Spanning tree on Cisco

[BCSCB]

Hi,

I am setting up a resiliant link so there is no single point of failure.

We have 6 servers each with dual NIC Cards all on the same IP range. I have installed 2 3500-24. These are connected via gbic ports to the core network (6500's)

Switch 1 connects to port 1 on 1st 6500
Switch 1 connects to port 2 on 2nd 6500

Switch 2 connects to port 2 on 1st 6500
Switch 2 connects to port 1 on 2nd 6500

I have configured Dot1q and trunks on all the ports as the Servers are in Vlan 221.

Thing is I cannot get spanning tree to enable, in affect causing a loop. Am I missing something stupid here.

Any help appreciated. Thanks

 

[BCSCB]

I think I have found the problem......

I have been trying to configure multiple spanning tree, as there is more thatn one Vlan.

I have just found out that the switches that I am using dont support it !!!

Guess I'll have to order 2 new switches

 

[rmcp2k]

spanning tree is on by default to prevent switching loops. if you do a show spanning tree one of the port in non root brige should be in blk mode. give us your run config on the switch.

 

[BCSCB]

ip subnet-zero
!
!
!
interface FastEthernet0/1
switchport access vlan 221
spanning-tree portfast
!
interface FastEthernet0/2
switchport access vlan 221
spanning-tree portfast
!
interface FastEthernet0/3
switchport access vlan 221
spanning-tree portfast
!
interface FastEthernet0/4
switchport access vlan 221
spanning-tree portfast
!
interface FastEthernet0/5
switchport access vlan 221
spanning-tree portfast
!
interface FastEthernet0/6
switchport access vlan 221
spanning-tree portfast
!
interface FastEthernet0/7
switchport access vlan 221
spanning-tree portfast
!
interface FastEthernet0/8
switchport access vlan 221
spanning-tree portfast
!
interface FastEthernet0/9
switchport access vlan 221
spanning-tree portfast
!
interface FastEthernet0/10
switchport access vlan 221
spanning-tree portfast
!
interface FastEthernet0/11
switchport access vlan 221
spanning-tree portfast
!
interface FastEthernet0/12
switchport access vlan 221
spanning-tree portfast
!
interface FastEthernet0/13
!
interface FastEthernet0/14
!
interface FastEthernet0/15
!
interface FastEthernet0/16
!
interface FastEthernet0/17
!
interface FastEthernet0/18
!
interface FastEthernet0/19
!
interface FastEthernet0/20
!
interface FastEthernet0/21
!
interface FastEthernet0/22
!
interface FastEthernet0/23
!
interface FastEthernet0/24
!
interface GigabitEthernet0/1
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 1-99,200-1005
switchport mode trunk
!
interface GigabitEthernet0/2
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 1-99,200-1005
switchport mode trunk
!
interface VLAN1
ip address 1.1.1.107 255.255.0.0
no ip directed-broadcast
no ip route-cache
!
ip default-gateway 1.1.1.1
snmp-server engineID local 000000090200000785B7F600
snmp-server community private RW
snmp-server community public RO
!
line con 0
transport input none
stopbits 1
line vty 0 4
password
login
line vty 5 15
password
login
!
end

CCMSwich2#

 

[rmcp2k]

i see what you're trying to do it doesn't support int range but if i remember it correct you can enable all interface with the command spanning tree default which enable ALL interface to portfast mode. You then need to remove portfast on those trunk interfaces to turn spanning tree back on.

 

[rmcp2k]

correct my mistake

the command is spanning tree portfast default to enable on non-trunking interface.

 

[BuckWeet]

are you referring to MST spanning tree mode?? PVST+ will do exactly what you need.. MST and PVST+ are much alike on cisco hardware.. there is a spanningtree instance per VLAN.. I advise on sticking with PVST+, or unless your 3500-24's support rapid spanning-tree..


BuckWeet

 

[BCSCB]

PVST+ sounds like its the correct route for me to persue.

IS it easy to configure as I hnever had to use it previously. Do I just confgure on the 3500's on the Gig Ports or do I also have to configure on the uplink ports on the 6500's aswell.

I would rather know how to do it correctly than do something wrong.
Cheers guys for your help, I owe you all a pint of Stella !!

 

[BuckWeet]

PVST+ is default on cisco boxes..

just configure the ports as trunk ports and you're good to go.

 

[BCSCB]

Hi BuckWeet,
Configured the ports as trunk ports as you stated,
I have also got
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 1-99,200-1005

When i connect the switch to the two 6500 both ports are active. I thought that one port should go to standby mode.

Am I missing the point here ??

Cheers

 

[BuckWeet]

the downstream switch will have the blocked port..

since the 6500's have a lower bridge priority than the 3500.. they will forward on all ports.. the 3500 would then have a blocked port going towards the higher priority 6500..


hope that helps..

 

[BCSCB]

Cheers BuckWeet.

I have substituted the 3500's with 3750's and hey presto it works Spanning-tree is blocking Gig1/0/26 vlan1 and 221 and forwarding all on gig1/0/25.

I can only assume that the Spanning-tree on the 3500's was not functioning correctly. I will have a play with the 3500's and see why i couldnt get it working. I had previously done exactly the same using a 3550 no problems.

One for the "Im not sure why " Pile !!!

 

[helpdeskdan]

Buckweet mentioned the bridge priority - you could and actually should be modifying that on a central root switch in your network to assure the proper operation. Probably on the 6500.

Just to clarify, it was mentioned that portfast disables spanning tree on that port; not true. It shortens the listening and learning to about zero. It's a common misconception; even the Exam Cram 2 book is completely wrong on the subject. Bpdu filtering is a good thing - for more information than you need to know:

http://www.cisco.com/univercd/cc/td/doc/product/lan/cat6000/12_1e/swconfig/stp_enha.htm

 

[BuckWeet]

In my opinion "Bpdu filtering" is not a good thing.. BPDUGuard is a good thing.. You never know when someone will bridge 2 NICs together in your environment or connect another switch when they're not supposed too..

BPDU Filtering can kill you if you have your ports misconfigured, which is easy to do when you get into hundreds to thousands of ports.

Take out the foreseeable landminds!

 

[helpdeskdan]

A good point. I would only use bpdu filtering globally which, for some silly reason, actually performs much different than if you enable it on a port. If you enable it on a port, you will get the operation which buckweet has described. However, enabling it globally, it will disable portfast as soon as it recieves a bpdu.

bpdu filtering is useful if you know other people will be working on the network; people who, for instance, do not understand stp yet might want to install a switch.