Differences

This shows you the differences between two versions of the page.

--- doc:appunti:net:ipv6_on_ppp [2024/07/05 13:00] – niccolo
+++ doc:appunti:net:ipv6_on_ppp [2024/07/05 15:37] (current) – [Troubleshooting IPv6 problems] niccolo
@@ Line 579: / Line 579: @@
 ===== Troubleshooting IPv6 problems =====
-Show our own IPv6 addresses:
+In general, to troubleshoot any networking issue, you use the **ping** command to check if the remote address is responding:
 <code>
-ip -6 address show dev enp0s7
+# ping -6 2a01:4f8:1c17:7636::1
+</code>
+In some cases it is useful also to **ping your own addresses** (you can have more than one). Discover all of them with:
+<code>
+# ip -6 address show dev enp0s7
 </code>
@@ Line 595: / Line 601: @@
 </code>
-In the example above the interface have two scope global addresses, one assigned via DHCPv6 and the other obtained via SLAAC. The first one has the **dadfailed** flag, which means the **duplicate address detection**
+In the example above the interface have two **global** scope addresses, one assigned via DHCPv6 and the other obtained via SLAAC. The first one has the **dadfailed** flag, which means that the **duplicate address detection** has detected a conflict in the network. This means that the IP address in question will not be used as the source address and it does not even respond to a self-ping.
-FIXME
+If you have only one global IP address which is **dadfailed**, you cannot reach remote hosts on IPv6. It may be a difficult situation to diagnose, because using the simple **ifconfig** command you see the assigned IPv6 address and the **default route** is OK:
-Notice the **dadfailed**!!! Cannot even ping itself.
+<code>
+# ip -6 route show
+a02:2420:503:1c03::2 dev enp0s7 proto kernel metric 256 pref medium
+a02:2420:503:1c03::/64 dev enp0s7 proto kernel metric 256 expires 86387sec pref medium
+fe80::/64 dev enp0s7 proto kernel metric 256 pref medium
+default via fe80::d003:a6ff:fef2:6fe8 dev enp0s7 proto ra metric 1024 expires 167sec hoplimit 64 pref medium
+</code>
-Enabling the DHCPv6 address only (i.e. disabling SLAAC configuration on the client) the IPv6 routing doese not work; we get the //Beyond scope of source address// error message. Sniffing the traffic on the default gateway we can see:
+**NOTICE**: The default router can be reached via its **link** scope address (as seen above) or via its **global** scope address: both can be used.
+If you sniff the ping request on the router, you can see the problem more clearly:
 <code>
+# tcpdump -i eth0 -n 'icmp6'
+...
 IP6 fe80::225:22ff:fedd:4598 > 2a01:4f8:1c17:7636::1: ICMP6, echo request,
     id 56698, seq 1, length 64
@@ Line 610: / Line 626: @@
 </code>
-The default gateway on the client seems OK (check it with ''ip -6 route show''), but the source address is set to the **link scope** address instead of the **global** one. You can confirm it with the command ''%%ip -6 route get <ipv6_address>%%'':
+The client uses its link scope address as source address, which causes the **beyond scope** error. You can confirm this problem on the client using the ''ip route get'' command:
 <code>
-ip -6 route get 2a01:4f8:1c17:7636::1
+# ip -6 route get 2a01:4f8:1c17:7636::1
 a01:4f8:1c17:7636::1 from ::
     via 2a02:2420:503:1c03::1
@@ Line 621: / Line 638: @@
 </code>
-You can compare the result when the SLAAC is enabled:
+You can compare the result when you have at least one working global IP address:
 <code>
-ip -6 route get 2a01:4f8:1c17:7636::1
+# ip -6 route get 2a01:4f8:1c17:7636::1
 a01:4f8:1c17:7636::1 from ::
     via fe80::d003:a6ff:fef2:6fe8
@@ Line 632: / Line 649: @@
 </code>
-In the first case the **src** address is the **link scope** one, not suitable for routing. In the second case it is the one received via SLAAC, which has a **global scope** and indeed it is working. Notice that the address of the router (shown as the **via** address) is not releveant, the //link scope// one does work.
+In the first case the **src** address is the **link scope** one, not suitable for routing. In the second case it is the one received via SLAAC, which has a **global scope** and indeed it is working. Notice that the address of the router (shown as the **via** address) is not releveant, even the //link scope// one does work.