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How can i handle doublee lines?


We got a solution from our leased line provider call Y-protection:

A leased line has to ends, but only one is completely available at a time. When endpoint one fails, number two takes over.

Now the problem:

Each endpoint is connected to a different router.

These interfaces have the same IP-address. As only one should be up at a time this makes no problem.

But these lines behave like that. Incoming traffic comes over both lines. Of course only one of the lines accepts traffic for transmitting.

The problem is that both routers see the incoming traffic at the same time. But only that interface that is active is used. But we get duplicate packets incoming.

How can i manage that the "passive" interface is down as long as no traffic can be trabsmitted.

We use hdlc at the moment. Can we handle it with another protocol?


Ralf Kosczor

Community Member

Re: How can i handle doublee lines?


Seems like your provider has configured HSRP. If it is true, then your description proves that the solution is working the way it is suppose to work.

In HSRP, two router acts as a virtual router and only the active router forward the traffic on behalf of the virtual router. Network clients send their packets to a virtual gateway, so there should not be a problem of duplicate packets.

Look at the following links to get more details on HSRP. Hopefully it will answer most of your questions.

HSRP Protocol:

HSRP Support page:

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