What Is an Adjacency?

What Is an Adjacency?

CEF describes a very high speed switching mechanism that a router uses to forward packets from the inbound to the outbound interface. CEF uses two sets of data structures or tables, which it stores in router memory:

• Forwarding Information Base (FIB) —Taken from the common International Organization for Standardization (ISO) usage, an FIB describes a database of information used to make forwarding decisions. It is conceptually similar to a routing table or route-cache, although it is very different from a routing table in implementation.
• Adjacency table —Two nodes in the network are considered adjacent if they can reach each other using a single hop across a link layer. For example, when a packet arrives at one of the router's interfaces, the router strips off the data-link layer framing and passes the enclosed packet to the network layer. At the network layer, the destination address of the packet is examined. If the destination address is not an address of the router's interface or the all hosts broadcast address, then the packet must be routed.
  At a minimum, each route entry in the database must contain two items:
• Destination address—This is the address of the network the router can reach. The router may have more than one route to the same address.
• Pointer to the destination—This pointer indicates that the destination network is directly connected to the router, or it indicates the address of another router on a directly-connected network towards the destination. That router, which is one hop closer to the destination, is the next-hop router. An adjacency represents the pointer to the destination.

Common Routing Problem with OSPF Forwarding Address

OSPF Forwarding Address

Концепция OSPF forwarding address была введена для предотвращения лишнего хопа, в процессе маршрутизации трафика во внешнюю автономную систему (external autonomous system), как это отражено на рисунке ниже.

На рисунке мы видим 2 маршрутизатора в OSPF домене, которые подключены к внешнему домену. Тем не менее, только Router 1 обменивается маршрутной информацией с Router 100. Router 1 перераспределяет (redistributes) полученную маршрутную информацию от Router 100 в OSPF домен.
При этом, Router 1 становится next hop (или forwarding address) для маршрутов которые были перераспределены (redistribute) в OSPF domain. Когда Router 2 получает пакет с внутреннего OSPF домена, направленный на external domain, он отправляет пакет на Router 1. Router 1 потом отправляет его на Router 100.

Концепция forwarding address позволяет избежать ситуации с дополнительным хопом, потому что становится возможным Router 1 назначить IP адрес другого роутера в качестве forwarding address. в нашем рисунке, Router 1 может назначить Router 100 в качестве  forwarding address для внешних маршрутов которые  Router 1 перераспределяет в OSPF домен. Когда Router 2 получает пакет с OSPF домена предназначенный для адреса во внешней AS, он отправляет его на Router 100, вместо Router 1. Как результат - мы избавились от лишнего и ненужного промежуточного узла на пути прохождения трафика.

Значение forwarding address устанавливается autonomous system boundary router (ASBR) (Router 1 на нашей картинке) и может быть как 0.0.0.0 так и non-zero. Значение 0.0.0.0  говорит о том, что originating router (the ASBR) является next hop-ом.. Forwarding address определяется по следующим критериям:

How Type 5 LSA Forwarding Addresses Can Affect Path Selection

Forwarding Addresses Not Set for Both LSAs

The topology shown below is used to demonstrate how the forwarding address in an OSPF type 5 LSA can affect the path selection of the type 5 LSA.

In the diagram above, all routers, other than Router 8, are running OSPF in area 0. For the purpose of this document, the configurations of Router 3 and Router 4 are most important because they are the autonomous system boundary router (ASBRs) generating the type 5 LSAs. As shown below, Router 3 and Router 4 have a static route to network 200.200.200.0 255.255.255.0, which is being redistributed into OSPF.

Unifi AP Password Restore

Use MongoDB to retrieve username / password.

1. Open the UniFi controller program, or make sure the service is running. 
2. If on Linux, skip to step 4. If on Mac or Windows, please download the mongoDB zip or tgz file by going to THIS site. Once at the site it should automatically detect the proper operating system. Make sure Previous Releases is selected choose a version from 2.2 from the drop down menu on the left.
3. Extract the contents of the container to your desired location.
4. Open Terminal (Mac/Linux) or Command Prompt (Windows) and change directory to the /bin folder found within the extracted folder. Do note that Linux users can run the command from any folder, only Mac and Windows users need to change to the /bin folder.
   

Cisco ASA. NAT.

Main Differences Between Network Object NAT and Twice NAT

The main differences between these two NAT types are:

•  How you define the real address. 

         – Network object NAT— You define NAT as a parameter for a network object. A network object names an IP host, range, or subnet so you can then use the object in configuration instead of the actual IP addresses. The network object IP address serves as the real address. This method lets you easily add NAT to network objects that might already be used in other parts of your configuration.
           – Twice NAT— You identify a network object or network object group for both the real and mapped addresses. In this case, NAT is not a parameter of the network object; the network object or group is a parameter of the NAT configuration. The ability to use a network object group for the real address means that twice NAT is more scalable.

•  How source and destination NAT is implemented.