Anyone else seeing RFC1918 addresses in external routes?

2. 172.16.25.106                                     0.0%    10    3.6   4.5   3.4  11.5   2.5
 3. 172.17.1.204                                      0.0%    10    1.6   1.8   1.5   3.0   0.6
 4. 172.16.18.226                                     0.0%    10    0.9   1.0   0.9   1.4   0.2
 5. ae2-775.cr1-man1.ip4.gtt.net                      0.0%    10    5.9  14.5   5.9  71.2  20.9
 6. et-0-0-0-0.cr10-lon1.ip4.gtt.net                  0.0%    10    7.3  19.1   6.4 122.6  36.4
 7. 72.14.221.145                                     0.0%    10    6.2   6.2   6.0   6.4   0.1
 8. ???
 9. 216.239.57.77                                     0.0%    10   10.2   7.6   7.2  10.2   0.9
10. google-public-dns-a.google.com                    0.0%    10    7.3   7.0   6.9   7.3   0.1

It's a way for budget ISPs to conserve IP address space within their network. It's not really an issue though, and shouldn't cause you any issues.

CGNAT

The router links don't need to be natted though, or publicly addressable, so wouldn't have thought this was anything to do with CGNAT

Nothing to do with CGNAT, the internal routers only need to be addressable to the hops before and after it so as long as those routers can talk with each other it doesn't matter that it's on private address ranges.

The only routers that really need public addresses are the internet peering routers and the one's acting as a gateway for the public subnets.

I heard about the CGNAT thing but these addresses from 172.16.0.0/12 are encountered beyond the dedicated public IP (for extra service fee) assigned to the router (hop 1 omitted).

So I was surprised to see Hyperoptic having to resort to private address space, and not public IPs nor from the shared address space as expected.

Was also seeking feedback whether this was considered normal practice or a symptom of newer ISPs struggling to obtain sizeable allocations of route-able IPv4s (other than by trading).

In reply to a post by prlzx:

Was also seeking feedback whether this was considered normal practice or a symptom of newer ISPs struggling to obtain sizeable allocations of route-able IPv4s (other than by trading).

Nah. This ISP has the same heritage as Be* and they ran with RFC 1918 addresses in their internal network too.

In any event the CG-NAT range is 100.64..0.0/10, not RFC 1918 space.

ISPs can use whatever they want in their network though as long as it's not being advertised to the outside world, to the point of using addresses allocated elsewhere if they wish, though that's not so smart, things can go wrong

From a non-CGNAT Hyperoptic connection.

3 172.16.28.44 (172.16.28.44) 2.641 ms 5.008 ms 2.775 ms
4 172.16.28.204 (172.16.28.204) 4.329 ms 5.023 ms 4.376 ms
5 172.16.24.34 (172.16.24.34) 10.423 ms 19.117 ms 10.693 ms
6 172.16.26.160 (172.16.26.160) 10.415 ms 10.190 ms 10.207 ms
7 172.16.17.81 (172.16.17.81) 9.074 ms 9.217 ms 9.066 ms
8 ae2-775.cr1-man1.ip4.gtt.net (77.67.123.169) 14.023 ms 14.105 ms 14.260 ms
9 89.149.137.150 (89.149.137.150) 14.131 ms 14.291 ms 15.550 ms
10 72.14.221.145 (72.14.221.145) 14.897 ms 15.243 ms 15.562 ms
11 108.170.246.129 (108.170.246.129) 14.231 ms
108.170.246.225 (108.170.246.225) 15.702 ms *
12 216.239.57.95 (216.239.57.95) 15.429 ms
72.14.237.179 (72.14.237.179) 14.091 ms
72.14.238.239 (72.14.238.239) 15.088 ms
13 google-public-dns-a.google.com (8.8.8.8) 15.061 ms 14.958 ms 14.963 ms

Hi there,

if you are experiencing any issues with your connection, please send us a PM. We'd love to assist if possible.

Best regards,

Jelena