EoMPLS xconnect between to 7206VXR is not working

[Ellad Yatsko]

Hello!

I try the following diagram:

laptop - R1 - SW1 - SW2 - R2 - laptop

Both SWs have mtu 1600

R1 and R2 have successfully made up OSPF adjacency and they are also LDP neighbors.

R1's config:

interface GigabitEthernet0/2.4094
 encapsulation dot1Q 4094
 no cdp enable
 xconnect 193.124.254.104 4094 encapsulation mpls

R2's config:

interface GigabitEthernet0/2.4094
 encapsulation dot1Q 4094
 no cdp enable
 xconnect 194.135.135.200 4094 encapsulation mpls

Where xconnect IPs are corresponding Lo0 addresses. They are also visible in LDP.

sh mpls l2 vc 4094 detail
Local interface: Gi0/2.4094 up, line protocol up, Eth VLAN 4094 up
  Destination address: 193.124.254.104, VC ID: 4094, VC status: up
    Output interface: Gi0/1, imposed label stack {82}
    Preferred path: not configured
    Default path: active
    Next hop: 194.87.30.60
  Create time: 00:09:07, last status change time: 00:09:07
  Signaling protocol: LDP, peer 193.124.254.104:0 up
    Targeted Hello: 194.135.135.200(LDP Id) -> 193.124.254.104
    Status TLV support (local/remote)   : enabled/supported
      Label/status state machine        : established, LruRru
      Last local dataplane   status rcvd: no fault
      Last local SSS circuit status rcvd: no fault
      Last local SSS circuit status sent: no fault
      Last local  LDP TLV    status sent: no fault
      Last remote LDP TLV    status rcvd: no fault
    MPLS VC labels: local 87, remote 82
    Group ID: local 0, remote 0
    MTU: local 1500, remote 1500
    Remote interface description:
  Sequencing: receive disabled, send disabled
  VC statistics:
    packet totals: receive 1325, send 2824
    byte totals:   receive 104784, send 1213277
    packet drops:  receive 0, seq error 0, send 5

sh mpls l2 vc 4094 detail
Local interface: Gi0/2.4094 up, line protocol up, Eth VLAN 4094 up
  Destination address: 194.135.135.200, VC ID: 4094, VC status: up
    Output interface: Gi0/2.26, imposed label stack {87}
    Preferred path: not configured
    Default path: active
    Next hop: 194.87.30.59
  Create time: 00:10:40, last status change time: 00:10:15
  Signaling protocol: LDP, peer 194.135.135.200:0 up
    Targeted Hello: 193.124.254.104(LDP Id) -> 194.135.135.200
    Status TLV support (local/remote)   : enabled/supported
      Label/status state machine        : established, LruRru
      Last local dataplane   status rcvd: no fault
      Last local SSS circuit status rcvd: no fault
      Last local SSS circuit status sent: no fault
      Last local  LDP TLV    status sent: no fault
      Last remote LDP TLV    status rcvd: no fault
    MPLS VC labels: local 82, remote 87
    Group ID: local 0, remote 0
    MTU: local 1500, remote 1500
    Remote interface description:
  Sequencing: receive disabled, send disabled
  VC statistics:
    packet totals: receive 2909, send 1413
    byte totals:   receive 1158473, send 148959
    packet drops:  receive 0, seq error 0, send 236

It seems all is working... But...

1) Pings are all ok.

2) UDP is working as well

3) Even TCP/HTTP for several sites is working to.. But really "heavy" sites as speedtest.net doesn't open!

I feel this is MTU problem but I can't understand where to look for. Please, help! :-)

I tried a lot (HUGE AMOUNT) configs using ip mtu 1460/ip tcp adjust mss 1400 - nothing helped. What's wrong with me? :-)

Oh! I forgot to mentions. When I try pseudowire-class with L2TPv3 Encapsulation ALL BECOMES EXCELLENT! But I'd like to understand why simple things are not working but they MUST.. I think I missed some details...

Both boxes are runnings the same IOS:

SH VER REVEALS:

disk2:c7200-advipservicesk9-mz.151-4.M2.bin

disk2:c7200-advipservicesk9-mz.151-4.M2.bin

Kind regards,

Ellad

[Ellad Yatsko]

I again forgot! I began with c7200-adventerprisek9-mz.124-24.T8.bin with the very same effect.

Regards

[Vinit Jain]

Hi Ellad

Few questions here:

Can you perform span capture on AC of both routers. What is the MTU of the core facing interfaces? Can you increase the same to 9000 or 9216?

Where are you defining the ip mtu or tcp adjust-mss config?

When you perform the ping test, what is the latency do you see?

If you notice the above show mpls l2 vc det outputs, there are send drops noticed:

"packet drops:  receive 0, seq error 0, send 236" 

Could you please check if these drops increment when you are initiating traffic for heavy sites.

Thanks

Vinit

[Ellad Yatsko]

Hello!

Can you perform span capture on AC of both routers. What is the MTU of the core facing interfaces? Can you increase the same to 9000 or 9216?

I'm not sure I understand "AC", I can run Wireshark on both the notebooks. Or do I need span Routers' port facing to CORE?

Do I need apply MTU on Routers? I tried but I had got a lot of troubles with OSPF in that case. I think it will make me to increase MTU on ALL participating routers in the core..

Where are you defining the ip mtu or tcp adjust-mss config?

On the interfaces facing to acess ports (where xconnect is defined).

When you perform the ping test, what is the latency do you see?

1/2/4 ms, avg 2 ms.

Could you please check if these drops increment when you are initiating traffic for heavy sites.

Yes! You are absolutely right:

    packet totals: receive 42930, send 35860
    byte totals:   receive 24586886, send 7605321
    packet drops:  receive 0, seq error 0, send 251

And a bit later:

    packet totals: receive 43381, send 36716
    byte totals:   receive 24616646, send 7733119
    packet drops:  receive 0, seq error 0, send 251

Kind regards,

Ellad

[Vinit Jain]

You need to perform SPAN on the router port on both the access link and the core facing link.

Also, if you can share the configuration of CE as well as Core facing interface, that will be helpful.

Regarding the MTU, You will have to account for two labels in the core which is 8 bytes for packet forwarding across the core. Also, it depends if the packets coming from the user are arriving with DF-bit set or not.

Hope this helps

Vinit

[Ellad Yatsko]

Hello Vinit,

Could you, please, explain what are the probable subsequences of Router's MTU changing besides OSPF problems which are easily resolved by issuing "ip ospf mtu-ignore". Session is UP. And I don't notice any traffic disruptions.

What are the possible troubles? Please, be patient, this is my the very first experience.. :-)

Kind regards,

Ellad