Showing posts from May 11, 2008

MPLS VPN RD 64-bit or 48-bit ?

MPLS Vol.2 P.5-22 The RD can be specified in one of these two formats:
。16- bit autonomous system(AS) number followed by a 32-bit decimal number(ASN:nn)
。32-bit IP address followed by a 16-bit decimal number(A.B.C.D:nn)
此時各位如果真的有認真看書的話,你會腦袋中浮現一個問號? RD不是8 bytes(64 bits)嗎? 怎麼這邊加起來只有16 + 32 or 32 + 16 bits ? 後來我詢問了一下我們家資深講師,我大概了解了其中原由,因為RD分為兩種類型(Type 0 & Type 1),因此事實還有兩個位元組(2 bytes * 8=16 bits)就是用來指定類型的。

後來我在網路上找到一篇Jeff Doyle的文章有提到關於這個部份的說明,因此順便摘錄如下:

The first requirement is met by using a Route Distinguisher (RD). The RD is a 64-bit value that is prepended to a prefix to associate it with a specific VPN user. The VPN service provider assigns a unique RD each user, and possibly to each user site. The RD is prepended to every prefix advertised by each user before the prefix is added to the BGP table. 
In our example of five different VPN users advertising, RDs might be prepended as follows:
-User A, at site 1:             1:1:
-User B…

TCP Sliding Windows & Sequence Number/Acknowledge Number

在Cisco ICND1的教材有不少地方的typo為學生所詬病,如果是初學者自修自己看這份教材有可能會被誤導觀念或是被confused,所以我在上課時就順手把這些資料訂正之後再來教導學生,為了讓大家都有一個更正確的概念,所以我把我修正後的Slide上傳上來分享給各位,其中大部份都是數字打錯的問題,各位可以回頭參考一下你手上的教材跟我上傳的圖片差異在那。