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A little known feature of the ICMP protocol is that it allows remote discovery of subnet masks. This is one of the many reasons why when firewalling data centers and corporate networks, you may allow ICMP echo/reply, but you probably want to restrict some other types of ICMP packet. Redirects and other ICMPs are potentially nastier in that they may allow an attack rather than just probing, but probing is one of the things firewalls are suppose to stop. However I now find I need a handy tool for discovering the subnet masks of interfaces of remote systems. Theory is fine but is there a small, lightweight, easy to configure, Linux tool to check the subnet mask of a specific host? Is it likely to be an option of some of the tools I already have? There are some heavyweight topology discovering programs, and plenty of tools for probing firewalls, but I just want to check out the machines listed in a specific traceroute or two, and all the machines listed under a specific RRset (multiple IP addresses for the same name). -- Are you using the Internet to best effect ? www.eighth-layer.com Tel: +44(0)1395 232769 ICQ: 116952768 Moderated discussion of teleworking at news:uk.business.telework -- The Mailing List for the Devon & Cornwall LUG Mail majordomo@xxxxxxxxxxxx with "unsubscribe list" in the message body to unsubscribe.