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Community Member

Newbie question

Hi,

just to get this clear once for all.

If I run MPLS only, I understood that there is no need for any IGP among the P routers ?

And what if I run MPLS VPN ?

Thank you

1 ACCEPTED SOLUTION

Accepted Solutions

Re: Newbie question

Hello,

Sorry to inform you, that you misunderstood something. For an MPLS network an IGP is needed in the core between all P and PE routers in a realistic scenario. The IGP will advertise f.e. Loopback IP addresses. Without them LDP would not be able to setup a TCP session between the two Loopback IP addresses of two LDP peers. So to start label exchange through LDP you need to have a TCP session

between two routers. To move the IP packets from one box to the other IP routing is inevitably nessessary.

So with or without MPLS VPNs you need IP routing in the core - static routing for the least, but in all productive environments of considerable size an IGP is used. In most cases either OSPF or ISIS is in place.

Hope this helps. Please rate all posts.

Regards, Martin

2 REPLIES

Re: Newbie question

Hello,

Sorry to inform you, that you misunderstood something. For an MPLS network an IGP is needed in the core between all P and PE routers in a realistic scenario. The IGP will advertise f.e. Loopback IP addresses. Without them LDP would not be able to setup a TCP session between the two Loopback IP addresses of two LDP peers. So to start label exchange through LDP you need to have a TCP session

between two routers. To move the IP packets from one box to the other IP routing is inevitably nessessary.

So with or without MPLS VPNs you need IP routing in the core - static routing for the least, but in all productive environments of considerable size an IGP is used. In most cases either OSPF or ISIS is in place.

Hope this helps. Please rate all posts.

Regards, Martin

Community Member

Re: Newbie question

Thank you!

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