Peter,

Thanks for your advice.

Actually there are other backbone link on R2-PE and use loopback setup MBGP, already advertise R2-PE loopback into IGP. Some specail prefixes only receive/accept on this specail link which use interface setup MBGP. We have to use this specail link interface setup MBGP, on other PE router, the next-hop is R2-PE interface IP address. So if this link down, traffic will shift to backup POP PE, instead of this POP other backbone link.

But this solution break the PHP, MPLS VPN is not working. If R2-PE can announce out one /32 of interface address to IGP, it will perfect.

Thank You

Jeffrey

Hi Mahesh

  R3 already generate a implicit-null label to R4 for 172.16.9.88/30, becasue it's connect interface.

so the ldp label will be pop on R4, but R3 don't know vpn label, packet dropped. R2 know the vpn label.

I expect R3 is PHP router, but if use interface setup MBGP R4 become PHP router.

That's why I want R2 advetise /32 and assign ldp label.

You can see label for prefix 9.88/30 is pop tag action on R4, packet forward to R3 leave vpn label will be drop.

R4>sho mpls forwarding-table
Local  Outgoing    Prefix            Bytes tag  Outgoing   Next Hop
tag    tag or VC   or Tunnel Id      switched   interface
416    Pop tag     172.16.9.88/30   0          Fa1/0      10.0.34.1

I expect like below forwarding table, I am not sure whether can achieve it.

R4>sho mpls forwarding-table
Local  Outgoing    Prefix            Bytes tag  Outgoing   Next Hop
tag    tag or VC   or Tunnel Id      switched   interface
416    300     172.16.9.89/32   0          Fa1/0      10.0.34.1

I tried set explicit-null on R3, and generate 0 label as you side.

R4#sho mpls forwarding-table
Local  Outgoing    Prefix            Bytes tag  Outgoing   Next Hop
tag    tag or VC   or Tunnel Id      switched   interface
416    0           172.16.9.88/30   40992      Fa1/0      10.0.34.1

R4#sh ip cef vrf a 1.1.1.1 detail
1.1.1.1/32, version 8, epoch 0, cached adjacency 10.0.34.1
0 packets, 0 bytes
  tag information set, all rewrites owned
    local tag: VPN route head
    fast tag rewrite with Fa1/0, 10.0.34.1, tags imposed {0 229}
  via 172.16.9.89, 0 dependencies, recursive, mpls required
    next hop 10.0.34.1, FastEthernet1/0 via 172.16.9.88/30 (Default)
    valid cached adjacency
    tag rewrite with Fa1/0, 10.0.34.1, tags imposed {0 229}

The label packet arrive at R3 can not forward to R2, dropped.

Label Packet arrive on R3 like below:

|label 0|label 229|dst 1.1.1.1|src 6.6.6.6|data ICMP|

It seem don't know how to pop label 0 and then forward to R2.

Thank You

Jeffery

Hi Jeffery,

Actually the problem is R3 which is having untag label for prefix.172.16.8.88/30. There is option to generate static label for any ip

with command

mpls label range 200 1048575 static 16 199 (Some router ask for reload to take this in affect)
mpls static binding ipv4 x.x.x.x 255.255.255.255 output x.x.x.x implicit-null.

So even If you generate static label from R2, but R3 is having this prefix is directly connected so it will declare it as untag by consulting cef.

Regarding mapping of explicit null label : yes there is option to crossconnect of labels but unfortunately there is no option to map explicit label

R2(config)#mpls static crossconnect ?
  <16-199>  Label Value <16 - 199>

so here also no luck.

Only thing is if we can overide this untag with some pop label at R3 then issue could be resolved.

Thanks for giving such wonderful scenario. It help me to rethink MPLS

rated as it deserves

regards

mahesh

Hi Mahesh,

Thank you so much let me learn more MPLS knowledge.

I found one command in configure globle, it seem can advertise /32 interface and assign label.

But I tested, it was not working. Not advertise /32 out to R3. No idear about it.

R2(config)#mpls ldp advertise-labels ?
  for        Access-list specifying controls on destination prefixes
  interface  Advertise /32 interface address
  oldstyle   Use old style (TDP) method for matching prefix acl
  vrf        VRF Routing/Forwarding instance information
 

tag-switching advertise-tags interface FastEthernet1/1

R2#sho run interface fastEthernet 1/1
Building configuration...

Current configuration : 164 bytes
!
interface FastEthernet1/1
ip address 172.16.9.89 255.255.255.252
duplex full
speed 100
mpls ldp discovery transport-address interface
tag-switching ip
end

We will change plan and decide to use loopback set up MBGP, instead of using interface.

Thank You

Jeffery

Hi Jeffery,

Normally, LDP advertises labels only for IP prefixes that are in the routing table. But if you want
force LDP to advertise a label for a prefix constructed from an interface address (/32) then you can use this command

Like I have tried

R2#
interface GigabitEthernet4/0.21
encapsulation dot1Q 21
ip address 10.0.3.6 255.255.255.252
mpls label protocol ldp
tag-switching ip
clns mtu 1460
end

mpls ldp advertise-labels interface GigabitEthernet4/0.21

and now i am getting below entry in LIB

R2#sh mpls ldp bindings 10.0.3.6 32
  tib entry: 10.0.3.6/32, rev 487
        local binding:  tag: imp-null

On R3

R3#sh mpls ldp binding 10.0.3.6 32
  lib entry: 10.0.3.6/32, rev 96
        remote binding: lsr: 10.0.0.2:0, label: imp-null

Regards

mahesh

Mahesh,

What IOS version and platform you have tried?

Can you tell me? I will try it.

Thank You

Jeffery

Mahesh,

I upgrade Version to 15.0(1)M2, and can see LIB assign /32 label in R2/R3 as you tested.

mpls ldp advertise-labels interface FastEthernet1/1

But don't advetise 89/32 prefix into ospf IGP, can not redistribute Local prefix 89/32.. I will try more test.

      172.16.9.0/24 is variably subnetted, 2 subnets, 2 masks
C        172.16.9.88/30 is directly connected, FastEthernet1/1
L        172.16.9.89/32 is directly connected, FastEthernet1/1---generate /32 ip route.

Thank You

jeffery

See if ip ospf network point-to-point on interis there or not

regards

mahesh

Hi Mahesh,

not set 'ip ospf network point-to-point' in interface, use default network type.

The prefixe /32 marked L-Local, I try to redistribute to OSPF but failed. It seem can not redistribute this kind of route to IGP.

L        172.16.9.89/32 is directly connected, FastEthernet1/1

router ospf 100
router-id 2.2.2.2
redistribute connected subnets

redistribute static subnets
network 2.2.2.2 0.0.0.0 area 0
network 172.16.9.89 0.0.0.0 area 0

Thank You

Jeffery