Application of BGP protocol in MPLS

In the previous article, we introduced MPLS technology. Many protocols have been applied in this Multi-Protocol Label technology. Today we will introduce the BGP protocol. Let's see how BGP works in MPLS. The specific application of the BGP protocol in MPLS technology. Let's take a look at the following article. all problems can be solved. When LSR assigns tags Based on the route table, it only assigns tags to route entries obtained from the IGP protocol. Why? This is of special significance! MPLS technology switching is enabled throughout Transit. Ensure that the CIDR blocks between ISP2 and the LSR-Border2 are published to the IGP routing protocol within the Transit AS, the same requirements are imposed on the CIDR blocks between ISP1 and the LSR-Border2.

Previously mentioned that when MPLS technology LSR assigns labels to route entries, it only assigns labels to Routes learned from IGP, and network 1.2.3.4 is released to the IGP routing protocol in Transit, it is certain that Core1 is available at Border1 to tell it about label 23 on the 1.2.3.4 network.

LSR-Border1, the formation of IBGP Neighbor Relationship Between the LSR-Border2, through the BGP protocol, the LSR-Border2 from the ISP2 learned 10.0.0.0/8 this route to the LSR-Border1, the next hop address of this route is 1.2.3.4, in this way, let the LSR-Border1 know to send data to the network 10.0.0.0/8, first to the data sent to the network 1.2.3.4. 1.2.3.4 is bound with Tag 23. Therefore, when generating the FIB table, a tag 23 is also bound to the segment 10.0.0.0/8.

In this way, if data is transmitted from ISP1 through Transit AS to ISP2, the 23 tag will be inserted to the IP package at Border1, And the generated tag package will be forwarded to core1, core1 only needs to analyze the label header and forward the label package! Because the core router of the Transit AS does not need to run the BGP protocol, the core router of the MPLS technology network will not know the route of the external user, thus reducing the route table of the core router, improved search efficiency.

We can also see that because of the label of MPLS technology, IP address headers are not analyzed on the core router, even if the IP address header contains private IP addresses such as 10.0.0.1, it will also be forwarded normally because only the tag is analyzed. This is what service providers are pursuing when providing VPN services. Of course, this must be repeated. LSP cannot be disconnected throughout the entire Transit AS. If it is disconnected, the label package will be restored to an IP package, and the core router will not include the user route, resulting in packet loss.

The role of BGP in MPLS technology networks opens the door for VPN services, but we should also be aware that the two basic requirements of VPN services are 1. users can independently plan IP addresses. 2. security is very important! The above are two VPNMPLS technology instances, with CE1 CE = Customer Edge device and S3.

However, if the IP address range 10.1.2.0/8 is the same as that of CE1 and S3. if you do not modify the PE1 router, PE1 can only consider that the data sent to 10.1.2.0/8 is either output from S0, either From S1. In this case, if CE1 is not CE1 or SSPS, the data sent from PE1 to the 10.1.2.0/8 network segment will not be received.