amd64/188990: dhclient does not accept DHCP Offer on FreeBSD 10 as Xen DomU Guest

[Thomas Zelch]

>Number:         188990
>Category:       amd64
>Synopsis:       dhclient does not accept DHCP Offer on FreeBSD 10 as Xen DomU Guest
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-amd64
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Fri Apr 25 12:20:00 UTC 2014
>Closed-Date:
>Last-Modified:
>Originator:     Thomas Zelch
>Release:        10.0-RELEASE-p1
>Organization:
>Environment:
FreeBSD hostname 10.0-RELEASE-p1 FreeBSD 10.0-RELEASE-p1 #0: Tue Apr  8 06:45:06 UTC 2014     root at amd64-builder.daemonology.net:/usr/obj/usr/src/sys/GENERIC  amd64
>Description:
When trying to get a DHCP Lease with the Xen-PV Network Device xn0, DHCP Offers from the DHCP Server are ignored and the following Error Message is shown:

[root at hostname ~]# dhclient xn0
DHCPDISCOVER on xn0 to 255.255.255.255 port 67 interval 3
DHCPDISCOVER on xn0 to 255.255.255.255 port 67 interval 3
DHCPDISCOVER on xn0 to 255.255.255.255 port 67 interval 6
DHCPDISCOVER on xn0 to 255.255.255.255 port 67 interval 14
DHCPDISCOVER on xn0 to 255.255.255.255 port 67 interval 14
5 bad udp checksums in 5 packets
DHCPDISCOVER on xn0 to 255.255.255.255 port 67 interval 20
No DHCPOFFERS received.
No working leases in persistent database - sleeping.

When taking a tcpdump while dhclient is running, the DHCP Offers from the DHCP Server are visible, but it seems dhclient is ignoring them, as the udp checksum is bad out of whatever Reason.

As Google search turned up a lot of Bugs in Linux which were caused by UDP Checksum Offload, i have tried disabling all NIC Features both in the FreeBSD Guest and the dom0, without any success.

See tcpdump Output below:

14:07:26.709519 IP (tos 0x10, ttl 128, id 0, offset 0, flags [none], proto UDP (17), length 328)
    0.0.0.0.68 > 255.255.255.255.67: [udp sum ok] BOOTP/DHCP, Request from 00:16:3e:19:5e:75, length 300, xid 0x738d8779, secs 4, Flags [none] (0x0000)
	  Client-Ethernet-Address 00:16:3e:19:5e:75
	  Vendor-rfc1048 Extensions
	    Magic Cookie 0x63825363
	    DHCP-Message Option 53, length 1: Discover
	    Client-ID Option 61, length 7: ether 00:16:3e:19:5e:75
	    Hostname Option 12, length 7: "hostname"
	    Parameter-Request Option 55, length 9:
	      Subnet-Mask, BR, Time-Zone, Classless-Static-Route
	      Default-Gateway, Domain-Name, Domain-Name-Server, Hostname
	      Option 119
	    END Option 255, length 0
	    PAD Option 0, length 0, occurs 27
14:07:26.710162 IP (tos 0xc0, ttl 64, id 13977, offset 0, flags [none], proto UDP (17), length 345)
    10.1.0.1.67 > 10.1.0.15.68: [bad udp cksum 0x1568 -> 0x37a9!] BOOTP/DHCP, Reply, length 317, xid 0x738d8779, secs 4, Flags [none] (0x0000)
	  Your-IP 10.1.0.15
	  Server-IP 10.1.0.1
	  Client-Ethernet-Address 00:16:3e:19:5e:75
	  Vendor-rfc1048 Extensions
	    Magic Cookie 0x63825363
	    DHCP-Message Option 53, length 1: Offer
	    Server-ID Option 54, length 4: 10.1.0.1
	    Lease-Time Option 51, length 4: 43200
	    RN Option 58, length 4: 21600
	    RB Option 59, length 4: 37800
	    Subnet-Mask Option 1, length 4: 255.255.255.0
	    BR Option 28, length 4: 10.1.0.255
	    Default-Gateway Option 3, length 4: 10.1.0.1
	    Domain-Name-Server Option 6, length 4: 10.1.0.1
	    Domain-Name Option 15, length 14: "localdomain"
	    Hostname Option 12, length 7: "hostname"
	    END Option 255, length 0
>How-To-Repeat:
Execute a dhclient xn0 on the Guest.
>Fix:


>Release-Note:
>Audit-Trail:
>Unformatted: