The error IS in the XS code. I added a printf() line to ARP.xs: 
char *
arp_lookup(dev, ip, mac)
        unsigned char *dev;   
        unsigned char *ip;
        unsigned char *mac;
        CODE:
          char tmp[20];
          printf("TMP(%d) IS %s\n", strlen(tmp), tmp);
          if(SOCK_TYPE == SOCK_RAW)
          {
            arp_lookup_bsd(dev,ip,tmp);
          }
          else
          {
            arp_lookup_linux(dev,ip,tmp);
          }

          mac = tmp;

        OUTPUT:  
        mac

[download]
Then I ran this: 
#!/usr/bin/perl

use Net::ARP;

my $mac = "";
Net::ARP::arp_lookup(eth1 => '172.18.0.1', $mac);
print "mac=$mac\n";
Net::ARP::arp_lookup(eth1 => '172.18.0.1', $mac);
print "mac=$mac\n";

[download]
I get this as output: 
TMP(0) IS 
mac=
TMP(8) IS pï¿ï¿½ï¿½
mac=00:0E:D7:80:37:20

[download]
The simple fix is change char tmp[20]; to char tmp[20] = "unknown";. I will be sending a bug report to the author.
Jeff japhy Pinyan, P.L., P.M., P.O.D, X.S.: Perl, regex, and perl hacker
How can we ever be the sold short or the cheated, we who for every service have long ago been overpaid? ~~ Meister Eckhart

In reply to Re: Of Net::Arp and Hashes by japhy
in thread Of Net::Arp and Hashes by cmilfo

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