2

I just got this router, fresh out of the box. I turn it on and set it up and I get these weird IPs:

Pinging 192.168.1.1 with 32 bytes of data:
Reply from 74.x.x.254: TTL expired in transit.
Reply from 74.x.x.254: TTL expired in transit.
Reply from 74.x.x.106: TTL expired in transit.
Reply from 74.x.x.254: TTL expired in transit.

Ping statistics for 192.168.1.1:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),

Never seen this before. Is this a Cisco thing?

  • What happens if you traceroute to the same IP? – Keller G Nov 21 '13 at 3:50
6

My best guess here without more information is that you hooked up a WAN port to your existing network. The new router got an IP from DHCP, along with a default gateway. When you try to ping 192.168.1.1, the packet is routed to your default gateway.

For whatever reason, your network routes the packet out to the Internet, where it loops around in no-man's land until the 30-hop TTL expires. A traceroute to the same IP should tell us more about what's going on in case my guess is incorrect. =)

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  • Yep, that sounds about right. I was wondering why it jumped out to the internet then came back. – Jason Nov 21 '13 at 4:04
4

This is a simple case of private addressing leaking into a public network. Trust me, this isn't reaching the internet; it may reach the edge of your provider's network, but that it.

It's common practice to block/filter/null route RFC1918 space at the edge of your network. ISPs should filter this crap on customer ingress links. (but best practices just aren't followed.)

In Cisco-speak:

ip route 10.0.0.0 255.0.0.0 Null0 254 permanent
ip route 172.16.0.0 255.240.0.0 Null0 254 permanent
ip route 192.168.0.0 255.255.0.0 Null0 254 permanent

On linux (iproute2):

# blackhole RFC1918 private address space
ip route add prohibit 10.0.0.0/255.0.0.0
ip route add prohibit 172.16.0.0/255.240.0.0
ip route add prohibit 192.168.0.0/255.255.0.0

(you might want to include RFC3927 [169.254/16], too)

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