TE in Ring Topology

HI,
I have 3 Rings in Hiearchy in my MPLS/Ethernet network. Acc, Agg, Core. I want to run Traffic Engineering solely for Fast Convergence & minimise traffic loss due to failures.
RSVP FRR ( link & node protection) is usually explained in context where partial mesh or triangle topology is used.
I read Path Protection is better suited for Ring topology..
Can u suggest a good model to achieve fastes convergence ( sub 50ms or near) & least traffic loss in ring topology network..
Say most of the traffic enters through ACC ring nodes and goes to Core ring and then moves out..
Thx,
Gaurav

FRR protects NH ( link ) NNHOP ( node). If I take example of FRR link protection in ring topology with 1Hop primary RSVP TE tunnel and multihop backup tunnel, if the primary TE tunnel fails , the traffic will reroute on backup tunnel in reverse direction ( other side of ring), reach the same next-hop router. IN this case there will be extra traffic reverse and then again towards the destination..
r1----r2----r3---r4----r4-----r5-----r6---r1
Say the ring consists of 6 routers connected via one hop primary tunnels and multi-hop backup tunnel. say traffic with source r1 and destination r5.
now r1 --r2 link fails... the traffic goes into Backup Tunnel (r1--r6--r5--r4---r3--r2) reaches r2 and then again goes from r2 towards r3 --r4--r5, to reach the destination. So, suboptimal back and forward traffic to destination, till the r1----r2 Primary TE tunnel comes up.
Do we agree on this ?
Thx,
GP

Similar Messages

CAC in ring topology WAN

Hi,
I have to apply CAC to a ring topology WAN with 5 sites. The network is build for resiliance if one of the WAN connections are lost, traffic i routed the other way.
Site 1 is main site, and connected to site 2 and 5, site 2 is connected to site 1 and 3, site 3 is connected to site 2 and 4, etc. Site 3 and 4 is not connected directly to main site.
Should I define a "dummy" region site, define BW policy of 100kb for each media and assign these to each site, BW policy of what I need and assign these to intersite links or is there another way of doing CAC in this type of network??
/Kenneth

Hi,
Here is a great blog simulating Lync Server 2010 CAC in a lab environment:
http://blogs.technet.com/b/nexthop/archive/2011/03/28/simulating-lync-server-2010-call-admission-control-in-a-lab-environment.aspx
Kent Huang
TechNet Community Support

MPLS TE tunnel protection (FRR) in a ring topology

Hi Friends,
Requesting you all to please share your experiences on MPLS-TE protection (in a ring), like best practices, caveats, feasibility, 'should I really think about it', etc...
Thanks
~sultan

Hello Martin,
Glad to see your response!
My objective is to achieve sub sec failover for L2/L3VPNs.
Basic background:
Currently we have two POPs for providing L2/L3VPNs, and will be adding two more.
We have FRR enabled with static LSPs.
We use 7600 for L3VPNs (7600 PE/P) and connecting to the STM backbone.
While for L2VPNs we use ME6524 (PE for L2VPN) with 7600 acting as 'P' for the same.
There are TE tunnels on 7600 for L3VPNs and 6524s for L2VPNs.
Connectivity within the POPs is through GigE links.
I hope these details would help...
Thanks again..
~sultan

Token ring

can anyone explain in an easy way how this works, do people still use it, do you still need a switch to set this up or is it from pc to pc ?
thanks

Token Ring ... I thought I was out, but they pulled me back in ......
Token Ring, as the name suggests, uses a logical ring topology (topology = "What shape is it?") that is usually a physical star (i.e., central hub, with spokes to the hosts).
One of the hosts on the ring is considered a "Master;" he generates a bit pattern that is recognized as a "token."
The Token is send to the Master's downstream neighbor. The rule of Token Ring is that a station is not allowed to put data on the ring unless it controls the Token.
If the station that has the Token doesn't have any data to send, it regenerates the Token and sends it to his downstream neighbor. This continues ("passing the Token") until one of the hosts has data to send.
If the host has data, it sets a flag in the Token, affixes the data, and send the Token+Data downstream.
As each host receives the Token+Data, it looks at the destination address. If it is addressed to him, he copies the data (and send it up the stack), sets another flag in the Token to indicate the the data was "copied." When the transmitting station gets the Token(+Data) back, he sees the "copied" flag, and flushes the data.
The Master watches the Token+Data circulate on the ring; if he sees the same Token+Data more than once, he decides that the transmitter was lost and removes the Data, regenerates the Token, and sends it on.
That's it in a very basic nutshell.
You cannot do back-to-back connections with Token Ring ... you must use a Multi-Station Access Unit (MAU) or a device that emulates one (Token Ring Switch). This is because the original Token Ring was meant to be able to have MAUs in the ceiling (for example) where there is no power. Each station provides (indivisually and collectively) the power to operate the MAU.
The 802.5 spec also provides a sequence for how a host enters the ring ... that cannot really be emulated in a host-to-host connection.
Again, that's it in a very brief nutshell. There is not enough space in a single post to provide a detailed description.
Token Ring is still being used in some shops, most are using "Big Iron" (IBM Mainframes). Token Ring is very dependable and provides a self-healing physical architecture.
It tends to be a little on the expensive side.
Let us know if you have any additional questions.
Good Luck
Scott

SGE2010P ring of 4 switches reports one "link down"

Any help appreciated. I called Cisco Support but they didn't have an answer.
We have 4 SGE2010P switches in a ring using ports 24 and 48 to connect. All are same hardware and firmware and the stack is working nicely.
Problem is - System - System Management - Stack Management page of web interface shows one link in the ring down yet it does not appear to be down. If we pull a cable from one of the other links then this "down" link is magically back.
Two questions:
1. Is the switch purposely breaking the chain to avoid a loop condition? If so, does that mean a 1-2-3-4 ring requires switch 1 to go the long path through 2 and 3 to communicate with 4?
2. Even if all is working as a ring and this is just a status reporting error, we have a problem in that one link failure cannot be detected since it shows down even when it isn't. That is bad for remote management and I cannot see any way to determine status of all 4 links shorts of visiting all switches and physically eyeing the ports in question.
Any insights appreciated.
Thanks.
John,

Hi John
With this stack, you haven't had to worry about spanning tree, the stack takes care of making sure that a broadcast storm isn't created by a loop, one of the interfaces becomes inactive. But if you had a real interface failure or a stacking port was to fail, the ring topology would still allow all switches in the stack to still be connected.
Well stacking becomes convenient for a few situations;
reduce the number of infrastructure IP hosts that need managing on your network
Allowing for Link Aggregation from servers to multiple switches in a stack.
You always have the option for;
taking the switches out of stack mode
running Link Aggregation with RSTP as per the rough diagram below;
The better more proactive solution is to use a ONPLUS appliance, which will proactively inform you when there is a problem on your end user network.
ONPLUS is more than just a cloud based service, there are alot of benefits of this appliance in fascilitating a pro-active support for your end user.
We produced p/n ON100-K9 appliance to allow our partners to provide a more proactive professional services enviironment for their customers . Even though my personal network can stand a failure, I utilize a ON100-K9 unit for demonstration purposes .
Because I use my network for experiments and it may change daily, the onplus appliance (p/n ON100-K9) send me quite often emails warning me of changes via the cisco cloud based service. Here is an example below of a warning i receive via email.
For an independent description of ONPLUS appliance and the cloud based service, check out this review from smallnetbuilder
http://www.smallnetbuilder.com/lanwan/lanwan-reviews/31805-cisco-onplus-reviewed
John , I am happy to also have a quick chat via phone to discuss the topology options and better understand your needs. If you wish send me your contact details to;
dhornste at cisco.com (just remove the spaces and replace the at with @ )
regards Dave
Systems Engineer
Cisco Systems, Inc.
Research Triangle Park
NORTH CAROLINA

9000V with Simple Ring - Dual Host configuration

When using Cisco 9000V's in a Simple Ring Topology with Dual ASR9k Hosts, are there any implications if the ASR9k's are running two different versions of IOS-XR even if only for a short period of time?

Since 5.1.1 is the first release which allows simple ring yes.
Now when 5.1.2 comes out it shouldn't be a problem, but this is not something I have tested.
The difference in 5.1.1 and earlier releases is the ability to configure L2 fabric, the underlying architecture is different, and we have an updated satellite control protocol. All of these allow for topologies such as simple ring.
In the future with newer topologies if the underlying architecture changes enough, or the control protocol goes through a major revision then it is possible you would see an issue, but I don't see it being an issue with the next few releases.
HTH,
Sam

Power Redundancy problem for cisco 3750 stack switches

Hi Team,
I have installed and configured cisco 3750X series switches in stackwise. Those are having dual power supply.
Power redundancy test performed:
1. Removed one of the power supply and inserted it back.
2. once the first power supply is ready, removed another power supply and switch got rebooted.
please find the below stack-power output:
JP2-RDC-DIS-02#sh stack-power detail
Power Stack           Stack   Stack    Total   Rsvd    Alloc   Unused Num Num
Name                  Mode    Topolgy Pwr(W) Pwr(W) Pwr(W) Pwr(W) SW   PS
Powerstack-2          SP-PS   Stndaln 700     477     223     0       1    2
Powerstack-1          SP-PS   Stndaln 700     477     223     0       1    2
Power stack name: Powerstack-2
    Stack mode: Power sharing
    Stack topology: Standalone
    Switch 2:
        Power budget: 223
        Power allocated: 223
        Low port priority value: 22
        High port priority value: 13
        Switch priority value: 4
        Port 1 status: Not connected
        Port 2 status: Not connected
        Neighbor on port 1: 0000.0000.0000
        Neighbor on port 2: 0000.0000.0000
Power stack name: Powerstack-1
    Stack mode: Power sharing
    Stack topology: Standalone
    Switch 1:
        Power budget: 223
        Power allocated: 223
        Low port priority value: 22
        High port priority value: 13
        Switch priority value: 4
        Port 1 status: Not connected
        Port 2 status: Not connected
        Neighbor on port 1: 0000.0000.0000
        Neighbor on port 2: 0000.0000.0000
Can anyone help what went wrong here?
Thanks
Manish

Cosmetic bug
CSCui21029    3750X Stack no standalone stays in running configureation as standalone
Symptom:
When you are configuring a 3750x stack and initially putting it into a stack ring topology by configuring the following.
Switch(config)#stack-power switch 1
Switch(config-switch-stackpower)#sta
Switch(config-switch-stackpower)#no stan
Switch(config-switch-stackpower)#no standalone
You will see that in the running configuration it shows up as standalone mode
stack-power switch 1
switch mode: standalone
stack-power switch 2
switch mode: standalone
Conditions:
3750X stacks with any license level
Workaround:
none

Help with GBIC selection LH vs ZX

Dear Support,
I now have the estimated Attenuation values from our fibre provider, and wondering if anyone could help with determining if I can utilise the cheaper (LH modules) across the 20 & 15 KM streches.
Thanks in advance (many thanks to Josh for helping out with my previous post - below)
HQ to DC1 = 1310nm: 2.5dB, 1550nm: 2.2dB.
DC1 to DC2 = 1310nm: 14.5dB , 1550nm: 13.1dB
DC2 to HQ = 1310nm: 10.1dB, 1550nm: 9dB
=========================================
Dear Support,
Sorry but new to optical networking, but need some assistance on an upgrade that we are performing.
We currently have two data centres that hold our servers and are planning to upgrade from LES circuits to Gigabit links, and triangulate our topology. (effectively a ring topology)
I have already spoken to our proposed fibre provider and they have provide me with rough distances, but due to one of the data centres being more than 10 km away we need to use ZX based GBICs. Summary of distances below;
HQ -> dc1 (1 2 km)
HQ -> dc2 (15 km)
Dc1 -> dc2 (20 km)
From our HQ to dc1 we will use LH (via a GLC-LH-SM= in a 2970G) and a to dc2 we will use ZX (via a GLC-ZX-SM= in another 2970G)
From DC1 to HQ we will use LH (via a WS-G5486 in a 7204VXR) and a to dc2 we will use ZX (via a WS-G5487 in another 7204VXR)
From DC2 to HQ we will use ZX (via a WS-G5487 in a 7204VXR) and a to dc1 we will use ZX (via a WS-G5487 in another 7204VXR)
Hope this doesnt confuse things more.
Now to the question.
From the Cisco web site it mentions the following;
When shorter distances of single-mode fiber are used, it might be necessary to insert an in-line optical attenuator in the link to avoid overloading the receiver:
A 5-dB or 10-dB inline optical attenuator should be inserted between the fiber-optic cable plant and the receiving port on the Cisco 1000BASE-ZX GBIC at each end of the link whenever the fiber-optic cable span is less than 15.5 miles (25 km).
We havent yet had the fibre survey performed, but once they have advised me of the attenuation on the link, how should I calculate what level of in-line optical attenuator I should need or should all reputable fibre providers advise me of this detail.
Thanks in advance.
Regards, Adrian

Summary of Optical Levels:
GLC-ZX-SM:
Transmit: 0 to +5
Receive: -23 to 0
GLC-LH-SM:
Transmit: -9.5 to -3
Receive: -20 to -3
G5486:
Transmit: -9.5 to -3
Receive: -20 to -3
G5487:
Transmit: 0 to 5.2
Receive: -24 to -3
Given the above:
HQ -> DC2: maximum receive level will be 5-10.1 = -5.1 dB, which is OK for the G5487
HQ <- DC2: maximum receive level will be 5.2-10.1 = -4.9 dB, which is OK for the GLC-ZX-SM
HQ -> DC1: maximum receive level will be -3-2.5 = -5.5 dB, which is OK for the G5486
HQ <- DC1: maximum receive level will be -3-2.5 = -5.5 dB, which is OK for the GLC-LH-SM
DC1 -> DC2:maximum receive level will be 5.2-14.5 = -9.3 dB, which is OK for the G5487
DC1 <- DC2:maximum receive level will be 5.2-14.5 = -9.3 dB, which is OK for the G5487
Therefore, you do not need attenuators anywhere.
Now, to your next queston. If you used the LH modules, you the minimum possible receive levels now become:
HQ -> DC2: minimum possible receive level will be -9.5-10.1 = -19.6 dB, which is only just OK for the G5486
HQ <- DC2: minimum possible receive level will be -9.5-10.1 = -19.6 dB, which is only just OK for the G5486
DC1 -> DC2: minimum possible receive level will be -9.5-14.2 = -24 dB, which is too low for the G5486
DC1 <- DC2: minimum possible receive level will be -9.5-14.2 = -24 dB, which is too low for the G5486
Therefore, my recommendation is to stick with the ZX modules for these links.
Hope that helps - pls rate the post if it does.
Paresh

MST/RSTP not quite working

Hi,
I have 6 x 3560 switches all connected in a redundant ring topology and interconnected using fibre.
I have enabled the fibre ports as trunk ports with dot1q encapsulation.
I have created 6 VLANS and defined ports on each device as members of the configured VLANS, and also defined a VTP root switch (all VLAN info appears to be propagating correctly between all switches).
I have enabled MST on all the devices and created an instance 1 with a name and revision number on all of the switches which are identical.
I have also used the root and secondary mst commands to define a root and secondary switch.
E.G:-
spanning-tree mode mst
spanning-tree extend system-id
spanning-tree mst configuration
name ABC
revision 1
instance 1 vlan 1-200
The problem I am seeing is that if I remove the fibre from the ROOT port from the ROOT switch, the comms fail and I see a time out of approx 8-10 seconds before the link is re-established using the redundant path (second fibre port. I see the port swap the MST01 from DESG to ROOT, when the previous ROOT port goes down (cable removed).
Ive reduced the forward time to the minimum 4 seconds, which has improved the recovery time, but still not <1 second which I need.
Im confused as to why when I setup a device on 1 switch to ping a device on the adjacent switch (ie next device in the fibre), but is on the same VLAN, that the layer 2 comms should be affected by the removal of the Root switch link (physicaly not even connected to the 2 devices which need to talk).
I can see if the root switch is totally removed from circuit, that the secondary takes over fine.
Im also not doing any layer 3, inter-vlan routing.
Can anyone help?

If tuning the forward delay timer had any effect, it means that your network is not taking advantage of the MST protocol. Reconvergence is achieved with no use of the forward delay timer in your scenario. Check that all the links in your ring are seen as point-to-point by the STP. You can also adjust the max-hop parameter to a value closer to the size of your ring (assuming that your MST network is only this ring, you could tune it down to 8 for instance). Also, you may want to upgrade your software release if it's an old one, as the response to agreement have been optimized (it may save some few seconds). At last, if you are only using one instance, the simplest and the most efficient is to keep the default configuration, where all the vlans are mapped to instance 0 (but I guess your network is more complex than what you exposed).
MST uses a sync mechanism that explains that the communication between your edge switch could be affected by a failure on the root. That should be short though.
Regards,
Francois

Stackpower switches show in standalone mode

Hi,
I have a stack of 8 3750x switches connected via Stackwise. In addition, I have these switches configured as two Powerstacks. When I look at the Powerstacks, they are showing as being in power-sharing mode. When I look at the individual switches, they show as standalone.   Right now, I have 1 switch in each powerstack that has two power supplies, and then the other three have a single power supply. Below is the output for "Show stack-power detail" as well as the Powerstack configurations.
Power Stack           Stack   Stack    Total   Rsvd    Alloc   Unused Num Num
Name                  Mode    Topolgy Pwr(W) Pwr(W) Pwr(W) Pwr(W) SW   PS
Powerstack_1          SP-PS   Ring     2145    45      570     1530    3    3
Powerstack_2          SP-PS   Ring     2860    60      760     2040    4    4
Powerstack_1-1        SP-PS   Stndaln 1430    520     190     720     1    2
Power stack name: Powerstack_1
    Stack mode: Power sharing
    Stack topology: Ring
    Switch 4:
        Power budget: 700
        Power allocated: 190
        Low port priority value: 20
        High port priority value: 11
        Switch priority value: 2
        Port 1 status: Connected
        Port 2 status: Not connected
        Neighbor on port 1: Switch 3 - e4d3.f15c.6880
        Neighbor on port 2: 0000.0000.0000
    Switch 2:
        Power budget: 700
        Power allocated: 190
        Low port priority value: 21
        High port priority value: 12
        Switch priority value: 3
        Port 1 status: Not connected
        Port 2 status: Connected
        Neighbor on port 1: 0000.0000.0000
        Neighbor on port 2: Switch 3 - e4d3.f15c.6880
    Switch 3:
        Power budget: 700
        Power allocated: 190
        Low port priority value: 22
        High port priority value: 13
        Switch priority value: 4
        Port 1 status: Connected
        Port 2 status: Connected
        Neighbor on port 1: Switch 2 - 6073.5c53.df80
        Neighbor on port 2: Switch 4 - 6073.5c51.dd00
Power stack name: Powerstack_2
    Stack mode: Power sharing
    Stack topology: Ring
    Switch 8:
        Power budget: 700
        Power allocated: 190
        Low port priority value: 20
        High port priority value: 11
        Switch priority value: 2
        Port 1 status: Connected
        Port 2 status: Connected
        Neighbor on port 1: Switch 7 - e4d3.f15e.fd80
        Neighbor on port 2: Switch 5 - e4d3.f12d.2c00
    Switch 6:
        Power budget: 700
        Power allocated: 190
        Low port priority value: 21
        High port priority value: 12
        Switch priority value: 3
        Port 1 status: Connected
        Port 2 status: Connected
        Neighbor on port 1: Switch 5 - e4d3.f12d.2c00
        Neighbor on port 2: Switch 7 - e4d3.f15e.fd80
    Switch 7:
        Power budget: 700
        Power allocated: 190
        Low port priority value: 22
        High port priority value: 13
        Switch priority value: 4
        Port 1 status: Connected
        Port 2 status: Connected
        Neighbor on port 1: Switch 6 - e4d3.f15e.c400
        Neighbor on port 2: Switch 8 - e4d3.f15a.4100
    Switch 5:
        Power budget: 700
        Power allocated: 190
        Low port priority value: 19
        High port priority value: 10
        Switch priority value: 1
        Port 1 status: Connected
        Port 2 status: Connected
        Neighbor on port 1: Switch 8 - e4d3.f15a.4100
        Neighbor on port 2: Switch 6 - e4d3.f15e.c400
Power stack name: Powerstack_1-1
    Stack mode: Power sharing
    Stack topology: Standalone
    Switch 1:
        Power budget: 910
        Power allocated: 190
        Low port priority value: 22
        High port priority value: 13
        Switch priority value: 4
        Port 1 status: Shut
        Port 2 status: Shut
        Neighbor on port 1: 0000.0000.0000
        Neighbor on port 2: 0000.0000.0000
stack-power stack Powerstack_1
stack-power stack Powerstack_2
stack-power switch 1
stack Powerstack_1
switch mode: standalone
stack-power switch 2
stack Powerstack_1
switch mode: standalone
stack-power switch 3
stack Powerstack_1
switch mode: standalone
stack-power switch 4
stack Powerstack_1
switch mode: standalone
stack-power switch 5
stack Powerstack_2
switch mode: standalone
stack-power switch 6
stack Powerstack_2
switch mode: standalone
stack-power switch 7
stack Powerstack_2
switch mode: standalone
stack-power switch 8
stack Powerstack_2
switch mode: standalone

Cosmetic bug
CSCui21029    3750X Stack no standalone stays in running configureation as standalone
Symptom:
When you are configuring a 3750x stack and initially putting it into a stack ring topology by configuring the following.
Switch(config)#stack-power switch 1
Switch(config-switch-stackpower)#sta
Switch(config-switch-stackpower)#no stan
Switch(config-switch-stackpower)#no standalone
You will see that in the running configuration it shows up as standalone mode
stack-power switch 1
switch mode: standalone
stack-power switch 2
switch mode: standalone
Conditions:
3750X stacks with any license level
Workaround:
none

Spanning Tree Protocol

Fellas, I was wondering if someone can help me out here. I need to know if anyone out there in a metro ethernet or campus environment is running STP/MST/RSTP at a large scale. Large scale meaning about 200 switches. Can anyone point me to a link for a case study or a company doing this preferabley with Cisco gear but any gear would suffice.
Also, any links on STP scaling and free standards downloads?
I am searching myself but I recall this site has a tremendous amount of good folks.
Any help would be appreciated thanks..

STP as a standard recomends seven switches in a ring topology and RSTP may go up to 14 again recomended.There is no hard and fast rules as to how many switches to be accomodated in a ring.However my practical experience recomends the above. With RSTP typically the convergence is 600 msecs . This could be lowered by running multiple instances of STP in a ring through the use of VLANs (MSTP). In some cases it really can go up seconds unless the BPDY flooding accross rings or accross VLANs are not prevented through somemechanism.You can refer to cisco site for RSTP ,MSTP white papers. All metro providers (Reliance Infocomm,Tata telecomm.) are using MSTP in the rings with a maximum of 7 to 8 switches in a ring.

2960-X stacking, 5 switches with interwoven 0.5 M cables

I am trying to understand how to connect 5 switches using 0.5 M cables only. I have read this "best practices" document, but it leaves some unanswered questions.
http://www.cisco.com/c/en/us/products/collateral/switches/catalyst-2960-x-series-switches/white_paper_c11-728327.pdf
I would normally just daisy chain the switches and bring a connection from the bottom switch back up to the top to create a "ring" topology. But the documentation also states that switches can be connected with "interweaved cables". It makes no statement as to what if any performance considerations should be taken into account when designing stack interconnections, or whether this interwoven topology creates any operational complications. The only requirements that I have seen is that each switch must have 2 operational FlexStack links in order to be fully redundant and to fully utilize all available bandwidth. Does anyone have any guidance in this area?
Assuming no negative consequences by using the "interwoven" topology, does this make sense?
Thanks,
-Jeff

Well it probably wouldn't be confusing if I could find a clear set of ground rules. The documentation mentions "FlexStack protocol", but the discussions seem to indicate that this is a control plane protocol. Do the stacking modules operate as ethernet bridges when making forwarding decisions like any other switch port? If the answer is yes then at least I understand the principal of operation. But now if you throw multi-chassis etherchannel uplinks into the mix divining general layer 2 paths becomes a little murky.
Although now that I look at it, using this cabling has an advantage over a straight ring topology. Once a frame hits the stack it is never more than 2 hops away from it's destination. With daisy-chained switches it could be up to 4 hops. This is of course assuming standard 802.1d-like forwarding. This may be an invalid assumption. I don't see any way to get spanning tree info for the stack ports.
(EDIT: standard ring topology would also have a maximum of 2 hops to any switch, not 4)

Cisco 3850 x 5 Members with Stack Power

Good day Fellow Networkers,
Cisco Catalyst 3850 Series Switches Q and A states that "Up to four switches can become part of the same Cisco StackPower stack in a ring topology". If the stack contains 5 or more members then presumeably, stackpower will continue to deliver functionality provided that I power multiple members of the stack with a gap of no more than four switches?
Thanks in anticipation

Hi,
In this case the functionality is limited to 4 switches in the stack power due to physical limitations, if you have more then 4 then you will need to configure 2 different stack power instances.
Hope this helps.

Physical position of backup Cisco 3560 switch in relation to other produciton switches

We currently have three 3560 switches connected to each other using SPF interconnect cables. I have a backup switch ready in the event one of the three switches fails. I'd like to keep the backup switch configured and in the rack connected to the three switches. If a switch fails, do the interconnect cables have to be routed in the same way they're currently setup or can they be connected in any order. In other words, if I have the replacement switch in the rack at the bottom with the other three switches and the top switch fails, after loading the config of the top switch onto the replacement switch, can I keep the cables from the second switch connected to the third switch and run the interconnect cables from the failed switch, now switch 1, to the third switch, which is situated in the rack just above the replacement switch?
Thanks in advance.

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Posting
For 3560s, what SPF ports you use doesn't really matter.
If the backup will be a cold spare, you may need to worry about port configurations, before you connect it.
If the backup will be warm spare, again, you can interconnect the SPF ports however you like. If, though, you create any L2 loops, you need something to break the loop, e.g. STP, FlexLink.
If you want intentional redundancy, the simplest configuration would be a ring, and assuming the backup is just a warm spare, a root switch defined with the other two non-backup switches connected to it (on the ring). (The backup would connect to the two non-root switches.)
Besides a ring topology for redundancy, you might setup a dual star topology, or as you only have four switches, even a full mesh.

MSTP issue

We have ring created of 3750s and 2950 are connected to 3750 in spur. MSTP is running and multiple vlans are running across the ring. When one of 3750 is restarted 2950 connected to another 3750 is affected when 3750 goes down and comes up. Evenif STP path of 2950 and it's connected 3750 is not changing.

The MST Instances are all dependent on instance 0, the CIST. If there is a reconvergence in the CIST (in particular if the root port is changing for instance 0, which is very likely in the case of a link failure in a ring topology), there might be some "sync" events that affect all the instances, and as a result all the vlans.
Regards,
Francois

TE in Ring Topology

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