Subject: Re: loopback routes
To: Charles M. Hannum <>
From: Andrew Brown <>
List: tech-net
Date: 05/05/2000 23:18:29
>This is due to some special cases for IFF_LOOPBACK.  Could you try the
>following change?

well...that gives me the route that i expect, but now i get other
"weirdness".  :)

(1) on one tty, i do "ping" and on another, i do "tcpdump
-nilo0".  what i see is:

   # tcpdump -nilo0
   tcpdump: listening on lo0
   23:11:02.868037 > icmp: echo request
   23:11:02.868159 > icmp: echo reply [ttl 1]
   23:11:03.892777 > icmp: echo request
   23:11:03.892874 > icmp: echo reply [ttl 1]

yet the ping program doesn't recognize these responses.

(2) i start with "ifconfig lo1" (yes, i have more than one).
then i ping  here, i get different packet patterns.

   # tcpdump -nilo1
   tcpdump: listening on lo1
   23:12:34.134754 > icmp: echo request
   23:12:35.134750 > icmp: echo request

(3) i see that as soon as i ifconfig lo0, ipv6 automatically assigns it

   inet6 fe80::1%lo0 prefixlen 64 scopeid 0x2
   inet6 ::1 prefixlen 128

and then lo1 gets

   inet6 fe80::1%lo1 prefixlen 64 scopeid 0x2
   inet6 ::1 prefixlen 128

is this a problem?  "route get -inet6 ::1" reports lo0, but i expect
that's only because it's first in the "list".

(4) not really a problem...more of a question.  what theoretical
effect would setting IFF_BROADCAST on the loopback interfaces have?

|-----< "CODE WARRIOR" >-----|             * "ah!  i see you have the internet (Andrew Brown)                that goes *ping*!"       * "information is power -- share the wealth."