netdev
[Top] [All Lists]

routing table/cache question

To: net dev <netdev@xxxxxxxxxxx>
Subject: routing table/cache question
From: gg&ht forever <lighthouse@xxxxxxxxx>
Date: Tue, 20 Jun 2000 13:55:19 -0600
Reply-to: lighthouse@xxxxxxxxx
Sender: owner-netdev@xxxxxxxxxxx
Hello,

This is a Linux 2.2 question, although I suspect that it
applies to 2.4 as well. Please feel free to direct me to
RTFM or another list.

I've notice in 2.2.x that ICMP redirects don't get put in
the routing table but do get put into the routing cache, that
is the one that you can look at with route -Cn. There's no
flag for redirects there but the host entry appears. Is this
understanding correct?

Also can someone give me some insights into the use of the ibl
flags there? I can see that b means broadcast (also apparent from
the rt_cache.h file) and l means local (as in local destination?), 
and i seems only to apply to the lo interface. Is that correct?

Is there a write-up on this somewhere?

What really bothers me about the route cache are that there seem to
be some odd entries. For example, suppose my host is 172.16.1.1 and I
ping some external Internet host that I'll just call w.x.y.z (so nobody
can say I'm picking on them). Also suppose that I have my default
router on 172.16.1.1 set up so that when I ping w.x.y.z I get a
redirect.
OK. Ethereal reports one redirect and then all subsequent communications
go to the correct router. Also, route -Cn reports a host entry for the
redirect to w.x.y.z. But, route -Cn also reports (I left out ref & use):

Source  Destination     Gateway         Flags   Device
------  -----------     -------         -----   ------
w.x.y.z 172.16.1.1      172.16.1.1      l       lo

where the flag entry is a lower case L (hard to differentiate from a one
[1]).
What is this entry for???

Thanks for your time!

Regards,
Scott

<Prev in Thread] Current Thread [Next in Thread>
  • routing table/cache question, gg&ht forever <=