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Route is based on IP, right? How does it possible to route my packets so differently? One is success, but another is not. 

# traceroute A.com
traceroute to A.com (1.2.3.4), 30 hops max, 60 byte packets
1 ...
2 ...
3 ..
4 A.com


# traceroute zzz.A.com
traceroute to zzz.A.com (1.2.3.4), 30 hops max, 60 byte packets
1 ...
2 ...
3 ..
4 ..
5 ...
6 ..
7 ..
..
..
30 ***
Cheng
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3 Answers3

2

This could be a variety of things.

BGP routes are, in the loosest sense of the term - Random. Meaning they are contingent based on which BGP routes are currently in use and how reaching the endpoint AS is achieved for the least cost to your Top-level provider. Another potential issue is that you have a DNS record like DNAME or NAPTR which have caused similar problems for myself in the past. If the issue is persistent, consider the idea that your provider is doing some bizarre traffic shaping based on HTTP requests (admittedly unlikely). It would be helpful however to print the relevant traceroute information.

zetavolt
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2

I agree with Zephyr but I must add that it is possible for a provider to do IP route load balancing.

Let's say you're a random Internet provider and you have 4 equivalent links to the same point. You can chose to load balance the traffic in between those links. This means that the hops will not be the same.

Antoine Benkemoun
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It is extremely difficult to say anything sensible about this question, without actually having the full traceroutes and the real IP addresses. Please don't obscure data like this - IP addresses are not secrets.

Having said that, the only case where I can see this happening is when the destination IP addresses are simply not the same. Per-packet load balancing is sometimes done on (parts of) links, which can cause partial failures. However, then both traceroutes should show failures - not consistently just one of them.

So, given that the destination IP addresses are different, my best guess is that one of the destination IP addresses is simply not configured, or uses a stricter firewall. Traceroute will keep trying to look further until it receives a reply from the target host. If the target host does not exist or refuses to reply, traceroute will go on until it reaches it's limit, for which 30 hops is a common setting.