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LAN/WAN Design questions: redundant network core design and equipment

maximtretiakov
Beginner
Beginner

Dear All,

I have a growing network which inherited some reliability and scalability issues:

(Example of my existing network)

MainSite_CoreLayer_Upgrade_Proj.jpg

We have got POPs connected to us through FC lines, from which LSP are connected to our FC crosses on POPs.

Now there is a need to make the switching core (the switch with "?" mark) redundant

because it is the point of the concentration of all outside connections.

I have received an appointment to consider new equipment (now it is just Catalyst 3560) for that network block.

Unfortunately the budget is quite small.

I have the following considerations:

I think that the main problem is that the most of the connections are L2 trunk links and it is hard to prevent that.

It seems that I need to duplicate all FC links to LSPs, POPs, and branches (this looks feasible) and rely on STP! (this looks bad)

with all those links.

At this moment I have two options for core block:

1. Two Catalyst 3750 have duplicated links. (e.g. CSW1-LSP1, CSW2-LSP1) and rely on STP

2. One Catalyst 4500 series switch with two redundant supervisors (probably they allow to buy it if there are strong arguments) have duplicated links and rely on STP.

Both options do not look good because I have to rely on STP with LSPs.

I would like to use L3 redundancy protocols and features but do not know how to avoid the trunks

I have no experience with fancy hardware like Catalyst 4500/6500 series.

Could anybody please advice me alternatives for design and hardware options and either confirmation or retraction of my options.

Also, I would be grateful if anybody could help me to find strong arguments for acquisition of Catalyst 4500 series switch on the core.

Thank you very much in advance.

Best regards,

Max

1 ACCEPTED SOLUTION

Accepted Solutions

Marwan ALshawi
Advisor
Advisor

Hi Max,

from the diagram and description you provided the switch you need to replace is a edge device that is working in L2 only at the moment,

if you are planing to move to L3 communications in this device then you need to review your entire network design and also review/discuss with the SP how this can be converted to L3 communications

if you want to keep it the same as L2 and introduce in device or devices for redundancy i would prefer having two redundant devices of one redundant chassis what i mean pair of 3750 is more reliable from one 4500 chassis with redundant equipment such as SUPs, PSUs however its an option as well and still reliable for sure

if you count on STP for the redundancy what is the issue here ? is it convergence time or what is your concern about it ?

hope this help

View solution in original post

6 REPLIES 6

Marwan ALshawi
Advisor
Advisor

Hi Max,

from the diagram and description you provided the switch you need to replace is a edge device that is working in L2 only at the moment,

if you are planing to move to L3 communications in this device then you need to review your entire network design and also review/discuss with the SP how this can be converted to L3 communications

if you want to keep it the same as L2 and introduce in device or devices for redundancy i would prefer having two redundant devices of one redundant chassis what i mean pair of 3750 is more reliable from one 4500 chassis with redundant equipment such as SUPs, PSUs however its an option as well and still reliable for sure

if you count on STP for the redundancy what is the issue here ? is it convergence time or what is your concern about it ?

hope this help

Hi Marwan,

Thank you for your answer.

Yes, that is correct.

     The reason of my hesitation is related to the posibility that SP could filter BPDUs, or BPDUs can lose somehow in another AS and loop could be formed.
     But there are features like LoopGuard which should help to prevent network crash in this case, I guess. Root guard could help to reject casual supperior BPDUs, if it does matter. Conveergence time shold not be the issue for me with RSTP. Are there other possible threats for the network stability in L2 case?
How would you shuggest to pair C3750s: in stack or etherchannel?

Best regards,

Max

Hi Max,

for the STP concerns and redanduncy over 2 links per SP i would recommend you to discuss it the SP and see there recommendations and standards

for the 3750 put it in a stack for ease of management and each switch with redundant PSU

hope this help

if helpful rate

Hi Marwan,

Thanks for your answer.

I discussed the matter with the SPs, and one of them could not let BPDUs traverse through their network, they are still considering.

If they not allow BPDUs, that would be a problem for the whole plan. In that case, is there only L3 solutions?

Best regards,

Max

well i think you can control which link to be the primary by tuning STP cost per link in this case from you edge switch you can have active/standby paths !

or you may have a look at QinQ technology if it could add something good or not taking into consideration the frame size with QinQ

using L3 can be an option but as i mentioned this requires review to your entire network design end to end

hope this help and thanks for the nice rating

Thank you for your help           

One of the LSPs suggested to use two 3750s in stack and Etherchannel of two links between SP and 3750s as a redundancy solution:

stack

[3750_1 ]

   |          \ __Etherchannel1__ (         )

   |            __Etherchannel1__(   SP1  )

   |          /                                (        )

[3750_2]

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