Issues about USG2205 as a PE router constitutes BGP neighbor with peer-end PE unstably

Publication Date:  2012-09-14 Views:  196 Downloads:  0
Issue Description
Customer constitutes MPLS VPN with another PE through USG2205 as a PE router, two PEs constitute BGP neighbor with loopback address, two devices connected with private line directly. Ping success between PEs, but the status of BGP neighbor is unstable, switch between constitute and leisure status repetitiously, and that leads to access between CEs connect and disconnect sometimes. 
[usg2000-1-Serial6/0/0:0]disp bgp peer
14:50:24  2012/03/08
BGP local router ID : 10.163.234.222
Local AS number : 31021
Total number of peers : 1              Peers in established state : 0
Peer                     V    AS    MsgRcvd   MsgSent    OutQ  Up/Down       State   PrefRcv
10.163.234.41       4  31021       25           51            0       00:00:29        Idle       0
[usg2000-1-Serial6/0/0:0] [usg2000-1-Serial6/0/0:0]disp bgp peer
14:50:31  2012/03/08
BGP local router ID : 10.163.234.222
Local AS number : 31021
Total number of peers : 1              Peers in established state : 1
Peer                 V      AS     MsgRcvd   MsgSent    OutQ    Up/Down       State        PrefRcv
10.163.234.41   4    31021      147                53       0         00:00:04      Established      14
Alarm Information
NULL
Handling Process
1、 OSPF as IGP, ping peer end PE success from usg2205 side, but ping loopback address of peer end PE with loopback address, connect and disconnect sometimes, OSPF matters is the primary judgment.
2、  Review the status of two-end PEs, always be FULL, review loopback route of peer end PE repetitiously on USG2205, route exist all the time in ping loopback address of peer end connect and disconnect sometimes process, it says that USG could learn the route of peer end PE announced, review route of USG on peer end PE, finding out that route of USG2205 loopback address exist when ping successes, and this route doesn’t exist in route table when ping failed. We can judge that the reasons of this phenomenon caused by is address collision with USG2205 exists in the network of peer end PE, which leads to routing table of peer end PE refurbish continuously, another reason is USG2205 announces route unstable.
3、 Validate analysis result of step 2: change loopback interface address of USG into an address which couldn’t exists in this network, constitute BGP neighbor normally, no packet dropped when ping loopback address of peer end PE with loopback address, which validate that it’s address in network of peer end PE side collision with loopback interface address of USG2205 leads to exceptional routing table.     
Root Cause
1、 private network unstable.
2、 Wrong configuration of router.
3、 others 
Suggestions
NULL

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