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routing table - route got added automatically

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jasonK_1
Frequent Advisor

routing table - route got added automatically

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

 

 

7 REPLIES
donna hofmeister
Trusted Contributor

Re: routing table - route got added automatically

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.

jasonK_1
Frequent Advisor

Re: routing table - route got added automatically

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

Steven Schweda
Honored Contributor

Re: routing table - route got added automatically

 
jasonK_1
Frequent Advisor

Re: routing table - route got added automatically

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

Solution

Re: routing table - route got added automatically

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

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.

jasonK_1
Frequent Advisor

Re: routing table - route got added automatically

Thanks for your info.  It helps alot.