I guess I just wanted to get into a high level discussion on using BGP in regards of a design I'm trying to put together. A little background, our lead network engineer left in the middle of our poject to redesign the WAN and I'm taking over in the middle of it. So far he's put together a pretty comprehensive plan to use BGP across two ISPs. I'm new to setting up BGP and I was wondering if I have this straight.
I want to basically use ISP X for user traffice and ISP Y for our www, e-mail, ftp, etc. However I want to advertise bother IP spaces across both links so that in the event one ISP goes out the other one can handle the traffic. (The data center and the main campus is connected with two port channeled 10 Gbps links.) Am I barking up the right tree here? I
So all I care about is two goals:
1) With everything running correcly the traffic from the users and the traffic from the data center are seperate.
2) If we lose an ISP (I know... that's rare but I've seen it happen) that the other link can take over till the problem is solved.
I've attached a visual.
As I see it you can do it like this :
- If both prefixes can be aggregated : you can advertise the aggregate to each ISP + one specific prefixe per ISP
- if you cannot aggregate the prefiexes :
- to the ISP1 advertise prefix1 without any change and prefix2 prepended
- to the ISP2 advertise prefix2 without any change and prefix1 prepended
- you can use conditional advertisement with non-exist map :
- in normal conditions you advertise only one prefix per ISP : prefix1 to ISP1 and prefix2 to ISP2
- if the peering to ISP1 goes down advertise the prefix1 to ISP2. ( same for prefix2 )
In the original post the first requirement is that "With everything running correcly the traffic from the users and the traffic from the data center are seperate." BGP is not an effective way to achieve this requirement. To separate the traffic you will need something like Policy Based Routing.
The second requirement is to fail over from one ISP to the other ISP. BGP is usually the preferred tool to achieve this. If you really want one ISP to be used and the other just as failover then I really like the suggestion from Dan about conditional advertisement.
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Are these ISP provide Internet connections and Internet BGP, or some type of private WAN cloud? If the latter, you might consider using both providers for all traffic and use QoS to treat traffic differently.
You can control which ISP you send traffic to, but you can't control which ISP the traffic will return from when you advertise your ip space to each ISP.
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