ISP Failover

[ommidi]

We have a block of public IP address advertised from our ISP. We recently introduced another ISP for failover/loadbalancing purpose

Do we need the new ISP to also advertise our IPs?

[Joseph W. Doherty]

That depends whether you have public IPs you want to be reached from other ISP. (I.e. source Internet and destination your IPs.)

If your "public" IPs are "owned" by your 1st ISP, 2nd ISP will probably not want to advertise them.

[Richard Burts]

This is a bit more complicated question than it looks at first and to provide good answers we need more information about your environment and a better understanding of your requirements. Based on the very limited information available so far I have these comments:

- if you want to do load balancing with ISP 2 it is possible to advertise your address space to them, or it is possible for them to use static routes to send traffic to you. When dealing with 2 ISP it is more common to use BGP and to advertise the address space to the ISP. Getting ISP 2 to use static routes to send traffic to you could be especially tricky if your address space really belongs to ISP 1 and is assigned to you (as Joseph has mentioned).

- we really need a better understanding of what you mean when you say you want failover. Does that mean that while ISP 1 is available you want to send your traffic to them and to send traffic to ISP 2 only when ISP 1 has failed? In that case the best solution is to use BGP and configure it so that you only advertise to ISP 2 when ISP 1 is not available. Or does failover mean that you send some traffic to both ISP and ISP 2 is available to carry all of the load when ISP 1 fails?

It is not uncommon for an organization to have its IP address space assigned to it from its first ISP and then to want to advertise that address space to the second ISP. You can make a request to the first ISP and it can give you a Letter of Authorization which allows you to advertise that address space through another ISP. And in my experience it usually works out that the second ISP will be willing to advertise that address space (after obtaining the Letter of Authorization) since they recognize that they will not get your business if they do not agree to advertise your address space.

HTH

Rick

[ommidi]

Yes we do have public IPs that need to be accessed from the internet for different services that we are hosting. At the moment they can only be accessed through the old ISP

We are connect to both ISPs through point to point fibre links and NATing to public IP for internet access on old ISP. we want to be able to also NAT to the new ISP using some of our public IPs for internet access

[Jon Marshall]

Are the public IPs provider independent or do they belong to the first ISP ?

Jon

[ommidi]

Yes IP provider and the ISP are independent

[Richard Burts · Accepted solution]

In reading this discussion another time I realize that the original post asks a very simple question:

Do we need the new ISP to also advertise our IPs?

There is a simple answer. Yes if you want the Internet to be able to reach your network through the second ISP then the second ISP needs to advertise that address space.

I was addressing valid aspects of networking when I talked about load sharing and about failover. But I was providing a complicated answer to a simple question. After we accept that it is necessary for the second ISP to advertise the address space then there may be questions about doing load sharing or about failover. But first let us answer a simple question with a simple answer.

HTH

Rick