Learning IOS and JUNOS

第一次學習OSPF的同學遇到NBMA時總會覺得大腦不夠用，怎麼記都很容易搞混，到底什麼時候要設定Neighbor，什麼時候要選擇DR/BDR? (請參考下圖) 我在這邊提供兩個快速記憶法： 只要是OSPF Mode內含 nonbroadcast 字串(包含NBMA)皆需 手動設定Neighbor 因為不支持broadcast(multicast)無法傳送multicast hello，所以一定要設定Neighbor改用unicast 只要是OSPF Mode開頭為 Point-to-XXX 字串皆 不須選擇DR or BDR Point-to-XXX常見於WAN的環境，因此沒有DR/BDR這類代表multiaccess broadcast的需求 除了標準LAN( Broadcast )/WAN( Point-to-Point ) 之外 的OSPF Mode Hello Timer皆為30 secs 希望對各位在學習過程中可以有些幫助!

晚上閒來無事檢查一下e-mule的成果，看到了一份古早的multicast course slide + content的PDF，真的有點衝動想要把它整本印出來，裏面的內容真的很詳細很棒，但是現在完全沒有教這些來龍去脈，所以我想現在的學生就算是考過CCNP/CCIP對於multicast也只是一知半解。 在文章裏面我剛好看到了一個也出現在BSCI課文中的一個專有名詞 Designated Router/Querier，更重要的是…Cisco BSCI 教科書中那段文章還是錯的，它把highest IP寫成了lowest IP...(心中OS:習慣就好 習慣就好 教書教了三年還真的仍不習慣~) • Designated Router (DR) – For multi-access networks, a Designated Router (DR) is elected. In PIM Sparse mode networks, the DR is responsible for sending Joins to the RP for members on the multi-access network and for sending Registers to the RP for sources on the multi-access network. For Dense mode, the DR has no meaning. The exception to this is when IGMPv1 is in use. In this case, the DR also functions as the IGMP Querier for the Multi-Access network. • Designated Router (DR) Election – To elect the DR, each PIM node on a multi-access network examines the received PIM Hello messages from its neighbors and compares the IP Address of its interface with the IP Address of its PIM Neighbors. ...

Thanks to CCIE#20586 who re-organized the terminal server menu configuration for my BSCI course. It is modified from ICND1 configuration file and it is good for students who like to change console connection without disconnect the previous one. version 12.4 service timestamps debug datetime msec service timestamps log datetime msec no service password-encryption ! hostname BSCI-CS ! boot-start-marker boot-end-marker ! no logging console enable secret cisco ! no aaa new-model ! resource policy ! ip tcp synwait-time 5 ! ! ip cef ! ! no ip domain lookup ip host P3R4 2081 1.1.1.1 ip host P1R1 2066 1.1.1.1 ip host P1R2 2067 1.1.1.1 ip host P1R3 2068 1.1.1.1 ip host P1R4 2069 1.1.1.1 ip host P2R1 2070 1.1.1.1 ip host P2R2 2071 1.1.1.1 ip host P2R3 2072 1.1.1.1 ip host P2R4 2073 1.1.1.1 ip host P3R1 2078 1.1.1.1 ip host P3R2 2079 1.1.1.1 ip host P3R3 2080 1.1.1.1 ip host FRSW 2074 1.1.1.1 ip host BBR1 2075 1.1.1.1 ip host BBR2 2076 1.1.1.1 ip host Pagen 2077 1.1.1.1 ip host SW 2078 1.1.1.1 ! ...

Posted by stretch in  Networking  on Thursday, 2 Oct 2008 at 3:36 a.m. GMT There are two major classes of routing protocol: distance vector and link-state. It's easy to remember which protocols belong to either class, but comprehending their differences between the two classes takes a bit more effort. Distance vector  routing is so named because it involves two factors: the  distance , or metric, of a destination, and the vector , or direction to take to get there. Routing information is only exchanged between directly connected neighbors. This means a router knows from which neighbor a route was learned, but it does not know where that neighbor learned the route; a router can't see beyond its own neighbors. This aspect of distance vector routing is sometimes referred to as "routing by rumor." Measures like split horizon and poison reverse are employed to avoid routing loops. Link-state  routing, in contrast, requires that all routers know about the paths reachable by...

自從我成為Cisco講師以來，一直有一個無解的問題在我腦海中，那就是EIGRP Metric的計算公式與課本中所提到相關EIGRP會考慮到的相關參數一直無法搭配上去。 課本教材裏(不論是ICND 2.3 or BSCI 3.0)都提到了EIGRP Metric有五個參數(Bandwidth, Delay, Reliability, Load, MTU)，其中預設會使用的參數是Bandwidth & Delay(因為在EIGRP Metric計算公式中預設K1=K3=1，K2=K4=K5=0)，因此其他的參數在預設情況之下並不會納入考量。 以下就是EIGRP的Metric計算公式: metric = [K1 * bandwidth + (K2 * bandwidth) / (256 - load) + K3 * delay] * [K5 / (reliability + K4)] 因此問題就浮現了…在這個公式運算中根本沒有看到MTU這個參數的存在，但是翻遍Cisco Documents & Course Material就是找不到任何一段正式的說明直接表示MTU雖然屬於EIGRP Metric交換的一部份但是在EIGRP Metric的計算過程中並未加入計算。 今晚我在準備新版ICND2 1.0的教材時，終於看到了一段話: "Note: Although MTU is exchanged in EIGRP packets between neighbor routers, MTU is not factored into the EIGRP metric calcaulation." 除此之外，我覺得CCNA這次的大改版其實在內容上相較於CCNP 3.0改版來說在內容是比較紮實的...尤其是ICND1，所談論的領域大幅地增加(有好也有壞，因為談得愈多就愈不深入…)，不過在許多文字敘述上及觀點的糾正有很多改進(如: show vtp status中VTP Version常常讓人誤解的意思/VTP Domain Name會自動學習的特色/設備之間改口建議使用FIX手動設定SPEED/Duplex的註解..)都有助於導正學生因為文字上的說明不清而誤解意義。 PS:EIGRP計算metric中的Delay，所使用的單位比較特別，是將mili...