point to point networking between DC and DR

Question

I have two geographically separated DC and DR sites with hosts on the same subnet. The hosts on respective networks are connected with each other through respective switches at each site. Both the switches are GigaBit switches. I have a point to point link between the locations which is 5Mbps.

When I connect the networks with the point to point link, I get a ping latency of about 18 ms. However as soon as clients start accessing the DC, through a WAN link on a router in front of the switch, I experience serious degradation of connectivity (ping latency = 400 ms and 50% drops).

Could someone please tell me, what do I need to do, to alleviate the problem?

Here are the details:

• Switches are GigaBit layer2 Ethernet switches .
• Wan link is wireless Point To Point 5 MBps Link.

Topology is as below.

(DC) Servers ------>Switch----------->Router----Clients on ILL WAN Link
                      :
                      :
                      :
         WAN Point to point link (5Mbps)
                      :
                      :
                      :

(DC) Servers ------>Switch----------->Router----currently no clients

All servers have Gigabit NICs. All ports on both the switches are on "Auto" mode. Users connect to servers on each side through separate ILL links which terminate into respective routers.

The P2P link connects the respective switches at the DC and DR. There is no traffic on the P2P WAN link currently. Just the ping traffic, that i use to test. The ping connectivity/latency is fine when no users are connected to DC, but as soon as users get connected, it starts facing problems. Subnets on DC and DR are same.

Please let me know if you need any more details.

Answer 1

Taking into consideration that you haven't posted your switches makes and configs, your WAN link could be your bottleneck.

While saving on some costs it is usually a half-duplex connection.

Recommendation:- For the desired bandwidth between your sites, it makes more sense to rent fibre (or sdsl) from a Telco/ISP provider as a point-to-point between your two sites (or install your own fibre).

Answer 2

Knowing the brand/model of switch would be helpful too, but based on your description, the most likely problem is that your WAN link simply can't keep up with the traffic. The link is congested, and therefore you are dropping packets. If your wireless link is 802.11, you're lucky if you can get 2-3 Mbps actual throughput. You don't say how many servers you have, but it wouldn't take very many to completely saturate that link. Simply put, you need (a lot) more bandwidth.