Commit e5cb65b5 authored by JackV's avatar JackV
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Add debug section

parent f9b5b5df
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......@@ -40,6 +40,71 @@ all these topics can come together
---
## You can't connect to the Internet, now what?
When setting up a network it might happen that everything
breaks, we will go through some tools that might help debug
network configuration problems
---
### Network checklist
* Does the network have working routing?
* Does the network resolve domain names?
* Are response packets coming back?
* Are there problems in upper layers?
---
### Quick routing check: ping & traceroute
* **ping** is useful to check that we have working routing
a quick `ping 1.1.1.1` can tell us if we can reach a known
ip (in this case cloudflare DNS)
* **traceroute** can help with identifying routing
nodes that are dropping packets
---
### DNS check: ping (again) & dig
* Again **ping** can be used to quickly check if DNS resolution
is working as intended, `ping poul.org` will return an ip
address is DNS is working
* **dig** can help to check more complex problems,
using `dig poul.org` will tell us if the system DNS
(found in `/etc/resolv.conf`) is working, whereas
`dig @1.1.1.1 poul.org` will tell us if there is some
external problem related to DNS
---
### Checking for responses
* Tools like **tcpdump** and **Wireshark** can help debug
problems related to responses not coming back, just point to
the right interface and filter for the traffic (usually __icmp__)
* Only have ssh but want to have a gui? No problem!<br>
```
ssh root@<ip> 'tcpdump -i eth0 -s0 -w -' | wireshark -k -i -
```
---
### Upper Layer Problems
So far we only talked about L1-3 problems, but there can be just as many
in L4-7, however these usually require specific tools to debug
* **curl** can be used to detect a [TCP Blackhole](https://en.wikipedia.org/wiki/Path_MTU_Discovery#Problems) and a whole other lot of problems
```
curl -vv https://example.org
```
----
# Wireguard
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