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VoBB Services Interrupted due to modem not getting ip address

Publication Date:  2012-07-27 Views:  94 Downloads:  0
Issue Description
T Operator in Malaysia is using ME60-16 as Bras. Triple-play services are running on platform such as high speed internet, VoBB and VoD.

Software version: V6R2C02SPC500

Topology: Refer to Image

Alarm Information
Null
Handling Process
So why and how ARP detection feature being implemented in the T-Operator ME60 Network.
The reason ARP detection depolyed by RAS/BRAS is:
 If customer connect his/her PC to SIP port on RG. He/she can run some hacker tools to simulate thousand s of PC to apply IP address from DHCP server reside in BRAS or a real DHCP server. In few seconds or minutes, IP Pool of DHCP server will be exhausted by this kind of attack if there is no security scheme to deploy on BAS. (This case has happened before in China Telecom or NZ Telecom). To avoid DHCP DDoS attack from subscriber some BRAS Vendors initial ARP unicast request packet to detect if ip address which applied by users is still available. If the user never reply ARP request for specific ip, BRAS will release corresponding  
User session and IP address resource for other users. BRAS will also send a DHCP release information to DHCP server to synchronize available IP address information
ARP detection feature in ME60 = 30sec * 5,          

Before running this command, set the access type of the user to layer2 subscriber or layer2-leased-line by the access-type command.
Example
# Set the number of times for detecting users to 5 and the detection interval to 30 seconds.
<HUAWEI>system-view
[HUAWEI] interface GigabitEthernet 3/0/0.3
[HUAWEI-GigabitEthernet3/0/0.3]bas
[HUAWEI-GigabitEthernet3/0/0.3-bas]access-type layer2-subscriber
[HUAWEI-GigabitEthernet3/0/0.3-bas]user detect retransmit 5 interval 30

Root Cause
Certain VOBB customer that using Z-Msan that connecting to BSR is having not be able to use the VOBB service due to not getting IP address for VOBB service. Huawei found that the issue happened was because ARP detection was failed. We have being informed that Z-VDSL modem doesn’t support ARP detection feature. Sample Offline message in BSR as per below:
 
User name          : ME6001-10000060800000@vobb
  User MAC           : 0025-12f0-740f
  User access slot   : 10
  User interface     : GigabitEthernet10/0/0.4
  User access PeVlan/CeVlan    : 608/0
  User IP address    : 10.1.6.224        
  User IPv6 address  : -
  User ID            : 85569
  User authen state  : Authened
  User acct state    : AcctReady
  User author state  : AuthorIdle
  User acct sessionID: ME6001000006080000033adc1085569
  User login time    : 2010-08-16 16:29:13
  User offline time  : 2010-08-16 16:32:14
  User offline reason: ARP with detect fail
 
The ARP pattern problem is after getting DHCP, then about 3-5 minutes, BRAS send Release as there’s no response from Z-VDSL Modem for ARP packet
Suggestions
Solution:

 Turn off ARP positive detection function on BRAS to avoid VOBB user reside in modem which doesn’t support ARP protocol to be forced to offline.

<HUAWEI>system-view
[HUAWEI] interface GigabitEthernet 3/0/0.3
[HUAWEI-GigabitEthernet3/0/0.3]bas
[HUAWEI-GigabitEthernet3/0/0.3-bas]access-type layer2-subscriber
[HUAWEI-GigabitEthernet3/0/0.3-bas]user detect retransmit 10 interval 0
 

END