Switch Traffic

Unanswered Question
Aug 18th, 2009

Hello all,

Please help me to achieve the attached scenerio.

Have L3 Cisco Switch(Parent/Main) which is connected with L3 Switch-1 by Connectivity A (L2 Connectivity) and with L3 Switch-2 by Connectivity B (L2 Connectivity). Have to desing a scenrio where in case of failure of Connectivity A between Switch-1 and Parent/Main Switch,,, Traffic(L2)on Switch-1 will auto shifted on Proposed connectivity between Switch-1 & Switch-2 connected to each other with gig ports(i.e Switch-1 Traffic will flow via Switch-2 towards Parent Switch)...and Same for in case of Failure of Connectivity B, i.e Switch-2 Traffic will flow via Switch-1 towards Parent Switch. and after restoration of Connectivity A or Connectivity B traffic could again auto reverted on their actual connectivity towards Parent Switch.

Note:- New or required configs to achieve this to be done only on Switch-1 & Switch-2.

pls suggest.

I have this problem too.
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Mohamed Sobair Tue, 08/18/2009 - 09:06

Hi,

You have STP running on all switches of course.

1st: Set the root of the STP to be bridge parent/main.

2nd: you are good to go, as traffic will flow as you described incase of a failure on l2 connectivity A or l2 connectivity B to the root bridge.

HTH

Mohamed

netbeginner Tue, 08/18/2009 - 21:36

Hi Mohammed,

Yes u r right.

But as i mentioned, preferrely we don't want to make any changes on Parent Switch as other access connectivities are also running on the same with heavy traffic and many Vlans. Do we have any other solution which we have to excute only on Switch-1 And Switch-2.

Mohamed Sobair Wed, 08/19/2009 - 04:04

Hi Sam,

You dont require additional config, Hosta on Switch A will reach hosts on Switch parent through Switch B if the primary link to parent fails. and vice versa.

HTH

Mohamed

netbeginner Wed, 08/19/2009 - 08:56

Ok, then pls tell how to configure/achieve your first point.(mentioned in your first post).

But as i informed that we need to ensure that other access connectivities(L2 connectivity) from Parent Switch will not be affected by these new changes. There are about 30-35 different Vlans running with Parent Switch for different access connectivity. For some L2 access connectivity some Vlans are kept same. for eg:- Say Vlan 10 is allowed on four Access L2 connectivities.

Mohamed Sobair Thu, 08/20/2009 - 14:31

Hi Sam,

Ok, The root bridge is elected based on the bridge-id. The bridge id is 6 byte mac address + 2 byte priority.

The lowest Bridge priority influence the Switch to be the root. If the priorities are all the same, then the bridge with the lowest mac address would be the root.

Check what is the current root bridge for those vlans including vlan 10 by (sh spanning-tree vlan x)

If the parent switch is the root then you dont need any changes, If parent is not the root, then ensure both switch-1 & switch-2 has the highest priority set for those vlans by issuing:

spanning-tree vlan x priority 32768

If the priorities on both switch A and Switch b are the highest and the root elected is on of them based on MAC, then you will have to manually set it on the Parent switch.

Those changes shouldnt affect you any down time.

HTH

Mohamed

netbeginner Sun, 08/23/2009 - 09:18

Hi Mohamed,

I have checked the Root Bridge status of Parent Switch, Switch-1 & Switch 2. Parent switch is reflecting as root bridge only.

**** Parent Switch ****

Cisco_Switch_Parent#sh spanning-tree vlan 10

VLAN0010

Spanning tree enabled protocol ieee

Root ID Priority 32780

Address 0016.c50d.06d0

This bridge is the root

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

+++++++++++++++++++

**** Switch-1 ****

Cisco_Switch_1#sh spanning-tree vlan 10

VLAN0010

Spanning tree enabled protocol ieee

Root ID Priority 32780

Address 0016.c50d.06d0

Cost 4

Port 1 (GigabitEthernet1/8)

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

+++++++++++++++++++++++++++=

**** Switch-2 ****

Cisco_Switch_2#sh spanning-tree vlan 10

VLAN0010

Spanning tree enabled protocol ieee

Root ID Priority 32780

Address 0023.04d1.62c0

Cost 4

Port 47 (GigabitEthernet1/10)

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Apart from these, Now i also have one more same topololoy, but this time here is two Parent L3 Switches from where "Switch-1" is connected to "Parent Switch-A" (L2 Connectivity witn multiple same Vlans) ....and "Switch-2" is connected to "Parent Switch-B" (L2 Connectivity with multiple same Vlans). Again expectation is same here. i.e In case of failure of L2 connectivity between "Parent Switch-A" & "Swicth-1" all Traffic of "Switch-1" will shift on Propesed L2 connectivity between "Switch-1" & "Switch-2" and then towards "Parent Switch-B" and same will be for L2 connectivity failure between "Parent Switch-B" to "Switch-2" --> Traffic of " Switch-2"will be via "Switch-1" and then towards "Parent Switch-A".

New Scenerio attached herewith.

Also, Will be greatfull if anyone clear me "How to Trace from which switch eaxactly L2 loop generating on a LARGE L2 network...if any specific command for that".

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