Design help

[sridhar ch]

Hi,

I have been assigned a task to plan for a 300 seater (site B) for my company expansion in the same location but few miles away. The new site will not be having direct connectivity to my Corporate. All connections to corporate to from the new site should take MPLS links terminated in the current office.(site A)

i would like to know what is the best connectivity provided i have 2 circuits between site A and B. My initial plan is to extend the VLAN's running at my primary site A to site B by creating trunk ports. FYI, i am running BGP on my MPLS routers and OSPF in LAN.

Thanks,

Sridhar

[Reza Sharifi]

Hi,

If you are already running OSPF on site-A, than you can't extend the vlans from site-A to site-B.

You can simply create a new vlan for site-B with SVI terminating at the local switch and use OSPF or static routes to connect to site-A.

HTH

[sridhar ch]

Thank you HTH. I have attached the diagram for your reference.

Between site A & B will that be L3 or L2? Believe it is L3.

Site A:

collapsed core model and running OSPF & HSRP

MPLS routers are running BGP and redistribution enabled between OSPF & BGP

Site A will act as transit for SiteB to reach out to Corporate using MPLS

Site B:

VLAN's will be local to site B

HSRP will be enabled between the two switches for FHRP

OSPF will be enabled between the two 

Since at Site A, both core A and Core B are running OSPF, also both the switches at Site B connects to switches at Site A using STM circuits, is there any possibility of creating routing loops as both switches at site B learns the routes of corporate (other sites via MPLS) bcoz both swicthes at Site B forms adjacency?

[Nick Cutting]

Always route the traffic where you can.  Only stretch vlans between sites when you absolutely have to (legacy multicast apps etc)  

There wont be a routing loop, but you may see equal cost load balancing, and in these situations, I like to change the cost so that one circuit is always preferred.

Will the 2 links between the sites be equal in terms of latency and bandwidth? If they are the same, you could use both links, however the CEF switching engine is responsible for choosing the next hop based on source destination ip's etc, and it may not be the same in the reverse direction, but depending on what your traffic flows are between the sites, this may not matter at all.

 If the links are exactly equal (are the fiber runs similar in length etc) Also think about bundling the links into an etherchannel, to simplify routing. Either layer 2 with Vlan interfaces on each end, or layer3 port-channel.  Etherchannel does the assemtry work for you, as according to cisco (I haven't tested this on many platforms) etherchannel ECLB guarantees that return traffic takes the same path as the initial traffic flow.

Hopefully LACP frames will make it over the links. Otherwise you should route both links seperately.

[sridhar ch]

yes, both links/circuits will be of same BW. we dont want to load balance.