redistribute customer routes into IGP in service provider backbone

[Louey]

Hi

I have a general question, what would be the reasons of ditributing customer routes (xDSL customers for example) into a service provider IGP backbone ? why don't just use BGP to manage routes ? 

BR

[Iaroslav]

Usually BGP is indeed used to transport routes alongside with MPLS backbone. Moreover, redistribution into IGP is not recommended due to scalability reasons.

However, at some point before MPLS widespread, if you needed BGP-free core, then the only viable option was to redistribute BGP into IGP. However, that's is not the case anymore for a long time.

[MHM Cisco World]

CE can 
1- use NAT 
use NAT to interface connect CE to PE (provider side), here the SP Core not need to know what CE prefix use it only need to know IP of link between CE and PE. 
2- not use NAT
no use NAT and CE want to advertise it prefix to other PE-CE, here you need to use protocol between CE-PE like BGP,OSPF,EIGRP and static route. 

[Louey]

Hi

By IGP I mean the routing protocol used in the backbone, eg IS-IS, what reasons make a provider reditribute its customer subnets learned via PE from CEs, into its IGP (IS-IS). As the IGP, normally should only be a transport routing protocol that only knows other routers IP (PE, core, aggregation routers) to ensure connectivity between them.

[MHM Cisco World]

what is SP core type you have ? MPLS or IP Core ?