>Number: 187094
>Category: misc
>Synopsis: FreeBSD DHCP ignores dhcp option interface-mtu
>Confidential: no
>Severity: non-critical
>Priority: low
>Responsible: freebsd-bugs
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: sw-bug
>Submitter-Id: current-users
>Arrival-Date: Wed Feb 26 20:10:00 UTC 2014
>Closed-Date:
>Last-Modified:
>Originator: Robert Blayzor
>Release: 10.0
>Organization:
INOC, LLC
>Environment:
FreeBSD rootbsd.ops.inoc.net 10.0-RELEASE FreeBSD 10.0-RELEASE #0 r261846: Tue
Feb 25 13:50:12 UTC 2014
r...@rootbsd.ops.inoc.net:/usr/obj/.amd_mnt/juno/pub/FreeBSD/10.0-RELEASE/sys/ESXBSD
amd64
>Description:
Upon PXE booting FreeBSD kernel trying to set a higher MTU via DHCP.
Using "option interface-mtu ...." in ISC-DHCP, MTU never properly gets set to
anything higher than 1500.
Attempting to change the MTU in rc startup scripts only appears to cosmetically
change..
dev@rns0 [~] cat /etc/rc.conf | grep vmx
ifconfig_vmx0="mtu 9000"
dev@rns0 [~] ifconfig vmx0
vmx0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 9000
options=60039b<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,VLAN_HWCSUM,TSO4,TSO6,RXCSUM_IPV6,TXCSUM_IPV6>
ether 00:50:56:a7:03:22
inet6 fe80::250:56ff:fea7:322%vmx0 prefixlen 64 scopeid 0x1
inet 10.0.0.20 netmask 0xffff0000 broadcast 10.0.255.255
nd6 options=21<PERFORMNUD,AUTO_LINKLOCAL>
media: Ethernet autoselect
status: active
dev@rns0 [~] sudo ping -D -c 1 -s 1600 10.0.0.200
PING 10.0.0.200 (10.0.0.200): 1600 data bytes
ping: sendto: Message too long
dev@rns0 [~] sudo ping -D -c 1 -s 1472 10.0.0.200
PING 10.0.0.200 (10.0.0.200): 1472 data bytes
1480 bytes from 10.0.0.200: icmp_seq=0 ttl=64 time=0.064 ms
--- 10.0.0.200 ping statistics ---
1 packets transmitted, 1 packets received, 0.0% packet loss
>How-To-Repeat:
Using dhclient or PXE boot configure DHCP server to use MTU > 1500. ie:
option interface-mtu 9000;
System boots and gets IP address properly but MTU cannot be set.
>Fix:
None.
Attempting to set MTU via rc.conf startup does not work.
>Release-Note:
>Audit-Trail:
>Unformatted:
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