet0/24
switchport access vlan 2
!
snmp-server community private RW
snmp-server community public RO
snmp-server chassis-id 0x0E
!
line con 0
exec-timeout 0 0
stopbits 1
line vty 0 4
exec-timeout 0 0
password cisco
logging synchronous
login
line vty 5 14
exec-timeout 0 0
logging synchronous
login
!
end
<snip>
Pierre-Alex
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