Re: Request for TEXT: [LARTC] "onlink" option for ip route

[bert hubert <ahu@ds9a.nl>]

On Sun, Mar 25, 2001 at 12:43:07AM -0300, Rogerio Brito wrote:
> On Mar 24 2001, bert hubert wrote:
> > If someone manages to write a reasonable explanation for the
> > 'onlink' option, I'll put it in the HOWTO ASAP.
> 
> 	As far as I understand it, the situation is as follows:
> 
> - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
> 	Sometimes, you may want to send packets via a machine
> 	(i.e., a gateway) which is physically connected to your
> 	network, but to which you don't specifically have a route in
> 	your kernel routing table.

I'm more confused then ever!

Alexey says this: 
 A: Yes, in 2.2 the rule that {\em normal} gateway must reside on directly
 connected network has not any exceptions. You may tell kernel, that
 this particular route is {\em abnormal}:
 \begin{verbatim} 
   ifconfig tunl0 10.0.0.1 netmask 255.255.255.255
   ip route add 10.0.0.0/8 via 193.233.7.65 dev tunl0 onlink
 \end{verbatim}
 Note keyword \verb|onlink|, it is the magic key that orders kernel
 not to check for consistency of gateway address.
 Probably, after this explanation you have already guessed another method
 to cheat kernel:
 \begin{verbatim} 
   ifconfig tunl0 10.0.0.1 netmask 255.255.255.255
   route add -host 193.233.7.65 dev tunl0
   route add -net 10.0.0.0 netmask 255.0.0.0 gw 193.233.7.65
   route del -host 193.233.7.65 dev tunl0
 \end{verbatim}
 Well, if you like such tricks, nobody may prohibit you to use them.
 Only do not forget
 that between \verb|route add| and \verb|route del| host 193.233.7.65 is
 unreachable.

However, our HOWTO says this:

 ip tunnel add netb mode gre remote 172.19.20.21 local 172.16.17.18 ttl 255
 ip link set netb up
 ip addr add 10.0.1.1 dev netb
 ip route add 10.0.2.0/24 dev netb

We don't use onlink - might it be that 'onlink' is only useful for ipip
tunnels?

> 	Please let me know if this is acceptable. I could write with
> 	more details (giving a more concrete example), but I'm very
> 	busy right now. :-(

Once this is cleared up, your text will do fine. Thanks!

Regards,

bert

-- 
http://www.PowerDNS.com      Versatile DNS Services  
Trilab                       The Technology People   
'SYN! .. SYN|ACK! .. ACK!' - the mating call of the internet

_______________________________________________
LARTC mailing list / LARTC@mailman.ds9a.nl
http://mailman.ds9a.nl/mailman/listinfo/lartc HOWTO: http://ds9a.nl/2.4Routing/