Hello, everyone.
Today, I'd like to share with you the principles and an experiment of the BGP free core.
1.BGP Free Core Technology Overview
(1) Principle
On an IP backbone network, if BGP is deployed to carry service routes, all routers on the backbone network must run BGP, as shown in the following figure.
If the core router on the backbone network does not run BGP, service traffic will be discarded because the core router does not have routing entries destined for the destination. (It is not reasonable for edge routers to import BGP routes to IGP.)
If the core router has insufficient performance, high pressure, or does not want the core router to carry service routes, you can use the BGP Free Core technology to enable the LDP LSP to forward service traffic.
An implementation of the BGP Free Core is as follows: Run BGP between PEs to exchange service routes. IGP, MPLS, and MPLS LDP are deployed on PEs and P routers. BGP service routes are iterated to MPLS LSPs on PES. P routers only need to perform MPLS forwarding and do not need to carry service routes, as shown in the following figure.
(2) Advantages
a. In addition to edge routers, core routers do not need to run BGP and do not carry service routes. This reduces the usage of CPU, memory, and routing entries on core routers, especially when core routers are obsolete, performance is insufficient, or the live network is overloaded.
b. The core router is more stable. When the service route of the edge router changes, the core router is not affected.
2. Experiment
The following figure shows the topology and the main configurations. All devices are located in AS100, and OSPF, MPLS, and MPLS LSP are deployed. IBGP is deployed between PE1 and PE2. The IP addresses of loopback1 interfaces on PE1 and PE2 are used to simulate service addresses and are advertised in BGP network mode.
The eNSP project has been uploaded at the end of the post.
Verifying the Running Result
By default, an unlabeled BGP route or a static route can only be iterated to the outbound interface and next hop, but not a tunnel. The route recursive-lookup tunnel command enables tunnel iteration.
(1) Before the route recursive-lookup tunnel command is run on the PE.
Check the peer service route in the FIB of the PE1. The next hop of the BGP is 4.4.4.4 (PE2), and the next hop of the route is 10.0.0.2 through IGP iteration. The route is not iterated to Tunnel (Tunnel ID 0x0).
Ping fail from loopback1 of PE1 to loopback1 of PE2.
(2) After the route recursive-lookup tunnel command is run on the PE.
Check the peer service route in the FIB of the PE. The route is iterated to Tunnel (Tunnel ID 0x3).
Ping succeed from loopback1 of PE1 to loopback1 of PE2.
