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WAN Link Redundancy

Posted on 2012-04-03
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Last Modified: 2012-06-27
Hello Experts.  We have an issue with circuit redundancy and I was hoping for a little help.  We have 2 layer2 p2p circuits (different providers) between our main datasite and our new colo.  We are currently using a port-channel combining both circuits between the 2 sites.  It works great until one of the carriers falls offline (maintenance, service outage, etc.)  The ports on both end see themselves as up and continue to try and send packets across the dead links.  I called Cisco and they recommended flex links.  These sound great but we would still have the issue of the ports not detecting when the carrier is down.  Does anyone have an idea whether an IP SLA solution can exist at layer 2 or if we should purchase a device (wan accelerator?) that can detect carrier outages on a circuit?

Thank you in advance for the assistance.

Chris
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Question by:AUDAX-IT
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schmitty007 earned 750 total points
ID: 37802702
You could always use a routing protocol for load balancing/redundancy between your two different carriers circuits. Not  being familiar with your network and what equipment you have using EIGRP/BGP or even OSPF with the two equal cost paths you should be able to accomplish this and the routing protocols can and will determine if one of the routes is unavailable.  My understanding about Flex links is they act more as backups and not load balancing.
I can see where port-channel would cause that issue because it will still see the interface link between your equipment and the carriers equipment as up, although the circuit itself would be down.

As for a WAN optimizer when our group looked into these at the time I don't recall part of their feature package being redundancy between multiple circuits but, makes sense that they would. But that always means buying and implementing new hardware.  

If you have L3 switches you could do as I mentioned above. We actually do this between one of our data sites and our colo I found when we do have a circuit drop it does take a slight amount of time for convergence depending on which protocol you are using but that would be better then what you are facing now.
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Author Comment

by:AUDAX-IT
ID: 37802890
Thanks Schmitty.  The load balancing isn't really important but more the redundancy.  We would actually prefer the single circuit with one in standby/backup.  We have layer3 switches between the sites but it's a flat layer2 environment between the datasite and the colo.  We have it setup as a layer2 because we wanted to have the same IP schema at both sites and have the colo as a flat extension of our datasite network.  Basically think of the colo as a different floor of our datasite with 2 trunk links running to it.  We're trying to find a way to keep this as layer2 if at all possible.  A layer3 design for us could turn into a nightmare with our current environment.
Any other ideas?  Thank you.

Chris
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by:Nayyar HH (CCIE RS)
Nayyar HH (CCIE RS) earned 750 total points
ID: 37805275
This might sound weird but I'd strongly recommend you give it a try

Enable UDLD in aggressive mode on these inter-links.

The idea being should UDLD stop receiving control frames from the peer (even though the link is up) it will assume one channel on the link has actually failed and then shutdown the link!

Here's a link to some useful info

http://www.cisco.com/en/US/tech/tk389/tk621/technologies_tech_note09186a008009477b.shtml


Good Luck!
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Author Closing Comment

by:AUDAX-IT
ID: 37806234
Thanks a lot Schmitty and Nazsky.  We'll give the UDLD a go and if this doesn't work for us we may try out a hardware device.  Still researching our options here.  Thanks for the help guys.<br /><br />Chris
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