Automatic routing table changes

Automatic routing table changes

Post by Rober » Mon, 18 Jun 2001 23:20:13



Hi,

what may be the purpose of the automatic changes of routing table on
aix 4.3 (RS/6000 H80) ?

I do route delete x.x.x.x  y.y.y.y,
and two second after when I check netstat -rn, I got the same entry
which I've just deleted.

Robert

 
 
 

Automatic routing table changes

Post by Rodney Clar » Tue, 19 Jun 2001 17:04:01


Probably you have at least two routers in your network.
As a guess you have one as default router.
If the default router receives a pacaket that should be routed via the other
router.
It sends a icmp redirect to you .
This redirect results in a static host route being added so that you now
send all future packets directly to the right router.
You can switch this off but probably shouldn't you can expire them though
which is nicer.
Look at the no options to find the right one cannot remember it now.


Quote:> Hi,

> what may be the purpose of the automatic changes of routing table on
> aix 4.3 (RS/6000 H80) ?

> I do route delete x.x.x.x  y.y.y.y,
> and two second after when I check netstat -rn, I got the same entry
> which I've just deleted.

> Robert


 
 
 

Automatic routing table changes

Post by Ken Be » Wed, 20 Jun 2001 11:53:50




>what may be the purpose of the automatic changes of routing table on
>aix 4.3 (RS/6000 H80) ?

>I do route delete x.x.x.x  y.y.y.y,
>and two second after when I check netstat -rn, I got the same entry
>which I've just deleted.

If you see "W" under the "Flags" field, then you're looking at
cloned routes that are intended to support Path MTU Discovery.

You can turn off this behavior using the commands:

     /usr/sbin/no -o udp_pmtu_discover=0
     /usr/sbin/no -o tcp_pmtu_discover=0

You'll probably want to add them to a file like /etc/rc.net so that
they run after every reboot.

--

 
 
 

1. How Do Routing Table Entries Get Added to Routing Table at Bootup?

I have, what I think, is a simple question for the TCP/IP guys out there
who are familar with routing tables on AIX 4.1.5/4.2.1 in an IBM SP
environment. Or maybe not.

I have recently noticed that when I execute a 'netstat -r' on a
particular node in the SP environment, there are routing table entries
that I know I didn't put in there. I have to delete these "unwelcomed"
entries and re-add the correct ones. This is undesireable and maybe a
quick crash course in routing tables is justified. These unwelcomed
routing table entries seem to be automatically added right after I have
IPL'ed the node in question.

How did these routing table entries get added in the routing table? Does
anybody know the process?

Thank you in advance for your responses.

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