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sandu_nastas1
Beginner

3 remote sites interconnection issue

Given :

- 2 Datacenters + 1 Users Site.

- Every site has a Layer 3 switch as a core.

Task :

To interconnect the 3 sites in a triangle as in the picture attached

The interconnection between Datacenter1 and Datacenter2 has to be a L2 extension in order to have High Availability Clusters on 2 sites

Solution:

I decided to inteconnect the sites as follows:

- DC1 (Datacenter1) - DC2 : L2 Trunk link

- DC1 - Users site : L3

- DC2 - Users site : L3

OSPF between the 3 cores

DC1 - Users Site is the OSPF prefered link

For the extended VLANs (Between DC1 and DC2) there will be HSRP implemented on DC1 and DC2 core switches.

PROBLEM :

The problem comes when the trunk link between DC1 and DC2 Core switches goes down:

Suppose that in HSRP - DC1 Core is Active and DC2 Core is Passive.

1. When the trunk link goes down, HSRP of DC1 thinks that DC2 went down - so it stays Active. But DC2 HSRP thinks that DC1 is down, so it changes the state from Backup to ACTIVE. So now we have 2 IP addresses of 192.168.10.1 on the network.

2. The servers (.10 and .11) will also loose the interconnection. So they will also both be active.

This is a big problem.

Question :

How can we solve this issue ? Is there a way to make few changes in the design in order to assure that VRRP and HSRP continue to work correctly if the trunk link goes down ? (Duplication of trunk link is not an option)

Thanks in advance. Any answer is highly appreciated.

1 REPLY 1
Wilson Bonilla
Participant

Hello

in first place I would say the link between DC1 and DC2 shouldn't go down.

I would suggest
create a port-channel between DC1 and DC2, don't see it from bandwidth aggregation stand point but from high availability.

Regards
Wilson B.

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