[2 days left] What’s wrong with your cloud strategy? Learn why multicloud solutions matter with Nimble Storage.Register Now


Using BGP between two Internet Service Providers for internet redundancy

Posted on 2013-01-08
Medium Priority
Last Modified: 2013-02-14
I understand that for BGP, I need to purchase an AS number and a minimum of a class C subnet.  This is fine, I know it won't be a problem, but here's my question.  Right now I only have one internet circuit, (I'm not doing BGP with them right now, but they can do it).  We are bringing in a 2nd ISP who can also do BGP so we will have internet redundancy.  My question is do I need a class C subnet from both ISP's?  With the ISP I currently have I have a /30 WAN connection, and a /28 public routable IP Block.  Any assistance would be greatly appreciated.  Thanks. .
Question by:denver218
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 2

Accepted Solution

Leeeee earned 1000 total points
ID: 38755574
If you purchase a class C and AS from ARIN, you will be able to advertise the class C to both providers and can use BGP AS-Path Prepending for redundancy. If you purchase a /24 from the provider, they generally speaking will not allow you to advertise that block to another provider as it is part of a larger network owned and advertised to the internet by that ISP. This is something you will want to confirm with your ISP.

If you just need internet redundancy for strictly outbound access, you can use the /28 with your primary provider without BGP and when you fail over, you can then NAT everything to the range on the second circuit. Keep in mind this will reset users connections as they will start using a new IP.

Or, If you purchase a /24 from your provider (not from ARIN), when you failover to the other circuit, you could just PAT all the traffic to the outside interface of your second internet connection. This way, you will not need to lease another block of IP's. Let me know if this makes sense.

What I see most often when companies desire redundant Internet access, purchasing an AS and /24 from ARIN is often the path they take
LVL 20

Assisted Solution

rauenpc earned 1000 total points
ID: 38755654
You actually can use a /24 from a provider and advertise it to another provider, but you need to jump through a few hoops. There are forms that need to be filled out and sent to both ISP's in order to get them to be in agreement over accepting the subnet to be advertised. I had a customer do this about a year back... it took like 4+ months for the forms to get handled, and I'm not sure if it was due to the customer, ISP, or just how the process goes.

Of course, the above is all dependent on the ISP's being willing to do this.

This may not be an issue for you, but when you only have 1 class C and two ISP's, you can have failover but you need to make sure the ISP's DON'T use local preference settings. Most ISP's set a local-pref value to any subnets advertised by directly connected customers. This means that if a packet goes through their network destined for yours, they will always route through their own network instead of passing it off to someone else's network. This allows a packet to leave your network out ISP A but return through ISP B due to the destination being closer to ISP B and routing through ISP B. Removing the local-pref values allow you to control traffic flow using prepending.

This all gets much more complicated if you want to split the class C internally for redundant data centers, but it is an internal complication and not with the ISP.

Expert Comment

ID: 38755689
Rauenpc is correct regarding advertising PA address space to another ISP. It's possible, but not as cut and dry as obtaining AS/block from ARIN.

Author Closing Comment

ID: 38890384

Featured Post

Moving data to the cloud? Find out if you’re ready

Before moving to the cloud, it is important to carefully define your db needs, plan for the migration & understand prod. environment. This wp explains how to define what you need from a cloud provider, plan for the migration & what putting a cloud solution into practice entails.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

This past year has been one of great growth and performance for OnPage. We have added many features and integrations to the product, making 2016 an awesome year. We see these steps forward as the basis for future growth.
When speed and performance are vital to revenue, companies must have complete confidence in their cloud environment.
Both in life and business – not all partnerships are created equal. As the demand for cloud services increases, so do the number of self-proclaimed cloud partners. Asking the right questions up front in the partnership, will enable both parties …
As a trusted technology advisor to your customers you are likely getting the daily question of, ‘should I put this in the cloud?’ As customer demands for cloud services increases, companies will see a shift from traditional buying patterns to new…

656 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question