From: Karelis, Pete (2507) (Pete.Karelis@xxxxxxxxxx)
Date: Mon Aug 06 2001 - 10:58:46 GMT-3
Just becase the IP address is RFC-1918 doesn't mean you can't transmit a
packet FROM that IP.
What happens is that as the traceroute packet travels through the network,
one of the privately numbered interfaces replies with the "TTL expired in
transit" icmp messages (that traceroute uses to discover the path the packet
is taking).
Since routers route data based on their routing tables using the DESTINATION
IP address of the packet, and since the ICMP TTL expired in transit message
is destined to an internet routable IP address, the packet is transmitted to
you (Source IP: 172.20.6.11 Dest. IP: access.net.id).
Now, if the destination IP address of the packet were an RFC 1918 address,
then that would be dropped since it won't exist in the Internet routing
tables.
Hope that helps,
-Pete Karelis
-----Original Message-----
From: Leonard @ iname.com [mailto:Leonard_Ong@iname.com]
Sent: Monday, August 06, 2001 9:20 AM
To: ccielab@groupstudy.com
Subject: Routing
Hello Guys,
I found some traceroute that really bothers me and I don't know the
answer. Would you kindly explain it to me ?
traceroute from access.net.id to 202.156.227.140
1 202.180.0.4 (202.180.0.4) 2.502 ms 2.017 ms 1.641 ms
2 202.155.7.25 (202.155.7.25) 91.019 ms 28.084 ms 30.019 ms
3 202.155.7.85 (202.155.7.85) 55.545 ms 59.557 ms 23.195 ms
4 202.155.7.246 (202.155.7.246) 62.904 ms 25.812 ms 68.068 ms
5 500.POS1-2.IG2.SAC1.ALTER.NET (157.130.193.221) 210.419 ms 210.405
ms 305.777 ms
6 0.so-0-0-0.XR2.SAC1.ALTER.NET (152.63.54.118) 240.747 ms 208.259
ms 216.579 ms
7 0.so-0-0-0.TR2.SAC1.ALTER.NET (152.63.3.197) 247.044 ms 217.252
ms 253.461 ms
8 127.ATM5-0.IR2.SAC1.ALTER.NET (152.63.11.113) 209.069 ms 226.315
ms 208.555 ms
9 POS3-0.IR2.SAC2.ALTER.NET (137.39.31.209) 204.193 ms 209.688
ms 265.266 ms
10 210.80.49.230 (210.80.49.230) 441.732 ms
335.ATM5-0-0.TR2.SIN1.ALTER.NET (210.80.51.142) 514.855 ms
435.ATM5-0-0.TR2.SIN1.ALTER.NET (210.80.51.134) 526.292 ms
11 POS1-0-0.XR2.SIN1.Alter.Net (210.80.48.62) 456.046 ms 473.853
ms 472.113 ms
12 312.ATM3-0-0.GW2.SIN1.Alter.Net (210.80.2.202) 451.268 ms 458.89
ms 434.287 ms
13 scv-gw-33.customer.alter.net (202.95.97.14) 544.822 ms 450.079
ms 460.404 ms
14 172.20.6.11 (172.20.6.11) 466.566 ms 516.396 ms 464.313 ms
15 172.20.2.15 (172.20.2.15) 458.438 ms 464.12 ms 446.679 ms
16 172.20.15.2 (172.20.15.2) 465.278 ms 476.811 ms 570.675 ms
17 mcns140.docsis227.singa.pore.net (202.156.227.140) 493.695 ms 494.196
ms 525.214 ms
If you check the entry 14-16 it is private address which is supposedly not
routeable... and it goes at entry 17 to end-host of this ISP/cable... which
is routeable address... Any idea ?
Thanks
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