[gnome-network] Re: new modules consensus

[Alan Cox <alan lxorguk ukuu org uk>]

On Maw, 2004-08-17 at 16:17, Germán Poó Caamaño wrote:
> May you give some detail or approach that I could follow to get
> in shape nettool? (I mean, traceroute and routing tables or whatever
> else that needs some love).

Lets start with an easy one. The traceroute parser assumes packets
follow a single path. Probably your network looks like that ? but
traceroutes can often look like this

3  aa1-hg3.ilford.broadband.bt.net (217.47.56.74)  18.333 ms  17.865 ms 
18.091 ms
 4  aa1-fer1G30.ilford.broadband.bt.net (217.47.56.1)  17.916 ms
aa1-fer2gig3.ilford.broadband.bt.net (217.47.56.2)  17.809 ms
aa1-fer2G10.ilford.broadband.bt.net (217.47.56.34)  17.779 ms
 5  aa1-nteatm2.1.ilford.broadband.bt.net (217.47.56.106)  19.841 ms 
19.867 ms aa1-nteatm2.2.ilford.broadband.bt.net (217.47.56.110)  18.032
ms
 6  aimless.aaisp.net.uk (217.169.20.3)  19.893 ms  17.933 ms  19.928 ms

You'll see the output format is a little different and this breaks the
traceroute probe.


Routing in the Linux world is a bit more complex. netstat is sort of a
legacy "simplistic" view of the routing tables. It is mostly there for
backward compatibility with simple setups.

The ip command allows access to the full tables. Each table entry
contains a lot more information than "route" shows..

194.168.151.0/27 dev eth0  proto kernel  scope link  src 194.168.151.30
169.254.0.0/16 dev eth0  scope link
127.0.0.0/8 dev lo  scope link
default via 194.168.151.3 dev eth0


It has scopes. It also knows the source ip to use for the route, the
mtu, mss, tcp window, and a lot more things.

There are also multiple routing tables, and the table used can be
selected by routing prefixes and input policy.  (ip rule)

(btw ip link also knows some things about network interfaces that may be
of interest including the queue discipline)

Alan