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Beginner

L3VPN using MPBGP without MPLS/GRE .?

Hi,

i want to understand for can we create L3VPN using MP-BGP only ,why we need MPLS/GRE Tunnels.

if we have all Routers running MPBGP sessions, can they exchange VRF Information, VRF routes without MPLS / GRE..

what would be missing or limited if we do this. 

Please help with answer , this would be help in clearing a few doubts.

" why we need MPLS , when all work for L3VPN information is created and carried with MPBGP itself."

Regards

Sourav

Everyone's tags (4)
1 ACCEPTED SOLUTION

Accepted Solutions
Cisco Employee

Hi,

Hi,

The one you highlighted in the picture is RD. It is different from label. RD is used by control plane (MP-BGP in this case) to differntiate same address from different VPN customers. For example, PE can receive 10.1.1.1/32 from Customer A and B via any PE-CE protocol. It uses RD to make it unique in BGP table and advertise the same to remote neighbors. 

While advertising, it assigns a unique label for each VPN prefix. In the above example, 10.1.1.1/32 from Custoemr A may have label 100 and same prefix from Customer B may have 101. All labels are assigned from same pool and so will be unique for each prefix.

Label is used in the dataplane to identify the forwarding action.

HTH,

Nagendra

7 REPLIES 7
Cisco Employee

Hi Sourav,

Hi Sourav,

MP-BGP are normally enabled between edge routers which are connected by otehr core routers. While we can use MP-BGP to exchange the VPN prefixes to remote edge routers, actual traffic will fail in core if it is not tunnled/encapsulated as the core routers will not be aware of VPN routes.

So we use any tunneling mechanism like MPLS, GRE etc between edge routers.

HTH,

Nagendra

Beginner

Hi Nagendra,

Hi Nagendra,

Can we form vpnv4  neighbor without need of MPLS / GRE ?

and the VPN label for a VRF is fixed in nature independent of prefixes in RIB/ lFIB. ?

Thanks

Sourav

Highlighted
Cisco Employee

Hi Sourav,

Hi Sourav,

Can we form vpnv4  neighbor without need of MPLS / GRE ?

<Nagendra> As long as the neighbor is reachable and enabled with relevant AFI/SAFI, VPNv4 session will be established. It does not check if MPLS or GRE is enabled to the neighbor.

and the VPN label for a VRF is fixed in nature independent of prefixes in RIB/ lFIB. ?

<Nagendra> Not sure I understood this question. Can you explain it more?.

-Nagendra

Beginner

Hi,

Hi,

the VPN label for a VRF is fixed in nature independent of prefixes in RIB/ lFIB. ?

<Nagendra> Not sure I understood this question. Can you explain it more?.

i think as i understand working of MPLS with LDP, all RIB prefixes get label under LFIB.

but for any VPNV4 / vrf prefix identity is there any MPLS Label which is fixed, is it any different from labels generated for Prefixes.

attaching a snapshot, which show VPN label for VRF identity,.

thanks !

Cisco Employee

Hi,

Hi,

The one you highlighted in the picture is RD. It is different from label. RD is used by control plane (MP-BGP in this case) to differntiate same address from different VPN customers. For example, PE can receive 10.1.1.1/32 from Customer A and B via any PE-CE protocol. It uses RD to make it unique in BGP table and advertise the same to remote neighbors. 

While advertising, it assigns a unique label for each VPN prefix. In the above example, 10.1.1.1/32 from Custoemr A may have label 100 and same prefix from Customer B may have 101. All labels are assigned from same pool and so will be unique for each prefix.

Label is used in the dataplane to identify the forwarding action.

HTH,

Nagendra

Beginner

just to add something,

just to add something, Nagendra's answer was great.

Sourav, what you are describing is the unsolicited downstream LDP method. that works for the "global" ips (non-vrf) when you are using LDP (as an example the MPLS core routes, loopbacks and so)

Remember that as multiple protocols can feed the RIB (OSPF, BGP and so), same happens with LFIB. LDP, RSVP, BGP feeds the LFIB.

BGP can set a label per prefix in a vrf, or it can just set a "global vrf label" to identify all the prefixes that are from a specific vrf. 

good luck guys!

Beginner

is there any fixed label for

is there any fixed label for per VRF, to identify that VRF.

as labels are used to ipv4 forwarding as well is MPLS is enabled.

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