Add/deleting an entry in the Routing table.

Posted on 2002-03-29
Last Modified: 2013-12-23

I want to add/delete a entry to/from unix routing table, using ioctl(..., SIOCADDRT, ...).

I am using SunOS 5.6.

Can anyone give me an working example of such program (URL is also okay), which will complie and run without any problem..

-- arupam

Question by:arupam
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LVL 16

Expert Comment

ID: 6927630
If you're looking for a somewhat generic solution, look into one of the publicly available routing daemons (routed, gated, etc) - the source for those should have many examples of the function calls you are looking for.  I can look up the URLs for you really want...



Author Comment

ID: 6927797
Hi Jon,

Thanks for Ur reply,

Actually, I wanted to cange the routing table thru the code. I had written a code, In some cases it is working fine. But some cases it is code is masking last few bytes of the destiation in the routing table.

For example, if I try with the destination address "x.y.z.0" and the gateway "a.b.c.d", I am getting the following entry in the routing table:

  Destination           Gateway           Flags  Ref   Use   Interface
-------------------- -------------------- ----- ----- ------ ---------
   x.y.0.0             a.b.c.d           UG       0      0  

But some cases, I am getting

  Destination           Gateway           Flags  Ref   Use   Interface
-------------------- -------------------- ----- ----- ------ ---------
   x.y.z.0             a.b.c.d           UG       0      0  

Where the only change is the destination IpAddress x.y.z.0. Is the code taking some default mask (may be depending on the IpAddress class?).

here is part of my code:
    struct rtentry *rt;
    struct sockaddr_in dest;
    struct sockaddr_in gway;

    rt = (struct rtentry*) malloc (sizeof (struct rtentry));
    memset (rt, 0, (sizeof (struct rtentry)));

    memset (&gway, 0, sizeof (struct sockaddr_in));
    gway.sin_family = AF_INET;
    gway.sin_addr.s_addr = inet_addr (My_gateway)

    dest.sin_family = AF_INET;
    dest.sin_addr.s_addr = inet_addr (My_dest);

    rt->rt_gateway = *((struct sockaddr *)&gway);
    rt->rt_dst = *((struct sockaddr *)&dest);
    rt->rt_flags = RTF_UP | RTF_GATEWAY ;
    rt->rt_use = 0;

    if (ioctl (skfd, SIOCADDRT, rt))
        perror ("SIOCADDRT Error!");
        close (skfd);
        exit (1);

If I try the same thing on the prompt, "route add -net x.y.z.0 -netmask a.b.c.d" It works fine..

What can be the problem and how can I solve this?

Also can we specify any netmasks in the code for SunOS 5.6 or 5.8? The structure rtentry does not have any netmask field.



Expert Comment

ID: 7246637
The problem is related to the netmask you didn't assign in your ioctl. If you set the entry by command line (route add....) you are setting also the netmask
Probably when you get x.y.0.0 you are trying to assing a class B destination network
In rt_flags you should use RTF_MASK
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LVL 16

Expert Comment

ID: 7248226
Do you own a copy of "Unix Network Programming" by Stevens?  Seems to be one of the more definitive works on the subject...

I would be happy to confirm alex's musings if I could find my own copy (currently buried).

I will see if I can dig it up.


Author Comment

ID: 7259076
Hi all,

Thanks for Ur replies. Now I am using routing sockets, and it works fine!

-- Arupam


Expert Comment

ID: 7259100
Ok, but in any case I think you should assign points to someone

Bye and enjoy your job ;-)
LVL 16

Expert Comment

ID: 7261204
I found my copy of the Stevens tome, if you still need specific examples.

In any case, I agree w/ alex.

LVL 16

Expert Comment

ID: 7266552
Stevens doesn't talk about much other than SIOCADDRT - are you using a different method, or simply a routing that everntually calls SIOCADDRT?

Please elaborate your solution.


Accepted Solution

arupam earned 0 total points
ID: 7295908
Hi Jon,

What I did is:
-- open a routing socket via socket call.
-- Make a structure which contains the rt_msghdr and the dest, getway and mask address.
-- Fill proper values in the structures.
-- Write it to the socket...

Very easy. :-)

I wanted to give some points to someone, but the comments were not close enough to any solution. RTF_MASK also did not help me much.. So I cannot accept them as solution... :-)

-- Arupam


Expert Comment

ID: 9157223
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