Re: Simplest Data Center Interconnect?

steve_mils · ‎12-22-2009

Hi all,

What's a simple way to implement a L2 network across 2 L3 DCs connected by 2x1Gig links using a 6504-E with SUP720-3C?! The DCs are only a few kilometres apart and our local service provider can only provide 1Gig fiber links between DCs (which I can then configure as L2 or L3). I do not want to simply configure flat L2 across both DCs - I would like to keep each DC as a separate L3 site and run OSPF for fast convergence and therefore avoid spanning-tree altogether.

At the moment each DC uses 3750 switches connected by L3 links and runs EIGRP. We then use separate hardware (7200) and L2TPv3 to create some shared L2 networks across that. We're moving to the 6500 platform and so it's a good opportunity to redesign things - and hopefully I can minimise the amount of hardware needed and consolidate using only the 6500 platform in each DC.

I also have a Cisco ACE appliance to fit at each site and to have redundancy for these they need to live in a shared network! That's what happens when the design process starts after the kit has already been brought (not my choice btw!).

Any ideas?

shailesh.h · ‎03-30-2010

>> What is the purpose of gettin 2X1gigabit Ethernet if you don't want to extend the LAN across two DC

>> You may run OSPF or any other L-3 tolopogy using low cost links as well

Did you finished design? if yes you may share to review

steve_mils · ‎03-30-2010

Howdy,

The 2x1Gig links are to connect the 2 DCs together - but the question is what's the best way to do this? For example, best practice dictates that sites should be L3 only. However, I also need some kind of L2 connectivity for certain clustered services which require L2.

What I've ended up doing is a bit of both L2 and L3. Basically I created a L2 etherchannel which only allows 2 things - a VLAN which is used to provide a small /30 link so that I can create SVIs on each end and run L3 on top; and VLANs which are used as pure L2 which run HSRP. Here's the config:

DC1 switch

----------------

interface Port-channel1
description Link to DC2 - Po1
switchport
switchport trunk encapsulation dot1q
switchport trunk native vlan 2
switchport trunk allowed vlan 2,120
switchport mode trunk

interface Vlan2
ip address 10.x.x.9 255.255.255.252
ip ospf network point-to-point

interface Vlan120
description Shared VLAN
ip address 10.120.0.253 255.255.255.0
standby 120 ip 10.120.0.254
standby 120 priority 150
standby 120 preempt

DC2 switch

----------------

interface Port-channel1
description Link to DC1 - Po1
switchport
switchport trunk encapsulation dot1q
switchport trunk native vlan 2
switchport trunk allowed vlan 2,120
switchport mode trunk

interface Vlan2
ip address 10.x.x.10 255.255.255.252
ip ospf network point-to-point
ip ospf priority 0

interface Vlan120
description Shared VLAN
ip address 10.120.0.252 255.255.255.0
standby 120 ip 10.120.0.254
standby 120 preempt

It does seem to work ok - for example I have different networks at each DC which I can reach independently and I have a couple of VLANs which stretch across sites. The only problem that I can see is that there would be serious problems if the 2 Gig links went down between the 2 switches - each would then be HSRP master. Also there's a trombone effect with traffic from DC2 using DC1 as its default gateway but there's no way around this unless we use OTV or similar!

Any thoughts are very welcome! Thank you.

shailesh.h · ‎04-01-2010

This configuration attached is for VLAN extension across two DC but with Layer 2 Extension with EoMPLS. But definately can suit to u r requirement with modification..

>> I can help you if you share me the detailed requirements and expections and number of VLANs to extend and seperate VLAN...

>> How you WAN / Internet accessing DC's

>> Are u r routers (WAN) working in HSRP

>> Are u r applications working in active - active DC mode?