VMs on NSX Segments fail to receive IP addresses from an external DHCP server.
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VMs on NSX Segments fail to receive IP addresses from an external DHCP server.

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Article ID: 419891

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Updated On:

Products

VMware NSX

Issue/Introduction

  • In vCenter, you observe that the newly deployed VMs are getting an APIPA IP address in the range of 169. #.#.#

  • Capturing packets on the edge host uplink, we can see that the DHCP requests are leaving the ESXI host uplink, but there were no response/offer packets from the external DHCP server:
    [root@is-esx-###:~] pktcap-uw --uplink vmnic# --capture UplinkSndKernel,UplinkRcvKernel -o - | tcpdump-uw -enr - | grep -i BOOTP/DHCP

The session capture point is UplinkSndKernel,UplinkRcvKernel.
pktcap: The output file is -.
pktcap: No server port specified, select 15456 as the port.
pktcap: Local CID 2.
pktcap: Listen on port 15456.
pktcap: Main thread: 351908125888.
pktcap: Dump Thread: 351908656896.
pktcap: The output file format is pcapng.
pktcap: Recv Thread: 351909185280.
pktcap: Accept...
reading from file -, link-type EN10MB (Ethernet)pktcap: Vsock connection from port 1038 cid 2.
, snapshot length 65535
08:11:25.778347 0#:5#:5#:6#:#0:5# > 00:X2:Xd:f8:X9:ff, ethertype IPv4 (0x0800), length 400: 10.#.2##.X9.64430 > 10.#.###.##.6081: Geneve, Flags [none], vni 0x1X4X5, proto TEB (0x6558), options [8 bytes]: 0X:5X:X6:X6:4X:52 > 0X:5X:X6:X6:X3:00, ethertype IPv4 (0x0800), length 342: 10.##.##.#.## > 1X0.X5.1X0.2X.6X: BOOTP/DHCP, Request from 0#:5#:#6:9#:#f:#d, length 300
08:11:54.357349 0#:5#:5#:6#:#0:5#:56 > 00:X2:Xd:f8:X9:ff, ethertype IPv4 (0x0800), length 400: 10.#.2##.X9.63939 > 10.#.###.##.6081: Geneve, Flags [none], vni 0x1X4X5, proto TEB (0x6558), options [8 bytes]: 0X:5X:X6:X6:4X:52 > 0X:5X:X6:X6:X3:00, ethertype IPv4 (0x0800), length 342: 10.##.##.#.## > 1X0.X5.1X0.2X.6X: BOOTP/DHCP, Request from 0X:5X:X6:9X:Xb:X2, length 300
08:11:58.033446 0#:5#:5#:6#:#0:5#:56 > 00:X2:Xd:f8:X9:ff, ethertype IPv4 (0x0800), length 400: 10.#.2##.X9.64430 > 10.#.###.##.6081: Geneve, Flags [none], vni 0x1X4X5, proto TEB (0x6558), options [8 bytes]: 0X:5X:X6:X6:4X:52 > 0X:5X:X6:X6:X3:00, ethertype IPv4 (0x0800), length 342: 10.##.##.#.## > 1X0.X5.1X0.2X.6X: BOOTP/DHCP, Request from 0#:5#:#6:9#:#f:#d, length 300
08:11:58.363300 0#:5#:5#:6#:#0:5# > 00:X2:Xd:f8:X9:ff, ethertype IPv4 (0x0800), length 400: 10.#.2##.X9.63939 > 10.#.###.##: Geneve, Flags [none], 0x1X4X5, proto TEB (0x6558), options [8 bytes]: 0X:5X:X6:X6:4X > 0X:5X:X6:X6:X3:00, ethertype IPv4 (0x0800), length 342: 10.##.##.#.## > 1##.9X.1##.2X.X7: BOOTP/DHCP, Request from 0X:5X:X6:9X:Xb:X2, length 300
08:12:01.484896 0#:5#:5#:6#:#0:5# > 00:X2:Xd:f8:X9:ff, ethertype IPv4 (0x0800), length 400: 10.#.2##.X9.63939 > 10.#.###.##: Geneve, Flags [none], 0x1X4X5, proto TEB (0x6558), options [8 bytes]: 0X:5X:X6:X6:4X > 0X:5X:X6:X6:X3:00, ethertype IPv4 (0x0800), length 342: 10.##.##.#.## > 1##.9X.1##.2X.X7: BOOTP/DHCP, Request from 0#:5#:#6:9#:#f:#d, length 300

Environment

VMware NSX Datacenter.

Cause

The external DHCP server is not configured with a scope that matches the CIDR of the NSX Segment, causing the server to ignore or drop DHCP Discovery/Request packets originating from those segments.

Resolution

  • Creating a DHCP scope for the VM's subnets should resolve the issue.

Additional Information

Reference KB for capturing the packets:

KB345925

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