1. Configure Service Provider A internal network according to topology:

           1.1 Configure loopback0 interfaces and links between routers.

           1.2 IGP - only create level-2 databases, route metric should be represented by 24bits, disable                              CSNP flooding

           1.3 iBGP - only exchange VPNv4 address-family, minimize the required number of iBGP                                      peering sessions

           1.4 MPLS - use minimal amount of commands to enable MPLS and LDP

2. Configure Service Provider B internal network according to topology: 

           2.1 Configure loopback0 interfaces and links between routers. 

           2.2 IGP - use network type that allows faster convergence. minimize the number of commands                            required to enable OSPF on interfaces. 

           2.3 eBGP - configure R7 to establish eBGP peering with R9, and advertise prefix 22.0/16. 

3. Configure Service Provider C: 

           3.1 Create loopback0 interface

           3.2 Create interfaces loopback11, 33 and 55 with addressess 11.11.11.11/32, 33.33.33.33/32 &                  55.55.55.55/32. 

           3.3 eBGP - configure eBGP session with R7 and advertise networks 8.0/24, 11/8, 33/8 & 55/8.

4. Configure Carrier supporting Carrier solution:
                use networks 21.0.23/24 and 21.0.46/24 for links  between AS21 and AS22. 
          4.1 AS22 should provide connectivity between the two AS21 sites 1 & 2.
          4.2 All routers of AS21 should be able to access the Internet via AS8.
          4.3 Use eBGP protocol for routing between CSC-CE and CSC-PE devices.
          4.4 Assume that AS22 is an ISP, and all routers of AS22 carry full Internet routing table.                           Configure the AS22 and AS21 accordingly.
          4.5 R1 is only allowed to have BGP peering with R2.
         

Highlight the text below to reveal the solution.


This solution requires understanding of L3VPN Carrier-supporting-carrier configuration. 
For this task, eBGP is used for  CSC-CE to CSC-PE routes exchange, which is the more common case, and the only configuration supported by IOX-XR. 
This task also contains some requirements related to OSPF and ISIS configuration. 

Requirement #1 - disable default ipv4 unicast address family. configure R5 as route-reflector and R3,                              R6 as clients, set is-type to level-2-only to disable level-1 database, use wide                                        metric (24 bit ), use "mpls ldp autoconfig" to enable LDP on all ISIS interfaces, use                              point-to-point interfaces.

Requirement #2 - use network type point-to-point to speed up convergence ( vs the default broadcast                                network type). on IOS routers, use "network 0.0.0.0 255.255.255.255 area 0"                                        command, instead of configuring OSPF on individual interfaces.  


Requirement #4 - on CSC-CE to CSC-PE eBGP sessions apply filter to only allow prefixes from                                       22.0/16 range into the CSC-PE VRF for AS22. otherwise CSC-PE routers will                                     receive the full BGP table view from the CSC-CE routers, which must be avoided. 
                              Since R1 is only allowed to peer with R2, configure R2 as route reflector, and R1                                 as route-reflector client. 


Note: IOS-XR only allows eBGP + labels for CSC-CE- CSC-PE protocol in CSC solution. For IOS routers, another option is to exchange routes using IGP and enable LDP on the CSC-CE - CSC-PE link. 

R1: 

!
interface Loopback0
 ip address 22.0.1.1 255.255.255.255
 ip ospf network point-to-point
!
interface Ethernet0/0
 ip address 22.0.12.1 255.255.255.0
 ip ospf network point-to-point
!