Linux routing state determines which next hop, interface, and source are eligible for an IP destination. The legacy route -n view is still encountered, but ip route exposes modern kernel routing concepts more directly.
Routing · Lesson 2
Routing Table
Learn how to read Linux routes and inspect the route selected for a destination.
Reading IPv4 Routes
Example output can look like:
$ ip -4 route show
default via 192.168.224.2 dev eth0 proto dhcp src 192.168.224.10 metric 100
192.168.224.0/24 dev eth0 proto kernel scope link src 192.168.224.10 metric 100
The connected /24 route sends matching destinations directly through eth0. The default uses next-hop gateway 192.168.224.2. proto describes how the route was installed, src is a preferred source for matching traffic, and a metric helps rank otherwise comparable routes.
What does via 192.168.224.2 indicate?
Connected and Default Routes
A route with scope link and no via next hop treats the prefix as directly reachable on the interface. A default route matches every address but loses to any eligible more-specific route.
How is a connected scope link destination normally reached?
Prefix Length and Metric
Route selection considers policy rules and chooses the longest eligible prefix. Metrics rank routes within appropriate comparable sets; a low-metric default does not override a matching /24 merely because its number is lower.
Which route normally matches 192.168.224.50 more specifically?
Policy Rules and Multiple Tables
Linux can consult several routing tables according to ip rule policy based on source, mark, interface, or other selectors. Viewing only the main table can therefore miss the actual path:
$ ip rule show
$ ip route show table all
Network namespaces and VRFs can hold separate state as well. Run inspection in the same context as the affected process.
Why might ip route show alone not explain an application's path?
Querying an Effective Route
Ask the kernel to evaluate a destination and optional source:
$ ip route get 203.0.113.10
$ ip route get 203.0.113.10 from 192.168.224.10
The result predicts the local lookup at that moment. It does not send a probe or prove neighbor, downstream, firewall, or application reachability.
What does ip route get not do?
Lesson complete
You finished Routing Table
You can now read Linux routing entries and query the effective local decision.
Distinguish connected routes from routes through a gateway.
Read prefix, interface, protocol, source, and metric fields.
Apply longest-prefix matching before comparing relevant metrics.
Account for policy tables, namespaces, and VRFs.
Treat
ip route getas a lookup, not a reachability test.
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