Routing Principles

Administrative Distance.

Route Source	Default Distance
Connected Interface	0
Static Routes	1
EIGRP Summary route	5
External BGP	20
Internal IGRP	90
OSPF	110
IS-IS	115
RIP	120
EGP	140
External EIGRP	170
Internal BGP	200
Unknown	255

Routing Decision

• First check is the Administrative Distance for routing decision, in case of the same protocol, the metrics will be the decision which will depend for each protocol how the metric is built.
• Default, Cisco router supports up to 4 equal metric paths to a common destination. Maximum of 6 paths can be configured by the IOS. IP Load balancing is enable by default.
• RIP metric is the hop count
• IGRP metric is composite of Bandwidth, delay, reliability, load and MTU. Only Bandwidth and Delay are enable by default.

Router Forward Traffic

• Routing protocol maintain neighbor relationship with adjacent routers
• Router forwarding the traffic based on the next hop logical device.

Classful

• RIPv1 and IGRP
• Routing table does not carry the routing MASK.
• In the network, the class is assumed
• The creation of classful summary route at major network boundaries is handled automatically by classful
• Classful requires all the routers interfaces with the same subnetmask in case of use subnetting.

Classless

• OSPF, EIGRP, RIPv2, IS-IS and BGP
• RIPv2 and EIGRP are distance vector technologies, but they advertise mask, which is the characteristic of the classless routing. RIPv2 sends periodically updates and EIGRP send event-triggered updates
• Classless can support different subnet masks (VLSM)

Distance Vector Operation

• In a pure distance vector environment, the routing table update includes a complete routing table. Routing updates are only propagated to directly connected neighbors.
• RIP use UDP (Protocol number 17, TCP is 6) with port number 520

Characteristic	RIPv1	RIPv2	IGRP	EIGRP
Count to infinity	X	X	X
Split horizon	X	X	X	X
Hold-down timer	X	X	X
Triggered updates with route poison	X	X	X	X
Load balancing equal paths	X	X	X	X
Load balancing unequal paths			X	X
VLSM support		X		X
Routing algorithm	B-F	B-F	B-F	DUAL
Metric	Hops	Hops	Composite	Composite
Hop count limit	15	15	100*	100*
Scalability	Small	Small	Medim	Large

B-F : Bellman-Ford

DUAL: Diffusing Update Algorithm

* Hop count limit is 100, but the maximum is 255

Link State Routing

• Link state generate a update only when has an change in the network
• When the Router detect the change, create a LSA (Link State Advertisement) concerning that link . The LSA is propagate to all neighbors devices using a multicast address. Each router, make a copy of the LSA , update the database and forwards the LSA to all neighbors. This flooding of LSA is required to ensure that all routers update their databases.
• Most Link State routing protocol require a hierarchical design, especially to support proper address summarization. The hierarchical creating multiples area, reduce the need of flood an LSA to all devices in the routing domain.

Characteristic	OSPF	IS-IS	EIGRP *
Hierarchical topology required	X	X
Retain all possible routes	X	X
Route summarization manual	X	X	X
Route summarization automatic			X
Event Triggered announcements	X	X	X
Load balancing equal paths	X	X	X
Load balancing unequal paths			X
VLSM support	X	X	X
Routing Algorithm	DIJKSTRA	IS-IS	DUAL
Metric	Cost	Cost	Composite
Hop count limit	Unlimited	1024	100**
Scalability	Large	Very Large	Large

EIGRP is an advanced distance vector protocol, but demonstrates some Link state feature

Default configuration is 100, but the maximum is 255.

Convergence

• • Convergence is the time it takes for all routers to agree on the network topology after a change.
  • Convergence time affected by:

1. update mechanism (hold down timers)
2. Size of topology table
3. Route calculation algorithm
4. Media type
5. Hold down time for RIP is 180 seconds
6. Hold down time for IGRP is 280 seconds
7. EIGRP convergence is very fast
8. OSPF convergence may vary between 6 to 40 seconds in a small network

Routing updates

• Distance vector send a full table
• Link state send only a single entry (change), when the event happen.
• Classful does not send the subnet mask information
• Classless does send the subnet mask information

Routing table

• The entries are listed in a efficient search order, which simplifies the search mechanism
• Load balancing is enable by default
• Commands: SHOW IP ROUTE or CLEAR IP ROUTE

Routing Protocol Comparison

Characteristic	RIPv1	RIPv2	IGRP	EIGRP	OSPF
Distance Vector	X	X	X	X
Link State					X
Automatic Summarization	X		X	X
VLSM support		X	X	X	X
Proprietary			X	X
Scalability	Small	Small	Medium	Large	Large
Convergence time	Slow	Slow	Slow	Fast	Fast

IP Addressing Scheme

Subnetting

• Moving the network boundary to the right creates additional subnetworks at the expense of fewer hosts on each segment

IP Address Classes

• 001 – 126 Class A
• 128 – 191 Class B
• 192 – 223 Class C
• 224 – 239 Class D – Multicast use (OSPF 224.0.0.5, 224.0.0.6, RIPv2 224.0.0.9, EIGRP 224.0.0.10)
• 240 – 254 Class E – Used for experimental purpose

Hierarchical Addressing

• Reduce the number of route table entries by summarize multiple addresses into route summaries. Reduce the router requirements, like CPU, memory, fast convergence, easier troubleshooting.
• Efficient allocation of addresses via contiguous addressing allow to use all possible addressing. Main in case of classful.

VLSM

• Provide the ability to include more than one subnet mask within a network and ability to subnet an already subnneted network address. Basically, we have to map all the subnet and check where we have a common subnet for all subnets.

Route Summarization

• Routing protocols can summarize addresses of several networks into one address.
• Routing summarization is also called ROUTE AGGREGATION and SUPERNETTING
• Route summarization is more effective within a subnetted environment when the network addresses are in contiguous block in powers of two.
• Classless routing protocols support route summarization based on subnet addresses, including VLSM addressing.
• Classful routing automatically summarize routes based on the class network boundary.
• To determine the summary route, the router determines the number of highest order bits match in all network addresses, to allow the router to aggregate the most number of IP addresses into a single route summary.
• Implementations considerations:
  1. Multiple IP Addresses must have the same highest order bits
  2. Routing decisions are made based on the entire address
  3. Routing protocols must carry the prefix length (Subnet mask)

Route summarization at Cisco Routers

• /32 Host
• /27 Subnet
• /24 Network
• /16 Block of networks
• /0 Default

Summarizing Discontinuous Network

• RIPv1 and IGRP do not support Discontinuous Network
• OSPF, EIGRP and RIPv2 can advertise subnets and therefore can support discontiguous subnets
• This situation can be resolved by using RIPv2, OSPF or EIRGP and not using summarization, because the subnet routes would be advertised with their actual subnet mask. The Classless routing protocols use the longest prefix match when selecting a route from the routing table.
• IP Unnumbered feature permits noncontiguous subnets to be separated by an unnumbered link.

Classless Interdomain Routing (CIDR)

• CIDR is a mechanism develops to help alleviate the problems of IP address exhaustion and routing table growth. The idea behind CIDR is that blocks of multiple Class C addresses can be combined or aggregated to create a larger classless set of IP addresses.
• Blocks are summarized in routing tables

IP Unnumbered Interfaces

• IP unnumbered interface enable IP processing on a serial interface without assign an explicit address to the interface
• Serial interface using HDLC, PPP, LAPB , FR and SLIP can be unnumbered, but it is not possible with X.25 and SMDS
• You cannot ping the interface, because has no address, but you can use the SNMP to check the status of the interface.
• Important: Using unnumbered serial interface line between two major networks requires a special care. If each end of the link there are different major networks assigned to the interfaces you specified as unnumbered then any routing protocol running across the serial line must not advertise subnet information.

Configuration example:

a. Interface Ethernet 0

b. Ip address 10.10.1.1 255.255.255.0

c. Interface serial 0

d. Ip unnumbered Ethernet 0

Obs: Loopback is often used because is more stable interface because never goes down.

Helper addresses

· Router do not forward broadcast by default, helper address provide selective connectivity to same broadcast.

· Sometimes clients do not know the server address, helper address change local broadcast to unicast or directed broadcast to reach the server. By defaul the command IP DIRECTED BROADCAST is disable

IP Helper commands:

· Under interface. Ip helper-address ip address

· Under global. Ip forward-protocol UDP port/ND/SDNS

· By default, when we enable the ip helper-address command, we forwarding the following UDP ports automatically :

a. TFTP – 69

b. DNS – 53

c. Time – 37

d. Netbios name service – 137

e. Netbios datagram service – 138

f. Bootp server – 67

g. Bootp client – 68

h. TACACS – 49

Configuring OSPF in a Single Area

• OSPF is a link state technology, as oppose to a distance vector technology. The OSPF protocol performs the two basic primary functions of every routing algorithm : Path Selection and Path Switching.

Benefits of the OSPF

· Fast convergence

· Supports VLSM

· Processes updates efficiently, only send updates when changes happen. Only send one update every 30 minutes to synchronize, but not every 30 seconds like RIP updates.

· Selects path based on bandwidth is based on the cost which for the Cisco routers is based on the speed of the connection.

· Supports equal-cost multipath

OSPF in IP Packet

· OSPF is a link state routing protocol

· Relies on IP packet delivery routing information

· Use protocol number 89. ( Don’t use TCP or UDP)

OSPF Terminology

· Interface: The connection between the routers and the attached networks.

· Link State: The status of the link between two routers, that is, a router interface and its relationship to its neighboring routers. The special packet used to advertise the link states is called LSA (Link State Advertisements)

· Cost: The value assigned to a link . Rather than number of hops, link state protocol assign a cost to a link . For OSPF on Cisco router, the cost is based on the speed of the media, associated with the output side of each router interface, referred to as Interface Output Cost.

· Autonomous System: A group of routers exchanging routing information using a common routing protocol

· Area: A collection of networks and routers that have the same area identification

· Neighbors: Two routers that have interfaces on a common network. A neighbor usually discovered and maintain by Hello protocol.

· Hello: Protocol used by OSPF to establish and maintain neighbor relationships

· Neighborship database: A list of all the neighbors to which a router has established bi-directional communication.

· Link State Database: Also called topological database. Show the network topology

· Routing table: Also called forwarding database which is generated by the algorithm.

OSPF Topologies

Broadcast Multiaccess Topology

• Examples of operation in Broadcast environments are Ethernet or Token Ring.
• Hello packets are sent periodically using IP Multicast address 224.0.0.5
• Information in the hello packet:
• Router ID – 32 bits number that unique identifies the router within AS. The highest IP address on active interface is chosen by default. Also is used to decide the DR and BDR election processes if the priority values are equal.
• Hello – Interval for Broadcast Multiaccess networks is 10 seconds. Dead intervals is four times hello interval by default.
• Neighbors – Indicates when the router see itself listed in the neighbor hello packet
• Area ID – Share the common segment, should belong to the same are.
• Router priority – An 8 bit number that indicates the priority of this router when selecting a designated DR and BDR
• DR and BDR IP Address – If known , will have the IP address of the DR and BDR
• Authentication password – If the authentication is enable, two routers must exchange the same password. Authentication is not required, but if enable all peer must have the same password.
• Stub area flag – Two routers must agree on the stub area flag in the hello packets.N

All the parts of the Hello packet in bold must match in the neighboring.

• Hellos elect DR and BDR to represent segment
• Each router then forms adjacency with DR and BDR
• Priority to elect the DR and BDR

· Router with highest priority is the DR

· Router with second highest priority is the BDR

· Default OSPF priority in the interface is 1. If all routers are using 1, the highest Router ID will become the DR. Usually the highest IP address on active interface is used as the router ID

· Router set priority to Zero is ineligible to become the DR and BDR

• Exchange Process
• Down state: Have not exchanged any route
• Init state: When receive a hello packet and add the route of the neighbor
• Two-way state: At this point, all the router have the neighbor in their list of neighbors.
• Exstart state:
• Exchange state:
• Discovering Routes after DR and BDR have been elected start to execute the EXCHANGE PROTOCOL:

· Exstart state

· Exchange state

· Loading state

· Full state

Maintain the routing information

· Router use the flooding process

· Router A notifies all OSPF DRs on 224.0.0.6

· DR notifies others on 224.0.0.5

Point to point topology

· Router automatically detects its neighbor router using hello protocol

· No election: Adjacency is automatic as soon as two routers can communicate

· OSPF packets are always sent multicast 224.0.0.5

· The default OSPF hello and dead intervals on point to point topologies are 10 seconds and 40 seconds, respectively.

Nonbroadcast Multiaccess Topology

· Single interface interconnects multiples sites

· NBMA topologies support multiple routers but without broadcasting capabilities

· The default OSPF hello and dead intervals on point to point topologies are 30 seconds and 120 seconds, respectively.

· By default , a frame relay network provides NBMA connectivity between remote sites. Routing updates have to be replicated by the routers

· DR Selection in NBMA topology, OSPF considers NBMA to be like other broadcast media. DR and BDR need to have full physical connectivity with others routers. DR and BDR need a list of neighbors.

· NBMA Modes:

Nonbroadcast Multiaccess (NBMA) – RFC : Simulate OSPF in Broadcast Multiaccess . The routers exchange update traffic to identify their neighbors and elect DR ad BDR. This configuration seen in fully meshed networks. Some configuration, which will be described later in this lesson, is necessary on the router for this mode work properly. ( THE NEIGHBOR WILL HAVE TO BE CONFIGURED STATICALLY) This process is CPU and Bandwidth intensive.

Point to Multipoint – RFC : Treats the Nonbroadcast network as a collection of point to point links. In this environment, the routers identify their neighbors but not elect a DR and BDR. Subinterfaces, typically used in NBMA topologies can be point to point and point to multipoint. Subinterfaces were originally created to better handle issues caused by split horizon over NBMA and Distance vector protocols. Point to point subinterfaces has the properties of any physical point to point interface. Multipoint subinterfaces routing IP, all routers are in the same subnet. The default OSPF mode on a point to point subinterface is point to point mode; the default OSPF mode on a point to multipoint subinterface is NBMA mode.

NBMA Mode Neighborship

· Usually full meshed

· DR/BDR

· Neighbor must be statically configured

· One IP subnet

· Stability of the network may be an issue

· Replicate LSA packets

· RFC2328

Point to Multipoint

· Partially meshed or star topology

· No DR/BDR

· Neighbors do not need to be statically configured, because the Point to Multipoint is threat as a collection of point to point.

· One IP Subnet

· Replicate LSA packets

· RFC2328

Point to Multipoint NBMA – Cisco It is an extension of the RFC and with this mode statically define neighbors , can modify, if necessary, the cost of the link to the neighbor to reflect the different bandwidth in each link. The RFC was develop to allow dynamic neighbor discovery, however some point to multipoint networks use non broadcast media (such as classic IP over ATM) and therefore cannot use the RFC mode because the router cannot dynamically discover its neighbors

Broadcast – Cisco This approach is workaround for statically listing all existing neighbors. The interface will be logically set to broadcast and will behave as if router were connected to a LAN. DR and BDR election still be performed and a Static selection of the DR based on the interface priority.

Point to Point – Cisco The point to point mode is used when only two nodes exist on NBMA network. This mode is typically only used with point to point subinterfaces. Each point to point connection is one ip subnet. There is no DR and BDR.

Configuring OSPF

· Router ospf ID-Process

· Network ip prefix wild mask area number

· Int level – IP ospf priority (0-255) Default is 1 and 0 define that cannot be elect as DR or BDR

· Int level – Ip ospf cost cost (default is 1 for 100Mbps)

Configurinf OSPF over NBMA

· (config-int) ip ospf network non-broadcast (NBMA Mode)

· (config-int) ip ospf network point-to-multipoint (Point to Multipoint mode)

· (config-int) ip ospf network broadcast (Broadcast Mode)

· (config-int) ip ospf network point-to-point (Point to Point mode)

Verify OSPF Operation

· Show ip route

· Show ip protocols

· Show ip ospf interface (Display area-id and adjacente)

· Show ip ospf (Display OSPF timers and statistics)

· Show ip ospf neighbor detail (Display DR, BDR and neighbor)

· Clear ip route *

· Debug ip ospf (options: events, flood, packet, retransmission, spf, tree)

Interconnecting Multiple OSPF Areas

OSPF Hierarchical Routing

· Consists of areas and autonomous systems

· Minimizes routing update traffic

Type of Routers

· Internal Routers

· ABR – Area Border Routers

· ASBR – Autonomous Systems Boundary Router

· Backbone Routers

Type of LSA

· Type 1: Router link entry – Only flooded within the particular area

· Type 2: Router network entry – Only flooded within the particular area generated by DRs

· Type 3 and 4: Summary link entry – Originated by ABRs. Type 3 LSA describe routes to networks within the local area and are sent to backbone area. Type 4 LSA describe reachability to ABSRs.

· Type 5: External link entry – Originated by the ASBR. These entries are flooded throughout an OSPF autonomous system except for STUB, TOTALLY STUB and NOT SO STUBBY AREAS.

· Type 6: Group membership entry

· Type 7: Not So Stub Area (NSSA). Similar to Type 5, but only flooded within the NSSA.

Type of Areas

· Stub Area – Does not accept external LSAs

· Totally Stubby Area – Does not accept external or summary LSAs

· Backbone Area – Interconnect all areas, accept all LSAs

· Standard Area – Configuring as Single area

Virtual Link

· Backbone is the center of communications

· Virtual link provide path to backbone

· Avoid configuring virtual link if possible

· Link discontiguous backbone: merge networks, redundancy, point to point

Configuring ISIS Protocol

OSI Protocols Terminology

· ES (Host)

· IS (Router)

· Area (former by contiguous hosts and routers)

· Domain is a collection of connected areas

There are two types of network layer are available to the OSI transport layer:

· CLNS/CLNP

· CMNS/CONP

OSI Network Services Routing Protocols

· ES-IS discovery protocols: routing between ES and IS (level 0)

· IS-IS routing protocols: hierarchical routing between IS (Level 1, 2 and 3)

OSI router in operation

· ESs discover the nearest IS by listening to ISH (hello) packets

· If the destination address of the ES is another area, level 1 router send to the nearest Level 2 router

· Routing between different domain is level 3 routing

· Routing between different areas in the same domain is level 2 routing

ISIS Routing

· ISIS is a dynamic link state routing protocol to routing CLNP

· Alternative to ISIS protocols is deploying CISCO ISO-IGRP and Static Routing

Integrated ISIS vs OSPF

· Integrated ISIS is an extended version of the ISIS for mixed ISO CLNS and IP environments

· Integrated ISIS represents an alternative to OSPF in the IP world

· Integrated ISIS and OSPF both are Link State Protocol:

§ Link state representation, aging, metrics

§ Link state database

§ Update, decision and flooding processes

· Area Design

§ OSPF is based on central backbone with other areas being attached to it

§ Each link belongs to one area

§ ISIS router belongs to exactly one level 2 area

§ ISIS allows a more flexible approach to extending the backbone (at least 1000 routers can reside in a single area)

· Resource usage

§ One link state packet per ISIS router in one area compared to many LSAs. ISIS needs less CPU

· Scalability

§ Convergence capabilities are similar. Based on the default timers, ISIS is quicker than OSPF. ISIS tends to be less CPU intensive than OSPF.

§ OSPF has more features

Operation ISIS

• The OSI addressing is implemented with NSAP
• ISIS-NSAP address is Area address, System ID and N-Selctor
• Total length of NSAP from 8 up to 20, the area field from 1 to 13.
• ISO-IGRP NSAP is Area Address, domain, System ID and N-selector
• ISO-IGRP requires at least 10 bytes, domain from 1 to 11 and area 2 octes, 6 for System ID and 1 for N-Selector (is ignored by ISO IGRP)
• NET Addressing is a NSAP address with service identifier of 00, used in routers to identify themselves in the LSPs and used for route calculation since they implement network layer only (base for SPF calculation)
• AFI=49 is for private addresses and AFI values from 39 to 47 represent the ISO Data Country Code.
• AREA address uniquely identifies the routing area and the System ID identifies each node.
• ES must be adjacency to level 1 router.
• The System ID must be unique inside the area for level 1 router a unique for domain in level 2 routers. Usually is used MAC address for CLNS and IP for Integrated ISIS

ISO ISIS PDU (Protocol Data Unit)

• ISIS header 0×83
• ESIS header 0×82
• CLNP header 0×81

The link state Packets Network representations are available in two modes:

• Broadcast – LANs
• Nonbroadcast – Media type must be address ES and are typically WAN
• The representations are: Broadcast for LANs and Point to Point to all other medias

Link state packets

• Router describe itself with Link State Packet (LSP)
• LSP contains LSP header ( with PDU type, Length , LSP ID, Sequence number, remaining lifetime – default 1200) and TLV (IS neighbor, ES neighbor, authentication information) variable fields
• The default sequence number is set initially to 1
• For Broadcast Media, is required a virtual router (pseudonode) for broadcast media to build a direct graph. For this reason, DIS (Designated IS) is elected by priority and the highest MAC address.
• There are four types of metrics associated with outgoing interface, Delay, default, expense and error, but Cisco only implement DEFAULT

Structure of routers

• Level 1 – Responsible for intra area routing. Has only intra area information database.
• Level ½ – Perform intra and inter area routing. Has only inter area information
• Level 2 – Perform inter area only. Router keeps two separate copies of Link State databases.L1 and L2 databases and inform L1 about exit point.
• L1 area is a collection of L1 and L1/L2 routers
• L2 area is a collection of L2 and L1/L2 routers (backbone area and has to be contiguous)

L1, L2 and L1/L2 LSP features

• LSP sent to unicast address on point to point and multicast address on broadcast networks.
• L1 and L2 require a separate types of link state packets
• Designated IS is a representative of LAN and perform additional duties: Pseudo Level 1 and 2 LSPs and separate DIS for L1/L2. NO BACKUP DIS
• There are 3 types of hello messages: ESH (between ES and IS), ISH (sent by IS to ES) and IIH (between ISs)

ISIS and ESIS communication

• ISIS exchange LSPs
• ES listen to IS Hellos to find their world
• Initially the ES picks a router randomly (whichever is heard)
• HELLOS sent every 10 seconds, holdtime 30 seconds (default)

Link State Database Synchornization

• SNP (Sequence Number PDU)
• PSNP (partial)
• For ack of LSPs on point to point
• To request missing pieces of link state database
• CSNP (Complete)
• Sent periodically by DIS on LAN to ensure reliability
• On point to point link when startup
• Integrated ISIS allow 3 types of routing domain : OSI, IP, DUAL.
• Integrated ISIS has all the features of any modern routing protocol, like VLSM, Redistribution and Summarization.
• Configuration, even if we are going to use only IP, still necessary configure the common CLNS parameters (NET), because routers still establish CLNS adjacencies and SPF calculation and use CLNS packets

Interconnecting ISIS domains:

- In pure IP use BGP

- In pure CLNS use ISO-IGRP or Static route

- IDRP (Cisco does not support)

Verify Commands:

- Show ISIS topology (Display the least cost path to the destination)

- Show CLNS route (Display de CLNS destinations)

- Show ISIS route (Display the level-1 routers to ISIS neighbors

- Show CLNS

- Show CLNS Protocol

- Show CLNS Interface

- Show CLNS neighbor

- Show isis route

- Show clns route

- Show isis database

Basic Integrated route configuration

- Define areas,

- Command: router isis

- Command: clns routing

- Command: net address

- Command: ip router isis

- Command clns router isis

Modeling WAN Networks

• Integrated ISIS over WAN
• 3 types: Point to point circuits, Dialup (Avoid ISIS) and Switched WAN (NBMA)
• Configuring ISIS over Switched WAN

Don’t use the broadcast model on NBMA clouds

ISIS can only work over NBMA clouds configured with a full mesh.

You should avoid use point to multipoint, use point to point sub interface instead.

Alternatively, as Integrated IS-IS uses CLNS packets for its routes propagation, ip unnumbered can be used on point to point interfaces

• Configuration Steps in ISIS NBMA
• Configure subinterfaces point to point
• Assign appropriated VC and Address (CLNS and IP)
• Define Mapping
• Start ISIS on a subinterface

Configuring EIGRP

EIGRP Supports:

· Rapid convergence

· Reduced bandwidth usage

· Multiple network layer protocols

EIGRP Features

· Advanced distance vector

· 100% loop free

· Fast convergence

· Easy configuration

· Less network design constraints than OSPF

· Incremental updates

· Support VLSM and discontiguous network

· Classless routing

· VLSM

· Hierarchical design

· Compatible with existing IGRP networks

· Protocol independent (support IPX and Appletalk)

Advantages of the EIGRP over Distance Vector Routing Protocol

· Use Multicast instead broadcast

· Utilizes bandwidth and delay

· EIGRP = IGRP metric X 256

· Unequal cost path load balancing

· More flexible than OSPF

· Manual summarization can be done in any interface at any router within the network

EIGRP is advanced distance vector routing protocol

· Protocol number is 88 (6-TCP, 17-UDP)

EIGRP Topologies

· Multiaccess (LANs)

· Point to point (HDLC)

· NBMA (Frame Relay)

EIGRP Terminology

· Neighbor table (Next hop , interface)

· Topology table (Successor and Feasible Successor)

· Routing table

EIGRP Operation

· Hello packet

· Update packet

· Query packet (ask neighbor about routing information)

· Reply packet (response to query)

· ACK (acknowledgement of a reliable packet)

EIGRP Neighbor Relationship

· Hello packet = 224.0.0.10

· Hello packet sent every 5 seconds on the following links:

· Broadcast media: Ethernet, Token Ring, FDDI

· Point to point: PPP, HDLC, Frame Relay/ATM subinterfaces

· Multipoint circuits with bandwidth greater than T1: ISDN PRI, SMDS, Frame Relay

· Hello sent every 60 seconds on the following links:

· Mulitpoint with bandwidth less than or equal to T1: ISDN BRI, Frame Relay, SMDS, and so on

· Hold time by default is 3 times the hello time

· EIGRP will not form neighbor if K-values are mismatched

· EIGRP will not form neighbor if AS numbers are mismatched

· EIGRP will form even the hold down time and hello time are different.

Configuring Basic BGP

BGP Overview

1. AS is a collection of networks under a single technical administration
2. IGPs operate within an AS
3. IGPs connect different Ass
4. AS is designated by 16 bits in range from 1 to 65535. A range of private AS are from 64512 through 65535.
5. IGP is used between AS and guarantee exchange of loop free routing information.
6. IGP is an Advanced Distance Vector with many enhancements
7. IGP use Path Vector or Attributes as Metric

When to use BGP

1. AS allow packets to transit through it reach other autonomous systems
2. AS has multiple connections to other AS
3. The flow of traffic entering and leaving your AS must be manipulated
4. And the effect of BGP are well understood. If the BGP not controlled and filtered properly, has the potential to allow an outside AS to affect your routing decisions.

How big is the Internet?

1. Over 100,000 BGP routes
2. Over 10,000 AS numbers
3. A routing table that uses more than 30Mb

When BGP is not appropriate

1. A single connection to Internet
2. Routing Policy and route selection are not a concern for your AS
3. Rack of memory or processor power on BGP routers to handle constant updates
4. Limited understanding of route filtering and BGP path selection
5. Low bandwidth between AS
6. USE STATIC ROUTE INSTEAD
7. COMMAND: ip route prefix mask address/interface [distance]

RIP Static Route Example:

· Ip route 0.0.0.0 0.0.0.0 S0

· Router rip

· Network 172.16.0.0

OSPF example

· Ip route 0.0.0.0 0.0.0.0 S0

· Router ospf 111

· Network 176.16.0.0 0.0.255.255 area 0

· default-information originate always – this command propagate a default route into OSPF routing domain. The always cause the default route to be always advertised whether or not the router has a the path up.