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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 - 192.168.255.6.646
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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