Final Exam Cheat Sheet PDF

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Dr. Mostafa El-Said Wide Area Network Engineering Final Exam Study Guide...

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Classful IP Address Structure Classes: A: 0 > 127, B: 128 > 191, C: 192 > 223, D: 224 > 239, E: 240 > 255 Classes Subnet Masks: A: 255.0.0.0/8, B: 255.255.0.0/16, C: 255.255.255.0/24 ….et c .( s eeCI DRt abl ei mage) Total possible networks: 2^14 = 16,384 Recall: RIP is a classful routing protocol –whi c hmeansmi x i ngs ubnetmas kl engt hsDON’ Twor kwi t hRI P! - RIP also uses hop count maximum value of 15, as 16 is unreachable. - RIP v2 supports VLSM but summarizes unless told not to summarize (no auto-summary) into classful addressing, which if disabled, allows it to route to non-classful addresses like 10.172.192.10 for example Other IOS Commands: show ip route, sh ip ospf, CIDR Format: Classless inter-domain routing, addresses provided by ISP in a certain block size to businesses and homes (think the slash /24 or /30). The largest number possible to have turned on bits is /30 because a minimum of 2 bits is required for hosts relevant to the Cisco Exam. Static routes have ADMIN DISTANCE of 1 default, modify admin distance to make it secondary to BGP! Static routing will NOT LEARN SHARE OR UPDATE so it saves CPU memory and bandwidth but engineer must update every router with the static route! Dynamic routing will LEARN SHARE UPDATE BGP have default admin distance of 20 cannot be changed on BGP either! Router prefers the lowest admin distance for the route to be used 0 to 255 BGP is border gateway protocol and is used to connect ISPs across the internet! Not used internally, and only used between ISP to advertise I think…. DCE is the modem while the DTE is the data circuit-terminating equipment. DCE is responsible for the clock rate, and is usually setup on the serial connections equip. The DCE performs signal conversion coding and line clocking. Without the modem, two devices would need a crossover cable or other media translator between them. RIP uses hop count to adjust preferred route most trusted route. RIP timers used: RIP has a max hop count 15 and 16 means unreachable - so 15 routes allowed with RIP which is bad for scalability Admin distance for RIP is 120 [2hops / 120admin] Load balancing round-robin will occur if the hops are equal for multiple routes! RIP TIMERS periodic update 30 seconds entire routing table sent to all neighbors Invalid timer 180 seconds opened for learned routes not directly connected ones Hold down timer 180 seconds still no response Flush timer 240 seconds time to remove the route from table if still no response OFFSET LIST for RIP hops: conf t | ip access list standard xyz | permit 192.168.100.0 0.0.0.255 (inverted subnet mask) Conf t router rip offsetlist xyz in 4 S (0+1+4 hops = 5 hops total now for this route) CONTIGUOUS NETWORK: OSPF LINK STATE: means link state is up or down, and link cost is the link speed or latency OSPF Designated Router (DR) – elected based on OSPF priority (lowest values) default is 0 and the tie break will be a highest router ID (RID tag) OSPF Router SHARES –224.0.0.5 OSPF routers all share | 224.0.0.6 only designated routers share all (MULTICAST ADDRESSES used to transmit routing update messages!) OSPF TABLES – routing table = best known routes to reach networks net0 connected net1 via B fastest, link state database table known routes to reach networks with speeds listed in table, neighbor table = all directly connected routers listed OSPF broken – VIRTUAL LINK required on boths ends to be configured so the backbone can connect itself (area 0) to all areas connected to Router1 VIRTUAL LINK COMMANDS –router1 #: area 1 virtual-link 3.3.3.3 | router3 #: area 1 virtual-link 1.1.1.1 RIP (simple but not scalable) OSPF (hard to configure but scalable) EIGRP (simpler and scalable) Summarization allows fewer messages to be sent EIGRP topology table, routing table, neighbor table - If the FD Cost is lost in the routing table, and then the FS Cost is lost in the topology table, then the “ possibility route”takes place to determine the available routes. EIGRP uses ACTIVE and PASSIVE states for its routers EIGRP LOAD BALANCING –By default will not load balance on different cost lengths. Therefore, using variance calculation is required to do load balancing. Maybe commands: #eigrp 10 | #variance 2 Other commands: #show ip eigrp technology

: @inject interface #: int s0 | #ip summary-address eigrp [process ID] [summary-net] [mask address] | looks like the following: #ip summary-address eigrp 10 172.20.128.0 255.255.128.0 EGP is the GLUE to connect networks –2 corporate or more networks on the internet to be made visible and advertised. (1. Do config. 2. Have ISP advertise the network with BGP). Example: ip route 0.0.0.0 0.0.0.0 192.128.1.1 (any traffic from any network will be directed to 192.128.1.1) To have basic connectivity with failover solution, STATIC ROUTING IS REQUIRED. It is the only method to change the admin distance! Same admin distance will create a load balancing between two destinations. I-BGP – interior bgp relationships is a TCP connection between 2 peers INSIDE of an autonomous system. BGP advertisement takes the autonomous system ID and network prefix (AS3, X) which says “ 3A is saying, network X can be found right behind me) UP TO 10x BGP attributes –install the advertised selected routes like: * AS3, X and AS2, AS3, X (the star means valid route) Corporates can have multiple BGP networks given to them by the ISP and also multiple autonomous networks as a result. A 4 node square can have 6 TCP connections to form the iBGP core relationship. Attributes: AS200, AS100, 160.10.0.0/16, 800 (two attributes after the AS systems. The network path and local preference value of 800 –a HIGHER PREFERENCE VALUE is the preferred route in this case!) IGRP vs EGRP – enhanced interior gateway routing protocol vs just interior gateway routing protocol. What are the different states that EIGRP uses to monitor the health of its routes? How does EIGRP load balancing work? By setting up variances. See commands above. Unequal cost load-balancing is an optional config but not discussed. Why does BGP is known as a path vector routing protocol? Because it maintains the path information that gets updated automatically dynamically. Avoids loop infinity problems. Autonomous system boundary routers….Learn share update! eBGP vs iBGP –External would be between two autonomous networks while internal indicates that the connection is within one autonomous network. MOST COMMON BGP ATTRIBUTES AND HOW THEY ARE USED AS_PATH – to help avoid loops and choose the best path for BGP route NEXT HOP – next hop neighbor IP address, well known mandatory attribute. LOCAL PREFERENCE – which route is the best and deserves a place in the routers routing table. Prefer the path with the highest local preference, with the shortest AS_PATH, and prefer the path with the lowest multi-exit-discriminator (MED)....