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Showing posts from November 18, 2019

EIGRP Adjacency

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

Cisco IOS - logging synchronous

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

EIGRP Interview Questions - Part 2

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.