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New Member

Design Query


I need some help in a network design.

Please refer to the attached files, as u can see in the IP file, there are 3 vlans in each cabinet/floor.

The switches in the main DC rack would be either 3750s or 4 Juniper EX4200s using virtual chassis to form a single switch.Top 2 of these chassis swithes serve the different servers as u can see in the scenario diagram and the gateway for these servers would be the SRX Firewall. While the bottom two are for fiber aggregation from cabinets.

Now according to the attached IP/vlans doc, what do u think would be the best place to configure a DHCP server? If I make it on main aggregation switch then I'll have to define 12 DHCP scopes for the differnet vlans rite? then the thin clients gateway would be the aggregate switch and at aggregate switch a default route pointing to the FW would have to be configured?

or should I have to make DHCP server on individual cabinet switches?....

Also, as shown its L2 links between distribution and cabinet switches so how would I fine tune spanning tree for this....What if I make it L3 in order to avoid spanning tree?

Please shed some light on this



Hall of Fame Super Blue

Re: Design Query

syedraheel wrote:


Personally i would use a server for DHCP and not the switches. Windows DHCP server works perfectly well and support DDNS etc.. You can use "ip helper-address x.x.x.x" command on the L3 vlan interfaces to point to the DHCP server, not sure what the equivalent for Juniper is.

As for your uplinks you should use etherchannel from your cabinet switches to the distribution, that way STP does not block any of the uplinks. I'm assuming your distribution switches are the 3750s/Junper switches. So because the 3750s can support cross stack etherchannel there is no need for blocking and non-blocking uplinks. Again not sure about the Junipers but you do suggest a virtual chassis. So you wouldn't particularly benefit from using L3 simply to get rid of STP.


New Member

Re: Design Query

thanks for the suggestions Jon.

As there are only two fiber uplinks for each cabinet that means If I make an etherchannel between top cabinet switch and distribution switch(virtual chassis switch), the failiure of that Top cabinet switch would compromise the whole cabinet connectivty(I cannot split the etherchannel across 2 switches on the cabinet end as these doesn't support virtual chassis).

How would you best utilize your resources in this case?

New Member

Re: Design Query

I can recommend you if you can share the details (make and model - u only shared that distribution switches are 3750 but no details abt other switches and connectivity distance and cable type) of equipment in each cabinet so that

optimization of the resource can be achieved..

With regards,

Shailesh Hardas

New Member

Re: Design Query

OK....the distance between distribution and cabinets is 700m and there are 2 fiber uplinks at each cabinet. So laying cat5/6 is not an option here.

The aggregation/distribution is EX4200 virtual chassis which is basically 4 switches but logiacally single. Top 2 switches at each cabinet are EX3200 which are layer 3 switches. The problem is at the ground floor cabinet where there are total 6 swicthes(2 L3 and 4 L2 switches).

What is the way to maximize the availability in this case where there are 2 uplink cables and 6 access switches in the cabinet? Kindly see the attached diagram. This could be an option but how to cope with Spanning Tree in this case? :S 

New Member

Re: Design Query

There are following couple of consideration and recommendation for you

  • Either you can have two layer or three layer architecture
    • In two layer all the switches to connect to central VX (four physical, one logical switch). To have redundancy you have to have 12 uplinks to central switch. The throughput would be more and minimum problem due STP
      • uplink ports = 12 and uplink cables =12
    • Other option is three tier in which you can select two of the switches. the swiches connected to central switch with uplink.
      • uplink port of sw1 = 1
      • uplink port of sw2 =1
      • All the other switches to have two uplink ports. One connected to sw1 and other connected to sw2
      • The throughput would be minimum, redundant link will be enable, PVST can be used for load balancing and loop avoidance.

This this architecture will provide simpler and loop free environment for you..