Please help me understand

redred · February 2007

This is my traceroute result.

Tracing route to google.com [72.14.207.99]
over a maximum of 30 hops:

1 21 ms 11 ms 28 ms 10.32.0.1
2 44 ms 13 ms 39 ms 172.20.32.129
3 22 ms 19 ms 9 ms 172.26.32.1
4 207 ms 192 ms 137 ms 172.20.8.81
5 23 ms 15 ms 12 ms 203.116.5.125
6 43 ms 14 ms 44 ms 203.118.3.233
7 52 ms 55 ms 51 ms 134.159.128.129
8 156 ms 70 ms 65 ms 202.40.161.10
9 55 ms 70 ms 74 ms 66.249.95.198
10 85 ms 105 ms 80 ms 72.14.232.166
11 97 ms 119 ms 133 ms 216.239.47.233
12 215 ms 196 ms 204 ms 209.85.248.131
13 195 ms 210 ms 214 ms 72.14.233.55
14 109 ms 126 ms 260 ms 72.14.233.118
15 249 ms 192 ms 193 ms 209.85.248.131
16 202 ms 192 ms 204 ms 72.14.233.55
17 252 ms 268 ms 267 ms 72.14.233.118
18 244 ms 261 ms 323 ms 72.14.207.99

Trace complete.

My WAN IP is 218.xx.xx.xx and I am behind a router with LAN address 192.168.x.x

1) How come traceroute is showing my 1st hop to be a private address 10.x.x.x? So is the 2nd to 4th results. Shouldnt it be a WAN address?

2)[client]192.168.0.10----192.168.0.1[myRouter]218.xx.xx.xx----10.32.0.1[ispRouter?]

This is what I am seeing according to traceroute. But to my understanding, the link between myrouter and isprouter must be on the same subnet right? And how does the my cable modem acquire the WAN ip address if it is going through a series of private switches?[/img]

sprkymrk · February 2007

I'm not sure why the first 4 hops would show private ip's, your first hop should be your router, then the cable modem. You might not see both interfaces of the routers you pass through, just the interface on your side, so that's why you might not see your own WAN ip. But if you can log into your modem via a web interface and see it's gateway address you should see that as part of your trace.

I have seen situations where the ISP uses private IP's on residential subnets to stop them from running their own public servers. You might get some more insight if you do an ipconfig /all on your computer, then log into your router and find all the same information there (ip address and gw) and again on your cable modem, which is typically where your public WAN address will really be. Compare all the results against the trace and let us know.

redred · February 2007

Hi sprkymrk,

I am using the motorola sbg1000, it is a router with cable modem built-in. I dont seem to see the interface for cable modem when I log into the router. However in the router interface, it reports:

LAN gateway is 192.168.0.1
WAN IP is 218.xxx.202.227
WAN Subnet Mask 255.255.252.0
WAN default gateway is 218.xxx.200.1

I was able to ping the the 1st hop address(10.32.0.1) and also found more hosts on that subnet by choosing a random address to ping, like 10.32.0.102, and got a reply.

Another thing, since I am directly connected to 10.32.0.1, shouldnt I have 10.32.0.x address too? How did the isp assign my modem an address that is 218.xxx.202.227? Are they actually doing something like forwarding BootP packets or using a DHCP relay agent to make this happen?

I am really confused here and hope someone could enlighten me.

redred · February 2007

Anyone knows? Should this ques be here or in the CCNA section

sprkymrk · February 2007

This looks funny to me. There's probably a logical explanation though. The ISP is most likely doing something strange to prevent residential users from running web servers or something from their homes. Possibly VLANs and NAT of some sort.

How about a call to your ISP and ask them? You could tell them you need to know how to RDP to your home computer from work or something.

redred · March 2007

Hmm I dont think my ISP will patronize me for such reason. Anyway though, could someone tell me how does my modem get a WAN IP if it is connected directly to my ISP switch which has a private address(10.x.x.x)?

Thank you.

netcom2000 · March 2007

If you are behind a router, you will see the private IP address as the first hop, anyway, which wil be your default gateway, as the ISP IP address alloted for you would be hidden, and your ISP will have other routers as well, on thier network, dont forget, each hop is a router interface that your packets will traverse as they pass throug routers, which operate at the network layer of the OSI.

netcom2000 · March 2007

You get your WAN IP address from your ISP's DHCP server, anyway try to log into your Router by using the following method, do an ipconfig/all at he command prompt, get your default gateway address which wil be the private address of 10.x.x.x, type http://10.x.x.x whatever the address is, into your browser, and you hould get to all the settings, for your router

redred · March 2007

Hi netcom,

Thanks for replying. But as I have said in my 1st post my LAN has an ip of 192.168.x.x and my default gateway is 192.168.0.1. I know how to log into my router's interface. And also, not all routers will show you their address as the 1st hop. Mine is one of those routers. The 10.x.x.x address is not from my LAN. It is probably from my ISP. But the problem is most people will see their wan ip by doing a traceroute, but I am seeing a private ip instead.

deneb829 · March 2007

I'd like to do a traceroute to you to see how those private IP addresses show up coming in, except you only gave your first octet of your IP address as 218.xx.xx.xx. If you feel that there is no harm, would you give your 1st 3 octets and your subnet mask? My hunch is on this end, we will lose it after hop 5 (on your list).

Traffic inside of an ISP's network can use private IP addresses if they configure their own routers to use them and to route the public IP addresses through them. Still, those address are inaccessible from the outside and are likely for shuttling traffic around between routers.

Hop 1 may actually be a point to point link between your cable modem (which may have its own built in firewall) and your router. I'll also bet that subnet is using a /24 which is all you.

I am guessing your ISP is Singapore based Starhub by the first routable IP address in your traceroute. If you are not using Starhub, then it looks like your ISP could be using Starhub for their backbone. The DNS records for that IP address point to cyberway.com.sg listed on Starhub DNS servers. If that is the case, then Cyberway may be getting it's routeable IP addresses from Starhub and moving them through their own network using private IP addresses. I am also guessing that Cyberway may be a smaller operation with maybe a few class C's, so they don't want to burn up their routable addresses using their own hardware if they don't have to ... of course, I could be completely wrong about all of this - lol!

Another interesting observation is that Hop #8 is a router in Hong Kong and Hop #9 drops you right on Google's network. That's 11 routers inside Google's network - meaning your packets spend more time (hop-wise) inside of Google's network than they do actually getting there from your location. Google has a TON of IP addresses, I guess they don't need to route with private IPs inside of their own network.

coldbug · March 2007

redred wrote:

Anyone knows? Should this ques be here or in the CCNA section

wow..u guys know this stuff much more than i do. I am not really good at reading outputs..i have basic knowledge on hop counts, traceroute, and IP addresses. I had like 2 questions on the net+ exam about interpreting the outputs, but i couldn't answer any of them since i was too lazy to study those..hehe
Well, i think the topic u gave belongs to CCNA board since it is more to do with routers, and Network+ covers only brief on these.
hmm..u remind me to go do some research on outputs, because i totally forgot about these.

by the way "anyone knows why no one ever invented OS platform that includes Automatic Subnetting Ability, yet?" Is it because Network administrators love to subnet, and they think it is fun? Do anyone feel that it is really a pain in the you know..? or is it just me finding it totally annoying..hehe

Mike

deneb829 · March 2007

Mikephyu wrote:

by the way "anyone knows why no one ever invented OS platform that includes Automatic Subnetting Ability, yet?" Is it because Network administrators love to subnet, and they think it is fun? Do anyone feel that it is really a pain in the you know..? or is it just me finding it totally annoying..hehe

Mike

Hey Mike, I know this is going to sound weird, but subnetting is easy once you understand it. I also don't mean that in any kind of boastful way.

Anyone who really understands subnetting can tell you that it was really hard to grasp at first. It's almost impossible to learn from a book and you need someone to show you it in binary and have the patience to stay there until you get it. But when you get it, you get it all at once. It's not something you learn a little bit at a time, you either completely understand how it works or you don't. Knowing that a 255.255.255.0 subnet can have 254 hosts, a network and broadcast address is not understanding subnetting. First thing is that you absolutely need to understand binary. If you can't subnet with the IP address and subnet mask in binary, it may never make any sense.

Here's what happened to me. In 2000, a coworker taught me subnetting in binary and he stuck with me until I got it. It took about 40 minutes and at times, it felt like my brain was going to explode. But he understood it and he knew that I was getting it.

When I got it, it was seriously a spiritual experience. The instant it clicked, the entire internet topology made sense. In my mind, I saw a packet leave the network out the router in the next room and make its way across the internet. I saw the routing tables and the subnets grow from /24's to /16's to /8's as the packet make its way on to the backbone (255.255.255.0 to 255.255.0.0 to 255.0.0.0) and shrink as the packet made its way back to the smaller networks until it found its destination. I reached a whole new level of geek that day and while I don't remember the exact date, I consider the moment I understood subnetting to be one of the most significant days of my career.

I wish I could sit everyone down who wanted to learn and explain subnetting in binary. Watching the light go on the moment a person gets it is a pretty cool experience. Stick with it Mike, you don't need automatic subnetting. Find someone who knows it, find a white board, and don't leave until you understand it. You'll be happy you did.

sprkymrk · March 2007

deneb829 wrote:

Mikephyu wrote:

by the way "anyone knows why no one ever invented OS platform that includes Automatic Subnetting Ability, yet?" Is it because Network administrators love to subnet, and they think it is fun? Do anyone feel that it is really a pain in the you know..? or is it just me finding it totally annoying..hehe

Mike

Stick with it Mike, you don't need automatic subnetting. Find someone who knows it, find a white board, and don't leave until you understand it. You'll be happy you did.

The other problem with "automatic subnetting" is that the computer has no idea what other hosts you want it to talk to or how big the network it resides on happens to be. If you assigned an ip address of 192.168.10.50 to a computer, and it automatically assigned 255.255.255.0 as a mask it would naturally think that it can talk to all 254 hosts by using arp (who has 192.168.10.159, tell 192.168.10.50) the destination is a broadcast to ff:ff:ff:ff:ff:ff. Now keep in mind, the router will ignore this broadcast. So if the admin were actually subnetting the class C address into multiple smaller networks using a mask of 255.255.255.224, then the packets would never make it to the destination because the recipient is on another network across the router. But by manually specifying the subnet mask the OS knows to use the default gateway. So it will send an arp broadcast asking for the mac address of the default gateway, thus enabling it to communicate with the host on another network.

Please help me understand

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