Loop

[saquib.tandel]

Hi

what configuration steps is needed to avoid loop on the network, its a Client / Server topology

Catalyst 4507 acting as core and distribution. All access switches are 2950, 2960 series.

thanks

ST

[Latchum Naidu]

Hi,

A loop in your network can bring down the whole network.
I would suggest STP to use in your scenario which can avoid a loop by using Spanning Tree protocol (STP).

Please see the below linke for more details.
http://www.petri.co.il/csc_preventing_network_loops_with_stp_8021d.htm

Also find the below link for the discussion to avoid network loops.
http://www.experts-exchange.com/Networking/Network_Management/Network_Analysis/Q_22647147.html

And this link is for your implement of STP in your network.
http://www.cisco.com/en/US/tech/tk389/tk621/technologies_configuration_example09186a008009467c.shtml

Hope this clear for you.

Please rate the helpfull posts.
Regards,
Naidu.

[saquib.tandel]

Hi

what is best practise from Cisco where you got One 4507 and 20 Access switches, none of the acccess switches got redundant connection.

Two of the 2960 switches are cascaded to one of the access-switch directly connected to Core (4507)

Numnber of Vlans are 12

I have gone through these, still confused which best fits or best practise from cisco. Spanning-tree commands needs to be applied on VTP server and client both or just Server.

Spanning-tree mode rapid-pvst

spanning-tree mode MST

spanning-tree bpduguard default

spanning-tree bpdufilter default

error-disable

uplink fast

thanks

ST

[davy.timmermans · Accepted solution]

loop prevention is needed as soon as you form a triangle or square

triange : access switch 1 --- to core 1  ------core 2 ------to switch 1

By default classical STP is enabled so no worries but it's better to activate RSTP

configuration on all switches the required vlans:

vlan 2

name test

vlan 3

name test2

vlan 4

name test4

spanning-tree mode rapid-pvst

vtp mode transparent

vtp domain ! can be the same or different on other switches

on the 4500 core distribution switch

previous config +

vlan 2,3,4 priority 8192     <--- this will make the 4500 as root of the entire l2 network

if you've a second core/distribution switch

vlan 2,3,4 priority 12288 <-- create a backup STP root

if you don't have a secondary core/distribution, don't configure it on another access switch

Ports connecting to an end user or server

interface fas0/1

spanning-tree portfast

spanning-tree bpduguard enable

switchport mode access

-----------------------------

HTH

please rate helpful posts

[saquib.tandel]

Thank you for supporing.

Do this config looks ok, any more suggestions on Loop and uplink config consideration

On 4500

it would be

VTP mode Server

VTP domain Cisco

VTP password XXX

vlan 2,3,4,5,6,7,8,9  ....20 ( just to show there are around 20 vlans )

interface vlan 2

ip add 192.168.1.1 255.255.255.0

interface vlan 5

ip address 172.16.1.1 255.255.255.252

Spanning-tree mode rapid-pvst

Spanning-tree vlan 1 prority 0

Spanning-tree portfast bpduguard default

interface fa 3/1

description Connected to Web01-Server

switchport mode access

switchport access vlan 2

spanning-tree portfast

interface fa 3/23

description Connected to "Wireless-Lan-Controller"

switchport mode access

switchport access vlan 2

interface fa 3/24

description Connected to "Service-Provider CPE"

switchport mode access

switchport access vlan 5

Interface gi 0/1

description "connected to Access-Switch-EX01"

switchport trunk encapsulation dot1q

switchport mode trunk

Interface gi 0/2

description "connected to Access-Switch-Floor_2"

switchport trunk encapsulation dot1q

switchport mode trunk

Interface gi 0/3

description "connected to Access-Switch-Floor_3"

switchport trunk encapsulation dot1q

switchport mode trunk

router ospf 1

network 192.168.1.0 255.255.255.0

network 172.16.1.0 255.255.255.252

network 172.20.2.0 255.255.254.0

network 172.16.16.0 255.255.252.0

()()()()()()()()(())()()()()()()()()()()(())()()()()()()()()()()()()()()()(()()()()()

On Access_Switches 2960

VTP mode client

VTP domain Cisco

VTP password XXX

Spanning-tree mode rapid-pvst

Spanning-tree portfast bpduguard default

interface gi0/0

description "connected to Core"

switchport trunk encapsulation dot1q

switchport mode trunk

[Latchum Naidu]

This looks fine.

Please do this config and check.

Regards,

Naidu.

[saquib.tandel]

Hi

I need clarification

What is difference between "vlan 2,3,4 priority 8192" and "spanning-tree vlan 1 priority 0"

Do I need "VTP Prunning"

also

4500-----------------connected-------------------Access_sw1------------------------Access_sw2

sw1 gi 0/0 is connected to 4500 as a trunk

sw1 gi 0/1 is connected to acces-sw2 as a trunk

do I need to configure access_sw2 with all relevant spanning-tree config / VTP config  or just switchport mode trunk config is enough

[Latchum Naidu · Accepted solution]

Hi,

VTP pruning makes more efficient use of trunk bandwidth by reducing unnecessary flooded traffic.
This you need when you need set of VLANS should travers on the link rest of all will not, so that the available bandwidth will use in sufficient way.

Regarding spanning tree config on access layers, what you mentioned in your previous post is enough.

Please rate the helpfull posts.
Regards,
Naidu.