VLAN stretching across two sites...

Unanswered Question
Aug 22nd, 2007
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Basically, I have two sites connected by a 100Mb Colt line with a Cisco 2600 at each end and then at each site I have a 3750 cluster providing LAN switching, routing etc.

I have set up each site to have the same VLAN numbers; VLAN10 - Servers, VLAN20 - Workstations etc and have applied a different subnet to each of these at each site; for VLAN10 at site 1 and for VLAN10 at site 2. Sounds simple so far....

I want to set up a vlan which spans the two sites for an Exchange 2007 cluster heartbeat, but aren't too sure how I would go about it. I can set up the same vlan (vlan50) at each site, but don't know how I would get them talking...

I know, I'm being thick...

Thanks in advance for any help...

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Overall Rating: 3.7 (4 ratings)
islam.irshaid Wed, 08/22/2007 - 08:12
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you have to know that VLAN is a layer 2 not 3

then you can using any routing protocol or static to to get the diff. networks talking with each other.

campbell.thomps... Thu, 08/23/2007 - 01:42
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I'm not sure that I understand. Can you give a bit more detail?

Thanks in advance...


anandramapathy Thu, 08/23/2007 - 06:18
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You can do Bridging to extend the LAN from the other location to this.

you have to create BVI interfaces on both sides search on cisco site for more details

hussainratlami Tue, 08/28/2007 - 23:37
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hiii, i dont think u can extend VLAN over the different sites

U can use router on stick feature to communicate between diffrent vlans, but can be on layer 2, not on layer 3

thomas.anthony Tue, 08/28/2007 - 23:48
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Here we go. VLANs are not scalable us we need for today's technology. The best way to get thinks work for you for this requirement would be start running MPLS on you LAN and get extended to other site LAN as well but your 3750 will not support

thomas.anthony Wed, 08/29/2007 - 01:52
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Transporting Labeled Packets over LAN Media

Exactly one labeled packet is carried in each frame.

The label stack entries immediately precede the network layer header,

and follow any data link layer headers, including, e.g., any 802.1Q

headers that may exist.

The ethertype value 8847 hex is used to indicate that a frame is

carrying an MPLS unicast packet.

The ethertype value 8848 hex is used to indicate that a frame is

carrying an MPLS multicast packet.

These ethertype values can be used with either the ethernet

encapsulation or the 802.3 LLC/SNAP encapsulation to carry labeled

packets. The procedure for choosing which of these two

encapsulations to use is beyond the scope of this document.

chk this RFC - http://rfc.net/rfc3032.html#p18

Chk this as well - http://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121newft/121limit/121ex/121ex8a/eompls9.htm

mheusing Wed, 08/29/2007 - 00:39
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Hi Campbell,

Besides bridging - as mentioned in another post - you could also go with L2TPv3 to "stretch your VLAN" between the two sites.

The config is fairly simple and straight forward, if you follow the guidelines in "L2TPv3: Layer 2 Tunneling Protocol Version 3"


One more note though: in any case bridging or L2TPv3 is fairly CPU intense, if large amounts of data are to be transported. You might want to do some performance tests with your 2600 running 12.3(2)T or newer before implementing it. You were only talking about heartbeat but there might be more traffic between the Exchange servers.

Hope this helps! Please rate all posts.

Regards, Martin

Pavel Bykov Wed, 08/29/2007 - 02:22
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If sites are connected using Ethernet interface, then you can setup subinterfaces. If VLAN would be for example 555, than it would be:


switch mode trunk

switch trunk allowed vlan 555

Router1 (on both interfaces - to switch and to the other site)

interface fast 0/0.555

encapsulation dot1Q 555


interface fast 0/0.555

encapsulation dot1Q 555


switch mode trunk

switch trunk allowed vlan 555

campbell.thomps... Wed, 08/29/2007 - 02:29
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I think that is exactly what I'm after. I need to be selective with the VLAN's that I'm pushing across; I don't want all traffic to go across the WAN, just those required.

I'm going to give this a go and see what happens.


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