networking - Linux PCs sending "ICMP udp port unreachable
After expiration of that timeout the client unbinds from the socket, causing icmp destination unreachable to be sent in response to anything arriving to that socket, including a valid DNS response. If you are interested in details, you can create a batch file like. @echo off for /l %%x in (1, 1, 60) do ( echo %%x netstat -p udp timeout 1 ) networking - Is ICMP port unreachable error generated by ICMP Port unreachable is a code 3 within type 3 3.3. Port Unreachable - generated if the designated transport protocol (e.g., UDP) is unable to demultiplex the datagram in the transport layer of the final destination but has no protocol mechanism to inform the sender ICMP destination unreachable to DNS server? - General
From 192.168.1.15 icmp_seq=1 Destination Port Unreachable Clearly it's using the static route I assigned. The problem seems to be that the OpenWRT router doesn't know how to route packets to 192.168.2.4, which is strange because that IP is directly connected to that router.
The TCP/IP Guide - ICMPv6 Destination Unreachable Messages The destination port specified in the UDP or TCP header was invalid or does not exist on the destination host. Note that Code value 2 is not used. Also, Destination Unreachable messages are only sent when there is a fundamental problem with delivering a particular datagram; they are not sent when a datagram is dropped simply due to congestion ICMP Message Types | Network Layer/Internet Protocols ICMP Type 3 message Destination Unreachable alerts a source host of delivery problems encountered while trying to reach the destination. Note that a destination host sends only code types 2 and 3; a router can send all codes. Destination Unreachable uses several code values to further describe the function of the ICMP message being sent.
The ICMP - Destination host unreachable message is one which a user would usually get from the remote gateway when the destination host is unreachable. If, in the destination host, the IP module cannot deliver the packet because the indicated protocol module or process port is not active, the destination host may send an ICMP destination protocol / port unreachable message to the source host.
May 18, 2017 · A Destination Unreachable message (Type 1) is generated in response to a packet that can not be delivered to its destination address for reasons other than congestion. The reasons for the non-delivery of a packet is described by code field value. host unreachable: the originator passes a frame from router, to router, etc, until reaching the destination gateway that believes it has a path to the host. it arps for the data link layer address, and if it does not receive one, a host unreachable is passed back. the important thing here is that a host unreachable implies that the intervening destination unreachableはトラブルでパケットを採取するとよく見るICMPです。 コード0のnetwork unreachableは途中のルーターまでは届いておりルーティングテーブルにも載っていますが、例として宛先まで届ける事が出来ない時に使われます。 Jun 08, 2020 · The closest method to an ICMP Ping port report that is available is to send a UDP packet to a specific port. If that port is not active, the transmission will provoke an ICMP message from the host of type 3 (destination unreachable) subtype 3 (destination port unreachable). So, although it is possible to provoke an ICMP message about a port, it