Routing

Intermediate system to intermediate system (IS-IS): "Both OSPF and IS-IS are link-state protocols and thus provide fast convergence. The convergence time depends on a number of factors (timers, number of nodes, type of router, and so on). IS-IS link-state database synchronisation is accomplished using special PDUs: PSNPs and CSNPs

(IS-IS):

Identifies the exit interface to use when forwarding packets to the destination network.

Outgoing interface:

: Identifies that the route was learned dynamically from another router using the RIP routing protocol.

R

Use RIPv2 as opposed to RIPv1 because RIPv2 supports VLSM.

RIPv2 as opposed to RIPv1

what sorts of memory do we have in the router

ROM: stores the routers bootstrap program, holds diagnostic software used on router power up. RAM: contains the running copy of the routers configuration file, stores the routing table. Contents are lost when the router is powered off. NVRAM (non-volatile random access memory): stores the startup configuration, which may include eg IP addresses, routing protocol info, the routers hostname etc. Flash memory: contains the Cisco IOS (the operating system).

longest match

most number of left most bits matching between the destination IP address and the route in the routing table

what does include routing table

network address and subnet mask for each interface

does routers pass the brodcast trafic

no

Use route poisoning to help prevent routing loops.

prevent routing loops.

You can see CDP information on your router / switch

show cdp neighbors' and 'show cdp neighbors detail' commands.

you will have to reconfigure the routing information if there is a topology change (ie where the existing next hop interface or exit interface are not accessible) and when the destination network no longer exists.

What do you have to do when use a static route

OSPF uses bandwidth to calculate the cost to a destination network.

What does OSPF use to calculate cost ?

1) Identifies how the network was learned by router 2) Identifies the destination network and how it is connected. 3)Identifies the interface the router connected to the destination network.

What does mack table do?

Identifies that the route was manually created by an administrator to reach a specific network. This is known as a static route.

What means S

Describe a router boot-up process (sequence):

When a router is powered on, it starts by (1.) performing a POST (power on self test) to verify that hardware is operations and present. The POST is stored in and run from ROM. 2. The bootstrap program (which is a program in ROM that is used to execute programs) checks the configuration register value to find out where to load the IOS. The default value of 0x2101 points the router to load the IOS Internetwork Operating System from Flash memory. 3. The IOS looks for a valid configuration file stored in NVRAM (startup-config). (Note: it can also look in other locations of there is not a config file in NVRAM). 4. Startup-config is loaded and the configuration commands in it are applied. 5. Once startup-config is loaded, the IOS will present the user with the CLI interface in user mode.

How does router work

When a router routes data it transmits the packet out of the correct interface to the next router, using information found in its routing table. This process is repeated router to router until the destination network is located.

The route lookup process:

1. Examine level 1 routes: if the best match is a level 21 ultimate route and is not a parent route then this route is used to forward the packet. 2. Examine level 2 (child) routes: if there is a match then that subnet is used to forward the packet, if no match then determine the routing behaviour type. 3. Determine classful or classless routing behaviour: if classful then the packet is dropped, if classless then the router searches level 1 supernet and default routes - if one exists then the packet is forwarded and if not the packet is dropped.

## measuring link utilisation (using SNMP) ## number of hops (hop count) ## speed of the path ## packet loss (router congestion/conditions) ## latency (delay) ## path reliability ## path bandwidth ## throughput [SNMP - query routers] ## load ## MTU In EIGRP, metrics is represented by an integer from 0 to 4,294,967,295 (The size of a 32-bit integer). In Microsoft Windows XP routing it ranges from 1 to 9999. A Metric can be considered as: ## additive - the total cost of a path is the sum of the costs of individual links along the path, ## concave - the total cost of a path is the minimum of the costs of individual links along the path, ## multiplicative - the total cost of a path is the product of the costs of individual links along the path." http://en.wikipedia.org/wiki/Metrics_(networking)

A Metric can include:

: Identifies the trustworthiness of the route source. IPv6 uses the same distances as IPv4. A value of 0 indicates the best, most trustworthy source.

Administrative distance

CRS

C = directly connected S = static route R = learned by the RIP routing protocol. If using you are using OSPF, routes learned via OSPF would be shown as O, if using EIGRP then D (eh? Yep, D for EIGRP Enhanced Interior Gateway Routing Protocol ) etc.

Device ID. ◾ Local interface. ◾ Holdtime. ◾ Capability. ◾ Platform. ◾ Port ID.

CDP

the process begins when the device is booting up. Each device sends out messages, which can also be called advertisements to all the other devices via a multicast IP address

CDP Operation

CDP

Cisco Discovery Protocol) for this process. CDP is used to share information about other directly connected Cisco equipment, such as IOS version and IP addressing etc. There is also an IETF neighbour discovery protocol called LLDP (Link Layer Discovery Protocol, which is part of the TCP/IP protocol stack and is typically used in wired Ethernet).

01-00-0c-cc-cc-cc

Cisco devices send CDP announcements to the multicast destination address

clear cdp counters

Clears all counters and sets holdtime etc to 0

Identifies that the route was learned dynamically from another router using the EIGRP routing protocol.

D:

Directly Connected 0 (Highest reliability) Static Route 1 EIGRP 90 Unknown 255 (Lowest Reliability)

Default Administrative Distance

The IPv6 address of the directly connected network.

Directly connected network

Uses hop count RIP, IGRP, IPX RIP

Distance Vector

Distance vector protocols (a vector contains both distance and direction), such as RIP, determine the path to remote networks using hop count as the metric. A hop count is defined as the number of times a packet needs to pass through a router to reach a remote destination.

Distance vector

The Bellman-Ford algorithm is an algorithm that computes shortest paths from a single source vertex to all of the other vertices in a weighted digraph. It is slower than Dijkstra's algorithm for the same problem, but more versatile, as it is capable of handling graphs in which some of the edge weights are negative numbers. The algorithm is usually named after two of its developers, Richard Bellman and Lester Ford, Jr., who published it in 1958 and 1956, respectively; however, Edward F. Moore also published the same algorithm in 1957, and for this reason it is also sometimes called the Bellman-Ford-Moore algorithm.

Distance vector:

Routing Information Protocol (RIP): Routing Information Protocol Version 2 (RIPv2): Routing Information Protocol Next Generation (RIPng), an extension of RIP version 2 with support for IPv6:

Examples of distance-vector routing protocols:

Distance vector routing protocols send their routing tables to directly connected neighbours.

How does the distace vector sendrouting table

Distance vector with more accurate update metrics IS-IS, EIGRP

Hybrid

Hybrid routing protocol:Hybrid routing protocol: have both the features of distance vector routing protocols and linked state routing protocols. One example is Enhanced Interior Gateway Routing Protocol (EIGRP)."

Hybrid routing protocol:

If you use several layer 3 protocols eg IP, IPX, Appletalk on a router, if vendor neutral routing is available (it should be) then OSPF is the best dynamic routing protocol to use.

If you use several layer 3 protocols eg IP, IPX, Appletalk on a router, if vendor neutral routing is available (it should be)

codes

L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2 i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2 ia - IS-IS inter area, * - candidate default, U - per-user static route o - ODR, P - periodic downloaded static route, H - NHRP + - replicated route, % - next hop override

Metrics are to do with choosing one route over another. The gateway / interface used is the route with the lowest metric. Router metrics are metrics used by a router to make routing decisions. It is typically one of many fields in a routing table. Metrics are used to determine whether one particular route should be chosen over another. The routing table stores possible routes, while link-state or topological databases may store all other information as well. For example, Routing Information Protocol uses hopcount (number of hops) to determine the best possible route. The route will go in the direction of the gateway with the lowest metric. The direction with the lowest metric can be a default gateway. Router metrics can contain any number of values that help the router determine the best route among multiple routes to a destination. A router metric typically based on information like path length, bandwidth, load, hop count, path cost, delay, Maximum Transmission Unit (MTU), reliability and communications cost.

Metrics

Uses Shortest Path First, Common View of Network NLSP, OSPF, IS-IS

Link State

cols calculate their network routes by building a complete topology of the entire network area and then calculating the best path from this topology or map of all the interconnected networks. SPF algorithm - Link-State routing protocols are designed around Dijkstra's Shortest Path First Algorithm (SPF) in which the shortest path from point A to point B is build around a metric of cost. Cost metric - SPF algorithm finds the shortest path based on a metric network link costs. Each router measures the cost of its own directly connected networks or "links." Cost is a measure of the quality of a link based mostly on bandwidth. Hello packets - Link-State routing protocols establish adjacencies with neighboring routers using hello packets. Link State Packets (LSP) - Initial flooding of link-states to all routers in the network. Topology or SPF Tree - Link-State routing protocols build and maintain a complete map or topology of the network area Link-State Advantages Faster Convergence - Unlike Distance Vector routing protocols which run algorithm calculations before sending updates, Link-State routing protocols send link-state updates to all routers in the network before running route calculations Triggered Updates - Unlike Distance Vector routing protocols (except EIGRP) which send periodic updates at regular intervals, Link-State routing protocols send LSPs during router startup (flooding) and when a link changes states like going up or down. If their are no changes in the network the protocol only sends hello packets to maintain adjacencies. Scalability - Link-State routing protocols support the ability to configure multiple routing "areas" which allows an administrator to segment a routing protocol processes to defined areas which supports the expansion and troubleshooting of much larger networks. Link-State Disadvantages Greater Processing Requirements - Link-State routing protocols typically demand greater processing power and memory resources from the router. Greater Administrator Knowledge - Link-State routing protocols can demand advanced administrator knowledge to configure and troubleshoot the network area

Link State

Link state verses distance vector - link state advantages: after the initial LSP flooding, they generally require less bandwidth to communicate changes in topology and each router independently determines the route to each network

Link state verses distance vector

Identifies the value assigned to reach the remote network. Lower values indicate preferred routes.

Metric

Identifies that the route was learned dynamically from another router using the OSPF routing protocol.

O:

When a packet arrives on a router interface, the router examines the IPv4 header, identifies the destination IPv4 address, and proceeds through the router lookup process.

Route Lookup Process

Identifies how the route was learned. Directly connected interfaces have two route source codes (C identifies a directly connected network while L identifies that this is a local route).

Route source:

• Ultimate route • Level 1 route • Level 1 parent route • Level 2 child routes

Routes are discussed in terms of:

show cdp interface fa0/0

Shows cdp information for that particular

• Route source: Identifies how the route was learned. • Destination network: Identifies the address of the remote network. • Administrative distance: Identifies the trustworthiness of the route source. • Metric: Identifies the value assigned to reach the remote network. Lower values indicate preferred routes. • Next hop: Identifies the IPv4 address of the next router to forward the packet to. • Route timestamp: Identifies from when the route was last heard. • Outgoing interface: Identifies the exit interface to use to forward a packet toward the final destination.

The entry identifies the following information:

• Route source: Identifies how the route was learned. Common codes include O (OSPF), D (EIGRP), R (RIP), and S (Static route). • Destination network: Identifies the address of the remote IPv6 network. • Administrative distance: Identifies the trustworthiness of the route source. IPv6 uses the same distances as IPv4. • Metric: Identifies the value assigned to reach the remote network. Lower values indicate preferred routes. • Next hop: Identifies the IPv6 address of the next router to forward the packet to. • Outgoing interface: Identifies the exit interface to use to forward a packet toward the final destination. When an IPv6 packet arrives on a router interface, the router examines the IPv6 header and identifies the destination IPv6 address. The router then proceeds through the following router lookup process. The router examines level 1 network routes for the best match with the destination address of the IPv6 packet. Just like IPv4, the longest match is the best match. For example, if there are multiple matches in the routing table, the router chooses the route with the longest match. A match is made by matching the far left bits of the packet's destination IPv6 address with the IPv6 prefix and prefix-length in the IPv6 routing table."

The entry identifies the following information: ip 6

bandwidth is not a realistic representation of modern networks. It is used only to provide a visual sense of link speed.

The reference bandwidth

istance Vector protocols know routes by measures of distance and vector(direction) as reported by neighboring routers,

istance Vector routing protocols.

fe80:

link-local addresses

An ultimate route is a routing table entry that contains either a next-hop IPv4 address or an exit interface. Directly connected, dynamically learned, and local routes are ultimate routes.

Ultimate Route

main kind of interface

lookback FDDI ATM Asynchronous Transfer Mode is a type of WAN / telecomms connection)

routing table entries

can come from directly connected networks, static routes or dynamic routes

Network discovery

etworking information from devices (eg routers, switches etc) on your network and advertising this information to other devices on the network. There are two (that I have found) methods of doing this, ARP cache discovery and Ping sweep discovery.

How can be configured routing information

static dynamic

rollover cable

used for connecting a PC to a console port.

EIGRP's to metrics are bandwidth and delay (both are used to determine a best path).

what does EIGRP use to metrics?