Network Layer Reviews

Routing

understanding routing Understanding Routing

Routing is the method of shifting packets by way of an internetwork, such because the Web.

Routing truly consists of two separate, however associated, duties:

  1. Defining paths for the transmission of packets by means of an internetwork.
  2. Forwarding packets based mostly upon the outlined paths.

Routing takes place in IP networks, based mostly on IP routing tables and its entries. The knowledge within the IP routing tables is utilized by IP hosts to switch knowledge over the internetwork. Routers are units working on the community layer of the OSI mannequin that use the IP routing tables to ahead visitors which it receives from a number or from a router.

Earlier than truly configuring LAN routing, one of many first elements to determine on is the connection sort that will probably be used for the distant website connection.

A lot of applied sciences exist that can be utilized for distant community connections, together with:

  • Body Relay: This can be a WAN know-how that makes use of different hardware elements to determine distant website connections. A body relay connection makes use of an ordinary leased line which connects the community website to the body relay supplier’s nearest level of presence (POP). The body relay supplier then delivers the connection to the body relay cloud. In an effort to use the body relay supplier for a LAN-to-LAN connection, it’s a must to set up a leased line at every website which connects the community to the closest level of presence (POP) of the body relay supplier. The body relay supplier is then answerable for connecting the strains to the identical body relay cloud so that a connection might be established between the 2 networks.The advantages of utilizing the body relay WAN know-how are:
    • Body relay supplies flexibility.
    • Every of your websites might be related to an area level of presence (POP) which in flip results in decreased value of the leased strains.
    • You possibly can hook up with a number of websites utilizing a single body relay connection.
    • You pay for less than the bandwidth that’s used.
    • Contracted bandwidth might be exceeded when heavy visitors circumstances are current.
  • Leased strains: Devoted leased strains are additionally sometimes used to attach distant networks. Whereas devoted leased strains are generally used for WAN hyperlinks to allow distant community connectivity, buying and sustaining leased strains are costly. Along with this, you must pay for allotted bandwidth on a regular basis. This is because of leased strains being classed as persistent connections. Because of this the connections are everlasting connections, and stay open on a regular basis.
  • Dial-on demand connections: Whereas the WAN connections offered by Built-in Service Digital Community (ISDN) and commonplace asynchronous modems are sometimes slower than devoted leased strains, they are often disconnected at any time, and can be used to allow connectivity to totally different places. One of many principal traits of dial-on demand connections is that you simply pay for the precise bandwidth that you’re utilizing.
  • Digital personal networks (VPNs): Distant entry VPNs supplies a standard surroundings the place many various sources comparable to intermediaries, shoppers and off-site staff can entry info by way of net browsers or e-mail. Many corporations provide their very own VPN connections by way of the Web. Via their ISPs, distant customers operating VPN shopper software program are assured personal entry in a publicly shared surroundings. Through the use of analog, ISDN, DSL, cable know-how, dial and cellular IP; VPNs are carried out over in depth shared infrastructures. Distant entry VPNs supply a number of benefits, together with the elimination of WAN circuit and modem prices, cable modems allow quick connectivity and are comparatively value environment friendly, new customers may be added with hardly any prices, and knowledge is definitely and speedily accessible to off-site customers via Web connectivity.

The elements of unicast IP routing are described under:

  • Static IP routing: You need to use the Routing And Distant Entry administration console to configure and handle static routes. Static routes are manually created, and have to be modified each time a change happens to the community configuration.
  • RIP variations 1, RIP model 2: RIP is a distance-vector routing protocol which is generally used for dynamic routing in small to medium sized internetworks.
  • OSPF: This can be a link-state routing protocol that’s used for dynamic routing in medium to giant sized internetworks
  • Community handle translation (NAT): NAT interprets personal IP addresses to Web IP addresses that may be routed on the Web.
  • IP packet filtering: This can be a safety function that lets you outline the visitors varieties which might be allowed to cross over an interface. Whenever you configure IP packet filters, you specify what visitors is allowed/denied, based mostly on the next:
    • Supply tackle
    • Vacation spot tackle
    • TCP port quantity
    • UDP port quantity
    • IP protocol numbers
    • ICMP varieties and codes
  • DHCP Relay Agent: This can be a relay agent that forwards DHCP messages between the DHCP servers and DHCP shoppers which might be situated on totally different community segments.
  • ICMP router discovery: ICMP router discovery makes is feasible to promote and reply to router solicitations.

The elements of IP multicast routing are described under:

  • Multicast forwarding: Multicast forwarding is a component of the TCP/IP protocol suite. You need to use the Routing And Distant Entry administration console or the Netsh command-line software to look at the content material of the multicast forwarding desk.
  • IGMP model 1 and IGMP model 2: IGMP is a protocol of the TCP/IP protocol suite that’s used to handle and management multicast group membership.
  • Multicast boundaries: You possibly can configure multicast boundaries, based mostly on the next:
    • Time-To-Reside (TTL) specified within the IP header.
    • IP multicast group handle.
    • Most multicast visitors allowed in kilobytes per second.
  • Particular forwarding and routing: A Home windows 2000 Server or Home windows Server 2003 router can help particular multicast forwarding and routing if IGMP Router mode and IGMP Proxy mode are enabled for interfaces.

The elements of IPX routing are described under:

  • IPX packet filtering: This can be a safety function that lets you outline the visitors varieties which are allowed to cross out and in of an interface. If you configure IPX packet filters, you specify what visitors is allowed/denied, based mostly on the next:
    • Supply and vacation spot IPX community
    • Packet sort
    • Node
    • Socket numbers
  • RIP for IPX: This can be a distance-vector routing protocol that’s used on IPX internetworks. You’ll be able to configure each static IPX routes and RIP route filters by way of the Routing and Distant Entry Service (RRAS).
  • SAP for IPX: This can be a distance-vector promoting protocol that advertises providers and every service’s location on IPX internetworks. By means of the Routing and Distant Entry Service (RRAS), you’ll be able to configure:
    • Static SAP providers
    • SAP service filters
  • NetBIOS over IPX: By way of the Routing and Distant Entry Service (RRAS), you’ll be able to configure:
    • RRAS to ahead NetBIOS over IPX broadcasts
    • Static NetBIOS names

Routing vs. Bridging and Switching

Routing is distinguished from bridging or switching by working on the Community Layer of the OSI Mannequin. Bridging and switching happen on the Knowledge Hyperlink Layer.

Static vs. Dynamic Routing

Routing might be completed by manually getting into the knowledge mandatory for packets to succeed in any a part of the internetwork into every router. That is referred to as static routing.

Static routing works fairly nicely for very small networks, however doesn’t scale nicely. When utilizing static routing, the routing tables on every router have to be up to date every time the community topology modifications — similar to when a community hyperlink fails..

In most networks, routing is managed routinely by way of using dynamic routing. In dynamic routing, routing protocols create and keep the routing tables routinely. Dynamic routing responds far more shortly to community modifications (and community failures) than static routing.

Understanding Static Routing

With static routing, routing protocols usually are not used to speak routing info between IP ruters. Directors should manually create and modify the routing desk entries. Every time a change happens within the community configuration, the entries within the routing desk should be modified to mirror these modifications. Static routing works nicely in a small community the place it’s simpler to configure a small variety of static routes than it’s to configure dynamic routing.

A couple of benefits of utilizing static routing are:

  • Static routing is straightforward to deploy and configure.
  • As a result of static routing doesn’t contain routers speaking between one another, it really works nicely for low bandwidth WAN hyperlinks.
  • Static routes can supply help for unnumbered connections.
  • Static routes usually are not as useful resource intensive because the dynamic routing protocols.

A number of disadvantages of utilizing static routing are:

  • Static routing solely works for small networks the place enlargement isn’t probably.
  • Sustaining static routes turns into pricey because the community expands.
  • Static routing supplies no fault tolerance. If a route is incorrectly configured, the route stays unavailable till the difficulty is manually resolved.

Understanding Dynamic Routing

With dynamic routing, the necessity to manually create and keep static routes is eradicated. Dynamic routing use routing protocols in order that IP routers can talk with one another. The routing protocols additionally allow routers to share the knowledge they’ve of their routing tables. A router that’s configured to make use of dynamic routing forwards its routing desk’s content material to the opposite routers configured for dynamic routing at common time durations or intervals. When a router doesn’t ship its routing desk on the specified time interval, the opposite routers merely take away the router from their routing tables. This course of prevents visitors from being forwarded to the failed router. As soon as the failed router is on-line once more, the router begins sending dynamic routing messages which allows the opposite routers to find out that visitors might be forwarded to the router once more. This in flip causes the opposite routers to replace their routing tables to incorporate the precise router as soon as extra.

One of many fundamental elements to think about when deciding on implementing dynamic routing is the precise routing protocol that you’ll use. The Routing and Distant Entry service (RRAS) consists of built-in help for the next dynamic routing protocols:

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