Multi-Protocol Label Switching

beef410's version from 2018-04-12 23:28


Question Answer
MPLSUsed because routing tables in an ISP cloud are massive, and traditional lookups would be nuts.
LSPLabel Switched Path, the unidirectional pre-discovered path for a packet across the MPLS network.
Provider EdgeProvider routers that face customer equipment
Customer EdgeCustomer equipment that faces provider equipment
PE Router RoleDecides which FEC a packet belongs to
FECForwarding Equivalence Class. All packets in the same class sharing final destination, local exit interface, and queuing priority
FEC AssignmentExample values used to determine FEC, IP subnet, QoS field like IP Precedence.
Label mappingEach FEC is mapped to a label value which is 'pushed' between the ethernet and IP headers of a packet
PushRouter puts a label on a packet without removing one if one already existed
LERLabel Edge Router, edge router that determines what LSP to send the packet through
LSRLabel Switched Router, a router capable of adding MPLS tagging and finding LSP's
LIBLabel Information Base, Label incoming to label outgoing table. IE comes in with label 1 per the table it leaves with label 24
SwappingIncoming label is removed, outgoing label is added.
Penultimate RouterSwaps a label of 0/null onto the packet as it leaves for the final edge router. This indicates the final router should pop the label and route normally.
PoppingRemoving the label before exiting the MPLS network
Multiple LabelsTop/most recently applied label, is the one that is considered when routing.
Penultimate Hop PopInstead of swapping to a null label on the penult router it will just pop it off and the final router will implicitly know to route the packet normally.


Question Answer
RequirementsEndpoint routers must have routing table entries to the destination (routing protocol)
OSPF / EIGRPWould require an adjacency to form between the PE and CE equipment
MPBGPISP routers would run Multi-Protocol BGP, not typically redistributed into customer equipment as BGP tables can be huge.
Route RedistrubutionDoes not have to be two-way. We can inject our routes into the ISP's BGP table and not inject theirs into ours.
PerformanceEdge routers can take a performance hit when redistributing routes.

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