| ##### **Distance Vector Protocols** Distance Vector routing protocols base their decisions on the best path to a given destination based on the distance. Distance is usually measured in hops, though the distance metric could be delay, packets lost, or something similar. If the distance metric is hop, then each time a packet goes through a router, a hop is considered to have traversed. The route with the least number of hops to a given network is concluded to be the best route towards that network. The vector shows the direction to that specific network. Distance vector protocols send their entire routing table to directly connected neighbors. \* source - Pluralsight - [Dynamic Routing Protocols: Distance Vector and Link State](https://www.pluralsight.com/blog/it-ops/dynamic-routing-protocol#:~:text=The%20vector%20shows%20the%20direction,IGRP%20%2D%20Interior%20Gateway%20Routing%20Protocol.) | ##### **Link State Protocols** Link state protocols are also called shortest-path-first protocols. Link state routing protocols have a complete picture of the network topology. Hence they know more about the whole network than any distance vector protocol. Three separate tables are created on each link state routing enabled router. One table is used to hold details about directly connected neighbors, one is used to hold the topology of the entire internetwork and the last one is used to hold the actual routing table. Link state protocols send information about directly connected links to all the routers in the network. \* source - Pluralsight - [Dynamic Routing Protocols: Distance Vector and Link State](https://www.pluralsight.com/blog/it-ops/dynamic-routing-protocol#:~:text=The%20vector%20shows%20the%20direction,IGRP%20%2D%20Interior%20Gateway%20Routing%20Protocol.) |
| RIP and IGRP | **OSPF** and IS-IS (EIGRP is considered a hybrid protocol because it uses both distance vector and link state.) |
| Only communicates with neighbor routers | Communicates with **all** other routers in an area |
| Calculates path based on distance and vector | Calculates shortest path based on link-state parameters |
| Passes entire routing table to directly connected neighbor routers | Passes link-state routing updates to other routers |
| ##### 1. LSR Router A send a link-state request (LSR) to gather route information from the neighbor router -- Router B | ##### 2. LSU Router B replies with a Link -State Update (LSU) containing the requested Link-State Advertisement (LSA) information. | ##### 3. LSAck Router A receives the LSU with LSA attached and sends a Link-State Acknowledgement (LSAck) back to Router B |
|  | Illustration of Dijkstra's algorithm finding a path from a start node (lower left, red) to a goal node (upper right, green) in a [robot](https://en.wikipedia.org/wiki/Robotics "Robotics") [motion planning](https://en.wikipedia.org/wiki/Motion_planning "Motion planning") problem. Open nodes represent the "tentative" set (aka set of "unvisited" nodes). Filled nodes are the visited ones, with color representing the distance: the greener, the closer. Nodes in all the different directions are explored uniformly, appearing more-or-less as a circular [wavefront](https://en.wikipedia.org/wiki/Wavefront "Wavefront") as Dijkstra's algorithm uses a [heuristic](https://en.wikipedia.org/wiki/Consistent_heuristic "Consistent heuristic") identically equal to 0. \* source: [https://en.wikipedia.org/wiki/Dijkstra%27s\_algorithm](https://en.wikipedia.org/wiki/Dijkstra%27s_algorithm) |
| **Network Type** | **DR/BDR Election?** |
| Point to Point | No |
| Broadcast | Yes |
| Non broadcast multiple access (NMBA) | Yes |
| Point to Multipoint | No |
| Decimal | Octet 1 | Octet 2 | Octet 3 | Octet 4 |
| 192.168.8.0 | 11000000 | 10101000 | 00001000 | 00000000 |
| 192.168.9.0 | 11000000 | 10101000 | 00001001 | 00000000 |
| 192.168.10.0 | 11000000 | 10101000 | 00001010 | 00000000 |
| 192.168.11.0 | 11000000 | 10101000 | 00001011 | 00000000 |
| SUMMARY IP | 11000000 | 10101000 | 00001000 | 00000000 |
| 192 | 168 | 8 | 0 | |
| Subnet Mask | 11111111 | 11111111 | 11111100 | 00000000 |
| /22 | 255 | 255 | 252 | 0 |
| ##### Directly Connected BGP Neighbors | ##### Multihop BGP Neighbors |
| BGP will use the Arp table to locate the Layer 2 address of the peer. | BGP will use routing table information to find the peer's IP address. |
| ##### Private 16-bit ASN Range | ##### Private 32-bit ASN Range |
| 64,512 - 65,535 | 4,200,000,000 - 4,294,967,294 |
| **Mnemonic** | **First Letter** | **BGP Path Attribute** |
| We | W | Weight |
| Love | L | Local\_pref |
| Oranges | O | Originate |
| As | A | AS\_path |
| Oranges | O | Origin type |
| Mean | M | MED (Multiple Exit Discriminator) |
| Pure | P | Paths |
| Refreshment | R | Router-ID |
| **eBGP** | **iBGP** |
| Administrative distance: **20** | Administrative distance: **200** |
| **Mnemonic** | **First Letter** | **BGP Path Attribute** | **Preference** |
| We | W | Weight | Higher |
| Love | L | Local\_pref | Higher |
| Oranges | O | Originate | Local vs Aggregate |
| As | A | AS\_path | Lower |
| Oranges | O | Origin type | IGP vs EGP vs ? |
| Mean | M | MED | Lower |
| Pure | P | Paths | eBGP vs oBGP |
| Refreshment | R | Router-ID | Lower |
| **Create a prefix list** | Router(config)#ip prefix-list \[list name\] permit \[network IP\] |
| **Create a route map** | Router(config)#route-map \[map name\] permit \[line #\] Router(config-route-map)#match ip address prefix-list \[list name\] Router(config-route-map)#set weight \[value\] |
| **Apply the route map to BGP configuration** | Router(config-router)#neighbor \[neighbor IP address\] route-map \[map name\] \[in/out\] |
| **Well-known mandatory** | This attribute MUST exist in the BGP UPDATE. If this attribute is missing a NOTIFICATION error is generated and the session is closed. Must be recognized by all BGP routers and must be included in every update message. Routing information errors occur without this attribute. |
| **Well-known discretionary** | Can be recognized by all BGP routers; can be included in every update message as needed. |
| **Optional transitive** | Transitive attribute between ASs. A BGP router not supporting this attribute can still receive routes with this attribute and advertise them to other peers. |
| **Optional non-transitive** | If a BGP router does not support this attribute, it will not advertise routes with this attribute. |
| **BGP Path Attribute** | **Category** |
| Weight | Cisco specific local to router |
| Local\_pref | Well-known discretionary |
| AS\_path | Well-known mandatory |
| Origin type | Well-known mandatory |
| MED | Optional non-transitive |
| Phase 1 Commands | Notes |
| crypto isakmp enable | |
| crypto isakmp policy 10 | The number can be any number between 1 and 10,000. It identifies the priority of the policy. |
| encryption aes | this could be 3des but aes is more robust. |
| hash sha | sha = secure hash algorithm. md5 could be used but sha is more robust. |
| group 1 | Specifies the Diffie-Hellman group identifier, which the two IPsec peers use to derive a shared secret without transmitting it to each other. Group 1 is 768-bit |
| lifetime 3600 | Specifies the Security Association (SA) lifetime. The default is 86,400 seconds or 24 hours. As a general rule, a shorter lifetime provides more secure ISAKMP negotiations (up to a point). However, with shorter lifetimes, the security appliance sets up future IPsec SAs more quickly. |
| authentication pre-share | |
| crypto isakmp key *ciscokey123* address 172.16.2.2 | The italicized text is just a text string that has to match on both sides of the connection. The IP address is the public IP address of our **peer on the other side of the VPN connection**. |
| Phase 2 Commands | Notes |
| crypto ipsec transform-set *vpnset* esp-aes esp-sha-hmac | The italicized text is the set name and can be changed. This could be esp-3des and esp-md5-hmac |
| crypto map vpnset 10 ipsec-isakmp | The number is any number between 1 and 65,535 that identifies the sequence to insert into the crypto map. |
| set transform-set vpnset | |
| match address 100 | Match the addresses in the access control list coming up. This will identify the inside-to-inside traffic flow. |
| set peer 172.16.2.2 | This is the other router's outside interface. |
| Phase 3 Commands | Notes |
| int s0/0/0 | Whatever the outside interface of the router is (f0/0, g0/2, etc.) |
| crypto map vpnset |
| Phase 4 Commands | Notes |
| access-list 100 permit ip 192.168.10.0 0.0.0.255 192.168.20.0 0.0.0.255 | These are the inside addresses of both routers. |