Traceroute IP-address mismatch

ip addressipv4traceroute

I'm doing some traceroute scans and just realized, that there is an IP-address mismatch. Closer, my public IP-address doesn't match with the next HOP IP-address of my ISP.

So, when I scan the public IP-address of my modem, tracert tells me, that the router with his public IP is one HOP away. Of course, because I'm inside the private network of this router. This as well means, that the "inside" IP-address of my router is 192.168.1.1 (for example) and my outside address is the public address of my router (81.81.81.81, for example).

But here is the question:

How does it come, that when I traceroute 8.8.8.8, the second hop IP-address, so after my gateway, is a private 10.0.0.0/8 address.

And what technology is used, that my outside IP is able to route to the private IP of the ISP?

Doesn't that mean, that my public address faces a private address?
Here is a tracert output:

  1    <1 ms    <1 ms    <1 ms  192.168.1.1
  2     3 ms     3 ms    11 ms  10.255.195.1

Best Answer

Your ISP could have network built based on RFC1918 IP addresses. Then somewhere on the way there is NAT applied to translate IP address.

Related Solutions

Routing – How to hosts with public IP addresses have nodes with private IP addresses in their traceroute

There is no tunneling. This is completely normal. With IP routing you are concerned about the source and destination address which doesn't change unless something is NAT'd. If a router in the middle has an RFC1918 address that's fine as it can still forward transit traffic as again the source and destination is unchanged.

Each router will simply reply to the source with their own directly connected interface address. The 10.14.0.1 above is not being routed over the internet, it's simply the device that is attached to the CPE on the WAN side.

There is no magic technology being used. It's pure standard routing.

6to4 IPv6 – Configuring Tunnel Address

The IPv6 address is the network address assigned to the interface of the tunnel. I don't know where you came up with the /128 because that is used for something like a loopback.

Specifies the IPv6 network assigned to the interface and enables IPv6 processing on the interface.

Something like this from the Cisco documentation:

Example: Configuring 6to4 Tunnels

The following example configures a 6to4 tunnel on a border router in an isolated IPv6 network. The IPv4 address is 192.168.99.1, which translates to the IPv6 prefix of 2002:c0a8:6301::/48. The IPv6 prefix is subnetted into 2002:c0a8:6301::/64 for the tunnel interface: 2002:c0a8:6301:1::/64 for the first IPv6 network, and 2002:c0a8:6301:2::/64 for the second IPv6 network. The static route ensures that any other traffic for the IPv6 prefix 2002::/16 is directed to tunnel interface 0 for automatic tunneling.

interface GigabitEthernet0/0/0
 description IPv4 uplink
 ip address 192.168.99.1 255.255.255.0
!
interface GigabitEthernet1/0/0
 description IPv6 local network 1
 ipv6 address 2002:c0a8:6301:1::1/64 
!
interface GigabitEthernet2/0/0
 description IPv6 local network 2
 ipv6 address 2002:c0a8:6301:2::1/64 
!
interface Tunnel0
 description IPv6 uplink
 no ip address
 ipv6 address 2002:c0a8:6301::1/64 
 tunnel source GigabitEthernet0/0/0
 tunnel mode ipv6ip 6to4
!
ipv6 route 2002::/16 tunnel 0

Best Answer

Related Solutions

Routing – How to hosts with public IP addresses have nodes with private IP addresses in their traceroute

6to4 IPv6 – Configuring Tunnel Address

Related Topic