Date: Mon, 6 Aug 2001 14:35:38 +0100 (BST) From: Henry Whincup <henry@techiebod.com> To: "freebsd-net@freebsd.org" <freebsd-net@freebsd.org> Subject: BPF does not pick up loopback activity Message-ID: <20010806140314.O37365-100000@localhost>
next in thread | raw e-mail | index | archive | help
Take the following example:
# ifconfig fxp0
fxp0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
inet 192.168.2.1 netmask 0xffffff00 broadcast 192.168.2.255
ether 00:90:27:94:84:34
media: Ethernet autoselect (100baseTX <full-duplex>)
status: active
# tcpdump -ni fxp0 &
# ping 192.168.2.1
PING 192.168.2.1 (192.168.2.1): 56 data bytes
64 bytes from 192.168.2.1: icmp_seq=0 ttl=64 time=0.059 ms
64 bytes from 192.168.2.1: icmp_seq=1 ttl=64 time=0.057 ms
^C
--- 192.168.2.1 ping statistics ---
2 packets transmitted, 2 packets received, 0% packet loss
round-trip min/avg/max/stddev = 0.057/0.058/0.059/0.001 ms
# ping 192.168.2.2
PING 192.168.2.2 (192.168.2.2): 56 data bytes
64 bytes from 192.168.2.2: icmp_seq=0 ttl=255 time=3.134 ms
14:33:23.291728 arp who-has 192.168.2.2 tell 192.168.2.1
14:33:23.293210 arp reply 192.168.2.2 is-at 0:d0:ba:a:91:c0
14:33:23.293227 192.168.2.1 > 192.168.2.2: icmp: echo request
14:33:23.294782 192.168.2.2 > 192.168.2.1: icmp: echo reply
64 bytes from 192.168.2.2: icmp_seq=1 ttl=255 time=1.408 ms
14:33:24.297997 192.168.2.1 > 192.168.2.2: icmp: echo request
14:33:24.299352 192.168.2.2 > 192.168.2.1: icmp: echo reply
^C
--- 192.168.2.2 ping statistics ---
2 packets transmitted, 2 packets received, 0% packet loss
round-trip min/avg/max/stddev = 1.408/2.271/3.134/0.863 ms
#
Note that the packets sent to the local IP address are not picked up by
tcpdump. This can be tried with any traffic type, I have just used ping
as an example.
Is this the correct/desired behaviour? If it is, is there any other way
to capture these packets?
Thanks
Henry
To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-net" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20010806140314.O37365-100000>