hsrp layer 2

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Jul 17th, 2013
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Hi,


Could you please correct me if i am wrong




                         ------- Access SW A----------

                         |                                      |

                         |                                      |

                    Core A                              Core B


If i want hsrp, do i need a lyer 2 or layer 3 link between both? (i know layer 2 will defitnetly work but will a layer 3 work as well ?)


Thanks

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JohnTylerPearce Wed, 07/17/2013 - 03:34
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You will have a L2 trunk between Core_A and Core_B, and configure your HSRP on Core_A and Core_B, choosing one to be the master so to speak.


You can mix and match your priority values as well, to provide load balancing, so Core_A and Core_B share the load.

Network Pro Wed, 07/17/2013 - 04:16
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Thanks John, But can i use a lyer 3 instead of layer 2 link  and use HSRP between them ?

JohnTylerPearce Wed, 07/17/2013 - 04:32
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No, you can't have a Layer 3 Link.


Look at it this way. If you have two L3 links between the Access Switch (If its a L3 switch and enabled), two /30 links to Core_A and Core_B. And it's not the way FHRP works.

Network Pro Wed, 07/17/2013 - 04:43
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no sorry let me explain better


Scanerio A

l2 links between core A and access switch and Core B and Access Switch and L3 link between two Cores - will this work ?


Scenario B

l2 links between core A and access switch and Core B and Access Switch and L3 link between two Cores  and another Layer 2 link between both cores - will this work ?

JohnTylerPearce Wed, 07/17/2013 - 04:54
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Scenario A, will work without any problems.


Scenario B, should work as well

Network Pro Wed, 07/17/2013 - 05:00
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Scenario A - i thought you said we needed a l2 link (trunk) bettwen Core A and Core B and not layer 3 link ?

JohnTylerPearce Wed, 07/17/2013 - 05:30
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I was talking about a L2 trunk between the Access Layer and your core, because I thought you were talking about being L3 from Access Layer to core at the time.


You will be fine, with 802.1q to the core, and the L3 between the core.

Network Pro Wed, 07/17/2013 - 06:27
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ok let me understand this correctly.


The link between access switch and core is layer 2.


The question i have is, if i need hsrp, between core A and Core B, will a lyer 3 link work ? (if it does how will it work, because you cant have teh same vlan span across a lyer 3 link, isnt it ?)


Second question, will layer 2 link and layer 3 link betrween Core A and Core B work ?


Sorry just trying to get my head around this

MUKUL JOSHI Wed, 07/17/2013 - 08:20
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Hi Network,


If u are using Layer 3 link between two core switches that would not create any issue your vlans are spanning through the layer 2 trunk port(with access switch). 


Second scenario will also work however in second one if l2 links are used between all the switches then one of them would be blocked depending on STP root bridge election.


HTH

MJ

Network Pro Thu, 07/18/2013 - 02:10
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thanks Mukul,


but i dont understand scenario A. if i use l2 links between access sw to Core A and access sw to Core B and Layer 3 link between Core A and Core B, how will hsrp work.


for example:

                        L3

          Core A -----------------Core B

              |                           |

L2 link     |                           |  L2 link

              |____ACC SW____|



HSRP

Vlan 10:10.10.10.1


Core A :

Vlan 10 : 10.10.10.2


Core B

Vlan 10: 10.10.10.3


Acces Sw: 10.10.10.4



Now if there is layer 3 link between Core A and Core B, how can we have vlan 10 on both sides of layer 3 link ? (layer 2 cant be spanned over layer 3 link, can it unles we do fancy stuff like OTV or bridge irb ?)


Please clarify as i am trying to get my head around this


Thanks

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