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Replies

MPLS unlabelled with static route

   

   Hello,
I have a wrong label problem on my last hop in a MPLS network.
Routers are Cisco ASR9K with IOS-XR.
I try to simplify as much as possible.
I have this static:

router static
address-family ipv4 unicast
217.27.XXX.132/32 100.126.0.70

And I get this wrong result (unlabelled).
Next-hop is a MPLS node:

RP/0/RSP0/CPU0:ASR9001-B#show mpls forwarding | include 100.126.0.70
Local  Outgoing    Prefix             Outgoing     Next Hop        Bytes
Label  Label       or ID              Interface                    Switched
------ ----------- ------------------ ------------ --------------- ------------
24475  Unlabelled  217.27.XXX.132/32  BE100.1000   100.126.0.70    0

If I remove the static and use OSPF I have the right LFIB:

RP/0/RSP0/CPU0:ASR9001-B#show mpls forwarding | include 100.126.0.70
Local  Outgoing    Prefix             Outgoing     Next Hop        Bytes
Label  Label       or ID              Interface                    Switched
------ ----------- ------------------ ------------ --------------- ------------
24475  Pop  217.27.XXX.132/32  BE100.1000   100.126.0.70  4603959 

I don't understand the difference. Having an

unlabelled

instead of

Pop

means that the MPLS tunnels are broken.
Why there is this label-to-IP passage?
I'm gonna keep OSPF but I would like to understand the problem.

Thank you

Gianrico Fichera

 

 

1 Accepted Solution

Accepted Solutions

Spoiler
 

Thanks for the additional information @GIANRICO FICHERA .

Try configuring the

static route

as follow. It should change the outgoing label from "Unlabelled" to "Pop".

router static
address-family ipv4 unicast
217.27.XXX.132/32 BE100.1000 100.126.0.70

Regards,

Harold Ritter
Sr Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México

View solution in original post

8 Replies 8

Giuseppe Larosa
Hall of Fame
Hall of Fame

Hello @GIANRICO FICHERA ,

have you got

LDP

configured to be in sync with IGP ?

This is a first sight guess of a possible reason to explain the behaviour when the

static route 

is configured.

Hope to help

Giuseppe

 

Thank you Giuseppe, yes it is up:

RP/0/RSP0/CPU0:ASR9001-B#show mpls ldp igp sync interface bundle-ether 100.1000
Mon Aug 28 19:09:30.371 MEDT
Bundle-Ether100.1000:
VRF: 'default' (0x60000000)
Sync delay: Disabled
Sync status: Ready
Peers:
217.27.xxx.132:0

I'll check it out...

I add the OSPF is enabled in both cases.

Harold Ritter
Cisco Employee
Cisco Employee

Hi @GIANRICO FICHERA ,

You would normally need OSPF to bring up the

 LDP

session. Without the

LDP

session, it is normal to see the outgoing label as

Unlabelled

in the show mpls forwarding output.

Regards,

Harold Ritter
Sr Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México

Thankyou Harold, the

ldp

session is up in both cases, the ospf is always up too.

Spoiler
 

Thanks for the additional information @GIANRICO FICHERA .

Try configuring the

static route

as follow. It should change the outgoing label from "Unlabelled" to "Pop".

router static
address-family ipv4 unicast
217.27.XXX.132/32 BE100.1000 100.126.0.70

Regards,

Harold Ritter
Sr Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México

Thankyou very much Harold,
    there is an explanation about this behaviour?
It is something specific to ASR9k? Perhaps is the fact that in the CEF table in this way there is no recursive call?

Hi @GIANRICO FICHERA ,

> It is something specific to ASR9k?

This behavior is not specific to the ASR9k platform and applies to XR across the board.

Perhaps is the fact that in the CEF table in this way there is no recursive call?

That is precisely the reason the interface is required as part of the

static route

, to avoid recursion.

Regards,

Harold Ritter
Sr Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México

Hello,

As @Harold Ritter mentioned it should be normal for this scenario. It reality it means the same thing jut a different way of expressing it. The

Pop

label is sent from one router to another announcing it is the router connected to the route you're trying to get to. Its the end of the line. This notifies

downstream routers

that it can

pop

the label (or in other words send an

unlabeled packet

to the

 upstream router

with that network). This is so the end router doesn't have to do 2 lookups (label and route lookup). Since you configured the

static route

the router sees that the network is the next

hop router

....but since it didn't learn it from the

upstream router

and its locally configured it needs a way to identify itself as not sending a label (

pop

off the label it has). It wont receive a

 pop 

(remove this label for me) message so it has to identify it itself. 

 

Hope that helps

-David

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