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Data Center Interconnect – MPLS over GRE

Data Center Interconnect – MPLS over GRE

 

There are multiple implementations options available for connecting two data centres. This first part will discuss the implementation of Layer-3 interconnect using a private MPLS VPN backbone. This solution requires a single GRE tunnel between a pair of edge routers in the data centres.  This GRE tunnel runs LDP over the GRE tunnel. The VRF routes are exchanged using MP-BGP.
All MPLS traffic is GRE encapsulated.
The edge routers connect to the service provider, which provides connectivity between the edge routers. The edge routers create a GRE tunnel and runs LDP over it.

GRE Tunnel Configuration

Edge Router 1-
interface Tunnel10
 ip unnumbered FastEthernet0/0
 mpls ip
 tunnel source FastEthernet0/0
 tunnel destination 192.168.255.14
!
Edge Router 2-
interface Tunnel10
 ip unnumbered FastEthernet0/0
 mpls ip
 tunnel source FastEthernet0/0
 tunnel destination 192.168.255.6
!
Each edge routers have the following VRFs-

VRFs on Edge Routers

ip vrf APP
 rd 1:100
 route-target export 1:100
 route-target import 1:100
!
ip vrf DB
 rd 1:101
 route-target export 1:101
 route-target import 1:101
!
And lastly, the edge routers run MP-BGP between them to exchange VRF routes.

BGP Configuration on Edge Router

router bgp 65001
 no synchronization
 bgp log-neighbor-changes
 neighbor 2.2.2.2 remote-as 65001
 neighbor 2.2.2.2 update-source Loopback0
 no auto-summary
 !
 address-family vpnv4
  neighbor 2.2.2.2 activate
  neighbor 2.2.2.2 send-community extended
 exit-address-family
 !
 address-family ipv4 vrf APP
  no synchronization
  redistribute connected
 exit-address-family
 !
 address-family ipv4 vrf DB
  no synchronization
  redistribute connected
 exit-address-family
The following output shows LDP neighbor relationship over GRE tunnel.

LDP Neighbor

R1# show mpls ldp neighbor
    Peer LDP Ident: 192.168.255.14:0; Local LDP Ident 192.168.255.6:0
        TCP connection: 192.168.255.14.26907 Р192.168.255.6.646
        State: Oper; Msgs sent/rcvd: 78/78; Downstream
        Up time: 00:59:13
        LDP discovery sources:
          Tunnel10, Src IP addr: 192.168.255.14
        Addresses bound to peer LDP Ident:
          192.168.255.14  2.2.2.2
The following output shows VRF routes exchanged over GRE tunnel.

BGP VPNv4 Routes

R1# show ip bgp vpnv4 all
BGP table version is 7, local router ID is 1.1.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i – internal,
              r RIB-failure, S Stale, m multipath, b backup-path, x best-external
Origin codes: i – IGP, e – EGP, ? – incomplete
   Network          Next Hop            Metric LocPrf Weight Path
Route Distinguisher: 1:100 (default for vrf APP)
*> 10.100.1.0/24    0.0.0.0                  0         32768 ?
*>i10.100.2.0/24    2.2.2.2                  0    100      0 ?
Route Distinguisher: 1:101 (default for vrf DB)
*> 10.200.1.0/24    0.0.0.0                  0         32768 ?
*>i10.200.2.0/24    2.2.2.2                  0    100      0 ?

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