Comment # 20 on bug 1188949 from Reinhard Max

(In reply to Jonathan Kang from comment #19)

> I guess you're the maintainer of dhclient.

yes, I am the maintainer of the dhcp package, but not a deep expert in DHCP.

> Do you have any idea about what could go wrong here?

I discussed this with Marius, but we couldn't find a possible reason within
dhclient that would explain this. To narrow this further down we want to see if
the missing DHCPACK packages are not being sent by the router, being filtered
by the kernel, or being silently ignored by dhclient, because it thinks they
are invalid.

For that, please disable your firewall (if it is active) and change some
settings:

# sysctl -w net.ipv4.conf.all.log_martians=1
# sysctl -w sysctl -w net.ipv4.conf.all.rp_filter=0

Then record all DHCP packages over at least one occurance of dhclient sending a
request and seemingly getting no ack:

# tcpdump -W /tmp/dhcp4.pcapng -s 65535 -Uvnfi any 'port 67 or port 68'

Interrupt tcpdump with Ctrl-C when done and upload /tmp/dhcp4.pcapng as an
attachment.