Troubleshooting firewall and routing on Linux

Are there any tools or API hooks for troubleshooting iptables or routing on Linux? (besides the obvious -j LOG) In other words: what to do when tables with 200 or 300 firewalling rules after adding a new rule still doesn’t allow new traffic. Or when a router with over a dozen network interfaces replies to … Read more

How to choose source IP from multiple virtual IP’s based on specific destination

I am having two private IP attached to an interface. inet brd scope global eth1 inet brd scope global secondary eth1 When traffic leaves the eth1 interface it uses (primary) as the src IP. How can I change the src IP to use (secondary) based on specific destination. For … Read more

Debian – Dual WAN – Static Route on a DHCP Interface

I’ve got two WAN interfaces coming into a Debian 8 VM. WAN 1 – All Internet and local traffic. ( Has a a static IP, thus IP, netmask and gateway are fixed values. WAN 2 – Specific private subnet traffic only ( IP obtained via DHCP, can be anywhere in the range. I don’t … Read more

Linux route policy based on tos returning wrong gateway

I have a simulated ad-hoc network running on Docker, using Ubuntu 16.04 as a base. I have a number of routing tables. The table in question, table 102, appears as: root@b22e0eafe06d:~# ip route show table 102 via dev eth0 proto static via dev eth0 proto static via dev eth0 … Read more

How to understand this output of ip route list table 255 [closed]

Closed. This question needs details or clarity. It is not currently accepting answers. Want to improve this question? Add details and clarify the problem by editing this post. Closed 3 years ago. Improve this question broadcast dev rmnet_data1 proto kernel scope link src local dev rmnet_data1 proto kernel scope host src … Read more

Routing config between internet load balancers and backend

Im facing a problem due my lack of experiencie on routing. I need to config the next things (all run on my computer virtualized, if works, i will pass it to hardware) [internet] —- [DMZR]–/–[GATEWAY]—/—[LoadBalancer]—/—[BACKEND] internet: gateway: Loadbalancer: | Backend: Loadbalancer has 2 nic, on on the same net as gateway : … Read more

Can a machine(physical or virtual) accept and process UDP packets with a different IP address coming from a known device?

Before everything, thanks for reading the next question. I have script,(ipUDPspoof.rb), which is a client/server script in Ruby (you choose the parameter 1 to be server and 0 to be client, at initialization…for example “sudo ruby sandbox.rb 1” to initialize the server) that will create and send/receive RAW packets in UDP protocol, with different IP … Read more

How to DHCP request a second, different, IP for the same physical interface?

(Similar to this question, but with two different DHCP-assigned IPs) Is there any way to let dhclient or dhcpcd request two different IPs for one physical interface, e.g. via virtual interfaces eth0 and eth0:1? Maybe by letting eth0:1 have a different MAC? Or by creating a virtual eth1 bridged to eth0? Or can I use … Read more