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Asked: 2021-08-13 16:09:43 +0800 CST

Binding to random IP from IPv6 subnet (/64) doesn't work

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I got a scaleway.com server (DEV1-S) which offers me a /64 IPv6 subnet. I want to use an IP from this subnet to make a HTTP request (will use wget in the examples) but I can't get it to work. The request (with wget but also with other programs & programming languages) will hang.

The IPv6 adress is 2001:bc8:1830:1b18::1, the gateway is 2001:bc8:1830:1b18:: and the netmask is 64.

Running ip -6 addr, on the clean / just created server, will output the following:

root@test:~# ip -6 addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 state UNKNOWN qlen 1000
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: ens2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP qlen 1000
    inet6 2001:bc8:1830:1b18::1/64 scope global 
       valid_lft forever preferred_lft forever
    inet6 fe80::dc2e:4cff:fe57:a019/64 scope link 
       valid_lft forever preferred_lft forever

I read on forums and other questions/answers that in order for you to be able to bind to an address from a subnet, you need to run the following commands:

ip add add local 2001:bc8:1830:1b18::/64 dev lo
ip route add local 2001:bc8:1830:1b18::/64 dev ens2
sysctl -w net.ipv6.ip_nonlocal_bind=1

After these commands, the output of ip -6 addr is the following:

root@test:~# ip -6 addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 state UNKNOWN qlen 1000
    inet6 2001:bc8:1830:1b18::/64 scope global 
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: ens2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP qlen 1000
    inet6 2001:bc8:1830:1b18::1/64 scope global 
       valid_lft forever preferred_lft forever
    inet6 fe80::dc2e:4cff:fe57:a019/64 scope link 
       valid_lft forever preferred_lft forever

I can now ping6 e.g. 2001:bc8:1830:1b18::9 instead of only 2001:bc8:1830:1b18::1, but only from my own server. Not from other servers/networks.

Without the sysctl -w net.ipv6.ip_nonlocal_bind=1, wget would return this:

root@test:~# wget --bind-address=2001:bc8:1830:1b18::2 -v google.com
--2021-08-13 00:29:45--  http://google.com/
Resolving google.com (google.com)... 2a00:1450:400e:802::200e, 142.250.179.174
Connecting to google.com (google.com)|2a00:1450:400e:802::200e|:80... failed: Cannot assign requested address.
Connecting to google.com (google.com)|142.250.179.174|:80... failed: Address family not supported by protocol.

Now after the 3 commands, when I run wget with the --bind-address flag set to an address in the subnet other than 2001:bc8:1830:1b18::1, the request will hang forever:

root@test:~# wget --bind-address=2001:bc8:1830:1b18::1 google.com
--2021-08-12 23:55:48--  http://google.com/
Resolving google.com (google.com)... 2a00:1450:400e:802::200e, 142.250.179.174
Connecting to google.com (google.com)|2a00:1450:400e:802::200e|:80... connected.
HTTP request sent, awaiting response... 301 Moved Permanently
Location: http://www.google.com/ [following]
--2021-08-12 23:55:48--  http://www.google.com/
Resolving www.google.com (www.google.com)... 2a00:1450:400e:80f::2004, 142.251.36.4
Connecting to www.google.com (www.google.com)|2a00:1450:400e:80f::2004|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: unspecified [text/html]
Saving to: ‘index.html’

index.html                                                                       [ <=>                                                                                                                                                                                         ]  13.03K  --.-KB/s    in 0.009s  

2021-08-12 23:55:48 (1.44 MB/s) - ‘index.html’ saved [13342]

root@test:~# wget --bind-address=2001:bc8:1830:1b18::2 google.com
--2021-08-12 23:55:52--  http://google.com/
Resolving google.com (google.com)... 2a00:1450:400e:802::200e, 142.250.179.174
Connecting to google.com (google.com)|2a00:1450:400e:802::200e|:80...

lsof for the wget process says the following: wget 3413 root 3u IPv6 58660 0t0 TCP [2001:bc8:1830:1b18::2]:56623->ams15s41-in-x0e.1e100.net:http (SYN_SENT)

What am I doing wrong? Thanks a lot in advance!

subnet ipv6 scaleway

0 Answers