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STP/PVST+/RSTP+ & MST

Hi Im aware of the following:

STP 802.1d/PVST - Functions a '1 Root Bridge per network':
1. What if there was 2 networks - ?
2. Cannot be configured on Cisco switches (What then) - ?
3. I thought this STP 802.1d was the standard STP - ?

PVST+ - spanning-tree mode pvst:
4. Means each vlan has its own 'root bridge' by adding priorities for each separate vlan which can also achieve some load-balancing:

int fa0/x,
spanning-tree vlan x port-priority 16 or 32 or 48 etc etc upto 128 or leave as default of 128 - ?

RSTP/Rapid-pvst+/802.1w - spanning-tree mode rapid-pvst:
5. Does this mean automatically each individual vlan will have its own 'root bridge' although No4 has 'priorities' added manually - ?

MST/802.1s:
 
int fa0/x
spanning-tree mode mst
spanning-tree mst configuration
name apollo
revision 10
instance 1 vlan 1, 10-20
instance 2 vlan 30, 40-50, 70

6.  Vlans that span different regions, so Im assuming this means London, Cardiff, Scotland, or Usa etc ?

7. Can anyone advise on my interpretation as I always get confused with which is which - ?
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mikey250
Asked:
mikey250
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8 Solutions
 
rochey2009Commented:
802.1d is the original standard for spanning-tree protocol which takes between 30 to 50 seconds to converge because of the timers used for a port to move from blocking to forwarding. Supports a single STP topology.

CST is for 802.1Q trunking, same rules at 802.1d but again only one STP topology which multiple VLANs used.

Cisco's PVST which was for ISL trunking which supported a separate topology for each VLAN. (802.1d rules)

Cisco's PVST+ which is confusingly configured with spanning-tree mode pvst. This was for 802.1Q trunking and again supported a separate topology for each VLAN. (802.1d rules)

Cisco also introduced some enhancements - portfast, uplinkfast and backbone fast to improve on 802.1d. End user ports (configured with portfast) and alternate ports (uplinkfast, when root is no longer seen on root port) can move quickly to forwarding. Backbone fast reduced the STP convergence time from 50 to 30 seconds for indirect link failures.

802.1w is the rapid spanning tree, which dramatically improved on convergence times. This doesn't rely on timers but on syncronisation messages between switches which are point to point.

Cisco's RPVST+ is the rapid per VLAN spanning tree which uses 802.1w rules but also supports a separate topology for each VLAN.

Cisco's MST uses 802.1w rules but reduces the number of STP topologies that a switch has to keep track of. A simple three switch triangle has two useful topologies for load balancing. So if you have 100 VLANs, there's no point in running 100 STP's, just run 2 STP's and map VLAN's to each instance.
A region consists of a group of switches which has the same name, revision number and instance to vlan mappings.
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mikey250Author Commented:
Hi rochey,  You mention about 'enhancements:

Qns1. Uplinkfast - this means to me when there are at least 2 cables being used if one link goes down then it will automatically switch to the other 'Good' cable - ?

Qns2. Can I configure 'IP CEF & FEC' on same cables although I realise upto 8 cables can be used for FEC to provide upto 16Gbs - ?

Qns3. Or for neat & tidy would a Network Admin, make 'Uplinkfast separatee from IP CEF & FEC' - ?

Qns4. Rapid STP - 802.1w - when would this be used or is it down to which company can afford it?

Qns5.  Not sure what you mean when you say: A simple 3 switch triangle has 2 useful topologies for 'load-balancing', although I am aware if this 3 switch triangle has 'copper on 1 side to root bridge and fibre on the other then presumably the fibre will be chosen - ?

Qns6.  Im also aware I think that if a 3 switch triangle is being used again for example and every connection is using 'copper' then priorities or costs can be used I think although Im not sure of the difference - ?

Qns7.  Cisco MST uses 802.1w - Im under the impression that these 'Regions are geographically' located differently although 'YES' configured with 'SAME NAME' - (My main thread was not an exact config of MST but just an example) - ?
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rochey2009Commented:
Hi,

Qns1. STP uplinkfast will switchover to alternate root ports if the current root port fails. Alternate root ports are kept in blocking until the current root port fails and can be switched to quickly (they don't have to wait for twice the forwarding delay).

Qns2. IP CEF works with layer 3. If your FEC is layer 2 then IP CEF will not have an impact. If it's layer 3 then IP CEF can be configured if it's not on by default.

Qns3. Uplinkfast is separate from Etherchannel, but it could be used in conjunction with it if you had a redundant etherchannel.

Qns4. You don't pay extra for this, Cisco's latest IOS comes with rapid spanning-tree and other flavours of STP. RSTP is preferrable over 802.1D because of it's faster convergence times. If you've got RSTP then you should use it because of the <1 second failover compared to 30 - 50 seconds of 802.1D.

Qns5. If you have three switches A, B and C, A and B are distribution layer and C is at the access layer. A is the root bridge, B is the secondary root B. Switch C will have it's uplink to A forwarding and it's uplink towards B blocking. This is one topology. If you reverse the roles of A and B, B is now the root bridge and A is the secondary root. In this topology C's uplink towards A is now blocking and C's uplink towards B is now forwarding. These are your two useful topologies for load balancing and MST lets you map VLANs to each topology. Each of the topologies would be an MST instance 1 and 2 (MST 0 is reserved for the IST).

Qns6 Both port-priority and cost can be used to influence which ports end up forwarding and blocking. If you have two switches switch A and B with two connections between them C1 and C2. If switch A is the root switch and C1 is forwarding and C2 is blocking at B. If you want C2 to be forwarding at both ends instead of C1, you could either set the priority on switch A port C2 so that it's lower than switch A port C1 or you could lower the cost of switch B port C2 so that it's lower than switch B port C1. This is because of the way the tie breakers are used.

1 Lowest Root Bridge ID
2 Lowest Root Path Cost
3 Lowest Sender Bridge ID
4 Lowest Sender Port ID

Qns7 You could have a number of MST regions in one location.
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mikey250Author Commented:
Qns5.  So when connecting a 3 switch or 4 or even 5 switch then, presumably there would always need to be a root secondary if the root primary fails so that 'uplinkfast' would then know what to do - ?

I have 2 types of Bridge Priority:

root bridge
spanning-tree vlan x priority 4096 - As it goes up in multiples of 4096..
&
secondary bridge
spanning-tree vlan x priority 8192...

2nd option commands:

spanning-tree vlan 1-4094 root primary
&
spanning-tree vlan 1-4094 root secondary

Not sure which one to choose or is it either or down to preference - ?

Thanks for the other useful information...!!!
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mikey250Author Commented:
Correction the following is based on 'Assuming that all other switches are at default priority, ie the root primary command will set a value of 24576 instead...ie 1 switch set as presumably as VTP Server and the other as VTP Client or is it NOT that and just out of the box set as below:?

2nd option commands:

spanning-tree vlan 1-4094 root primary
&
spanning-tree vlan 1-4094 root secondary

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rochey2009Commented:
Uplinkfast is based around the root and alternate ports. The secondary root switch doesn't play a part until of course when the primary fails. But you need to specify both the primary and the secondary so that the network behaves as you want it to when the root is available and when the root has failed.

I tend to use the priority rather than the root primary and root secondary macros. The root primary macro will refuse to set a priority of 0, so you'll have to use priority in that case. root secondary is only useful if all the other switches are set to the default of 32768.
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mikey250Author Commented:
Ok I will have a go at this tomorrow as I have 3 2950 L2 switches..if thats ok..!?

I have 3 2950 L2 switches so: A root 4096, B secondary 8192 then and C Im assuming will be left as default..

Im thinking 2 cables would connect to the root A..
1 x cable can be port 1 to port 1 - Main cable
1 x cable can be port 2 to port 2 - would automatically be 'Alternate'
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rochey2009Commented:
It doesn't have to be a direct connection to the root. You could have one direct link to the root and the alternate connection to the secondary.
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mikey250Author Commented:
Oh ok..  Will set this up tomorrow thanks for that!!!!!!!!:)
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mikey250Author Commented:
Morning Im am just setting up all 4 of my L2.
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mikey250Author Commented:
Hi What I did was just set up the following as: L2 switches are all 12 port:

Switch A - Vtp Server
Port 1 connects to Port1 Switch B
Port 12 connects to Port 12 Switch C

Switch B - Transparent
Port 10 connects to Port 10 Switch C
Port 11 connects to Port 11 Switch C

Switch C - Transparent
Port 10 connects to Port 10 Switch B
Port 11 connects to Port 11 Switch B

Switch A - sh spanning-tree:
Int       Role  Sts   Cost   Prior.Nbr   Type

fa0/1    Desg  Fwd  19      128.1       P2p
fa0/12  Desg  List   19      128.12     P2p

Switch B - sh spanning-tree:
Int       Role   Sts   Cost   Prior.Nbr   Type

fa0/1    Root  Fwd  19      128.1       P2p
fa0/10  Desg  Fwd  19      128.10     P2p
fa0/11  Desg  Fwd  19      128.11     P2p

Switch C - sh spanning-tree:
Int       Role  Sts   Cost   Prior.Nbr   Type

fa0/10   Altn  Blk   19      128.10      P2p
fa0/11   Aln   Blkt  19      128.11      P2p
fa0/12   Root Fwd  19      128.12      P2p

I see that Switch 12 was in 'listening' mode - All good
I see that Switch B port 1 was in 'Root' mode - All good
I see that Switch C port 10 & 11 by default were in 'Altn' mode and obviously port 12 was in 'Root' mode.

After confirming the above I can then for 'Admin order', then complete Switch A VTP Domain, Password & pruning & md5 then change both

Qns1. Switch B & C from Transparent to Client.  Then continue other configurations for pc's server etc - ?

Qns2. As another backup so that 'NO' superior remote or Local switch tries to 'hack in' for example I could now add:

spanning-tree backbonefast - ?
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mikey250Author Commented:
Correction:
I see that Switch A 12 was in 'listening' mode - All good
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mikey250Author Commented:
By the way I switch the following:

Switch A
spanning-tree vlan 1 priority 4096

Switch B
spanning-tree vlan 1 priority 8192

Switch C
spanning-tree vlan 1 priority 12288

Qn1. I presume this was correct ?
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rochey2009Commented:
Hi,

Yes the configuration is ok, although you could have left switch C at it's default of 32768, although I would have connected the switches in a triangle.

If you're using VTP, then you would normally have two VTP servers and the rest of the switches will be VTP clients. If it's just a few switches then maybe VTP transparent on all switches is ok.

If you want to prevent other switches from being connected to your network and taking the role of root switch then you could you root guard or bpdu guard.

Root guard puts the port into spanning-tree inconsistent state until it stops seeing a superior bpdu and bpdu guard puts the port into err-disabled if it receives any STP bpdu. Normally, ports connecting to end users would have portfast for fast transition to forwarding and bpdu guard enabled to prevent anyone from connecting a switch to your network.
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mikey250Author Commented:
Hi Ok thanks for the reminder ie all I need to do is set 'root & secondary root' and leave others as default setting 32768..

You say 'I would have connected as triangle' - What do you mean as Im only using 3 switches in a triangle - ?

You say if using VTP then you would normally have 2 VTP Servers - I didn't realise that.... Although then again that would make sense as Im assuming after setting 'root & secondary root' then yes you would be right - ?

I agree that as long as all nodes attached to this single switch and on 'SAME VLAN' then yes 'Transparent' would be ok......but if vlans span more than 1 switch then 'Transparent' would not fit.....

bpduguard - Yes I was planning on adding 'spanning-tree guard root' - On Switch A/Vtp Server ports 1 & 12 as they are the 'Uplinkfast'...and presumably NOT on the 'root ports' connected to Switch A ports 1 & 12... - ?

- Those ports that are NOT 'spanning-tree guard root' - Can be set on each 'Interfaces as 'spanning-tree bpduguard enable OR 'Global as 'spanning-tree portfast bpduguard' - ......to automatically be put on all other ports instead of adding each one manually....

Will not add 'spanning-tree bpdufilter enable' -  as this stops the 'tx & rx'...of DTP traffic, unless required for some reason....
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rochey2009Commented:
Sorry I misread your topology. I see you have triangle but you've doubled up on the ports between B and C.

The two VTP servers are just for resilience.

I prefer BPDU guard on user ports rather than root guard.

Are you studying for any certifications or is this for your job?
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mikey250Author Commented:
Hi,  Yes the following is:

Switch A - Is the Root Bridge
Switch B - Is the secondary
Switch C - Is Client

I thought you said yesturday that when making use of 'Altn & Backup' that instead of having traffic pointing in the direction of Switch B to A that I could instead have it pointing from Switch C to A.  Oh yes I see what you mean I should have put the 'secondary root' on Switch C instead of Switch B....!!!

Yes I understand that the 2 VTP Servers are for fault-tolerance.../resilience..!!!

Yes 'bpduguard' will be on user edge ports or pc's servers or any device.. & 'root guard' would be only on the 'uplink ports'...?

CCNA...as had some experience but since economic crisis around the world I need to pass certifications to get back into employment....
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mikey250Author Commented:
I have also gone through the CCNP...but not certified so starting from beginning as been trying to put my limited on the job practical experience together first as bought equipment from ebay.  Later once practical upto scratch then I will evolve to using: GNS3...!
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mikey250Author Commented:
Qns1. Ive just looked at my 'triangle' again and I think I did not need to remove 'secondary root' from Switch B as all I needed to do was remove 2nd cable port 11 and connect between Switch C to Switch A...?
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rochey2009Commented:
You wouldn't use root guard on the uplink ports because this is where your root bridge is. You would use it where you wouldn't want a new root bridge to be connected.

Good luck with the job hunt. I hope you find something soon.
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mikey250Author Commented:
Yes Ive read my instructions wrong.. It states the following:

Root Guard - Ensures that the port on which it is enable is the 'Designated ports' - So I would disregard ports 1 & 12 which link to up other 2 switches B & C and put 'spanning-tree guard root' on all other Designated ports...!

When reading about this it has been confusing thats why I needed assistance.... !!!

What about my questions on previous thread: 3705311 - ?
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rochey2009Commented:
Can you restate them?
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mikey250Author Commented:
Hi,  I did originally have the following:

Qns1.
Switch A - Is the Root Bridge
Switch B - Is the secondary root
Switch C - Is Client

Then 'YOU' said - Sorry I misread your topology. I see you have triangle but you've doubled up on the ports between B and C.

What I should do is remove that B and C cable and put between Switch C port 11 to Switch A port 11 - ?

If the above is correct does that mean my 'Secondary root' should should be on Switch C and NOT Switch B, Im assuming so - ?

Yes I understand that the 2 VTP Servers are for fault-tolerance.../resilience..!!!

- 'bpduguard' will be on user edge ports or pc's servers or any device
-  'root guard' would be on the 'Designated ports' 'NOT' the ports connecting to Switch B & C - ?
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rochey2009Commented:
                                            DP             RP
                               A (root)  ---------------  B (secondary root)
                         DP  |                                  | DP
                               |                                  |
                               -----------   C   -----------
                                         RP        AP

RP = root port, AP = Alternate Port which is blocking, DP = Designate Port

http://www.cisco.com/en/US/tech/tk389/tk621/technologies_tech_note09186a00800ae96b.shtml

Have a look at the link for an application of root guard.
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mikey250Author Commented:
Hi I can see your diagram in this thread above although no 2nd Altn cable between C & A although it is an example.!!!

I do realise all ports from Root Bridge are Designated ports and those ports from Switch B & C connecting to Switch A are Root ports. Ive always understood that..!!! Please bare with me..!:)

Ive looked at the url although somewhat confusing but I do understand, it is just get the practical right...

This is what I have below on my switches below what you think:

Switch A - Vtp Server (Root Bridge)
spanning-tree uplinkfast
spanning-tree vlan 1 priority 4096
Ports 2 - 10 - spanning-tree guard root

Port 1 connects to Switch B Port 1 (Main - Uplink) (Desg)
Port 12 connects to Switch C Port 12 (secondary - Uplink) (Desg)
Port 11 connects to Switch C Port 11 (Altn) (Desg)

Switch B - Vtp Server - (2nd Root Bridge)
spanning-tree uplinkfast
spanning-tree vlan 1 priority 8192
Ports 2 - 9 & 11 & 12- spanning-tree guard root

Port 1 connects to Switch A Port 1 (Rp)
Port 10 connects to Switch C Port 10 (Desg)

Switch C - Client
spanning-tree uplinkfast
spanning-tree vlan 1 priority 12288 - Although could leave as default 32768..
Ports 1 - 9 - spanning-tree portfast
Ports 1 - 9 - spanning-tree bpduguard enable

Port 10 connects to Switch B Port 10 (Altn)
Port 11 connects to Switch A Port 11 (Rp)
Port 12 connects to Switch A Port 12 (Altn)
-----------------------------------------------
Switch A - sh spanning-tree:
Int       Role   Sts    Cost   Prior.Nbr   Type

fa0/1    Desg  Fwd  19      128.1        P2p
fa0/11  Desg  Fwd  19      128.11      P2p
fa0/12  Desg  Fwd  19      128.12      P2p


Switch B - sh spanning-tree:
Int       Role   Sts   Cost    Prior.Nbr   Type

fa0/1    Root  Fwd  19      128.1        P2p
fa0/10  Desg  Fwd  19      128.10      P2p

Switch C - sh spanning-tree:
Int       Role   Sts   Cost   Prior.Nbr   Type

fa0/10  Altn   Blk   19      128.10      P2p
fa0/11  Root  Fwd  19      128.11      P2p
fa0/12  Altn   Blk   19      128.12      P2p

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rochey2009Commented:
You would only use uplink fast on switch C.
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mikey250Author Commented:
Hi, Yes Ive been reading my notes and seen that it said add 'uplinkfast' on access layer switches only...huurraayyyy!  So my config is good then ?

Having 'Uplinkfast' on all 3 switches like I did do, can it cause problems ?

Then I think were all done..:)
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mikey250Author Commented:
So even though Switch A & B are also access layer switches they are not in this case....!?
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rochey2009Commented:
Yes you are correct. Good luck.
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mikey250Author Commented:
Perfect...!!!!!!!!:))
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