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Cisco Bug: CSCuo45873 - BGP sessions going down when there is no NLRI in MP_REACH field on NXOS

Last Modified

Oct 04, 2016

Products (7)

  • Cisco Nexus 7000 Series Switches
  • Cisco Nexus 7000 10-Slot Switch
  • Cisco Nexus 7000 4-Slot Switch
  • Cisco Nexus 7000 18-Slot Switch
  • Cisco Nexus 7700 18-Slot Switch
  • Cisco Nexus 7000 9-Slot Switch
  • Cisco Nexus 7700 10-Slot Switch

Known Affected Releases

6.2(2a)

Description (partial)

Symptom:
MP-BGP going down between Nexus 7k and and MP-BGP peer due to "bad msg length error".

Below are logs observed on the Nexus 7k

2014 Apr  1 12:14:25 C22RRGX01-VM22RRGIDX01 %BGP-5-ADJCHANGE:  bgp-65500 [7655] (default) neighbor 10.200.255.202 Up 
2014 Apr  1 12:14:25 C22RRGX01-VM22RRGIDX01 %BGP-5-ADJCHANGE:  bgp-65500 [7655] (default) neighbor 10.200.255.202 Down - bad msg length error
2014 Apr  1 12:14:36 C22RRGX01-VM22RRGIDX01 %BGP-5-ADJCHANGE:  bgp-65500 [7655] (default) neighbor 10.200.255.202 Up 
2014 Apr  1 12:14:37 C22RRGX01-VM22RRGIDX01 %BGP-5-ADJCHANGE:  bgp-65500 [7655] (default) neighbor 10.200.255.202 Down - bad msg length error
2014 Apr  1 12:14:46 C22RRGX01-VM22RRGIDX01 %BGP-5-ADJCHANGE:  bgp-65500 [7655] (default) neighbor 10.200.255.202 Up 
2014 Apr  1 12:14:46 C22RRGX01-VM22RRGIDX01 %BGP-5-ADJCHANGE:  bgp-65500 [7655] (default) neighbor 10.200.255.202 Down - bad msg length error
2014 Apr  1 12:14:57 C22RRGX01-VM22RRGIDX01 %BGP-5-ADJCHANGE:  bgp-65500 [7655] (default) neighbor 10.200.255.202 Up 
2014 Apr  1 12:14:58 C22RRGX01-VM22RRGIDX01 %BGP-5-ADJCHANGE:  bgp-65500 [7655] (default) neighbor 10.200.255.202 Down - bad msg length error
2014 Apr  1 12:15:09 C22RRGX01-VM22RRGIDX01 %BGP-5-ADJCHANGE:  bgp-65500 [7655] (default) neighbor 10.200.255.202 Up 
2014 Apr  1 12:15:10 C22RRGX01-VM22RRGIDX01 %BGP-5-ADJCHANGE:  bgp-65500 [7655] (default) neighbor 10.200.255.202 Down - bad msg length error
2014 Apr  1 12:15:22 C22RRGX01-VM22RRGIDX01 %BGP-5-ADJCHANGE:  bgp-65500 [7655] (default) neighbor 10.200.255.202 Up 
2014 Apr  1 12:15:23 C22RRGX01-VM22RRGIDX01 %BGP-5-ADJCHANGE:  bgp-65500 [7655] (default) neighbor 10.200.255.202 Down - bad msg length error
2014 Apr  1 12:15:34 C22RRGX01-VM22RRGIDX01 %BGP-5-ADJCHANGE:  bgp-65500 [7655] (default) neighbor 10.200.255.202 Up



On the Nexus 7k, if we do "debug bgp packet update"  below logs can be observed.
2014 Apr  9 06:49:37.543844 bgp: 65500 [7655] (default) UPD: Peer 10.200.255.202 nexthop length in VPNv4 MP reach: 12, rd: 0:0 
2014 Apr  9 06:49:37.543898 bgp: 65500 [7655] (default) UPD: Recvd NEXTHOP 10.200.49.249 
2014 Apr  9 06:49:37.543982 bgp: 65500 [7655] (default) UPD: Sending NOTIFY bad msg length error of length 20 to peer 10.200.255.202 
2014 Apr  9 06:49:37.544058 bgp: 65500 [7655]      00290301 02800E11 0001800C 00000000
2014 Apr  9 06:49:37 C22RRGX01-VM22RRGIDX01 %BGP-5-ADJCHANGE:  bgp-65500 [7655] (default) neighbor 10.200.255.202 Down - bad msg length error

Conditions:
Condition is : MP-BGP peering on Nexus7k.
if the MP-BGP peer sends an Update packet which does not have NLRI field with in MP_REACH_NLRI, Nexus will reset the BGP session with the error message "bad msg length error of length"

If the BGP Notification message generated from the Nexus 7k is analysed, it will explain the the issue


80 0e 11 00 01 80 0c 00 00 00 00 00 00 00 00 0a c8 31 f9 00 ---------------------> BGP notification packet's data

MP_REACH_NLRI ( 20 bytes )
80 - FLAG ( 1 )
0e - MP_REACH_NLRI Type Code (1)
11 - Length ( 17 )
00 01 - AF: IPV4 ( 2 )
80 - Sub AF: Labeled VPN Unicast ( 1 ) 
12 - Length (1)
10.200.49.249 (12)
0 - Subnet Points of Attachment (1)


In the "debug bgp packet update" on the Nexus 7k below message were observed 

2014 Apr  9 06:49:37.543844 bgp: 65500 [7655] (default) UPD: Peer 10.200.255.202 nexthop length in VPNv4 MP reach: 12, rd: 0:0 
2014 Apr  9 06:49:37.543898 bgp: 65500 [7655] (default) UPD: Recvd NEXTHOP 10.200.49.249 
2014 Apr  9 06:49:37.543982 bgp: 65500 [7655] (default) UPD: Sending NOTIFY bad msg length error of length 20 to peer 10.200.255.202 

2014 Apr  9 06:49:37.544058 bgp: 65500 [7655]      00290301 02800E11 0001800C 00000000 
2014 Apr  9 06:49:37 C22RRGX01-VM22RRGIDX01 %BGP-5-ADJCHANGE:  bgp-65500 [7655] (default) neighbor 10.200.255.202 Down - bad msg length error
2014 Apr  9 06:49:37.544274 bgp: 65500 [7655] (default) UPD: Error parsing attributes in UPDATE message from peer 10.200.255.202, attr len 87 
2014 Apr  9 06:49:37.550908 bgp: 65500 [7655] (default) UPD: [VPNv4 Unicast] Starting update run for peer 10.200.49.246 (#10081466)
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