DHCP server crashes on Edge

Products

• VMware NSX-T Data Center
• VMware NSX

Issue/Introduction

• dhcp_backend process crashes on an Edge node.
• A core file is found as /var/log/core/core.dhcp_backend.***.gz.
• You can find relevant log entries in Edge syslog under /var/log/syslog

2023-09-06T01:37:00.251398+00:00 edge-01 kernel - - - [209409.594488] dhcp_backend[10552]: segfault at 98 ip 00001d#####20f18 sp 0000#####4c61670 error 6 in dhcp_backend[1dbd07124000+8bf000]

2023-09-06T01:37:00.251401+00:00 edge-01 kernel - - - [209409.594498] Code: 05 22 fe 5f 00 ## 89 85 70 fa ff ff 48 ## 05 26 fe 5f 00 48 89 ## 78 fa ff ff 4e ## 84 c5 00 fa ff ff ## 3f 01 00 00 0f ## 00 <49> 83 84 cc ## 00 00 00 01 ## 89 fc ff ff ## 8b 8d a0 ## ff ff ##

2023-09-06T01:37:00.251403+00:00 edge-01 kernel - - - [209409.594512] grsec: Segmentation fault occurred at 0000000000000098 in /opt/vmware/nsx-edge/bin/dhcp_backend[dhcp_backend:10552] uid/euid:128/128 gid/egid:128/128, parent /opt/vmware/edge/dhcp/entrypoint.sh[entrypoint.sh:10532] uid/euid:128/128 gid/egid:128/128

2023-09-06T01:37:33.991Z edge-01 NSX 4594 - [nsx@6876 comp="nsx-edge" subcomp="node-mgmt" username="root" level="WARNING"] Pid of dhcp changed from 10532 to 8105

2023-09-06T01:37:33.993Z edge-01 NSX 4594 - [nsx@6876 comp="nsx-edge" subcomp="node-mgmt" username="root" level="INFO"] Service dhcp coredump at 2023-09-06 01:37:01 file /var/log/core/core.dhcp_backend.1693964220.8.128.11.gz

2023-09-06T01:37:59.016Z edge-01 NSX 4594 - [nsx@6876 comp="nsx-edge" subcomp="node-mgmt" username="root" level="WARNING" eventFeatureName="infrastructure_service" eventType="edge_service_status_changed" eventSev="warning" eventState="On"] The service dhcp changed from STARTED to CRASHED.

Environment

VMware NSX-T Data Center
VMware NSX

Cause

If only IPv4 is configured for a DHCP server and IPv6 is not configured, it crashes on receiving DHCPv6 packets because it references a null IPv6 DHCP server.

Resolution

This issue is resolved in VMware NSX 3.2.4
This issue is resolved in VMware NSX 4.2.0

Workaround:

• Add IPv6 DHCP server addresses to your DHCP servers.
  • No need to configure IPv6 address pool if you don't actually need DHCPv6.
• Configure your environment so that Edge does not receive DHCPv6 packets. For example,
  • Configure guest OS not to send out DHCPv6 packets.
  • Configure DFW to drop DHCPv6 packets sent from VMs.