Path selection on CE router connected to MPLS network

[rwu]

Hi, I have a question about the path selection on CE in MPLS network:

The attached is the topology. 

1. In MPLS network, 3 PE's are in separate AS number, AS1, 2, 3. 

2. in each site, CE sets up iBGP with the local PE. 

3. Only CE's in AS1 & 2 can be configured by me. 

4. Now, there's default route in above two sites (Data centers). Is there a way I can modify configs on AS1 & 2 CE's so that on AS3 CE, it will choose one data center path over the other? Say, I want the left side data center path to be the primary and the other one is the secondary. 

I though about all the possibilities but it seems that unless PE router configs are modified, I can't realize what I want. 

Thanks. 

Thanks. 

[Georg Pauwen · Accepted solution]

Hello,

I would say no. Your AS1 and AS2 are not connected, so they cannot compare any parameters such as AS-PATH. So in order to achieve any sort of MPLS traffic engineering, you would need to work with your ISP...

[rwu]

Thanks for the reply Georg. 

If eBGP is set up between CE and PE, it should work right? We can prepend AS-PATH on AS2 CE so that from AS3 PE, it'll choose the route to AS1 PE as the preferred BGP route and then advertise to AS3 CE. 

The attached image is the current network of the client. Don't know why iBGP is between CE and PE. Normally, eBGP should be between CE and PE right? Between PE's, it can be either iBGP or eBGP. 

[Georg Pauwen]

Hello,

if eBGP instead of iBGP is used  between the CE and PE routers, you could indeed configure AS-PATH prepending. That obviously requires a change on the PE routers, it was my understanding that these are not under your control ?

[rwu]

Yeah, only CE can be configured. Anyway, thanks for the confirmation. I'll ask the client to talk to ISP.