Internetwork Design

Dynamic Host Configuration Protocol (DHCP) is used to dynamically assign IP addresses to workstations on the network. It allows network administrators to more easily manage the deployment of the IP address space by managing the IP addresses and reallocating unused addresses.

The following address spaces have been set aside by the Internet Assigned Numbers Authority. This department of InterNIC allows organizations to use these private IP address groups as they wish with no need to register them. These addresses are not unique and can only be used within an enterprise network. Private Class A addresses 10.0.0.0 (1 Class A) Private Class B addresses 172.16.0.0 - 172.31.0.0 (16 Class B) Private Class C addresses 192.168.0.0 - 192.168.255.0 (256 Class C)

The following address spaces have been set aside by the Internet Assigned Numbers Authority. This department of InterNIC allows organizations to use these private IP address groups as they wish with no need to register them. These addresses are not unique and can only be used within an enterprise network. Private Class A addresses 10.0.0.0 (1 Class A) Private Class B addresses 172.16.0.0 - 172.31.0.0 (16 Class B) Private Class C addresses 192.168.0.0 - 192.168.255.0 (256 Class C)

The following address spaces have been set aside by the Internet Assigned Numbers Authority. This department of InterNIC allows organizations to use these private IP address groups as they wish with no need to register them. These addresses are not unique and can only be used within an enterprise network. Private Class A addresses 10.0.0.0 (1 Class A) Private Class B addresses 172.16.0.0 - 172.31.0.0 (16 Class B) Private Class C addresses 192.168.0.0 - 192.168.255.0 (256 Class C)

IS-IS, RIP II and OSPF are link state routing protocols. These protocols support VLSM and transmit the subnet mask with their routing updates.

RIP and IGRP are standard Distance Vector routing protocols. These protocols do not advertise the subnet masks with the routing protocols. RIP and IGRP do not support VLSM or discontinuous subnets. The maximum hop count for distance vector routing protocols is 15 hops.

There are three types of connections defined by the OSPF routing protocol. Point-to-Point - Neighbor relationships are formed only with the other router on the Point-to-Point link. Broadcast Multiaccess - This router can communicate with all other routers on the LAN and shares learned information with other local routers. Neighbor relationships are formed dynamically using multicast hellos. Nonbroadcast Multiaccess - All routers might not communicate with each other. Neighbor relationships are manually configured.

There are four types of OSPF routers. Internal Router - A router with all directly connected routers in the same area Area Border Router - A router that connects multiple areas Backbone Router - A router that has an interface connected to the backbone Autonomous System Border Router - A router that shares information with other routers belonging to other autonomous systems.

There are four types of LSAs in OSPF Routing. Router Link Advertisement - Contains information about the sending router's links to its neighbor routers Network Link Advertisement - Contains a list of routers connected to the segment Summary Link Advertisement - Contains a list of routers that are reachable for outside the area External Link Advertisement - Contains information about routes to a destination outside the autonomous system.

All OSPF routers within an area have exactly the same link state database of all heard LSAs within the area.

The SPF hold down algorithm is called the Dijkstra Algorithm, after the scientist who invented it.

In an OSPF multiaccess network, it is necessary to have a designated router and a backup designated router (BDR). A designated router is the router with the highest priority. The priority for each interface is set with the IP OSPF PRIORITY command. The default priority value for an router interface is 1.

The address of the backbone in OSPF is Area 0 (0.0.0.0)

Virtual links are used to connect areas to the backbone that are not directly connected to the backbone. The performance of virtual links are slower then normal links and also add complexity and overhead to the network design. It is recommended that network designs which include virtual links be kept to a minimum.

OSPF supports discontinuous subnets because of the fact that the subnet mask is sent as part of the link state database updates.

OSPF routers exchange information with designated routers and the BDR on a preset interval. By default the OSPF Hello Timer is set to 10 seconds.

IS-IS, RIP II and OSPF are link state routing protocols. These protocols support VLSM and transmit the subnet mask with their routing updates.

To prevent routing loops IGRP uses Split Horizon. By default Split horizon is on. Split Horizon is off by default in a Frame Relay network.

In IGRP, a 1500 byte routing update can contain a maximum of 104 routes.

By default the Hold-Down timer is 280 seconds. The Hold-Down timer is three times the update interval plus 10 seconds.

The following are the default values for the IGRP timers: Update Interval: - Time between routing updates (90 seconds) Invalid Timer: - 3 times the update interval (270 seconds) Hold-down timer: - Three times the update interval plus 10 seconds (280 seconds) Flush Timer: Seven times the update interval (630 seconds)

To get IGRP to converge much more quickly it is necessary to turn off holddown. To turn off holddown with the NO METRIC HOLDDOWN command.

In IGRP the default value of the flush timer is seven times the update interval (630 seconds)

The following protocols are used by the Apple talk protocol suite: RTMP - Routing Protocol ZIP - Zone Information Protocol NBP - Name-to-Number Translation, Similar to IP DNS AARP - Apple talk Address Resolution Protocol

When using route summarization, only summary-link LSAs propagate into the backbone. Less traffic increases the stability and responsiveness of the network. The more summarization, the more stable the network becomes.

IS-IS, RIP II and OSPF are link state routing protocols. These protocols support VLSM and transmit the subnet mask with their routing updates.

Cisco has a unique terminology for commonly known encapsulations. Below is a list of the common technologies with there corresponding Cisco term:
Encapsulation - Cisco Terminology
Ethernet 802.3 - novell-ether
Ethernet SNAP - snap
Ethernet 802.2 - sap or iso1
Ethernet II - arpa
FDDI SNAP - snap FDDI
802.2 - sap or iso1
Token Ring - novell-tr
Token Ring SNAP - snap

In most cases IGRP converges in one second. In a worst case scenario it will take three times the hello interval plus one second to converge (16 seconds).

Novell Netware uses Service Advertisement Protocols (SAP) to advertise assorted services such as printer and server processes. Novell IPX RIP is a distance vector routing protocol used in the discovery of routes and routers on the network. NetBIOS emulation is used to allow Windows networking devices to communicate over an IPX network.

Novell uses RIP for its distance vector routing protocol. NLSP is used by Novell for its link state routing protocol.

The following is a breakdown of the RTMP protocol: RTMP - Routing Protocol Max HOP count - 15 Hops RTMP Updates - Every 10 seconds Split Horizons - Does not use Split Horizon Routing Table updates - Every 25 seconds.

The flush timer can be set as necessary, with the default value being 180 seconds.