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Mastering Development System & Network

Can’t access VPN server on remote LAN through client subnet

I’ve got a VPN server running on M1 which is behind a NAT N1. I’ve got a client M2 which is also behind a NAT N2 (scroll right): M2 (192.168.125.6) —–> N2 (70.23.34.56) ——–…———> N1 (80.23.34.45) —–> M1(192.168.178.2) | | VPN subnet (192.168.43.0/24) I’ve set the following rule for UFW: -A POSTROUTING -s 192.168.43.0/24 -o […]

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Mastering Development System & Network

Openstack instance lost internet access after ataching floating ip

Maybe someone has same problem I have installed Openstack Victoria on two virtualmachines (1 controller node, 1 compute node) running ubuntu 20.04. Each node has two network interfaces, mgmt network and provider network. I have created private network and I have attached it to router. With this configuration I am able to access internet. But, […]

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Mastering Development System & Network

Weird issue with ip routing on loopback interface

This question is based on my failed attempt to get the famous tool fragroute working in my environment. Problem description: I have a ubuntu OS 18.04 host with an (Intel) ethernet interface enp1s0f1 which is used for sending/receiving test traffic. I tried to develop an app that can modify the outgoing packets from this interface […]

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Mastering Development System & Network

Multiple subnets through VPN openvpn

I’m facing the following problem and after a huge amount of trial and errors i could use ask for some help. Situation: Scheme SiteA have LAN network: 192.168.101.0/24 while SiteB have LAN network 192.168.102.0/24. But on a Layer2 switch on SiteB there is an IP device with static ip 192.168.254.2/24. SiteA and SiteB are connected […]

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Mastering Development System & Network

SMTP networking failed on AWS

I have a home broadband network on which I also run an email server. As my provider won’t give me a fixed IP address due to my age 16 and I am preparing for certification for part time job. So on my gaming machine I created exchange 2016 server. I felt the simple solution I […]

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Apple User Help

macOS Big Sur Macbook does not respond to ping on neither ethernet or WiFi

I cannot ping my mac that is running macOS Big Sur 11.0.1 It seems to receive the ping packages but does not respond to them, and yes: Firewall is off I have tried turning stealth mode on and off I have even reinstalled/restored the OS from recovery mode They both have the same subnet mask […]

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Mastering Development System & Network

Client is sending ‘udp port 68 unreachable’ in response to DHCP ACK – why?

Please help me understand the following DHCP traffic. I’ve put my comments below each packet: 15:49:52.968450 d8:0b:9a:15:27:ec > ff:ff:ff:ff:ff:ff, ethertype IPv4 (0x0800), length 590: (tos 0x0, ttl 64, id 0, offset 0, flags [none], proto UDP (17), length 576) 0.0.0.0.68 > 255.255.255.255.67: [udp sum ok] BOOTP/DHCP, Request from d8:0b:9a:15:27:ec, length 548, xid 0x993a7913, secs 1, […]

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User Help

Mac computer receives ping but doesn’t respond

This is also posted on the Apple’s Support Forum. I found multiple similar questions but none of them helped me. I have a home network with 2 machines connected to the Wi-Fi router. Ping from A to B fails on timeout. tcpdump shows that machine B does see the incoming requests. Ping from B to […]

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Mastering Development System & Network

Identify Source / Trigger of / for Network Traffic locahost

I want to identify the application trat triggers network traffic like the one below. I have dissabled ethernet and wireless cards, and denied incoming traffic in firewall. $ sudo tcpdump -vv -e -i any 04:26:45.584729 in 00:00:00:00:00:00 (oui Ehernet) ethertype IPv6 (0x97dd), lenght 96: (flowlabel 0x745b5, hlim 64, next-header TCP (6) payload length: 20) ip6-localhost.58579 […]

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Linux Mastering Development

Inconsistent nslookup behaviour

When I run nslookup google.com 192.168.190.81 it works. tcpdump -n -vv output during above command is: 18:12:24.815483 IP (tos 0x0, ttl 64, id 8975, offset 0, flags [none], proto UDP (17), length 56) 192.168.190.85.50601 > 192.168.190.81.53: [bad udp cksum 0xfe2d -> 0xd17b!] 22170+ A? google.com. (28) 18:12:24.816513 IP (tos 0x0, ttl 128, id 42598, offset […]