Can same subnet be advertised from 2 MPLS PE routers to MPLS cloud?

[Herman2018]

Hi good day!, can anyone pls advise how same subnet can be advertised to MPLS cloud from 2 PE routers? This 2x PE routers are connected to same CE router and the user subnet is configured on CE router vrf User?  How to configure this 2x PE routers (locations)  so that the remote sites will choose  one PE as primary and another PE as backup? thanks in advance!

[Harold Ritter]

Hi @Herman2018 ,

If the CE runs BGP with the PEs, you can use AS path prepending towards the PE you select as the backup PE. This way the remote PEs will select the other PE as a primary as it has a shorter AS path. If the primary PE goes away the remote PEs will automatically converge to the backup PE.

Regards,

[Herman2018]

Thanks @Harold Ritter , @MHM Cisco World M02@rt37  for your reply!

The actuall CE1 is also PE1, same physical layer 3 device. but PE2 is another separate router. CE1 is some vlans under User VRF. 

the routing protocol between CE1 and PE2 is eigrp. Please advise how to config. Is it possible to use

vrf export map

? 

   MPLS -- PE2 --eigrp -- CE1 (PE1) -- MPLS

[M02@rt37]

@Herman2018 

You want to control the distribution of EIGRP routes from CE1 to PE2?

In MPLS architecture, CE is connected to PE. CE is a dedicated routeur. PE is in front of the CE and connected to P router. 

[M02@rt37]

Hello @Herman2018,

Do you know which routing protocol between CE-PEs ?

Also, it's important to have a symmetric flow. If CE choose PE-01 as "active link" then the response should go back throught PE-01 also, not PE-02. If PE-01 fail, the flow go through PE-02.

From the MPLS (Backbone) view, it's possible to advertise the same subnet to MPLS cloud from two PE routers, which are connected to the same CE router. To do this, you can configure both PEs with the same VRF instance and the same route target, so that both PEs can learn the routes from the CE router.

To ensure that remote sites choose one PE as primary and another PE as backup, you can configure different local preference values on both PEs, so that remote sites prefer one PE over the other. For example, you can configure a higher local preference value on the primary PE and a lower value on the backup PE.

[Herman2018]

Hi M02@rt37 , which address family should the

 route-map

to be applied to ? Below is the example of bgp config. 

Need to make the subnet (route) 222.222.222.222/32 advertised by this router to the backup one. 

router bgp 1
bgp router-id 2.2.2.2
bgp log-neighbor-changes
neighbor 1.1.1.1 remote-as 1
neighbor 1.1.1.1 update-source Loopback0
neighbor 3.3.3.3 remote-as 1
neighbor 3.3.3.3 update-source Loopback0
!
address-family ipv4
neighbor 1.1.1.1 activate
neighbor 3.3.3.3 activate
exit-address-family
!
address-family vpnv4
neighbor 1.1.1.1 activate
neighbor 1.1.1.1 send-community both
neighbor 3.3.3.3 activate
neighbor 3.3.3.3 send-community both
exit-address-family
!
address-family ipv4 vrf C
network 22.22.22.22 mask 255.255.255.255
network 212.212.212.212 mask 255.255.255.255
network 222.222.222.222 mask 255.255.255.255
neighbor 3.3.3.3 remote-as 1
neighbor 3.3.3.3 activate
neighbor 3.3.3.3 route-map T222-map out
exit-address-family

[Herman2018]

sorry  , typo. " make the subnet (route) 222.222.222.222/32 to be advertised by this router to be a " backup route" . pls help advise, thanks.

[MHM Cisco World]

Multi homed' 

Are your MPLS have RR or not ?

[Herman2018]

@MHM Cisco World , there are RR in MPLS ,any advise? thanks

[MHM Cisco World]

please check below 
thanks 
MHM

[Herman2018]

Thanks @MHM Cisco World for your advice. We really have RR, but in a central location, the VRF RT are same for this two branches, then 2 branches will advertise same subnet to MPLS, this 2x branches are connected to each other via a lease line and considered CE LAN. can we just use different local-preference values when advertised from branches? 

[MHM Cisco World]

hi again the command you need 

bgp additional-paths select backup <<-
bgp bestpath igp-metric ignore <<- to eliminate the igp-metric mismatch between two path 

then you need to check the

 show ip bgp

vpnv4 all 
the backup path will mark with letter "b"

[MHM Cisco World · Accepted solution]

PE2#show running-config
hostname PE2
!
ip vrf PE2
rd 200:1
route-target export 200:1
route-target import 100:1
route-target import 100:2
!
interface Loopback0
ip address 4.4.4.4 255.255.255.255
!
interface Ethernet0/0
ip vrf forwarding PE2
ip address 40.0.0.4 255.255.255.0
!
interface Ethernet0/2
ip address 130.0.0.4 255.255.255.0
mpls ip
!
router ospf 1020 vrf PE2
redistribute bgp 100 subnets
network 40.0.0.0 0.0.0.255 area 0
!
router ospf 100
network 4.4.4.4 0.0.0.0 area 0
network 130.0.0.0 0.0.0.255 area 0
!
router bgp 100
bgp log-neighbor-changes
neighbor 3.3.3.3 remote-as 100
neighbor 3.3.3.3 update-source Loopback0
!
address-family vpnv4
neighbor 3.3.3.3 activate
neighbor 3.3.3.3 send-community extended
exit-address-family
!
address-family ipv4 vrf PE2
bgp additional-paths select backup
redistribute ospf 1020
exit-address-family

[Herman2018]

Thanks @MHM Cisco World for your help and advice!