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MPLS is a significant part of the SPOTO CCIE RS 400 101 lab exam. However, some candidates found that it's difficult to master MPLS, SPOTO candidates passed these parts of the CCIE RS Lab exam easily. More info can be found in the SPOTO Cisco WhatsApp study group.
- MPLS can be used anywhere, no matter what medium is the layer, what protocol is the second layer?
- MPLS uses a 32-bit Label to be inserted between the Layer 2 header and the Layer 3 header (frame-mode MPLS) frame mode MPLS
- MPLS over ATM uses the MPLS of the VPI/VCI (cell-mode MPLS) cell model of the ATM header.
MPLS label format
The 32bits label is divided into the following 4 parts.
- 20bits Label - represents the label range (0~2^20)
- 3bits experimental position (lab line eld) one for QOS
- 1 bit of the bottom of the stack - used to indicate whether the next header immediately following the label is another label, or an IP packet (when the label is stacked, the bottom of the stack is all 0s, followed by 1)
- 8bits TTL bit - for anti-ring
MPLS label stack
The type field of the Layer 2 frame header (type 2 0x8847 of the Ethernet I!) indicates a unicast label packet.
The bottom of the stack is used to indicate whether the next header immediately following the label is another label (0) or an IP packet (1).
Each router only operates on the top label after receiving the label package.
0x0800 followed by the IP packet
0x08847 Ethernet II Unicast Label Pack
0x08848 Ethernet II Multicast Label Pack
0x0281 ppp unicast packet
Label Switch Routers: Label Switch Routers
- LSR: Core device in the MPLS domain, mainly performing label switching (Iabel swapping)
- EdgeLSR: border device of the MpLS domain
- Forward IP packets into the MPLS domain: impose
- Forward packets from the MPLS domain to the MPLS domain (PoP)
- No label(untagged) Pops a layer of labels and then checks the back part. If it is IP, continue to check FIB. If it is another label, discard it directly.
LSR architecture diagram
Edge-LSR architecture diagram
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