* Re: ifconfig appears to also add entry to routing table
2002-09-01 19:20 ifconfig appears to also add entry to routing table Jim Earl
@ 2002-09-01 19:41 ` pa3gcu
2002-09-01 20:04 ` Ray Olszewski
2002-10-04 16:26 ` Make Linux bootdisk Abhijit Vijay
2 siblings, 0 replies; 7+ messages in thread
From: pa3gcu @ 2002-09-01 19:41 UTC (permalink / raw)
To: Jim Earl, Linux Newbie
On Sunday 01 September 2002 19:20, Jim Earl wrote:
> Hello all,
>
> I have been configuring a linux box to function as a router, ran into some
> problems, and think that I traced the problem to a faulty routing table.
> So I brought down all my interfaces and routing table ( except lo ) and
> attempted to add them manually.
A complete routing table would have been of more help here;
>
> I was able to add an interface manually, assigning my eth0 device the IP
> addr 192.168.1.2. ifconfig verifys that this if is good to go.
>
> However, I found that I was unable to give a simple "route" command, for
> example:
>
> route add 192.168.1.2
There is nothing wrong there as what would a route to "yourself" be of any
use to you.
>
> gives the response:
>
> SIOCADDRT: No such device
Yup thats normal with that command.
>
> the man page for route implies that you can specify the device in the route
> command also:
>
> route add 192.168.1.2 dev eth0
>
> Still no good. Various stabs at syntax based on the route man page also
> yield nothing
As above, you cant and dont need a route to you "own interface".
> I have also found that after issuing the ifconfig command, the routing
> table is automatically updated with an entry for a route to that network:
>
> Destination Gateway Genmask Flags Metric REf Use Iface
> 192.168.1.0 * 255.255.255.0 U 0 0 0 eth0
>
> Though this seems sloppy- note that Flags column lacks an "N" for Network.
No not sloppy at all, note your netmask 255.255.255.0
So ifconfig adds a route accordingly.
If you dislike the above use the netmask option with "ifconfig"
>
> This is undocumented behavior, as everywhere I have looked it has been
> implied that one has to bring up an interface and also independently
> establish the route to it. I would like to be able to add a route to the
> host itself, indicating that it is its own gateway ( I believe this is the
> root of my router problem- no pun intended . Can someone verify this?)
Not at all, a route is assigned according to the netmask used with ifconfig.
I think it would be better if you stated your router problem and supply
details of the routing table and output of ifconfig.
route -ne
ifconfig -a
+ of course a description of just what you want to do.
The problem which most folks have is that they need to define a default route
via an interface.
Simply upping an interface on a machine does not automaticly mean you have a
working routing table.
>
> Of course, Thanks in advance,
>
> Jim
>
--
Regards Richard
pa3gcu@zeelandnet.nl
http://people.zeelandnet.nl/pa3gcu/
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^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: ifconfig appears to also add entry to routing table
2002-09-01 19:20 ifconfig appears to also add entry to routing table Jim Earl
2002-09-01 19:41 ` pa3gcu
@ 2002-09-01 20:04 ` Ray Olszewski
2002-10-04 16:26 ` Make Linux bootdisk Abhijit Vijay
2 siblings, 0 replies; 7+ messages in thread
From: Ray Olszewski @ 2002-09-01 20:04 UTC (permalink / raw)
To: Jim Earl, Linux Newbie
Jim --
First, the basics: What Linux distro, what kernel version? Does it use ifup
and ifdown, or do its init scripts call ifconfig and route directly?
Second, when you say " ifconfig verifys that this if is good to go" ... are
you sufficiently expert to be sure of this? If not, please repost with the
actual output if "ifconfig -a" as it appears just before you run the
unsuccessful "route" command.
Third, in my experience, I've found "route" to be a bit picky in ways that
the man page doesn't warn about. In your case, I'd suggest you try this
form of the command
route add -host 192.168.1.2 dev eth0
and see if it does any better for you.
(Of course, I can't comment on the "various stabs" that you do not
describe... it may be that you already tried this, without success.)
Finally, you write:
Destination Gateway Genmask Flags Metric REf Use Iface
192.168.1.0 * 255.255.255.0 U 0 0 0 eth0
Though this seems sloppy- note that Flags column lacks an "N" for
Network.
If you look at the list of flags in the man page for "route", you will
notice that N is not a choice. There is an H for host and a G for gateway,
but routes are assumed to be networks by default, so not specially labeled.
So no, it is not "sloppy".
As to the "undocumented" addition of this route ... I'm so used to this
stuff happening in the background that I don't recall offhand what command
does what (ifup and ifdown, the commands used on most modern, full-size
Linux distros, does handle both, and their man pages do say so). So you
might be more specific about the details of what you did (for example, was
the routing table empty *before* you brought the interface up?).
As to the source of your router problem, I wouldn't hazard a guess. Your
guess seems implausible, though ... routers do not usually need to be told
that they are their own gateways; indeed, I find it hard to imagine a
circumstance under which this would even work ... but you offer so little
description of your setup, any comments here are wild guesses. IF you want
help at that level, please tell us
what you want this system to route between (2 Ethernets?
an Ethernet LAN and a dialup connection
to the Internet? something else?) what interfaces
does it have (probably eth* and/or ppp*)?
whether the hosts on the LAN(s) have "real" (routable) IP
addresses or you want the router to use IP Masquerading
to NAT them for connections to the Internet
what "ifconfig -a" shows when the router does not route
what "netstat -nr" shows when the router does not route
what "cat /proc/sys/net/ipv4/ip_forward" shows when the
router does not route
if this is a connection to the Internet, how the interface to the
ISP is supposed to get its IP address (static? DHCP?
PPPoE?) and what the ISP says you are supposed to use
as a gateway address.
if this is a connection to the Internet, can you ping the gateway
address above? If not, HOW does ping fail (yes, there are
many different errors it can report, and they are diagnostic).
what the routing failures are? For EXAMPLE, can the router itself
make Internet connections, but not hosts on the LAN it is
supposed to route?
There may be more we need to know, but that will make a good start.
At 01:20 PM 9/1/02 -0600, Jim Earl wrote:
>Hello all,
>
>I have been configuring a linux box to function as a router, ran into some
>problems, and think that I traced the problem to a faulty routing table. So
>I brought down all my interfaces and routing table ( except lo ) and
>attempted to add them manually.
>
>I was able to add an interface manually, assigning my eth0 device the IP
>addr 192.168.1.2. ifconfig verifys that this if is good to go.
>
>However, I found that I was unable to give a simple "route" command, for
>example:
>
>route add 192.168.1.2
>
>gives the response:
>
>SIOCADDRT: No such device
>
>the man page for route implies that you can specify the device in the route
>command also:
>
>route add 192.168.1.2 dev eth0
>
>Still no good. Various stabs at syntax based on the route man page also
>yield nothing
>
>
>I have also found that after issuing the ifconfig command, the routing table
>is automatically updated with an entry for a route to that network:
>
>Destination Gateway Genmask Flags Metric REf Use Iface
>192.168.1.0 * 255.255.255.0 U 0 0 0 eth0
>
>Though this seems sloppy- note that Flags column lacks an "N" for Network.
>
>This is undocumented behavior, as everywhere I have looked it has been
>implied that one has to bring up an interface and also independently
>establish the route to it. I would like to be able to add a route to the
>host itself, indicating that it is its own gateway ( I believe this is the
>root of my router problem- no pun intended . Can someone verify this?)
>
>Of course, Thanks in advance,
>
>Jim
--
-------------------------------------------"Never tell me the odds!"--------
Ray Olszewski -- Han Solo
Palo Alto, California, USA ray@comarre.com
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^ permalink raw reply [flat|nested] 7+ messages in thread