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List:       freebsd-amd64
Subject:    amd64/188990: dhclient does not accept DHCP Offer on FreeBSD 10 as Xen DomU Guest
From:       Thomas Zelch <thomaszelch () gmail ! com>
Date:       2014-04-25 12:15:20
Message-ID: 201404251215.s3PCFK1v002266 () cgiserv ! freebsd ! org
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> 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@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@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:
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