topic Re: routing table - route got added automatically in Operating System - HP-UX

routing table - route got added automatically

jasonK_1 — Fri, 29 Jun 2012 19:26:50 GMT

Hi,

How can I stop my routing table from automatically added new route to a host. Some how a route for this certain host got changed to a different one.

OS: 11.31

Re: routing table - route got added automatically

donna hofmeister — Fri, 29 Jun 2012 19:34:03 GMT

changed or added? (i'll vote for added)

and i'll continue to speculate that everything got screwed up because the system tried using the new route, yes?

what to do? go find whatever it is that's spewing out ICMP (hi, i'm a router) message and pull the plug :-) seriously...this is a problem that needs to be dealt with at a different level. your network guys need to get involved as well as the owner of the misbehaving system.

Re: routing table - route got added automatically

jasonK_1 — Fri, 29 Jun 2012 21:31:40 GMT

I don't have access to the network! I just want to stop my routing table from adding any new route without my knowledge

Thanks

Re: routing table - route got added automatically

Steven Schweda — Sat, 30 Jun 2012 12:12:05 GMT

Re: routing table - route got added automatically

jasonK_1 — Tue, 24 Jul 2012 23:47:01 GMT

Below is the routing table, for destination 172.16.5.2, it looks weird

root@hp:/# netstat -rn
Routing tables
Destination           Gateway            Flags Refs Interface Pmtu
127.0.0.1             127.0.0.1          UH    0    lo0       32808
192.1.4.247           192.1.4.247        UH    0    lan0      32808
172.16.5.2            192.1.4.240        UGH   0    lan0          0
172.16.5.2            192.1.4.5          UGH   0    lan0       1500
10.1.2.110            192.1.4.10         UGH   0    lan0          0
10.1.2.128            192.1.4.10         UGH   0    lan0          0
192.1.4.0             192.1.4.247        U     2    lan0       1500
127.0.0.0             127.0.0.1          U     0    lo0       32808
default               192.1.4.5          UG    0    lan0       1500

Re: routing table - route got added automatically

Akio Kabutogi — Wed, 25 Jul 2012 04:50:15 GMT

Setting the following ndd parameter may help:

# ndd -h ip_ire_redirect_interval

ip_ire_redirect_interval:

    All routing table entries resulting from ICMP "Redirect"
    messages are deleted after this much time has elapsed,
    whether or not the entry has been recently used. Setting
    ip_ire_redirect_interval to 0 causes
    - all existing routing table entries specifying
      a redirect to be deleted after the previous value of
      ip_ire_redirect_interval has elapsed and
    - no further routing entries are created for the future
      ICMP REDIRECT messages.
    Processing of ICMP REDIRECT messages can be enabled again
    by setting ip_ire_redirect_interval to a non-zero, positive
    value.
    [0, -] Default: 300000 (5 minutes)

Basically, such entries will be created when the system receives ICMP redirect message from the default gateway. If the default gateway detects better path to the remote address, it will send ICMP redirect message to tell the system to use alternative GW. In this case, the default gateway thought

an alternative GW at 192.1.4.240 would be better and sent ICMP redirect message back to the HP-UX

box. If such an ICMP redirect message is received, such a route is created automatically and the alternative gateway is used.

Therefore, if you set the ndd parameter above to zero, you may see some network problem when you attempt to access a remote host over the default gateway. This is because the fact that you saw such a route created indicates that the default gateway has some difficulty to transfer the packet to the remote system and suggests us to use alternative path.

Thus, if you set the parameter to zero, you need to be well-aware of such risk. If you want to minimize the lifespan of such *tentative* route created by ICMP redirect message from the default GW, you can set the parameter value to smaller number than default.

Hope this helps.

Re: routing table - route got added automatically

Akio Kabutogi — Wed, 25 Jul 2012 04:52:49 GMT

Another thing I forgot to mention...

You'll probably see some significant number in the following counter in "netstat -s -p icmp":

# netstat -s -p icmp
icmp:
        162832 calls to generate an ICMP error message
        13130 ICMP messages dropped
        Output histogram

: : :

        Input histogram:
         echo reply: 150675
         destination unreachable: 546
         source quench: 147
         routing redirect: 1630    <----- Here

if you see such routes added from time to time.

Re: routing table - route got added automatically

jasonK_1 — Wed, 25 Jul 2012 18:24:25 GMT

Thanks for your info. It helps alot.