R2631E binds together with R3680E via two E1 (pure 2M access) links, and some packets are discarded when pinging big size.

Publication Date:  2012-07-27 Views:  74 Downloads:  0
Issue Description
 

1. Networking diagram: PCA---R2631=====2M transmission=====R3680E----PCB


2. Description: both equipments use 2E1 cards separately, and they are bound together.


 


Alarm Information
  1. When PCA pings PCB, packets bigger than 1450-byte will be dropped, about 30%; however, packets less than 1450-byte are normal then.  The problem persists when both routers ping each other directly;

2. Cancel the binding, and the problem is addressed;

3. Both 2631E and 3680E are: Release 1.740113. 

Handling Process
1. Configure as follows at 2631E router:

interface Serial0:0



    link-protocol ppp



    description 2*E1 To_QuidWay3680_QQT_MDCN_18F



    ppp mp



    ppp mp interface Virtual-Template1



  !



  interface Serial1:0



    link-protocol ppp



    ppp mp



    ppp mp interface Virtual-Template1



  !



  interface Virtual-Template1



    link-protocol ppp



    ppp mp lfi   //That’s it.



    ppp mp lfi delay-per-frag 180 //The value is configurable on demands.



    ppp mp max-send-frags 6



    ip address 10.245.128.14 255.255.255.252



2. Configure as follows at R3680E router:



  interface Serial0:0   



    link-protocol ppp



    description



    ppp mp



    ppp mp interface Virtual-Template1



  !



  interface Serial1:0



    link-protocol ppp



    ppp mp



    ppp mp interface Virtual-Template1



  !



  interface Virtual-Template1



    link-protocol ppp



    ppp mp lfi   //That’s it.



    ppp mp lfi delay-per-frag 180  // The value is configurable on demands.



    ppp mp max-send-frags 2



    ip address 10.245.128.13 255.255.255.252

Note: It is required to upgrade to the latest release, 1.740012 at least. Lower release than this does not support PPP MP LFI command. 

Root Cause
1. According to primary analysis, the problem may result from transmission quality and TCP windows size. In checkup on port, no error parameter is found; after changing the value of TCP MSS, the problem persists. After enabling fast forwarding functionality, fewer packets than before are discarded then. Optimizing the forwarding performance of interfaces of routers occurs to our minds. PPP MP LFI command could help adjust delay. Once the delay is revised, the failure disappears completely. It turns to normal to ping big size such as 1500, 2000, 1490, 4000, 5000, and 8000.

2. About ppp mp lfi command



ppp mp lfi [ delay-per-frag max-delay ]



undo ppp mp lfi [ delay-per-frag ]



View



Interface view of virtual template



Parameter



max-delay: maximum delay in seconds, within 11000.



Description



ppp mp lfi command is used to configure link fragments and interleaving features; undo ppp mp lfi command is used to restore the default configurations.



By default, its value is 10.



Example



# Set the maximum delay of each fragment to 100 milliseconds.



[Quidway-Virtual-Template0] ppp mp lfi delay-per-frag 100

 

END