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pjulian
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VLAN Redundancy

Sun Aug 19, 2012 11:28 am

Hi, hoping that somebody can advise some options for this situation we have a requirement for.

We are setting up a network for a customer, they currently have 2 x RB1100AHx2 routers to act as their core routers and want to use 2 for redundancy purposes.
The issue is that they have a layer 2 connection coming in from a supplier and get handed off vlans from that supplier, normally they would just terminate the vlan on the router and add layer 3 IP to it and away they would go.
However, they want to be able to provide redundancy for these vlans from this supplier across the 2 core routers, in some cases they only need to bridge the vlan onwards to another router, it just depends on whether they can terminate the IP on the main router or another edge router, often it ends up being another router.

Unfortunately I'm not an expert in layer 2 redundancy, and whilst I would be OK to do something if it were only layer three we had to terminate, I am unsure of the correct approach when dealing with layer 2 vlan redundancy.

If anybody could suggest some options of how we might be able to tackle this for the customer that would be appreciated.

Thanks
Paul
 
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Re: VLAN Redundancy

Sun Aug 19, 2012 12:04 pm

i think you will need to explane a bit more how this setup is done. and what is the goal to reach. like i understand U, u want to have a l2 in - terminate the vlans to one router, but have a second as a "backup". Then the "backup" need the same IP, on the vlans as the first router, to acct as the gateway? Then this is a l3 redundancy setup.

Or, is the redundancy just on the l2 net, before the IP is put to an interface?
 
pjulian
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Re: VLAN Redundancy

Sun Aug 19, 2012 1:10 pm

Thanks for your reply, yes basically we need to get layer 2 redundancy, layer 3 is pretty easy, but we need to be able to get vlans from supplier to routers past the core routers if necessary.

For example:


/----R2----\
/ \
R1--- --- R4
\ /
\----R3----/

R1 = supplier router which is presenting layer 2 vlans
R2 & R3 = customer core routers
R4 = router that vlans need to get to from R1 if R2 or R3 are down (obviously not both :-))

Hopefully this gives you a bit more information.

Regards
Paul
 
pjulian
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Re: VLAN Redundancy

Sun Aug 19, 2012 5:39 pm

Sorry, that doesn't look right....

R1 is the supplier router which would connect to R2 and R3 via different ethernet ports.
R4 connects to R2 and R3 in the same manner but on the other side.

So basically I need to get vlans from R1 to R4 and be able to handle a failure in R2 or R3 and still keep running.

I think I have worked it out now by doing some testing.

Take the following example:

R1 has vlan1 which it needs to get to R4, this vlan1 comes in from the supplier through ether3 of R1
R1 ether1 connects to R2 ether1
R1 ether2 connects to R3 ether1
R4 ether1 connects to R2 ether2
R4 ether2 connects to R3 ether2


So I would create a vlan interface with a vlanID of 1 on R1 ether1, R1 ether2 and R1 ether3 and add all 3 vlan interfaces into a bridge with STP enabled
On R2 I would configure vlan interfaces with a vlanID of 1 on ether1 and ether2, then create a bridge interface to bridge both vlan interfaces
On R3 I would configure vlan interfaces with a vlanID of 1 on ether1 and ether2, then create a bridge interface to bridge both vlan interfaces
On R4 I would configure a vlan interfaces with a vlanID of 1 on ether1 and ether2, the create a bridge interface to bridge both vlan interfaces with STP enabled

I believe from the testing I did that I should then be able to put an IP address on the bridge in R4 and be able to get layer 3 connectivity back past R1 to the supplier, and if either R2 or R3 failed the link should keep working.

Does this all sound correct and is it the right way to approach it ?

Thanks
Paul
 
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Re: VLAN Redundancy

Sun Aug 19, 2012 6:09 pm

It sounds like you need a true switch in the network and not a bridging solution. Depending on how critical this is, you probably need to put in a piece of equipment that is less of a single point of failure. I would look at a switch that has redundant power supplies and or processors.

If a single point of failure switch is acceptable between the edge and the routers that need the layer 2 handoff, then use someting like a Cisco 3550 or 3560 or put a MikroTik with a switch chip into a true switch state and tag the vlans needed through the ports. Switching performance is much better than bridging.
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Re: VLAN Redundancy

Sun Aug 19, 2012 11:25 pm

This can be done if you bridge all intertfaces and put RSTP. (also switch)

Eg. R1. rstp 8000hex
R2 Rstp 8000hex
R3 Rstp 9000hex
R4 Rstp 8000hex

Then it should all be ok.

At r1 and r4. bridge the 2 interfaces, and put vlans to bridge, and ip to vlans.

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