Re: nmap won't work with policy route

[David Fifield <david () bamsoftware com>]

On Fri, Mar 01, 2013 at 09:19:33AM +0800, Taburiss S wrote:
>     I'm trying to write a shell script to test every network interface in
> one server. I have some policy routing rules like below:
>
> #ip rule
> 0: from all lookup local
> 1:     from <IP of ppp0> look up ppp0_RT   // <-- （ppp0_RT = default via
> <gateway of ppp0>）
> 2:   from <IP of ppp1> look up ppp1_RT   // <-- （ppp1_RT = default via
> <gateway of ppp1>）
> 32766: from all lookup main
> 32767: from all lookup default
>
> And the main routing table is shown below
> Kernel IP routing table
> Destination     Gateway         Genmask         Flags Metric Ref    Use
> Iface
> 172.16.126.229  *               255.255.255.255 UH    0      0        0 ppp1
> 172.16.126.240  *               255.255.255.255 UH    0      0        0 ppp0
> default               *               0.0.0.0                U     0      0
>        0 ppp0
>
> Since I want to test every ppp interface, I need to use nmap -e to specify
> an output interface like this:
> # nmap -e ppp0 -sP 8.8.8.8
> This worked well, but
> # nmap -e ppp1 -sP 8.8.8.8
> end up with an error:
> nexthost: failed to determine route to 8.8.8.8
>
> I find that if ppp1 is not 'default' in main routing table, even I have a
> ip rule whose priority is higher than the main table, I can't use nmap -e
> to force my ping packet goes out through this ppp1 interface. The only way
> is to set it to the default dev in main table, but if I do that the same
> problem will happen to ppp0 which can not be 'default' anymore.
>
> In my opinion nmap should find the IP address of the interface that given
> by -e , and bind a raw socket to this IP, than send ICMP packet to 8.8.8.8.
> At this point my ip rules should work well, and the 'default' in main table
> should do nothing with this packet. Actually, I wrote a small program like
> that , and it do work well.

What version of Nmap are you using?

Newer releases of Nmap use the Netlink interface to ask the kernel for
all routing decisions, so I would expect it to work.

You can get quick feedback on Nmap's routing decisions with the
--route-dst option:

nmap -e ppp0 --route-dst 8.8.8.8
nmap -e ppp1 --route-dst 8.8.8.8

David Fifield
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