IP packets with TTL 0 shall not leave host.
But when I start application which multicasts UDP packets with TTL 0, I see packets with TTL 0 leaving host for few seconds, and coming to normal behavior of TTL 0. This most likely happens after reboot and first start of application.
I confirmed packets with TTL 0 leaving host with tcpdump:
05:31:39.048304 IP (tos 0x0, id 14487, offset 0, flags [DF], proto UDP (17), length 1344)
192.168.1.200.46968 > 239.0.0.1.1234: UDP, length 1316
05:31:39.049594 IP (tos 0x0, id 14488, offset 0, flags [DF], proto UDP (17), length 1344)
192.168.1.200.46968 > 239.0.0.1.1234: UDP, length 1316
05:31:39.051601 IP (tos 0x0, id 14489, offset 0, flags [DF], proto UDP (17), length 1344)
192.168.1.200.46968 > 239.0.0.1.1234: UDP, length 1316
05:31:39.053584 IP (tos 0x0, id 14490, offset 0, flags [DF], proto UDP (17), length 1344)
192.168.1.200.46968 > 239.0.0.1.1234: UDP, length 1316
As we can see ttl
is not displayed which means TTL 0, as confirmed from tcpdump man page: https://www.tcpdump.org/manpages/tcpdump.1.html (search ttl
, it clearly indicated: ttl is the time-to-live; it is not reported if it is zero).
There are no any iptables
rules running.
uname -a
: Linux mydevice 4.15.0-101-generic #102-Ubuntu SMP Mon May 11 10:07:26 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
lsb_release -a
:
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 18.04.4 LTS
Release: 18.04
Codename: bionic
What can be the cause for this behavior, and how can I resolve this?