Responding to parts of two emails:
On 27 Jun 2022, at 7:41, Marek Zarychta wrote:
W dniu 27.06.2022 o 13:44, Dave Cottlehuber pisze:
I've found a workaround for this issue, but don't understand why this
occurs. Reading RFC1122 has left me none the wiser. What am I
missing?
Is this a Linuxism or simple a standardisation loophole?
It has been standardized in RFC3021 over twenty years ago. FreeBSD
ifconfig(8) supports /31 netmask for a long time and the broadcast
address is correctly assigned in this case (255.255.255.255). Either
dhcp-options(5) "option broadcast-address" is missing on the DHCP
server or our dhclient(8) is misbehaving or maybe the Linux client is
better in figuring out the right broadcast address.
Looks like RFC3021 only says it applies to point-to-point interfaces,
and doesn’t consider other types. I don’t remember any code in
ifconfig
to special-case this, although the kernel will default the broadcast
correctly in this case (to the all-1’s address; I guess that’s an
extension).
That means something is giving the broadcast address to ifconfig
explicitly.
## Problem
- on 13.1-R, dhclient-set config works for all UDP, & outbound TCP
- but inbound TCP connections send no SYN/ACK at all back
- on Linux Ubuntu 22.04 & others, the DHCP supplied IP config
works as expected
Do you know if this worked with 13.0? (I made a change in 13.1,
but don’t quite see how it would cause this situation to change.)
failing FreeBSD config from dhclient:
inet 147.75.93.61 netmask 0xfffffffe broadcast 147.75.93.60
This is odd. I don’t know why the broadcast address would be host 0
on that network, but note that it is the same as the router address.
That is probably the root of the problem. I don’t see a broadcast
address in the lease below, so maybe dhclient is confused. The
default broadcast would be host -1, but of course that is the host
itself.
working Linux config (note broadcast)
inet 147.75.93.61 netmask 0xfffffffe broadcast 255.255.255.254
That’s an odd choice of broadcast, but it doesn’t really matter
here.
- full details below (dhcp lease, ifconfigs etc)
I worked around this by forcing broadcast-address in dhclient.conf:
## /etc/dhclient.conf
interface "ice0" {
supersede broadcast-address 255.255.255.255;
}
# repeat for other ifaces as required
Which is ~ok~ for the moment, but I'd like to understand why this
occurs, and fix it properly. Either at DHCPD end, or FreeBSD
config.
# Further details
- Ubuntu 22.04 from vendor
- FreeBSD 13.1-RELEASE amd64 vanilla install
- 4x ice(4) NICs (Intel E810) and 2x (unused) ix (igxbe)
- 2x of the ice(4) are bonded link aggregation
- dhclient only used to attach to 1 nic, ignoring FreeBSD side of
bonding
## Linux ip addr
# ip addr
8: bond0: <BROADCAST,MULTICAST,MASTER,UP,LOWER_UP> mtu 1500 qdisc
noqueue state UP group default qlen 1000
link/ether b4:96:91:d9:99:20 brd ff:ff:ff:ff:ff:ff
inet 147.75.92.187/31 brd 255.255.255.255 scope global bond0
...
## FreeBSD ifconfig
# ifconfig ice0
ice0: flags=8863<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu
1500
options=4e10438<VLAN_MTU,VLAN_HWTAGGING,JUMBO_MTU,LRO,VLAN_HWFILTER,RXCSUM_IPV6,TXCSUM_IPV6,NOMAP>
ether b4:96:91:d9:9b:48
inet 147.75.93.61 netmask 0xfffffffe broadcast 147.75.93.60
media: Ethernet autoselect (25G-AUI <full-duplex>)
status: active
nd6 options=29<PERFORMNUD,IFDISABLED,AUTO_LINKLOCAL>
...
root@metalBSD:~ # netstat -4rn
Routing tables
Internet:
Destination Gateway Flags Netif Expire
default 147.75.93.60 UGS ice0
127.0.0.1 link#7 UH lo0
147.75.93.60/31 link#3 U ice0
147.75.93.61 link#3 UHS lo0
root@metalBSD:~ # cat /var/db/dhclient.leases.ice0
- note no broadcast-address provided
- Linux & FreeBSD evidently derive it differently
lease {
interface "ice0";
fixed-address 147.75.93.61;
option subnet-mask 255.255.255.254;
option routers 147.75.93.60;
option domain-name-servers 147.75.207.207,147.75.207.208;
option host-name "intransigent09";
option dhcp-lease-time 172800;
option dhcp-message-type 5;
option dhcp-server-identifier 139.178.78.140;
renew 1 2022/6/27 18:40:06;
rebind 2 2022/6/28 12:40:06;
expire 2 2022/6/28 18:40:06;
}
A+
Dave
--
Marek Zarychta
