Category Archives: CISCO

Troubleshooting Boot Loader Prompt for Nexus 9K

If the system boots and falls into “loader>” prompt. Do the following steps. Step 1: Issue the command dir to check the directory and enter the command:boot nxos.9.2.1.bin ​ Step 2: Once the switch is boot up, set password for Nexus 9K, Step 3: Login to the switch. How to prevent Nexus 9K from dropping into “loader >” promptAs… Read More »

BGP as-path regular expressions

A regular expression is the character pattern that can be matched against an input string. Regular expressions can be built using letters (A through Z, a through z), numbers (0 through 9) and other keyboard characters, such as the exclamation point (!) or a tilde (~). A regular expression can be a single-character pattern or… Read More »

BGP Additional Paths

BGP routers only advertise the best path to their neighbors. When a better path is found, it replaces the current path. Advertising a path and replacing it with a new path is called an implicit withdraw. Since we only advertise the best path, a lot of other possible paths are unknown to some of the… Read More »

Default routes in BGP

There are 3 ways of advertising default route in BGP. Method 1: Using network 0.0.0.0 command. It requires only that the route 0.0.0.0 is present in the Interior Gateway Protocol (IGP) routing table. This is the preferred approach. Method 2: Using default-information originate command. It requires explicit redistribution of the route 0.0.0.0. This protects against… Read More »

FIB vs RIB

Terminology: RIB – Routing Information Base FIB – Forwarding Information Base RIB This is a routing protocols database of routing prefixes that could potentially be installed in the routing table. Derived from the control plane, it is not used for forwarding. Every protocol such as OSPF, EIGRP, BGP has its own RIB and select their… Read More »