BT Openwoe query

[lovingboth]

Does anyone know why on earth they block tracert?

Doing a tracert to anywhere from here goes something like

Tracing route to www.anywhere.com [x.x.x.x]
over a maximum of 30 hops:

1 20 ms 20 ms 20 ms btdhg513-hg1.ealing.broadband.bt.net [217.47.49.72]
2 10 ms 20 ms 20 ms 217.47.49.2
3 20 ms 20 ms 20 ms 217.47.49.106
4 10 ms 20 ms 20 ms inh3cs01-500.imsnet3.btopenworld.com [213.1.119.61]
5 * * * Request timed out.
6 * * * Request timed out.
etc

Comments

Wierd....

[kingginger.livejournal.com]

... usually its blocked only incoming to a server.

But I think that it could be for the destination you are tracert ing to perhaps?

Try an ip thats not a server for an isp or something...

Re: Wierd....

[lovingboth]

Nope, it affects everything from the mighty bt.com to my rather smaller colo server.

[conflux.livejournal.com]

Yes I get this as well with BT. I will be switching soon I think. I've had enough of them. I guess it is because BT have a firewall on inh3cs01-500.imsnet3.btopenworld.com set up to block the messages returned by a trace route query? If so they are majorly paranoid or don't know how to set up a firewall. You can crash badly set up routers with a very large payload ping so this could be the reason they did this, maybe?

[yesthattom.livejournal.com]

Sometimes it isn't that it's being blocked, per se, it's just that the host controllers on the intervening routers don't know how to get back to you. Tracert replies are sent to the host controller for processing, which (even though it is all one big box) may not be able to communicate with you (unlike the router interfaces, which route your packets.) Ironic, isn't it?

A good example of this is ISPs that use RFC1918 space (10.*.*.* and others) for their router management networks. The theory is that the internal management network shouldn't be accessed from the outside, so why waste public IP address space. The funny thing is that someday they will purchase another ISP and the collisions will be a disaster.

I can talk about this kind of thing for ages.