![]() ![]() ![]() Luckily, Linux already features a mechanism that allows user-space code execution within the kernel: the eBPF VM. This checkpoint should pass a packet to an user-space program that will decide what to do with it: drop it or let it continue through the normal path. However this idea could be generalized by adding a checkpoint in the Linux kernel network stack, preferably as soon as a packet is received in the NIC. By dropping packets at the lowest point of the stack, the amount of traffic that reaches the kernel’s networking subsystem gets significantly reduced.Ĭloudflare’s solution used the Netmap toolkit to implement its partial kernel bypass (Source: Single Rx queue kernel bypass with Netmap). Some queues of the NIC are still attached to the kernel while others are attached to an user-space program that decides whether a packet should be dropped or not. Their solution consisted of implementing what they called a “partial kernel bypass”. Under those circumstances, a Linux box starts to be overflooded by IRQ interruptions until it becomes unusable.īecause Cloudflare wanted to keep the convenience of using iptables (and the rest of the kernel’s network stack), they couldn’t go with a solution that takes full control of the hardware, such as DPDK. In the event of a DDoS attack, the amount of spoofed traffic can be up to 3 Mpps. Cloudflare leverages heavily on iptables, which according to their own metrics is able to handle 1 Mpps on a decent server (Source: Why we use the Linux kernel’s TCP stack). The design of XDP has its roots in a DDoS attack mitigation solution presented by Cloudflare at Netdev 1.1. In this new blog post I try to go deeper into XDP. However, I didn’t get much into the details on how XDP works. On the XDP side, I focused only on the motivations behind this new technology, the reasons why rearchitecting the Linux kernel networking layer to enable faster packet processing. ip firewall nat add chain=srcnat src-address=10.10.10.1-10.10.10.254 action=netmap to-addresses=11.11.11.1-11.11.11.In the previous article I briefly introduced XDP ( eXpress Data Path) and eBPF, the multipurpose in-kernel virtual machine. If you want to link a WHOLE Public IP Subnet (say 11.11.11.0/24) to a Local Private IP Subnet (say to 10.10.10.0/24), you should use Destination address translation and Source address translation With the "action=netmap". ip firewall nat add chain=srcnat src-address=192.168.0.109 action=src-nat to-addresses=10.5.8.200 Example of 1:1 Subnet Mapping. by having its source IP Address translated to 10.5.8.200): ![]() ip firewall nat add chain=dstnat dst-address=10.5.8.200 action=dst-nat to-addresses=192.168.0.109Īdds a rule that allows the Internal Server to talk to the Outer Networks (ie. ip address add address=10.5.8.200/32 interface=PublicĪdd a rule that allows access to the Internal Server from the External Networks: Add a Public IP Address to your "Public" interface:.Please note - for that to work, you should also use Source Network Address translation (please ref. This is done to allow the Local IP Address to talk to the Public IP Address. ip firewall nat add chain=srcnat action=masquerade out-interface=PublicĪbove example shows you how to configure NAT on a Mikrotik router.ĭestination NAT is used to “ link” the Public IP Address (say 10.5.8.200) to the Local IP Address of your liking (say 192.168.0.109). To use masquerading, a source NAT rule with action 'masquerade' should be added to the firewall configuration: Used to “hide” the private source IP Address (i.e.:192.168.1.109), aka masquerading. ip firewall nat add chain=srcnat src-address= action=netmap to-addresses= Source NAT. ip firewall nat add chain=dstnat dst-address= action=netmap to-addresses= Example of 1:1 Public-to-Private IP mapping. ![]()
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