Module 06
Routing and forwarding
How a packet crosses networks one hop at a time. Read routing tables, apply longest prefix match by hand, and watch TTL count down across a path.
Start lesson 1
Which way does this packet go? · 8 min · free, no account
NetworkOpen now
What you'll operate
- Reading a routing table
- Longest prefix match
- Default routes and TTL
- lessons
- 6
- minutes
- 50
Lessons in this module
- 1Which way does this packet go?Read a routing table: the list a router checks to decide where each packet goes next.Free, no account8 min
- 2Which route wins when several match?Apply longest prefix match by hand to a table of overlapping routes, default route included.Plus8 min
- 3What does a router change in a packet?Follow one packet across three routers: a new frame and one less TTL at every hop, the same IP addresses throughout.Plus8 min
- 4How does traceroute find every router?Let a packet run out of TTL, read the ICMP Time Exceeded that comes back, and use it to map a path.Plus9 min
- 5Where do routes come from?Compare static routes with routes learned from a routing protocol, and see how a router chooses between sources.Plus8 min
- 6Where did my packet die?Watch a routing loop burn through TTL, fix it, and read what each Destination Unreachable code tells you.Plus9 min
Lesson 1 is open to everyone, with no account. The other lessons in this module are part of Plus.