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New Member

Redundant architecture Please Advice

Host--Router A---64K---RouterX------Router B ---Host

**********|---------64K---RouterY---------|

Above is a configuration i am planning on setting up. A host on Router A needs to talk to a host at Router B. We are going to have two separate carriers with 64K circuits for redundancy. I am planning on using eigrp as the routing protocol and planning on using cef with per destination load balancing. Customers requirement stats minimum i mean less than 5 sec interruption in the event of a ciruit failure. I am aware that EIGRP automatically load balances across equal path but am concened with the duration it may take to switch to the successor. I know you see only one router at the two ends, however the host has two nics and if it sense a network down re route across another network not shown above

Any suggestions on if i should approach this problem differently?

thanks

5 REPLIES

Re: Redundant architecture Please Advice

Do you want load-sharing (balancing) or a backup link. For yhe case of load-sharing (I think this is the most appropriate because both are leased-lines and you'll pay even if you don't use) EIGRP can achieve this and you can't even be aware of it. Your topology seems OK for equal-cost load-balancing (RouterA will see destination with equal costs and EIGRP feasibility condition will be met) you EIGRP topology table and route table will see two routes at equal loads. In case of a failure on a link, this EIGRP route won't have to go into active state and I think in less than one minute the other circuit will take the full load.

Best Regards.

New Member

Re: Redundant architecture Please Advice

thank you

However if i want per destination load sharing instead of per packet would ip cef be an alternative also. Or i can use the ip route cache statement on the interfaces

thanks

New Member

Re: Redundant architecture Please Advice

If you turn on CEF and have equal cost paths across the serial links (on the same router), it should do per destination load balancing by default (alternatively you can turn on per packet load sharing). There should not be any noticeable downtime if one link is lost since there is already another path in the routing table.

See link below for more information on CEF and load balacing:

http://www.cisco.com/en/US/products/hw/modules/ps2033/prod_technical_reference09186a00800afeb7.html

New Member

Re: Redundant architecture Please Advice

You might look at Multi-link PPP to combine the 2 circuits at layer 2. I think the failover is much faster. I have done this with 2 circuits from the same provider, but not from two different providers. As long as the latency across each link is about the same, it should work.

Randy

New Member

Re: Redundant architecture Please Advice

Thank you all for your replies. I am leaning toward ip cef per destination solution. Also since this is a pretty small eigrp network, i may just let eigrp do its thing. Anyway will be testing with the vendor soon

thanks

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