On Thu, 11 January 2001, bgp4cn wrote:

yesterday our parner tell me that almost all carriers in North America implementing firewalls when they interlink with another carriers.

I do not know of a single major US carrier which inserts a "firewall" in its inter-carrier connections. Generally "firewalls" are used between the Internet and "terminal" networks, not between transit carriers. For historical reasons, traffic between most US commercial transit providers occurs on an "AUP-free" basis. However, the word "firewall" is one of those marketing terms which has variable meanings depending on the speaker and on the customer. Most carriers do have certain technical filters (i.e. a list of valid or invalid IP addressese) they apply to their inter-carrier peering links. For example, they won't accept a route with an address of 0.0.0.0 (i.e. default route) between backbones. Because a firewall by its nature imposes policy on all downstream connections, any carrier wanting to be a major international transit provider would not use a firewall on its peering links. Different countries have very different ideas what is or is not acceptable, international transit providers don't make that decision at the backbone level. Likewise they don't make that decision at the connections between major international transit providers. Even Singapore, which has fairly strict domestic controls, has an AUP-free policy for traffic between carriers at its international exchange point.