Routing traffic through 2 ISPs

Answered Question
Nov 6th, 2007

Hi,


I am working on adding a secondary data connection to our remote offices. Currently, we have an Internet router, firewall, and L3 switch at each site. I would like to add another router (connecting to the same L3 switch) for the secondary connection and have only Internet traffic running over it while the internal network traffic continues to use the current setup.


The L3 switch is running iBGP currently. It will also be running EIGRP after the secondary router is installed. The secondary router will also run EIGRP.


Can someone help make sure my thinking is correct here?


My plan:

1. Change the administrative distance for iBGP to 80 or something smaller than 90.

2. Make the default route point to the secondary router for Internet traffic.

3. If the secondary router goes down, the office would lose its Internet connection. Would it be possible to use a floating static route to point it to the primary router? Is this a wise move?


Thanks,

Lily

Correct Answer by Paolo Bevilacqua about 9 years 3 months ago

Hi,


I doesn't seem to me that point 1. above is necessary. But 2. and 3. as you mentioned, are the the correct approach.


Note however, a static floating route may not be enough, why is that, the internet router may loose connectivity, still the interface, as seen by the L2 switch, continues to be up.


In these case (usually referred as 'black hole'), you need to configure 'object tracking' on either the L3 switch (requires advanced services images) or on the router, with a track tied to the default route. The 'tracked object' can be as simple as a period ping to an host that you know is reliable on the internet.


Hope this helps, please rate post if it does!

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Paolo Bevilacqua Tue, 11/06/2007 - 12:14

Do you have BGP with both ISPs, and will they accept advertising you prefix independently from who gave it has assigned it to you ?

Or alternatively, you have no BGP and address of your own, and are you using NAT ?

Correct Answer
Paolo Bevilacqua Tue, 11/06/2007 - 13:14

Hi,


I doesn't seem to me that point 1. above is necessary. But 2. and 3. as you mentioned, are the the correct approach.


Note however, a static floating route may not be enough, why is that, the internet router may loose connectivity, still the interface, as seen by the L2 switch, continues to be up.


In these case (usually referred as 'black hole'), you need to configure 'object tracking' on either the L3 switch (requires advanced services images) or on the router, with a track tied to the default route. The 'tracked object' can be as simple as a period ping to an host that you know is reliable on the internet.


Hope this helps, please rate post if it does!

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