Automatic Failover?

Answered Question
Apr 5th, 2010

Hi all,

So I have a campus with two buildings, and each building has their own MPLS link. Also, these buildings have a microwave connection between them.

I'm looking for a way to utilize the microwave link to route local traffic between the buildings, but not MPLS traffic.

While I'm pretty solid with a manual solution for this scenario, I was hoping someone would be able to offer some advice for an automatic solution..

Any takers?

I have this problem too.
0 votes
Correct Answer by Giuseppe Larosa about 6 years 8 months ago

Hello Carl,

you haven't provided a key information that is how is routing performed over the two MPLS links:

are you using static routes pointing at PE IP address or a dynamic routing protocol?

In any case, the fist factor to look at is how specific are routes learned on the MPLS link about the other site IP subnets.

If you are able to learn more specific routes over the microwave links you can achieve your objective leaving the MPLS link free to be used to reach other destinations.

I guess with automatic failover you mean the use of a routing protocol.

For this kind of scenario EIGRP can be used between Cisco devices.

A common IP subnet is needed on the microwave links

10.10.130.0/30 can be the microwave link

10.10.0.0/17 can be the aggregate of routes of first site

10.20.0.0/17 the aggregate of second site

R1

router eigrp 100

network 10.10.0.0  0.127.255.255

network 10.10.130.0 0.0.0.3

no auto-summary

R2 on site 2:

router eigrp 100

network 10.20.0.0  0.127.255.255

network  10.10.130.0 0.0.0.3

no auto-summary

EIGRP AS (100) must match in order to build a correct neighborship

the microwave link is used for all specific IP subnets if over the MPLS link only the aggregate address (10.20.0.0/17 for site2, 10.10.0.0/17 for site1) is received

Hope to help

Giuseppe

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Correct Answer
Giuseppe Larosa Mon, 04/05/2010 - 23:40

Hello Carl,

you haven't provided a key information that is how is routing performed over the two MPLS links:

are you using static routes pointing at PE IP address or a dynamic routing protocol?

In any case, the fist factor to look at is how specific are routes learned on the MPLS link about the other site IP subnets.

If you are able to learn more specific routes over the microwave links you can achieve your objective leaving the MPLS link free to be used to reach other destinations.

I guess with automatic failover you mean the use of a routing protocol.

For this kind of scenario EIGRP can be used between Cisco devices.

A common IP subnet is needed on the microwave links

10.10.130.0/30 can be the microwave link

10.10.0.0/17 can be the aggregate of routes of first site

10.20.0.0/17 the aggregate of second site

R1

router eigrp 100

network 10.10.0.0  0.127.255.255

network 10.10.130.0 0.0.0.3

no auto-summary

R2 on site 2:

router eigrp 100

network 10.20.0.0  0.127.255.255

network  10.10.130.0 0.0.0.3

no auto-summary

EIGRP AS (100) must match in order to build a correct neighborship

the microwave link is used for all specific IP subnets if over the MPLS link only the aggregate address (10.20.0.0/17 for site2, 10.10.0.0/17 for site1) is received

Hope to help

Giuseppe

Carl Harbeck Tue, 04/06/2010 - 14:15

Hi Guiseppe,

The microwave and MPLS router for each building plug into a core switch. Internally we are using EIGRP and are using BGP in the MPLS cloud.

In discussing that further, your answer is what we will be doing, so thanks (clearly I am still new at this ).

Each site will go to their MPLS for outbound connections, and internally it will use the microwave since it is less hops. Should one of the MPLS links fail, it will use the less efficient (outbound) microwave route as an alternative.

Giuseppe Larosa Wed, 04/07/2010 - 00:49

Hello Carl,

if you want to use the microwave link as a backup when MPLS link fails you may need additional configuration like a default  route sent in EIGRP and redistribution of EIGRP into BGP in order to ensure that return traffic can come back or you need also to update NAT configuration at site 2 to accomodate also IP subnets of site1 and viceversa if you use the MPLS link also for internet access.

Hope to help

Giuseppe

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