Subject: [sidr] [SIDR][IDR]Does DBGP have to be contiguously deployed?

From: "Zhangmingui, (Mingui)" <[email-masked]>
Date: Thu, 26 May 2011 11:17:05 +0000

Hi all,

The answer is that DBGP does NOT require contiguous deployment in order to be effective. The key purpose of DBGP is to recognize and propagate the suspicious path segment via the DAS-PATH. When the AS router at the far side obtain the UPDATE message with the DAS-PATH missing some intermediate AS numbers, it doesn't matter. This AS router can still use this path segment for detection/validation purpose. Let's use the example in Figure 5.1 to explain (http://tools.ietf.org/html/draft-zhang-idr-decoupling-02).

The starter AS router of the DAS-PATH must have deployed DBGP. In this figure, "B" is the starter. "B" can recognize "X" as suspicious node and propagates this via DAS-PATH to "A". We suppose "A" has not deployed DBGP. When A's upstream AS router receives A's update message, it will find that the AS-PATH is "ABCO" and the DAS-PATH is "BX". The detection system just uses "BX" as the input. 

BTW, it is not recommended to complement the DAS-PATH according to the primary path contained in the same UDPATE message. You will easily find this kind of trick is in vain.

Best regards,
--
Mingui Zhang
Huawei Technologies Co.,Ltd