szabgab has asked for the wisdom of the Perl Monks concerning the following question:

I have to write a script that running on a Solaris box and given a distant IP address will tell me the local IP that will be used for sending packages to that IP.

There might be several network cards on the machine. For version 2 of the tool I also need support cases when there can be several IP addresses on one card.

Is there any module that would help me achive this?
(I could not find any.)
If no such module then how should I approach the problem?

Replies are listed 'Best First'.
Re: routing information on Solaris
by puploki (Hermit) on Sep 05, 2005 at 12:42 UTC

    I'm not a Solaris person, but I assume there's a route print command available? This should list network destinations, the bound NIC IP address and the gateway for the relevant destinations.

    For example, under Windows, you get the following output:

    Active Routes:
Network Destination        Netmask          Gateway       Interface  M
+etric
          0.0.0.0          0.0.0.0     155.198.52.1   155.198.52.89   
+    20
        127.0.0.0        255.0.0.0        127.0.0.1       127.0.0.1   
+    1
     155.198.52.0    255.255.255.0    155.198.52.89   155.198.52.89   
+    20
    155.198.52.89  255.255.255.255        127.0.0.1       127.0.0.1   
+    20
  155.198.255.255  255.255.255.255    155.198.52.89   155.198.52.89   
+    20
        224.0.0.0        240.0.0.0    155.198.52.89   155.198.52.89   
+    20
  255.255.255.255  255.255.255.255    155.198.52.89   155.198.52.89   
+    1
  255.255.255.255  255.255.255.255    155.198.52.89           10004   
+    1
Default Gateway:      155.198.52.1

    [download]

    You can then do some matching based upon the destination IP address and the routes available to you.

[reply]
[d/l]
      I assume there's a route print command available

      No, that information is supplied by netstat:

      # netstat -nr

Routing Table: IPv4
  Destination           Gateway           Flags  Ref   Use   Interface
-------------------- -------------------- ----- ----- ------ ---------
172.17.0.0           172.17.0.101         U         1 562395  hme0
224.0.0.0            172.17.0.101         U         1      0  hme0
default              172.17.0.6           UG        1 113291
127.0.0.1            127.0.0.1            UH       20  13053  lo0

      [download]

      You will want to to see whether the target address is matched by any of the addresses (hosts or networks) in the first column. cpan::Net::CIDR features Net::CIDR::cidrlookup will help in this regard. If none of them match then the default address is used.

      Aliases on Solaris cards follow the standard convention. E.g. if the first interface is hme0, the first alias will be named hme0:1 and so forth. You can enumerate the interfaces on the machine by parsing the output of ifconfig -a. AFAIK there are no modules that offer this functionality... Now there's an itch to be scratched...

      update: it's been a while... I was a bit wrong with the netstat switches. You need netstat -nrv which looks like:

      # netstat -nrv

IRE Table:
  Destination             Mask           Gateway          Device Mxfrg
+  Rtt  Ref Flg  Out  In/Fwd
-------------------- --------------- -------------------- ------ -----
+ ----- --- --- ----- ------
10.0.1.0             255.255.255.0   172.17.0.21                  1500
+*    0   0 UG       0     0
172.17.0.0           255.255.224.0   172.17.0.1           hme0    1500
+*    0   3 U   201577     0
224.0.0.0            240.0.0.0       172.17.0.1           hme0    1500
+*    0   3 U        0     0
default              0.0.0.0         172.17.0.6                   1500
+*    0   0 UG  728283     0
127.0.0.1            255.255.255.255 127.0.0.1            lo0     8232
+*    0   0 UH     221     0

      [download]

      You need to look at the Destination and Mask columns to determine if you are looking at a host or a network

      - another intruder with the mooring in the heart of the Perl

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