This time around, packets from one of my own DNS servers. If you would like to follow along, you can find the full unobfuscated packet trace here. (quick update... turns out that the router and DNS queries involved are part of www.nlnetlabs.nl, a network research labs that does experiment with DNS servers... so maybe this is all some side effect of an experiment they are running. Thanks to Don for pointing this out to me. After visiting their website, I did see a number of similar ICMP admin prohibited packets with flipped fragmentation bytes, but the embeded packet's source port was 80! . The link for this article located at SANS is no longer available. . Explore packet scrutiny, focusing on DNS evaluations and ICMP trials. Understanding these protocols uncovers networking challenges and helps optimize efficiencies.. Packet Analysis,DNS Issues,ICMP Operations,Network Security,Data Experimentation. . Benjamin D. Thomas
Today almost every organization employs firewalls for enhanced security. Firewalls can be set up in such a way that Internet Control Message Protocol (ICMP) requests are blocked, which means that traditional pings do not work. Setting a firewall to block ICMP requests is based on the theory that if a would-be hacker cannot "see" the target, he may not attack the host. . This makes system and network administration more difficult. A failed ping is no longer a valid test -- the user may have enabled a firewall that is blocking the ping, but the host may still be up. Before a network administrator can accurately determine if a host is down, the user needs to turn off all firewall applications -- or at least turn off any rules blocking ICMP -- which is probably asking too much of the average user. If traditional ICMP-based pings are no longer reliable unless you know in advance that there is no firewall blocking ICMP echo requests, what other options exist? One option is an Address Resolution Protocol (ARP) based ping using the arping utility. To know why ARP pings are virtually guaranteed to work while ICMP pings may not, one should understand the importance of ARP in networking. ARP is used by hosts on a network to resolve IP addresses into Media Access Control (MAC) addresses, which can be interpreted as a network interface's unique serial number. Hosts on an Ethernet network use MAC addresses rather than IP addresses to communicate. The link for this article located at Linux.com is no longer available. . Explore the role of firewalls in the realm of system and network administration, particularly in their ability to restrict ping operations and provide alternatives to ARP.. Firewall Configuration, Network Administration, ICMP Alternatives. . Brittany Day
The following article is part two of a two part series. "Alternately, you could create limit rules to accept only a certain number of requests every second. Or if you have monitoring software that requires your box to be "pingable," you could accept ICMP requests from only a certain IP or set of IP addresses." . . .. The following article is part two of a two part series. "Alternately, you could create limit rules to accept only a certain number of requests every second. Or if you have monitoring software that requires your box to be "pingable," you could accept ICMP requests from only a certain IP or set of IP addresses." The link for this article located at ZDNet AU is no longer available. . Delve into sophisticated firewall setups that incorporate connection quotas and ICMP policies to strengthen your Linux networking defenses.. Linux Firewall, Advanced Configurations, ICMP Security, Network Defense. . Anthony Pell
The Internet Control Message Protocol (ICMP) is simple, as Internet protocols go. Originally described in RFC 792 by Jon Postel, ICMP provides a way for IP stacks to send simple messages containing information or errors. ICMP is important for the Internet . . . . The Internet Control Message Protocol (ICMP) is simple, as Internet protocols go. Originally described in RFC 792 by Jon Postel, ICMP provides a way for IP stacks to send simple messages containing information or errors. ICMP is important for the Internet (and IP networks) to function correctly; however, ICMP can also have a negative effect on your network's security. For instance, ICMP has been used for scanning, Denial of Service (DoS) attacks, and tunneling (see "Distributed Denial of Service Attacks," March 2000, and "Firewall Vulnerabilities," August 1999,). A recent research paper by Israeli security consultant Ofir Arkin draws attention to some of the more arcane ways that ICMP can be employed in scanning networks (see Resources). At the end of his paper, Arkin suggests permitting only one of the 52 ICMP types and codes through a firewall, and that one only inbound. The link for this article located at Network Magazine is no longer available. . The Internet Control Message Protocol (ICMP) is simple, as Internet protocols go. Originally describ. internet, control, message, protocol, (icmp), simple, protocols, originally, describ. . Anthony Pell
Get the latest Linux and open source security news straight to your inbox.