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how can i make  vlan with same subnet

Posted on 2010-01-10
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Last Modified: 2012-05-08
I'm facing a problem in our Cisco routers 3845. We have 2 sites, physically separated and we need to connect them as a VLAN and to have the same subnet in both sites (L2). we are connecting the both site using 2 E1 data lines each 2mb/s However, we need to do that without using IP ROUTR to prevent making loops in the network. Can you help me out in this issue?
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Question by:Co0L_DBA
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11 Comments
 
LVL 13

Expert Comment

by:GuruChiu
ID: 26278364
You can use bridging to do that. This is one possible example:

Assuming you use MLPPP to bond the two E1 together. You probably can use CEF to create two path, but it complicated matters.

bridge irb

interface multilink1
bridge-group 1

interface f0/0
bridge-group 1

interface bvi1
 ip address 172.16.0.1 255.255.255.0

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LVL 50

Expert Comment

by:Don Johnston
ID: 26278392
This is a common question that pops up from time to time.

Basically, VLANs (Virtual LOCAL Area Network) are not consistent with WIDE Area Networks. So the short answer is no, you can't do it.

There are a couple work arounds, but none are what you would call... elegant. :-)

One is to bridge the traffic across. This is easiest. Although you are limited to a single VLAN over your WAN link.

Another method would be to tunnel the traffic over the link with a VPN or L2TP.

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LVL 10

Expert Comment

by:lanboyo
ID: 26279016
I don't understand why you fear loops with a L3 protocol more than a L3 protocol, but guruchiu's configuration above is the way to do it.
 
Things to consider, you probabally want to bond the e1s together, otherwise spanning tree will make one of them be in blocking mode, which will mean you are not using half of your bandwidth.

Also, you will be sending all your bropadcasts over the network, depending on the size of your sites this may be acceptable.
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LVL 34

Expert Comment

by:Istvan Kalmar
ID: 26279073
You able to config L2TPV3, which is able to do it with in a WAN link
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LVL 16

Expert Comment

by:Aaron Street
ID: 26281609
Look up layer 2 tunnling over ip.

Ikalmar has one solution but a quick search on google will bring up a few others.

GRE may be another you want to look at,

But both of these will allow you to tunnel layer 2 traffic over an IP link between two sites and give you the solution you are asking for.
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Author Comment

by:Co0L_DBA
ID: 26283966
many thanks guys for the replies, i will try it and get back to you...
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LVL 13

Expert Comment

by:GuruChiu
ID: 26296559
L2TP, tunneling or GRE are not needed. CoolDBA have 2 point to point E1 lines.
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Author Comment

by:Co0L_DBA
ID: 26301498
thank you GuruChiu it worked well, but i still can't  merge the 2 E1 lines in order to get 4mb/s bandwidth, any idea?
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LVL 13

Accepted Solution

by:
GuruChiu earned 2000 total points
ID: 26302018
This is one example of how to configure MLPPP:

interface Multilink1
bridge-group 1
 ppp multilink
 ppp multilink group 1

interface Serial0/0/0:0
 no ip address
 encapsulation ppp
 no fair-queue
 ppp multilink
 ppp multilink group 1
!
interface Serial0/0/1:0
 no ip address
 encapsulation ppp
 no fair-queue
 ppp multilink
 ppp multilink group 1
0
 

Author Comment

by:Co0L_DBA
ID: 26305276
many thanks, it worked well...
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