Date: Mon, 27 Jun 2022 11:44:55 +0000 From: "Dave Cottlehuber" <dch@skunkwerks.at> To: freebsd-net <freebsd-net@freebsd.org> Subject: missing SYN/ACK for inbound TCP solved by altering broadcast address - why? Message-ID: <b727be82-f90b-4391-b151-81660f204a00@www.fastmail.com>
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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?
## 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
failing FreeBSD config from dhclient:
inet 147.75.93.61 netmask 0xfffffffe broadcast 147.75.93.60
^^^^^^^^^^^^
working Linux config (note broadcast)
inet 147.75.93.61 netmask 0xfffffffe broadcast 255.255.255.254
^^^^^^^^^^^^^^^
- 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
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