Re: [tcptra-dev] tcptraceroute test suite

[Richard van den Berg <richard@vdberg.org>]

Michael C. Toren wrote:
> Are you able to successfully traceroute to either 127.0.0.1 or
> 62.234.101.241 if you specify the device to use by hand?

No. That is, the attaching works fine, but the actual traceroute fails. 
(Just a bunch of *s).

> Another test to help determine if it's a libpcap problem might be to
> see if tcpdump can attach to the loopback interface.  Something like:
>
> 	tcpdump -n -i lo0

This is a very useless command on Solaris. First off, Solaris comes with 
snoop, so tcpdump is not often installed. Secondly, packets sent over 
the loopback interface on Solaris do not travel high enough down and up 
the IP stack to be able to be sniffed. This is a major drawback when 
troubleshooting local connections: anything sent over lo0 cannot be seen 
by snoop or pcap.

Anyhow, build tcpdump 3.7.2 (using libpcap 0.7.2), and here we have it:

# ./tcpdump -n -i lo0
tcpdump: /dev/lo0: No such file or directory

on the other hand:

# snoop -d lo0
snoop: /dev/lo: No such file or directory

which is a little better (Solaris has 1 generic device in /dev for each 
interface type, not a device per interface).

Ok, something just hit me. Because of the above (packets over loopback 
never leave lower layers of IP stack), there was probably no use for a 
lookback DPLI interface in Solaris. So Sun never implemented one. Makes 
sense... why build something that's useless anyway?

I think the same reasoning goes for tcptraceroute not working to a local 
interface. Since we rely on pcap to tell us what the host receives. A 
test I did:

window1# snoop -d eri0
window2$ ping -s 192.168.0.2

Snoop does not see the packets either (the IP stack recognizes the 
packets are destined for the local machine, and never sends them high 
enough up the stack for snoop or pcap to see them).

Looks like this will never work on Solaris.

Sincerely,

Richard van den Berg

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