How to configure a firewall for domains and trusts — Chris Wonson
The Internet Control Message Protocol (ICMP) is a supporting protocol in the Internet protocol The ICMP header starts after the IPv4 header and is identified by IP protocol number '1'. .. Reasons for this message may include: the physical connection to the host does not exist (distance is infinite); the indicated protocol or. Communication Networks/IP Protocol and ICMP 5 IPv4 and IPv6; 6 Internet Control Message Protocol (ICMP); 7 Classful Address File:IP danunah.info The Windows Redirector also uses ICMP to verify that a server IP is resolved by the DNS service before a connection is made, and when a.
The premise is that TCP or other reliable protocols can deal with this type of packet corruption, and that if we're using an unreliable protocol like UDP, we shouldn't care about small amounts of loss.
Conversely, problems with the network will be reported immediately.
For example, if the IP TTL is reaching zero, there's probably a routing loop somewhere and no packets are going to get through. The end system needs to know about these types of failures.
ICMP is a protocol for sending various messages to report network conditions—it is not ping. The echo request is one of many messages. Never let anyone tell you ICMP is evil and should be blocked.
ICMP itself is quite complex. Each type of ICMP message, called the "major type," also has "minor codes. Every ICMP message will also contain the entire IP header from the original message, so that the end system will know which packet actually failed.
We need to realize that a few situations exist where ICMP will not send errors. ICMP messages will never be sent in response to a broadcast or multicast addresses either, to prevent broadcast storms.
IP address spoofing
Error messages are typically generated by routers, and sent to the original source of the packet. Most of the errors are also forwarded to the application concerned with the packet that was sent. Echo Reply 0 and Echo Request 8: Destination Unreachable 3 Source Quench 4: An ICMP message used to notify the sender that the router or host is congested, and the sender needs to slow down. We'll talk about this in detail in future routing issues of Networking This message has two uses.
The ports scanned but not shown below are in state: Vscan is available from http: Many security-conscious organizations filter ICMP messages to and from their Internet-based hosts, so it is often difficult to assess which UDP services are accessible via simple port scanning.
SuperScan 4 also supports UDP port scanning. If these ICMP messages are filtered by a firewall as they try to travel out of the target network, the results will be inaccurate. During a comprehensive audit of Internet-based network space, you should send crafted UDP client packets to popular services and await a positive response. The scanudp utility developed by Fryxar http: Use of fragmented probe packets that are assembled when they reach the target host Use of spoofing to emulate multiple fake hosts launching network scanning probes, in which the real IP address of the scanning host is inserted to collect results Filtering mechanisms can be circumvented at times using malformed or fragmented packets.
However, the common techniques used to bypass packet filters at either the network or system kernel level are as follows: These techniques can often be mixed to launch attacks using source routed, fragmented packets to bypass both filters and IDS systems. Fragmenting Probe Packets Probe packets can be fragmented easily with fragroute to fragment all probe packets flowing from your host or network or with a port scanner that supports simple fragmentation, such as Nmap.
After undertaking ICMP probing exercises such as ping sweeping and hands-on use of the sing utility to ensure that ICMP messages are processed and responded to by the remote host, fragtest can perform three particularly useful tests: Send an ICMP echo request message in 8-byte fragments using the frag option Send an ICMP echo request message in 8-byte fragments, along with a byte overlapping fragment, favoring newer data in reassembly using the frag-new option Send an ICMP echo request message in 8-byte fragments, along with a byte overlapping fragment, favoring older data in reassembly using the frag-old option Here is an example that uses fragtest to assess responses to fragmented ICMP echo request messages with the frag, frag-new, and frag-old options: Fragroute The fragroute utility intercepts, modifies, and rewrites egress traffic destined for a specific host, according to a predefined rule set.
When built and installed, version 1.
networking - Why ICMP is different that TCP and UDP? - Super User
Using the default configuration file, fragroute can be run from the command line in the following manner: When running fragroute in its default configuration, TCP data is broken down into 1-byte segments and IP data into byte segments, along with IP chaffing and random reordering of the outbound packets.
The fragroute man page covers all the variables that can be set within the configuration file. The type of IP fragmentation and reordering used by fragtest when using the frag-new option can be applied to all outbound IP traffic destined for a specific host by defining the following variables in the fragroute.
This ensures that you see decent results when passing probes through fragroute and allows you to check for adverse reactions to fragmented traffic being processed. Applications and hardware appliances alike have been known to crash and hang from processing heavily fragmented and mangled data! The TCP header itself is split over several packets to make it more difficult for packet filters and IDS systems to detect the port scan. While most firewalls in high-security environments queue all the IP fragments before processing them, some networks disable this functionality because of the performance hit incurred.
Nmap allows for decoy hosts to be defined so that a target host can be scanned from a plethora of spoofed addresses thus obscuring your own IP address. Source Routing Source routing is a feature traditionally used for network troubleshooting purposes. Tools such as traceroute can be provided with details of gateways that the packet should be loosely or strictly routed through so that specific routing paths can be tested. Source routing allows you to specify which gateways and routes your packets should take, instead of allowing routers and gateways to query their own routing tables to determine the next hop.Scapy with IP and ICMP
IP datagram format The format of the IP option data within a source-routed packet is quite simple. The first three bytes are reserved for IP option code, length, and pointer.