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New Member

Trouble with MPLS TE.

Hoi cisco.png

Hi everyone, i dont understand something about TE tunnel. R2,3,4,5,6 is in MPLS domain. Im made a TE tunnel between R2-R6 with a explicit-path R2-R4-R5-R6. So when R2 want to send packet that destination is R6, it ll take the TE explicit-path. Everything just fine except one thing, i create a loopback in R5. In R2, traceroute that loopback in R5 and the path it take is: R2-R4-R5-R6-R5. I dont understand why can it happen, can anyone explain that.........Thank you so much !

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Cisco Employee

Trouble with MPLS TE.

Hello,

Can you be more specific about how do you force the packets to enter the TE tunnel?

In any case, what you see is logical. Packets entering a tunnel must always traverse to its tailend - they can never exit the tunnel on some earlier router. So if the tunnel ends on R6, and you are pinging the loopback on R5, the tunneled packets will enter the tunnel on R2, pass as MPLS-labeled packets through R2, R4, R5 and end on R6 (note that R5 does not see an IP packet addressed to it but rather a labeled packet with next hop directed towards R6). The R6, as the end of the MPLS tunnel, will now process the IP packet and see that the intended destination is R5, so it sends the packet to R5 via the shortest available path. Hence - R2-R4-R5-R6-R5.

Does this clear things a little?

Best regards,

Peter

9 REPLIES
Cisco Employee

Trouble with MPLS TE.

Hello,

Can you be more specific about how do you force the packets to enter the TE tunnel?

In any case, what you see is logical. Packets entering a tunnel must always traverse to its tailend - they can never exit the tunnel on some earlier router. So if the tunnel ends on R6, and you are pinging the loopback on R5, the tunneled packets will enter the tunnel on R2, pass as MPLS-labeled packets through R2, R4, R5 and end on R6 (note that R5 does not see an IP packet addressed to it but rather a labeled packet with next hop directed towards R6). The R6, as the end of the MPLS tunnel, will now process the IP packet and see that the intended destination is R5, so it sends the packet to R5 via the shortest available path. Hence - R2-R4-R5-R6-R5.

Does this clear things a little?

Best regards,

Peter

New Member

Trouble with MPLS TE.

Trung,

Can you provide exactly what you are routing into the TE tunnel?

If 5.5.5.5 is being routed on R2 via the TE tunnel via static or policy routing, then what you see is correct, and what Peter says is correct.

If R2 is routing to 5.5.5.5 via an IGP (instead of via static/policy routing), then the above behavior should not happen.

David

New Member

Re: Trouble with MPLS TE.

Thank Peter and David for your reply.

i find out my problem. Normally, when R2 want to send packet to R5, it will take the path R2-R3-R6-R5 (Because link between R2-R3; R3-R6 is giga). But because my explicit-path, R2 CSPF calculate to choose the tunnel to pass traffic to R6 and that is why i see sub optimal routing, is that right ?

But when i use autoroute annouce, the result still the same

interface Tunnel1

ip unnumbered Loopback22

tunnel destination 6.6.6.6

tunnel mode mpls traffic-eng

tunnel mpls traffic-eng autoroute announce

tunnel mpls traffic-eng priority 1 1

tunnel mpls traffic-eng bandwidth  100

tunnel mpls traffic-eng path-option 1 dynamic

PE_R2#sh ip route 5.5.5.5

Routing entry for 5.5.5.0/24

  Known via "ospf 1", distance 110, metric 13, type intra area

  Routing Descriptor Blocks:

  * directly connected, via Tunnel1

      Route metric is 13, traffic share count is 1

Can you explain that! ? And R8, R9 which belong to VPN AAA can't ping each other anymore, i think it is not logical. I expect all VPN traffic of AAA and BBB will go through tunnel 1, but it doesnt.

New Member

Re: Trouble with MPLS TE.

Trung,

Can you provide the output of "sh mpls traffic-eng tunnels" on R2?

David

New Member

Re: Trouble with MPLS TE.

This is the output:

PE_R2(config-if)#do sh mpls traff tunn

Name: PE_R2_t1                            (Tunnel1) Destination: 6.6.6.6
  Status:
    Admin: up         Oper: up     Path: valid       Signalling: connected

    path option 1, type dynamic (Basis for Setup, path weight 2)

  Config Parameters:
    Bandwidth: 100      kbps (Global)  Priority: 1  1   Affinity: 0x0/0xFFFF
    Metric Type: TE (default)
    AutoRoute:  enabled   LockDown: disabled  Loadshare: 100      bw-based
    auto-bw: disabled

  InLabel  :  -
  OutLabel : GigabitEthernet2/0, 25
  RSVP Signalling Info:
       Src 2.2.2.2, Dst 6.6.6.6, Tun_Id 1, Tun_Instance 15
    RSVP Path Info:
      My Address: 10.1.23.2
      Explicit Route: 10.1.23.3 10.1.36.3 10.1.36.6 6.6.6.6
      Record Route:  NONE
      Tspec: ave rate=100 kbits, burst=1000 bytes, peak rate=100 kbits
    RSVP Resv Info:
      Record Route:  NONE
      Fspec: ave rate=100 kbits, burst=1000 bytes, peak rate=100 kbits
  History:
    Tunnel:
      Time since created: 3 minutes, 48 seconds
      Time since path change: 19 seconds
    Current LSP:
      Uptime: 19 seconds
    Prior LSP:
      ID: path option 1 [14]
      Removal Trigger: path option removed

New Member

Trouble with MPLS TE.

Trung,

To which routers do these addresses belong?

10.1.23.3

10.1.36.3

10.1.36.6

David

New Member

Trouble with MPLS TE.

10.1.23.x is the subnet between R2 and R3.

10.1.23.3 is the ip in  R3

10.1.36.3 is the ip in  R3

10.1.36.6 is the ip in  R6

In each router, i create a loop back. Ex: router 1, loopback is 1.1.1.1; router 2, loopback is 2.2.2.2 and so on

New Member

Trouble with MPLS TE.

Trung,

Looking at the "Explicit Route" section of the output of "sh mpls traffic-eng tunnels", it appears that the LSP for the TE-Tunnel goes from R2-->R3-->R6.  So when you performed a "sh ip route 5.5.5.5" and saw that 5.5.5.5 was being learned via the TE-Tunnel on R2, this suggests that the cost to get to R5 via the tunnel is less than the cost to get to R5 via R4.  You can confirm this by looking at the cost of the outgoing links on both the top and bottom paths to R5.

Also, if R2 indeed installed the route to 5.5.5.5 via the TE-Tunnel, then I would expect the traceroute from R2 to R5 to appear like this:  R2--->R3--->R6--->R5.

David

New Member

Trouble with MPLS TE.

It s exactly what you say, thank you !!!

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