Re: Narbik / Dan TS Lab 8 - question 12 (MPLS)

You should source your ping from the loopback interface.

On Fri, Dec 31, 2010 at 2:01 PM, Matt Sherman <matt.sherman2_at_gmail.com>wrote:

> - S0/0 - (R1) - F0/0 -
> | |
> S0/0 F0/0 EIGRP
>
> (R2) (R6) -----------------
>
> F0/0 F2/0 OSPF
> | |
> - F0/0 - (R3) - F0/0 -
>
>
> Hello,
>
> This one is stumping me. R2, R3, and R6 make up the MPLS network with an
> MPLS VPN between R2 and R6 with their local loopbacks being members of vrf
> V26.
>
> =======================================
> ((R2))
> interface Loopback26
> ip vrf forwarding V26
> ip address 26.26.0.2 255.255.255.255
>
> ((R6))
> interface Loopback26
> ip vrf forwarding V26
> ip address 26.26.0.6 255.255.255.255
> =======================================
>
> Both R2 and R6 are receiving each other's routes for that VRF but neither
> address is pingable.
>
> =======================================
> R2#sh ip route vrf V26
> C 26.26.0.2 is directly connected, Loopback26
> B 26.26.0.6 [200/0] via 99.0.6.6, 01:08:05
>
> R6#sh ip route vrf V26
> B 26.26.0.2 [200/0] via 99.0.2.2, 01:06:34
> C 26.26.0.6 is directly connected, Loopback26
> =======================================
>
> The cause of the problem is that R6 is advertising its LDP router ID with a
> /24 mask instead of a /32. R3 is receiving the route via OSPF from R6 as a
> /32 though. Why does R6 send the LDP advertisement as a /24?
>
> =======================================
> R3#*sh ip route | i 99.0.6
> *O 99.0.6.6/32 [110/2] via 99.2.36.6, 00:00:53, FastEthernet2/0.36
> O E2 99.0.6.0/24 [110/20] via 99.2.23.2, 00:00:53, FastEthernet0/0
> R3#*sh mpls forwarding-table 99.0.6.6
> *Local Outgoing Prefix Bytes tag Outgoing Next Hop
> tag tag or VC or Tunnel Id switched interface
> 17 *Untagged* 99.0.6.6/32 7095 Fa2/0.36 99.2.36.6
> R3#sh mpls ldp bindings neighbor 99.0.6.6 *99.0.6.0 24
> * tib entry: 99.0.6.0/24, rev 48
> remote binding: tsr: 99.0.6.6:0, tag: imp-null
>
> R3#sh mpls ldp bindings neighbor 99.0.6.6 99.0.6.6 32
> <nothing>
> =======================================
>
> And the stated fix is to enter the "ip ospf net point-to-point" command
> under the R6's Lo0 so that OSPF also advertises a /24.
> After making that change i'm sitll unable to ping between loopbacks on R2
> and R6
>
> =======================================
> R3#*sh mpls forwarding-table 99.0.6.6
> *Local Outgoing Prefix Bytes tag Outgoing Next Hop
> tag tag or VC or Tunnel Id switched interface
> 34 *Pop tag* 99.0.6.0/24 0 Fa2/0.36 99.2.36.6
>
> R6#*ping vrf V26 26.26.0.2*
> Type escape sequence to abort.
> Sending 5, 100-byte ICMP Echos to 26.26.0.2, timeout is 2 seconds:
> .....
> Success rate is 0 percent (0/5)
> =======================================
>
> 1st question - why did R6 advertise its loopback as a /24 via LDP?
> 2nd question - why didn't adding the "ip ospf net point-to-point" fix the
> problem?
>
> Thanks,
> Matt
>
>
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Received on Fri Dec 31 2010 - 14:05:26 ART