Proxies, Traffic & Routing

Proxy

A proxy is a middle service that sits between client and server, handling web requests and responses on your behalf.

Instead of talking to the server directly, you talk to the proxy, and it talks to the server. That middle position is useful for caching, filtering, hiding the client, or, for a tester, inspecting and modifying traffic.

Traffic has a direction

Traffic is the flow of data (packets) moving across a network.

• Ingress (inbound), data coming in. Example: a hacker probing your port 22 (SSH).
• Egress (outbound), data going out. Example: a file being uploaded off a machine.

Watching both directions matters: ingress shows who is knocking; egress can reveal data quietly leaving.

Routing

Routing is selecting the best path for packets to travel across a network. A router is the device that does it.

Inside one organisation, packets hop from router to router toward their destination. Between organisations, the scale jumps, and that is where a few big terms come in.

The internet-scale vocabulary

• Autonomous System (AS), a collection of connected IP networks and routers run by one entity (an ISP, a university, a cloud provider). Each has a number, e.g. AS15169 → Google, AS32934 → Meta.
• OSPF (Open Shortest Path First), finds best paths within a single AS (inside one network).
• BGP (Border Gateway Protocol), exchanges routes between Autonomous Systems (across the whole internet).

BGP is the glue of the internet, and when it goes wrong the effects are huge: the 2021 Facebook outage was essentially a BGP mistake that made Facebook's networks unreachable worldwide.

NAT

NAT (Network Address Translation) converts private IP addresses into public ones (and back).

Your home devices share one public IP. NAT lets many private addresses (like 192.168.1.x) reach the internet through that single public address, translating on the way out and back.

Takeaway

Proxies sit in the middle, traffic flows in (ingress) and out (egress), routing picks the path (OSPF inside, BGP between), and NAT bridges private and public address space. Together they describe how a packet actually gets anywhere.