Tag: OSPF

    What is IGRP (Interior Gateway Routing Protocol)?

    IGRP Protocol

    IGRP (Interior Gateway Routing Protocol) is an advanced distance-vector protocol developed by Cisco Systems in the mid-1980s, including some of the RIP errors.

    Different bandwidths can be used to configure the metric value, such as the user’s network latency, bandwidth, and latency depending on the relative speed and capacity of the interface.

    The load and reliability features are calculated based on the performance of the interface in actual network traffic management, although they are not enabled by default for routing decisions.

    Like RIP, it uses IP broadcasts to forward routing information to neighboring routers. However, IGRP has been designated as its transport layer protocol.

    To transmit network route information, UDP see is not connected to TCP. Since IGRP does not have a feedback mechanism, it works in a similar way to UDP.

    It offers three major improvements over the RIP protocol. First, the IGRP metric can support a network with a maximum of 255 router hop counts. Second, the IGRP metric can differentiate between the costs associated with sees of different types of connection media. Third, it should not wait for regularly scheduled times for updates, but rather by sending information about changes in the network when it becomes available.

    IGRP is a routing protocol based on distance vectors developed by CISCO.

    Improved Scalability

    On larger networks, routing has a maximum number of 100 hops by default but can be configured with 255 hops.

    Sophisticated Matrix

    A composite metric for greater flexibility in route selection. Interconnection delay and bandwidth are used and other parameters such as reliability, load and MTU can be included.

    Multiple Rotate support

    It can hold six different cost paths between source and destination networks. Various routes can be used to increase the available bandwidth or provide route redundancy. IGRP allows triggered updates.

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    Source: https://www.cisco.com/c/en/us/support/docs/ip/interior-gateway-routing-protocol-igrp/26825-5.html

    What is OSPF (Open Shortest Path First) Protocol

    Open Shortest Path First Protocol

    OSPF is used inside the networks as RIP, the operation is very simple. Each router knows the nearby routers and the addresses each router has. In addition, each router (measured on routers) knows how far each router is. So when you need to send a packet, you send it the same way you have to do fewer skips.

    For example, a router with a local network with one workstation, and a router with three network connections (A) with a fast 48Mbps square relay network and a 64Kbps ISDN (B) line. Three packets from the local network to A and B to two packets go to W. The packet passes through B regardless of the saturation of the line or the bandwidth of the line.

    OSPF Types

    Undoubtedly, OSPF is a complex protocol and requires a lot of work to understand how it works, and makes many practices to master. One of the most important concepts in OSPF is the design and operation of different areas, which is quite confusing when this protocol is known.

    To explain how each works, it is necessary to know the types of LSA (Link State Ads) that the OSPF uses to communicate between neighbors and transmit routing information between them.

    Type 1 (LSA Router)

    Each router in area X sends a type 1 LSA to its neighbors. This LSA never leaves the domain to which it belongs and contains the Router ID of the sender and all connections that connect it.

    Type 2 (Network LSA)

    Sent by the DR (Private Router) within the network. Tells others the networks and masks it is connected to. This LSA never leaves the area it corresponds to. So, an ABR does not transmit to another region.

    Type 3 (Summary LSA)

    They are sent by an ABR to transfer information from one region to another. OSPF calls them a “summary”.

    Type 4 (ASBR-Summary LSA)

    Represents an ASBR (Autonomous System Border Router)

    Type 5 (External LSA)

    Represents an external route redistributed from another protocol within the OSPF (Ex: EIGRP). The ASBR takes the route from the external protocol and transmits them as type 5 to all internal areas except Stub type.

    Type 7

    OSPF rules say that redistribution is required only in a Spine zone (Area 0). In an NSSA domain, a router with a connection to another external routing protocol (eg RIP) can be connected and the ASBR sends these networks in type 7 format so that the ABR receives them and redistributes them as type 5.

    Type 1 and 2 LSAs are found in all areas and are not shipped anywhere they belong. Other LSAs are sent between fields, depending on the function they perform.

    Field Types

    • Standard
    • Backbone (Area 0)
    • Stub Area
    • Totally Stubby Area
    • Not-so-stubby Area (NSSA)
    • Totally Stubby NSSA

    Standard

    This is the default field and allows links to be updated, summary paths, and external paths.

    Backbone (Area 0)

    OSPF is the main area of ​​topology. It must be present and all others must depend on it. The field is labeled 0 and has the same properties as a standard field.

    Stub Area

    Such a field does not accept information about external routes to the autonomous system (redistribution), such as paths from non-OSPF sources. If routers need to route to networks outside the autonomous OSPF system, they use a default route (0.0.0.0/0) sent by ABR to other internal routers in the Stub area. ASBR is not allowed in this area (unless ABR is also an ASBR)

    Totally Stubby Area

    This area belongs to Cisco and does not accept routes from external autonomous systems (redistribution) or abstracts from other internal regions of the autonomous system. As with the Stub fields, ABRs send a default route for all external and SUMMARY routes (this is the difference with Stub). ASBR is not allowed in this area (unless ABR is also an ASBR)

    Not-so-stubby Area (NSSA)

    Almost the worst name in the world chose this name. There are type 7 LSAs in this field, which are similar to the Stub field because they do not accept information from external routes to the autonomous system (OSPF world) and replace them with a default route originating from ABR. However, the difference is that the NSSA accepts an ASBR directly connected to another routing protocol (eg, RIP, EIGRP, etc.). The NSSA ASBR transmits pathways within the site as LSA 7, and the corresponding ABR converts them to type 5 for normal treatment.

    Totally Stubby NSSA

    If the old is almost the worst name, make sure it is the worst. Fully Stubby Not Left-Handed Area or Fully Stubby NSSA is a proprietary Cisco area that functions in the same way as the Fully Stubby Area, does not allow external or summary routes, but permits an ASBR such as NSSA.

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    Source: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_ospf/configuration/xe-16/iro-xe-16-book/iro-cfg.html