[Expert on-call] MPLS VPN technologies | Q&A event on Wednesday

Where do we need to connect? please share the complete details or a copy of the invite

Hello everyone, I am Li Sen.

I'm ready to receive your questions!

Hi Lisen,

When I'm using "display mpls interface" command I'm able to see a couple of MTU configuration values, can you help to explain what this MTU values means? I mark with bold letters the associated information below:

<HUAWEI>display mpls interface vlanif 100 verbose
No                    :  1
Interface             :  Vlanif100
Status                :  Up
TE Attribute          :  Disable 
Static LSPCount       :  0
Static CR-LSPCount    :  0
LDP LSPCount          :  0
RSVP LSPCount         :  0
MPLS MTU              :  -
Interface MTU         :  1500
Effective MTU         :  1500
TE FRR                :  Disable
Interface Index       :  0xd1

Thank you!

Hi 007,  

This is a good question, I will try to explain.

For Huawei LAN switch the data forwarding is made by ASIC or NP chipset.

For the ASIC CHIP, the switch will not check the MTU, so the MPLS MTU will not be set as we can see into the displayed command. Depending on the frame lenght, the switch will extract the lenght and compare with jumbo frame configuration. If the frame length is higher than configured  jumbo frame value, the switch will discard the frame.

For example S5700 EI has 1600 bytes default value for ethernet frame.

[R5_U24_S5700-GigabitEthernet0/0/1]jumboframe enable  ?                        
  INTEGER<1600-9712>  The max frame length, the default is 1600 bytes          
  <cr>

  To check if the switch discards frames, you can check the jumbo counter when display interface stats:

[R5_U24_S5700-GigabitEthernet0/0/1]dis thi int                                 
GigabitEthernet0/0/1 current state : UP                                        
Line protocol current state : UP                                               
Description:                                                                   
Switch Port, Link-type : trunk(configured),                                    
PVID :  600, TPID : 8100(Hex), The Maximum Frame Length is 1600                
IP Sending Frames' Format is PKTFMT_ETHNT_2, Hardware address is 9017-acb6-a810
Current system time: 2016-04-13 22:20+09:00                                 
Port Mode: COMMON COPPER                                                       
Speed : 100,    Loopback: NONE                                                 
Duplex: FULL,   Negotiation: DISABLE                                           
Mdi   : AUTO,   Flow-control: DISABLE                                          
Last 300 seconds input rate 1032 bits/sec, 1 packets/sec                       
Last 300 seconds output rate 1712 bits/sec, 1 packets/sec                      
Input peak rate 71856 bits/sec, Record time: 2016-04-13 22:20               
Output peak rate 99941088 bits/sec, Record time: 2016-04-13 22:20           
Input:  723618 packets, 87391651 bytes                                         
  Unicast:                     710706,  Multicast:                        1351 
  Broadcast:                    11561,  Jumbo:                               0 
  Discard:                          0,  Pause:                               0 
  Frames:                           0                                          

Back to the our display command, interface MTU refers system MTU or Layer 3 MTU, so it's the maximum IP packet length.

Effective MTU discribe the value of which is smaller between interface MTU and MPLS MTU.

Hi Lisen,

Thank you for your answer, I have another query :)

Can you tell me how the QoS mapping between IP network and MPLS network it's implemented by default on Huawei systems? For example, an IP packet marked with DSCP value 48 which EXP marking will have?

Thanks!

Hi Li Sen,

For VPN clients, do BGP routes have to be manually redistributed into MPBGP or are they automatically redistributed?

Thanks

Hi 007, 

Considering that you execute "trust DSCP" on ingress interface and add mpls-qos-ingress trust upstream default on system-view,
The DSCP 48 value is mapped to CS6 green and CS6 green is mapped to EXP value 6.
You can use below command to check how to system maps by default.

<HUAWEI> display diffserv domain name default
ip-dscp-inbound 48 phb cs6 green
mpls-exp-outbound cs6 green map 6