Tejas Jain

When your neighbor's router is on fire, your internet is not at stake! Wish the same were true in the EIGRP universe as well (unless you have a well designed redundant network, which unfortunately is not very often the case!) EIGRP works if and only if your router establishes an 'amicable' EIGRP neighborship with the adjacent EIGRP router. Well, this is not an issue in most cases. Of importance, here, is how do you quantify the 'amicability' of the EIGRP adjacency. Let's inspect various fields in the "show ip eigrp neighbor" output show ip eigrp neighbor Autonomous System (AS) number - Here, visible as "Process 100" - EIGRP uses the concept of  autonomous systems . An autonomous system is simply a group of EIGRP-enabled routers that should become EIGRP neighbors and exchange routes. Address: IP address of the EIGRP neighbor Interface : Which interface is this EIGRP adjacency is formed upon Hold timer: Hold down timer is the number of secon...

While configuring Cisco router you must have run into issues where the console tried to mess with your commands. (I have faced this more often than I am ready to accept!) Something like below: Cisco IOS - logging synchronous At a first glance, everything seems OK.. but wait.. where are my last three octets of the subnet mask?? The "link" and "line protocol" logs have kicked my three octets out.. What do I need to ensure that this doesn't happen? Disable console logging -- This, of course works! However, for someone who likes to feel the heat of his deeds, in the real time, it might not be very enjoying. Enable "logging synchronous" -- This needs to be done below the "line <console/vty> The latter is definitely desirable as it allows me to get the real-time logs along with, not messing up with my commands. Cisco IOS - logging synchronous configuration Of course, if you are telnet ing the device remotely, do this configuration under "line...

What is Advertised Distance in EIGRP? The Advertised Distance (AD) is the distance from a given neighbor to the destination router. Advertised distance is also called Reported Distance What is Feasible Distance? The Feasible Distance (FD) is the distance from the current router to the destination router. What is a Successor route? The EIGRP learned and computed best route that is eligible to be entered into routing table. By default, this is the route with the lowest metric and which meets the feasibility condition. What is Feasible Successor? If there is an alternate route and if it meets the feasibility condition, then it can be considered as a feasible successor. Do you use subnet mask or a wildcard mask in EIGRP "network" router command? EIGRP "network" command, by default, uses a classful network to advertise the connected networks. In order to be more specific in advertising the particular subnet, a wildcard mask is used.

Something about EIGRP.. Enhanced Interior Gateway Routing protocol It is an enhanced distance vector routing protocol based on Diffused Update Algorithm (DUAL) to calculate shortest path. Classless routing protocol Support for VLSM, route-summarization Supports unequal cost load balancing, incremental updates What parameters should match for EIGRP formation? Primary address should be used for forming EIGRP neighborship Autonomous System number K-values In case a static neighborship is configured, it must be done on both the sides What is the multicast address of EIGRP? 224.0.0.10 What are the packet types used by EIGRP? Hello Acknowledgement Update Query Reply What are the basic components of EIGRP? Diffused Update Algorithm - It is used for selecting the lowest cost loop-free path for a given destination Reliable Transport Protocol - RTP is used in EIGRP for detecting packet loss and to ensure ordered delivery of packets Protocol Independent Module - Support for IP, IPX, AppleTalk, IP...

How would you speed up OSPF convergence? Configure lower hello and dead interval timers Configure ISPF - incremental SPF --> The principle of ISPF is to update the affected nodes only without rebuilding the whole tree, thereby, resulting in a faster convergence and saving CPU intensive activity of processing. Configure OSPF's SPF throttling - The SPF throttling feature makes it possible to configure SPF scheduling in millisecond intervals and to potentially delay SPF calculations during network instability. Command : "timers throttle spf [spf-start] [spf-hold] [spf-max-wait] How do you modify the cost of a default route propogated into an area? Use the command "default-information originate [always] [metric value] [metric-type value] [route-map name]" where: metric value = numerical cost metric-type value = Type 1 / Type 2 etc. route-map name = name of the route-map Command to create a stub area area xx stub Command to create a totally stub area area xx stub no...

What are the tables maintained by OSPF? Neighbor Table : This table stores information about all the OSPF neighbors. Can be displayed using the command : show ip ospf neighbor Database / Topology Table : This table stores link state database of all the OSPF learned routes. Can be displayed using the command : show ip ospf database Routing table : After running the SPF algorithm on all the routes in the database table, the best route is selected and promoted to the Routing table. Can be displayed using the command : show ip route ospf What are the benefits of dividing an OSPF domain into multiple areas? Decrease routing overhead per router (this especially makes sense for internal non-backbone routers i.e. routers inside a single non-backbone area Ensure speedy convergence.. less routes implies faster processing Confine network instability into single area.. the inter-area summary routes and the routes from special areas such as stub, totally stub, NSSA, totally NSSA are usually ...

What are types of OSPF packets? Hello Database Description (DBD) Link-State Requests (LSR) Link-State Updates (LSU) Link-State Acknowledgements (LSAck) What is OSPF finite state machine? What are the states in OSPF neighborship? DOWN - No OSPF packets have been received on the interface ATTEMPT - Applies only to non-broadcast multi-access networks (NBMA) where the neighbors must be configured manually using the "neighbor x.x.x.x" command INIT - Router has seen a Hello message from an OSPF router TWO-WAY - A Hello message has been sent to the neighbor and the neighbor has replied with its Hello message. In Broadcast networks, the DR/BDR election takes place after this state EXSTART - DR and BDR establish OSPF adjacencies with each of the routers in the network. Master / Slave election takes place at this stage. The Master sends its DBD (Database Descriptor) first EXCHANGE - Routing information may be exchanged via DBD, Link State Requests (LSR) and Link State Updates (LS...