Plumbing the internet

OSPF area types allow networks to be segmented into smaller areas to reduce the amount of routing information that needs to be exchangedThe backbone area is the central area of the OSPF network and must exist in every OSPF network. Standard areas are connected to the backbone area and have their own LSDBs, while stub areas and NSSAs block external routing information to reduce the amount of routing information exchanged between areas. Totally stubby areas block both external and inter-area routes. Routers within the same area share the same LSDB and use it to calculate the shortest path to a destination network. OSPF defines several types of areas, each with different functions and characteristics below are the OSPF area types and their operations: Backbone Area (Area 0) - The backbone area (also called Area 0 - area id must be 0 / 0.0.0.0 in 32bit notation) is the central area of an OSPF network and it must exist in every OSPF multiarea network. All other areas must be connected to th...

  > Topology Overview: - Routers RG 31/32 - peering routers  - Routers RR-10 / RR-20 - route reflectors - Ps and PEs - core and customer connectivity BGP CONCEPTS > Pourpouse of BGP: - interconnect between different AS (interdomain communication) - widely used in Service Provider, Large Enterprise and Datacenter enviroments - multihomed customers - scalable  - created with stability in mind > Main considerations - trust one one - eBGP filter advertisment in and out  - policy based  - multiprotocol support IPv4/6, VPNv4/6 and VXLAN - reliable updates - triggered updates only - uses rich metrics/attributes > Internal BGP - neighbourship between two nodes in the same AS - AS-PAth is not updated when sending to iBGP - BGP Split-horizon is used to prevent the loops, iBGP updates are not forwarded to any other iBGP peer - BGP next-hop is not changed - used to carry partial of full table of internet routing prefixes > External BGP - neigborship between t...

What is IS-IS? - a link-state routing protocol defined in ISO/IEC 10589, originally designed as the routing protocol for CLNP (ISO 8473), the OSI connectionless network protocol - IPv4 support was added in RFC 1195 (Integrated IS-IS) and IPv6 support in RFC 5308 - runs directly over Layer 2, not over IP, but still uses OSI addresses (NETs) to identify routers. A side benefit: because it doesn't run over IP, it is hard to attack remotely - mostly popular in large ISP environments - similarly to OSPF, it runs the Dijkstra SPF algorithm - uses Hello packets (IIHs) to form and maintain adjacencies - uses a two-level hierarchy: Level 1 for routing within an area and Level 2 for routing between areas - elects a Designated Intermediate System (DIS), similar to the OSPF DR, but with no backup DIS - in general simpler than OSPF: fewer packet types, no LSA types to learn, no special area types (stub, NSSA), and TLVs make it easy to extend with new features Terminology - a router is an Interm...

grep basics grep is a command line tool for searching plain text to match a regular expression grep use examples: #grep 'import' test_requests.py - will display line in the file that contains word 'import' output:      f rom turtle import title      import requests      from bs4 import BeautifulSoup #grep -R 'import' . - will look for all files within the directory and subdirectories that contain word 'import ' output:      ./test_urllib:import urllib3      ./xml2-to-dict.py:import xmltodict      ./xml-to-dict.py:import xmltodict      ./eveng-request.py:import requests      ./parse_yaml.py:import yaml      ./test_requests.py:from turtle import title      ./test_requests.py:import requests      ./test_requests.py:from bs4 import BeautifulSoup      ./automate-l1.py:from __future__ import print_fun...

- YANG is defined in RFC 6020  - defines hierarhy of data, structures data models in to modules and submodules - used to model data for NETCONF - permits the definition of reusable groupings of nodes - RFC 6021 - describes common YANG types used in networking     these can be imported with import statment:        import "ietf-yang-types" {       prefix-yang;    }     - then as a reference when accessing definitions use "yang" as a prefix i.e.:     type yang:port-number      - Four types of nodes are used for data modeling:    a) Leaf node(s) - smallest component, one value i.e. ipv4 address     b) Leaf-list - a sequence of leaf nodes with exactly one value of a    particular type per leaf    c) Container nodes - group related nodes in a subtree    d) List nodes - defines a sequence of list entries - examples of build-in YANG data...

  BASH basics - acronym for "Bourne Again Shell" - allows for command and script processing - supports piping i.e.: $env | more  will add page breaks when displaying the information: - For help  "man" can be used to access detailed information about command i.e.: $man pwd will return: - sample commands: pwd - print current working directory ls - list files and directories, optionally can be used with "-a" (show all including hidden files) or "-l" to list permissions and user/group ownership, example: mkdir - create directory rm - deletes file or directory, useful flag " -rf " to force remove all files within deleted         folder cp - copy file or folder, does not delete the source file mv - move file/folder between directories, also can be used to rename files/folders         using  " mv -f " will force overwrite if destination file already exists cat - can be used to view or create files,...