MPLS packet and IP packet forwarding diagram

[TangoAlfa]

Hi everyone,

Can any one add some value in this diagram in terms of forwarding (MPLS packet and IP packet). 

This is how packet get flow right?

[MHM Cisco World]

Your flow is OK, but the FIB/LFIB is work together not separate, both IN CEF and use to forward LABEL or non-LABEL traffic 

[TangoAlfa]

@MHM Cisco World  as far I know  the MPLS packet doesn't lookup for the FIB it's directly lookup LFIB as LFIB created with the help of FIB. And IP packet doesn't look up for LFIB as his destination is not labelled.

LFIB buil by the help of LIB,FIB and RIB and all are in CEF. Please make me correct if I am wrong 

[MHM Cisco World]

this what I talking about. 

[TangoAlfa]

Does MPLS packet lookup for FIB? Or it's just lookup LFIB as LFIB build with the help of FIB. As far I know MPLS packet doesn't look up for FIB.

[Harold Ritter]

Hi @TangoAlfa ,

The ingress PE does a FIB lookup and pushes the label tied to the egress PE. From that point on, the LFIB will be looked up on each P router through the MPLS network. An additional FIB lookup might be performed on the egress PE as well.

Regards,

[TangoAlfa]

Hi @Harold Ritter what about ip packet (non mpls) when he traveled via MPLS network?

[Harold Ritter]

Hi @TangoAlfa ,

It is still possible for packets to travel unlabelled through the MPLS core if no label has been allocated for the destination prefix, as this core is built on top of an IP network. The FIB is used in this case.

Regards,

[TangoAlfa]

@Harold Ritter  perfect and this is what I understand but problem is that how do I check in lab. How do I make un labelled ip prefix which is learn via MPLS ip enable interface. That's what I tried above lab though I wanted to send prefix and make un labelled 

[Harold Ritter]

Hi @TangoAlfa 

There is many ways you can cause a destination prefix not to have a label assigned to it. One is to configure LDP filtering. Another one is to inject a default route in the IGP, as the default route does get a label assigned by default.

If you then inject traffic to follow the default route, you will see this traffic as unlabelled through the MPLS core.

Regards,

[TangoAlfa]

@Harold Ritter Hi

Yes I have chose filter option and below is success output what I understood. Thanks @Harold Ritter @MHM Cisco World 

Tracing the route to 192.168.3.10
VRF info: (vrf in name/id, vrf out name/id)
1 10.10.10.2 12 msec 12 msec 20 msec
2 10.10.20.2 52 msec 24 msec 20 msec
3 10.10.30.2 40 msec 60 msec 48 msec
4 192.168.3.10 136 msec 56 msec 52 msec
LER-PER-R1#

LER-PER-R1#trace 8.8.8.8
Type escape sequence to abort.
Tracing the route to 8.8.8.8
VRF info: (vrf in name/id, vrf out name/id)
1 10.10.10.2 8 msec 16 msec 8 msec
2 10.10.20.2 [MPLS: Label 309 Exp 0] 92 msec 40 msec 40 msec
3 10.10.30.2 [MPLS: Label 401 Exp 0] 120 msec 32 msec 40 msec
4 192.168.10.100 72 msec 80 msec 76 msec
5 8.8.8.8 164 msec 48 msec 52 msec
LER-PER-R1#

Filter:

access-list 1 deny 192.168.1.0 0.0.0.255
access-list 1 deny 192.168.3.0 0.0.0.255
access-list 1 permit any

no mpls ldp advertise-labels
mpls ldp advertise-labels for 1

[MHM Cisco World]

Friend you are so so welcome 

[MHM Cisco World]

PE(ingress)-P1-P2-PE(egress)
your flow above is work fine for P1 and P2 since it receive label packet and forward label packet 
but what about PE ingress and egress ??
PE ingress receive non label packet and attach label and forward it, i.e. there are two lookup.
PE egress receive label and remove it and forward it as non label, i.e. there  are two lookup

so as I mention before you must interconnect both FIB and LFIB in end.

[TangoAlfa]

Hi @MHM Cisco World You are right I will connect FiB and LFIB.

referring  to the below lab topology there is two communication one MPLS(red) and IP(green). now  

when I trace from (LER-PE-R-1/lo 1.1.1.1 ) to destination mpls and ip, I found the ip packet destination trace not with label and and MPLS destination comes with Label.

So  its proof that IP packet dont lookup LFIB. only FIB lookup they do and MPLS only lookup LFIB. however (FIB and LFIB work together) as @MHM Cisco World  said.

NOTE:The green line interface(interface mpls ip not enable) red line (mpls ip enable.). Though all the router the IP destination generating local label but not receive any remote label as its not under mpls enable interface.

[M02@rt37]

Hello @TangoAlfa,

MPLS process and Routing process.